Application of Monopotassium Dipropylene Glycoxide for Homopolymerization and Copolymerization of Monosubstituted Oxiranes: Characterization of Synthesized Macrodiols by MALDI-TOF Mass Spectrometry

Monopotassium dipropylene glycoxide, activated by a 18-crown-6 cation complexing agent (K-DPG/L, where DPG (dipropylene glycol) is a mixture of isomers) was used as an effective initiator of the homopolymerization and copolymerization of several monosubstituted oxiranes, i.e., propylene oxide (PO), 1.2-butylene oxide (BO), and some glycidyl ethers such as allyl, isopropyl, phenyl, and benzyl ones (AGE, IPGE, PGE, and BGE, respectively). The copolymers are novel and can be prospectively used for the fabrication of new thermoplastic or crosslinked polyurethanes. All processes were carried out in homogeneous mild conditions, i.e., tetrahydrofuran solution at room temperature and normal pressure. They resulted in new unimodal macrodiols with Mn = Mcalc in the range of 1500–8300, low dispersity Mw/Mn = 1.08–1.18 and a chemical structure well defined by several techniques, i.e., MALDI-TOF, size exclusion chromatography (SEC), 13C NMR, and FTIR. Monopotassium salts of homopolyether-diols, i.e., PPO-diol, PBO-diol, and PAGE-diol, appeared to be useful macroinitiators for the preparation of new triblock copolyether-diols by polymerization of glycidyl ethers. In BO/BGE random copolymerization initiated with K-DPG/L, macromolecules of copolyether-diol were exclusively formed. Macromolecules of copolyether-diol accompanied by homopolyether PPO-diol were identified in the PO/PGE system. However, AGE and PGE reacted by giving random copolyether-diol as well as homopolymer-diols, i.e., PAGE-diol and PPGE-diol. Macromolecules of prepared copolyether-diols contain various numbers of mers deriving from comonomers; the kind of comonomer determines the composition of the product. Several prepared homopolyether-diols and copolyether-diols could be useful for the synthesis of new thermoplastic polyurethanes.


Homopolyether-Diols
A monopotassium salt of dipropylene glycol (K-DPG) was obtained through the reaction of potassium hydride with an appropriate amount of glycol dissolved in THF at 20 • C. The initial concentrations of the monomer were 2.0 or 5.0 mol/dm 3 and the initial concentration of the initiator was 0.1 mol/dm 3 . For example, potassium hydride (0.08 g, 2.0 mmol) and THF (13 cm 3 ) containing 18C6 (0.53 g, 2.0 mmol) were introduced into a 50 cm 3 reactor equipped with a magnetic stirrer and a Teflon valve, enabling substrate delivery and sampling under an argon atmosphere. Then, dipropylene glycol (2.0 mmol) was added to the THF solution (0.5 mol/dm 3 , 4.0 cm 3 ) by a syringe. The reaction mixture was stirred for 30 min until all hydrogen (44.7 cm 3 ) was dissolved. This resulted in a solution of pure anhydrous monopotassium salt of dipropylene glycol activated ligand in THF. That system was used as the initiator, when propylene oxide (2.8 cm 3 , 2.3 g, 40.0 mmol) was introduced into the reactor. The reaction mixture was then stirred for several days. The course of polymerization was followed by assessing the changes in the content of oxirane groups in samples taken at various times from the reaction mixture. The content of oxirane groups was determined by the dioxane method [22]. A 0.2-0.7 g sample was taken from the reaction mixture and dissolved in 10 cm 3 of a 0.2 mol/dm 3 solution of HCl in 1,4-dioxane, the whole being then allowed to stand for 1 h at room temperature. The solution was then titrated with 0.1 mol/dm 3 KOH using phenolphthalein as an indicator, with a blank determination being run simultaneously. Final conversion of the monomers (~99%) was calculated by NMR technique taking into account signals of oxirane groups in the spectrum. After complete conversion of the monomer, the reaction mixture was neutralized with a HCl/H 2 O system (0.1 mol/dm 3 , 70 cm 3 ) and transferred to a separator containing chloroform (70 cm 3 ). After shaking for 5 min, two layers formed, a bottom polyether layer and a top layer containing water and the potassium salt. These layers were separated and the top layer was removed. After three washes with distilled water, polyether was obtained by evaporating chloroform and water.

solution of dipropylene glycol
Polymers 2020, 12, 2795 4 of 24 in tetrahydrofuran (4.0 cm 3 ) was added. The reaction mixture was stirred for 20 min until all the hydrogen (44.7 cm 3 ) was evolved. This resulted in a solution of monopotassium salt of dipropylene glycol activated with a 18C6 complexing agent. That system was then used as the initiator when 1,2-butylene oxide (3.5 cm 3 , 0.42 g, 40 mmol) was introduced into the reactor. In this system, the initial concentration of the monomer was equal to 2.0 mol/dm 3 and the initial concentration of the initiator was 0.1 mol/dm 3 . The reaction mixture was then stirred for several days. After complete conversion of the monomer, an equimolar amount of IPGE (4.7 cm 3 ) was introduced into the reactor and stirred until total conversion of IPGE was achieved. Then the reaction mixture was neutralized with a HCl/H 2 O system (0.1 mol/dm 3 , 50 cm 3 ) and transferred to a separator containing chloroform (70 cm 3 ). After shaking for 5 min, two layers were obtained, a bottom copolyether layer and a top layer containing water and the potassium salt. These layers were separated and the top layer was removed. After three washes with distilled water, copolyether was obtained by evaporating chloroform and water in a vacuum.
In subsequent experiments, various copolyethers were prepared in a similar way. The concentration of monomers during the polymerization was monitored by the NMR method. The final conversion was~99%, while the yields of the products were 97-99%.

Random Copolyether-Diols
Potassium hydride (0.08 g, 2.0 mmol) and tetrahydrofuran (6.4 cm 3 ) containing 18C6 (0.53 g, 2.0 mmol) were introduced into the reactor and then a 0.5 mol/dm 3 solution of dipropylene glycol in tetrahydrofuran (4.0 cm 3 ) was added. The reaction mixture was then stirred for 20 min until all the hydrogen (44.7 cm 3 ) was evolved. This resulted in a solution of monopotassium salt of dipropylene glycol activated with a 18C6 complexing agent. That system was then used as the initiator, when a mixture of 1,2-butylene oxide (3.5 cm 3 , 0.42 g, 40 mmol) and equimolar amount of benzyl glycidyl ether (6.1 cm 3 ) was introduced into the reactor and stirred until the complete conversion of monomers. Then, the reaction mixture was neutralized with a HCl/H 