Synthesis of 1,1,3,3,5,5-Hexamethyl-7,7-diorganocyclotetrasiloxanes and Its Copolymers

This paper reports a method for the synthesis of 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes by the interaction of 1,5-disodiumoxyhexamethylsiloxane with dichlorodiorganosilanes such as methyl-, methylvinyl-, methylphenyl-, diphenyl- and diethyl dichlorosilanes. Depending on the reaction conditions, the preparative yield of the target cyclotetrasiloxanes is 55–75%. Along with mixed cyclotetrasiloxanes, the proposed method leads to the formation of polymers with regular alternation of diorganosylil and dimethylsylil units. For example, in the case of dichlorodiethylsilane, 70% content of linear poly(diethyl)dimethylsiloxanes with regular alternation of units can be achieved in the reaction product. Using 7,7-diethyl-1,1,3,3,5,5-hexamethylcyclotetrasiloxane as an example, the prospects of the mixed cycle in copolymer preparation in comparison with the copolymerization of octamethyl- and octaethylcyclotetrasiloxanes are shown.

Cyclosiloxanes of mixed composition are of particular interest in modifying polydimethylsiloxane [24][25][26][27] to provide it with the required properties and to obtain a linear functional matrix containing reactive groups in the chain for further transformations and obtaining new polymers with a determined structure and a required set of characteristics [28,29]. Substituents of the silicon atom have a strong effect on the polymerization rate of cyclosiloxanes; as a result, it is difficult to obtain copolymers by polymerization of a mixture of cyclosiloxanes with different groups at the silicon level [30][31][32]. This problem can be solved by using mixed dimethylcyclotetrasiloxanes. In this regard, the development of simple and effective methods for their preparation is an urgent task. Until very recently, no effective methods for the synthesis of mixed cyclotetrasiloxanes could be observed in the literature. For instance, mixed dimethylcyclotetrasiloxanes containing one silicon atom with different substituents can be synthesized via the cohydrolysis of dichlorodimethylsilane and the corresponding dichlorodiorganosilane, but the yield of In addition, 7-hydro-1,1,3,3,5,5,7-heptamethylcyclotetrasiloxane, 7,7-diethyl-1,1,3,3,5,5-hexamethylcyclotetrasiloxane, 1,1,3,3,5,5,7-heptamethyl-7-phenylcyclotetrasiloxane and 1,1,3,3,5,5-hexamethyl-7,7-diphenylcyclotetrasiloxane were obtained analogously to this procedure in THF medium. The experimental results are presented in Table  1 (№ 3, 4, 5, 6, respectively).
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 °C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 °C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 °C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 °C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 °C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 °C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 °C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 °C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 °C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 °C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.
Synthesis of 1,1,3,3,5,5,7-heptamethyl-7-vinylcyclotetrasiloxane in MTBE medium (№ 2, Table 1). First, 20 g (0.07 mol) 1,5-disodiumoxyhexamethyltrisiloxane, 341 mL of anhydrous THF and 1 mL of anhydrous pyridine were added into a 1 L round-bottom flask equipped with a thermometer, reflux condenser and mechanical stirrer in an argon flow. Then, the reaction mass was heated to 66 • C with vigorous stirring and allowed to cool to room temperature. A solution of 11.9 g (0.08 mol) of dichloromethylvinylsilane in 341 mL of anhydrous THF was prepared in a separate flask. Then, into another 2 L flask equipped with 2 reflux condensers, a thermometer and a mechanical stirrer, with vigorous stirring and cooling to −60 • C, a salt solution in THF and a solution of chlorosilane in THF were added simultaneously and at the same rate. The reaction mass was stirred until room temperature (for 1 h). The pH of the reaction mass was 5-7. After this, the excess THF was distilled off on a rotary evaporator and MTBE was added. Then, the reaction mixture was washed with water to remove the precipitate, and the excess MTBE was distilled off on a rotary evaporator. The obtained siloxane product was analyzed by GLC and GPC. The results are shown in Table 1 (№ 1). Then, the product was distilled. As a result, 9.9 g containing of 96% of 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane was isolated. The 1,1,3,3,5,5,7-hexamethyl-7-vinylcyclotetrasiloxane yield was 45%.

Methods
GLC analysis was performed on a Chromatek Analytic 5000 chromatograph (Russia), a katharometer detector, a helium carrier gas, 2 m × 3 mm columns and a stationary phase SE-30 (5%) printed on Chromaton-H-AW. Registration and calculation of data were carried out using the program "Chromatek Analyst" (Russia).
GPC analysis was performed on a chromatographic system consisting of a STAYER series 2 high-pressure pump (Aquilon, Russia), a RIDK 102 refractometric detector (Czech Republic) (using eluent-toluene) and a JETSTREAM 2 PLUS column thermostat (KNAUER, Berlin, Germany). Eluents-toluene + 2% THF, flow rate-1.0 mL/min. Columns 300 mm long and 7.8 mm in diameter (300 × 7.8 mm) were filled with the Phenogel sorbent (Phenomenex, Torrance, CA, USA), the particle size was 5 mm, and the pore size was 10 3 A and 10 4 A (the passport separation range was up to 75,000 Da and up to 500,000 Da, respectively). The registration and calculation of data were performed using the Uni-Chrom 4.7 program (Belarus). 1

Methods
GLC analysis was performed on a Chromatek Analytic 5000 chromatograph (Russia), a katharometer detector, a helium carrier gas, 2 m × 3 mm columns and a stationary phase SE-30 (5%) printed on Chromaton-H-AW. Registration and calculation of data were carried out using the program "Chromatek Analyst" (Russia).
GPC analysis was performed on a chromatographic system consisting of a STAYER series 2 high-pressure pump (Aquilon, Russia), a RIDK 102 refractometric detector (Czech Republic) (using eluent-toluene) and a JETSTREAM 2 PLUS column thermostat (KNAUER, Berlin, Germany). Eluents-toluene + 2% THF, flow rate-1.0 mL/min. Columns 300 mm long and 7.8 mm in diameter (300 × 7.8 mm) were filled with the Phenogel sorbent (Phe-Polymers 2022, 14, 28 6 of 13 nomenex, Torrance, CA, USA), the particle size was 5 mm, and the pore size was 10 3 A and 10 4 A (the passport separation range was up to 75,000 Da and up to 500,000 Da, respectively). The registration and calculation of data were performed using the UniChrom 4.7 program (Belarus). 1 H and 29 Si NMR spectra of products were recorded using a Bruker Avance II 300 spectrometer. CDCl 3 was used as the internal standard with a chemical shift of δ = 7.25 ppm.
Differential scanning calorimetry (DSC) of samples was performed on the differential scanning calorimeter DSC-3 (Mettler-Toledo, Switzerland) at a heating rate of 10 • /min in an argon atmosphere (60 mL/min).
a katharometer detector, a helium carrier gas, 2 m × 3 mm columns and a stationary phase SE-30 (5%) printed on Chromaton-H-AW. Registration and calculation of data were carried out using the program "Chromatek Analyst" (Russia).
GPC analysis was performed on a chromatographic system consisting of a STAYER series 2 high-pressure pump (Aquilon, Russia), a RIDK 102 refractometric detector (Czech Republic) (using eluent-toluene) and a JETSTREAM 2 PLUS column thermostat (KNAUER, Berlin, Germany). Eluents-toluene + 2% THF, flow rate-1.0 mL/min. Columns 300 mm long and 7.8 mm in diameter (300 × 7.8 mm) were filled with the Phenogel sorbent (Phenomenex, Torrance, CA, USA), the particle size was 5 mm, and the pore size was 10 3 A and 10 4 A (the passport separation range was up to 75,000 Da and up to 500,000 Da, respectively). The registration and calculation of data were performed using the Uni-Chrom 4.7 program (Belarus). 1 H and 29 Si NMR spectra of products were recorded using a Bruker Avance II 300 spectrometer. CDCl3 was used as the internal standard with a chemical shift of δ = 7.25 ppm.
Differential scanning calorimetry (DSC) of samples was performed on the differential scanning calorimeter DSC-3 (Mettler-Toledo, Switzerland) at a heating rate of 10°/min in an argon atmosphere (60 mL/min).
Firstly, 1,5-disodiumoxyhexamethyltrisiloxane is a white hygroscopic powder, practically insoluble in most organic solvents. Its dissolution in tetrahydrofuran or pyridine is achieved only at temperatures up to 50-60 • C, but, even in this case, the solubility of the salt does not exceed 5 wt.%. Therefore, it was of interest to compare the process under homogeneous and heterogeneous conditions at the same concentration of reagent (5 wt.%) in the reaction mixture. THF was used for homogeneous conditions; MTBE was used for heterogeneous conditions. Regardless of other conditions, the reaction was carried out at −60 • C to prevent the processes of cleavage of the siloxane bond under the action of silanolate end groups. The reaction mixture was intensively stirred for 1 h after adding the reagents. If the pH was neutral or slightly acidic, the reaction mixture was stirred until room temperature. The siloxane product was isolated and analyzed by GPC, and the 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxane was isolated by distillation at reduced pressure. The purity and structure of the mixed cyclotetrasiloxanes were con- firmed by a combination of GLC and 1 H and 29 Si NMR spectroscopy methods. The reaction conditions and the composition of the products are shown in Tables 1 and 2. GLC data indicate the absence of side processes with the silanolate ends' participation. In all cases, depending on the type of diorganodichlorosilane and solvent, volatile products consisted of the target cyclotetrasiloxane by 85-98% (Figure 2a,b, Tables 1 and 2). In comparison, Figure 2c shows the GLC curve of the volatile products of the 1,5-disodiumoxyhexameth yltrisiloxane and dichlorodiethylsilane interaction under homogeneous conditions, where the processes of siloxane bond cleavage and rearrangement of the resulting products were found.
heterogeneous conditions. Regardless of other conditions, the reaction was carried out at −60 °C to prevent the processes of cleavage of the siloxane bond under the action of silanolate end groups. The reaction mixture was intensively stirred for 1 h after adding the reagents. If the pH was neutral or slightly acidic, the reaction mixture was stirred until room temperature. The siloxane product was isolated and analyzed by GPC, and the 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxane was isolated by distillation at reduced pressure. The purity and structure of the mixed cyclotetrasiloxanes were confirmed by a combination of GLC and 1 H and 29 Si NMR spectroscopy methods. The reaction conditions and the composition of the products are shown in Tables 1 and 2. GLC data indicate the absence of side processes with the silanolate ends' participation. In all cases, depending on the type of diorganodichlorosilane and solvent, volatile products consisted of the target cyclotetrasiloxane by 85-98% (Figure 2a,b, Tables 1 and  2). In comparison, Figure 2c shows the GLC curve of the volatile products of the 1,5-disodiumoxyhexamethyltrisiloxane and dichlorodiethylsilane interaction under homogeneous conditions, where the processes of siloxane bond cleavage and rearrangement of the resulting products were found. The effect of adding reagents on the reaction mixture was studied in the case of dichloromethylvinylsilane and 1,5-disodiumoxyhexamethyltrisiloxane. It was found that the order of reagent injection under homogeneous conditions and heterogeneous conditions did not significantly affect the yield of the target . Thus, under homogeneous conditions, the target cycle was formed in 45-55% yield, both when adding chlorosilane in THF to a solution of salt in THF (№ 1, Table 1) and with the simultaneous injection solutions of salt and chlorosilane in THF with the same molarity (№ 2, Table 1). The effect of adding reagents on the reaction mixture was studied in the case of dichloromethylvinylsilane and 1,5-disodiumoxyhexamethyltrisiloxane. It was found that the order of reagent injection under homogeneous conditions and heterogeneous conditions did not significantly affect the yield of the target heterogeneous conditions. Regardless of other conditions, the reaction was carried out at −60 °C to prevent the processes of cleavage of the siloxane bond under the action of silanolate end groups. The reaction mixture was intensively stirred for 1 h after adding the reagents. If the pH was neutral or slightly acidic, the reaction mixture was stirred until room temperature. The siloxane product was isolated and analyzed by GPC, and the 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxane was isolated by distillation at reduced pressure. The purity and structure of the mixed cyclotetrasiloxanes were confirmed by a combination of GLC and 1 H and 29 Si NMR spectroscopy methods. The reaction conditions and the composition of the products are shown in Tables 1 and 2. GLC data indicate the absence of side processes with the silanolate ends' participation. In all cases, depending on the type of diorganodichlorosilane and solvent, volatile products consisted of the target cyclotetrasiloxane by 85-98% (Figure 2a,b, Tables 1 and  2). In comparison, Figure 2c shows the GLC curve of the volatile products of the 1,5-disodiumoxyhexamethyltrisiloxane and dichlorodiethylsilane interaction under homogeneous conditions, where the processes of siloxane bond cleavage and rearrangement of the resulting products were found.  Table 2), obtained at the reaction temperature of −60 °C, and the product of the interaction of the salt with dichlorodiethylsilane at room temperature.
The effect of adding reagents on the reaction mixture was studied in the case of dichloromethylvinylsilane and 1,5-disodiumoxyhexamethyltrisiloxane. It was found that the order of reagent injection under homogeneous conditions and heterogeneous conditions did not significantly affect the yield of the target . Thus, under homogeneous conditions, the target cycle was formed in 45-55% yield, both when adding chlorosilane in THF to a solution of salt in THF (№ 1, Table 1) and with the simultaneous injection solutions of salt and chlorosilane in THF with the same molarity (№ 2, Table 1).

(D Me 2 ) 3 (D Et 2 ) (D Me 2 ) 3 (D Ph 2 )
. Thus, under homogeneous conditions, the target cycle was formed in 45-55% yield, both when adding chlorosilane in THF to a solution of salt in THF (№ 1, Table 1) and with the simultaneous injection solutions of salt and chlorosilane in THF with the same molarity (№ 2, Table 1). In this case, the sequence of reagent addition affected only the molecular weight distribution of linear oligomers (Figure 3). Under heterogeneous conditions, salt was added to a chlorosilane in MTBE (№ 4, Table 1) or chlorosilane to a suspension of salt in MTBE, and the yield of the product was 70-75% (№ 8, Table 1). In this case, the sequence of reagent addition affected only the molecular weight distribution of linear oligomers (Figure 3). Under heterogeneous conditions, salt was added to a chlorosilane in MTBE (№ 4, Table 1) or chlorosilane to a suspension of salt in MTBE, and the yield of the product was 70-75% (№ 8, Table 1).  (Table 1).
Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of   Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of Figure 3. GPC curves of products 1, 2, 7 (Table 1).
Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).  Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).  Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of  Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).  Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).  Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).  Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained  Further interactions were carried out by adding a solution of dichlorodiorganosilane to a solution or suspension of the salt in THF or MTBE, respectively.
Analysis of the data in Tables 1 and 2 allowed us to divide all cases into two groups. Vinylmethyl-and methyldichlorosilanes showed the highest preparative yield of and in MTBE, which is 55 and 75%, respectively (№ 3 and 6, Table 1). The opposite situation was observed using more sterically hindered chlorosilyl end groups such as diethyl-, methylphenyl-and diphenyldichlorosilanes: the highest yields of , and were achieved under homogeneous conditions, equal to up to 65, 67 and 70%, respectively (№ 8, 10, 12, Table 2). Such differences in the yields of products indicate significant opportunities for further optimization of the yield of each specific mixed cycle.
All dimethylcyclotetrasiloxanes were isolated with a purity of at least 95% according to GLC data; the structure of the obtained products was confirmed by 1 H, 29 Si NMR and IR spectroscopy. The relevant data are given in the Supplementary Materials (Figures S1-S15). The IR spectroscopy data of the isolated cycles indicate the absence of an absorption band in the region of 3400-3600 cm −1 , which is characteristic of silanol groups and confirms the cyclic structure of the isolated compounds ( Figures S1-S5). The 1 H and 29 Si NMR spectroscopy data of the isolated fractions indicate that the integral intensities of the protons signals of corresponding substituents at silicon atoms and silicon atoms themselves conform to the calculated values ( Figures S11-S15).
The data in Tables 1 and 2 show that the main reaction product may be a linear oligomer with a regular arrangement of modifying units under certain conditions. In particular, in sample 10 (Table 2), the product contained along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).

5 1Evaluation time/ min
along with the linear poly(diethyl)(dimethyl)siloxane with Mp = 1900 and content of 70%. The product was blocked with chlorodimethylvinylsilane to confirm the linear structure ( Figure 4) and its composition and molecular weight characteristics were determined by 1 H NMR spectroscopy and GPC methods ( Figure 5).   Table 2).  Table 2).
The correlation of the integral intensities of proton signals of ethyl, vinyl and methyl groups in the backbone and terminal silicon atoms allowed us to determine by the 1 Table 2).   Table 2).  Table 2).
The correlation of the integral intensities of proton signals of ethyl, vinyl and methyl groups in the backbone and terminal silicon atoms allowed us to determine by the 1 Table 2). The correlation of the integral intensities of proton signals of ethyl, vinyl and methyl groups in the backbone and terminal silicon atoms allowed us to determine by the 1 H NMR spectrum that the unit composition of the obtained product corresponded to the following formula: VinMe 2 SiO-{[Et 2 SiO] 1 [Me 2 SiO] 2,4 } 5,3 -SiMe 2 Vin with M n equal to~1640. The number-average molecular weights of the polymer calculated from the NMR and determined by the GPC method (M n = 1800, M w = 2300, M w /M n = 1.3) were consistent and confirmed the linear structure of poly(diethyl)(dimethyl)siloxane.
Thus, the interactions of 1,5-disodiumoxyhexamethyltrisiloxane with diorganodichloro silanes were investigated to obtain 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes. For the first time, it was shown that mixed dimethylcyclotetrasiloxanes can be obtained with a yield of 55 to 75% by this method. The ratio of linear and cyclic products of a mixed structure can be controlled within wide limits by selecting the reaction conditions. Using dichlorodiethylsilane as an example, it was shown that this method can be a promising means of obtaining linear oligomers with alternating diethyl-and dimethylsiloxane units.
The correlation of the integral intensities of proton signals of ethyl, vinyl and methyl groups in the backbone and terminal silicon atoms allowed us to determine by the 1 H NMR spectrum that the unit composition of the obtained product corresponded to the following formula: VinMe2SiO-{[Et2SiO]1[Me2SiO]2,4}5,3-SiMe2Vin with Mn equal to ~1640. The number-average molecular weights of the polymer calculated from the NMR and determined by the GPC method (Mn = 1800, Mw = 2300, Mw/Mn = 1.3) were consistent and confirmed the linear structure of poly(diethyl)(dimethyl)siloxane.
Thus, the interactions of 1,5-disodiumoxyhexamethyltrisiloxane with diorganodichlorosilanes were investigated to obtain 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes. For the first time, it was shown that mixed dimethylcyclotetrasiloxanes can be obtained with a yield of 55 to 75% by this method. The ratio of linear and cyclic products of a mixed structure can be controlled within wide limits by selecting the reaction conditions. Using dichlorodiethylsilane as an example, it was shown that this method can be a promising means of obtaining linear oligomers with alternating diethyl-and dimethylsiloxane units.

Preparation of Poly(diethyl)(dimethyl)siloxane
A simple and cheap method for the preparation of 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes opens up new prospects for the preparation of polydimethyldiorganosiloxanes with a controlled content of diorganosilyl groups via polymerization methods. It is known that, in order to obtain polydiethylsiloxanes, hexaethylcyclotrisiloxane is polymerized [51,52] since octaethylcyclotetrasiloxane is practically not polymerized. To obtain poly(diethyl)(dimethyl)siloxane copolymers, catalytic rearrangement of the cohydrolysis products of dimethyl-and diethyldichlorosilanes is carried out [53]. In our study, we paid attention to the prospects of using mixed , in is practically not polymerized. To obtain poly(diethyl)(dimethyl)siloxane copolymers, catalytic rearrangement of the cohydrolysis products of dimethyl-and diethyldichlorosilanes is carried out [53]. In our study, we paid attention to the prospects of using mixed  Table 2).
The correlation of the integral intensities of proton signals of ethyl, vinyl and methyl groups in the backbone and terminal silicon atoms allowed us to determine by the 1 H NMR spectrum that the unit composition of the obtained product corresponded to the following formula: VinMe2SiO-{[Et2SiO]1[Me2SiO]2,4}5,3-SiMe2Vin with Mn equal to ~1640. The number-average molecular weights of the polymer calculated from the NMR and determined by the GPC method (Mn = 1800, Mw = 2300, Mw/Mn = 1.3) were consistent and confirmed the linear structure of poly(diethyl)(dimethyl)siloxane.
Thus, the interactions of 1,5-disodiumoxyhexamethyltrisiloxane with diorganodichlorosilanes were investigated to obtain 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes. For the first time, it was shown that mixed dimethylcyclotetrasiloxanes can be obtained with a yield of 55 to 75% by this method. The ratio of linear and cyclic products of a mixed structure can be controlled within wide limits by selecting the reaction conditions. Using dichlorodiethylsilane as an example, it was shown that this method can be a promising means of obtaining linear oligomers with alternating diethyl-and dimethylsiloxane units.

Preparation of Poly(diethyl)(dimethyl)siloxane
A simple and cheap method for the preparation of 1,1,3,3,5,5-hexamethyl-7,7-diorganocyclotetrasiloxanes opens up new prospects for the preparation of polydimethyldiorganosiloxanes with a controlled content of diorganosilyl groups via polymerization methods. It is known that, in order to obtain polydiethylsiloxanes, hexaethylcyclotrisiloxane is polymerized [51,52] since octaethylcyclotetrasiloxane is practically not polymerized. To obtain poly(diethyl)(dimethyl)siloxane copolymers, catalytic rearrangement of the cohydrolysis products of dimethyl-and diethyldichlorosilanes is carried out [53]. In our study, we paid attention to the prospects of using mixed , in contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. , its copolymerization with x FOR PEER REVIEW 10 of 15 contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 • C. Trimethylchlorosilane was used as a termination agent.
Polymers 2022, 13, x FOR PEER REVIEW 10 of 15 contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight characteristics were analyzed by 1 H NMR spectroscopy and GPC methods (Figures S16-S18). The characteristics of the obtained products are shown in Table 3. contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight characteristics were analyzed by 1 H NMR spectroscopy and GPC methods (Figures S16-S18). contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight charac- contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight charac-  contrast to , for the preparation of (diethyl)(dimethyl)siloxane copolymers. Anionic polymerization of , its copolymerization with and copolymerization of and in the presence of potassium hydroxide were carried out to illustrate this statement (Figure 6a-c, respectively). The duration of anionic polymerization was 1 h at 140 °C. Trimethylchlorosilane was used as a termination agent. The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight characteristics were analyzed by 1 H NMR spectroscopy and GPC methods (Figures S16-S18). The content of the high-molecular and low-molecular parts of the products was determined by the GPC method (Table 3, Figures 7 and 8). The high-molecular-weight part was separated using preparative GPC, and its composition and molecular weight characteristics were analyzed by 1 H NMR spectroscopy and GPC methods (Figures S16-S18). The characteristics of the obtained products are shown in Table 3.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units. and the product of their copolymerization (№ 1, Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.   Figure 7. Characteristics of the initial mixture of / and the product of their copolymerization (№ 1, Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.   Figure 7. Characteristics of the initial mixture of / and the product of their copolymerization (№ 1, Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units. was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table 3): GPC data for the initial mixture (green curve) and the product (red curve); GLC curves of the initial mixture of monomers (top right) and volatile fraction after copolymerization (bottom right); 1 H NMR spectrum (top left) and GPC curve (bottom left) of obtained copolymer. As expected, the content of the high-molecular part was three times higher in the case of the copolymerization of and (№ 2, Table 3) than in the copolymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units.  Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copolymerization of and mixed to the calculated value, in contrast to the copolymerization of and , where the polymer composition was enriched with dimethylsilyl units. and ymerization of homocycles and with various substituents (№ 1, Table   3), where low conversion of the was observed. It follows from a comparison of the GLC data for the initial mixture of monomers and the low-molecular-weight fraction of the products (Figure 7). Analysis of the high-molecular-weight fractions of the products showed the correspondence of the structural unit of the copolymer obtained by the copol- The polymerization of mixed forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 °C ~ -131 °C and the absence of crystallization.
Thus, firstly, the advantages of used for the preparation of poly(diethyl)(dimethyl)siloxanes with a controlled unit composition were demonstrated in comparison with the mixture of and .

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as byproducts, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 • C~-131 • C and the absence of crystallization.
Thus, firstly, the advantages of The polymerization of mixed forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 °C ~ -131 °C and the absence of crystallization.
Thus, firstly, the advantages of used for the preparation of poly(diethyl)(dimethyl)siloxanes with a controlled unit composition were demonstrated in comparison with the mixture of and .

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as byproducts, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. The polymerization of mixed forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 °C ~ -131 °C and the absence of crystallization.
Thus, firstly, the advantages of used for the preparation of poly(diethyl)(dimethyl)siloxanes with a controlled unit composition were demonstrated in comparison with the mixture of and .

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as byproducts, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results. The polymerization of mixed forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 °C ~ -131 °C and the absence of crystallization.
Thus, firstly, the advantages of used for the preparation of poly(diethyl)(dimethyl)siloxanes with a controlled unit composition were demonstrated in comparison with the mixture of and .

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as byproducts, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as by-products, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of The polymerization of mixed forms poly(diethyl)dimethylsiloxane with a Mn close to the calculated value, a broad molecular weight distribution and a structural unit composition corresponding to the calculated one (№3, Table 3, Figure 8 (on right)). According to DSC data ( Figures S19 and S20), the obtained poly(diethyl)dimethylsiloxanes (№ 2 and 3 of Table 3) had a low glass transition temperature of −132 °C ~ -131 °C and the absence of crystallization.
Thus, firstly, the advantages of used for the preparation of poly(diethyl)(dimethyl)siloxanes with a controlled unit composition were demonstrated in comparison with the mixture of and .

Conclusions
Mixed tetrasiloxane cycles have high potential for practical application; however, the lack of selective methods for its preparation has been a limiting factor for the realization of this potential for a long time. This work shows that high selectivity of mixed cycle synthesis can be achieved based on 1,5-disodiumoxyhexamethyltrisiloxanes, a unique reagent that we described earlier [49]. The yield of these cyclosiloxanes in the best experiments reaches 70%. It is important that linear alternating oligomers are formed as byproducts, which can be used independently. Moreover, the ratio between linear and cyclic products can be changed within wide limits.
The second part of the article demonstrates the advantages of mixed cyclosiloxane polymerization in comparison with a mixture of two cyclosiloxanes with a homogeneous structure. This result is a consequence of the low reactivity of in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.

Conflicts of Interest:
The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
in comparison with the high reactivity mixed cycle in anionic polymerization.
We believe that the considered method opens up new prospects both for expanding the range of cyclic siloxane products with a specific composition and structure, which have many different applications, and for obtaining linear polymers with a controlled content of modifying units and new materials based on them. Mixed cycles have many other applications, including fluids with controlled properties. The realization of these and other potential applications requires further research and is an important subject of current research.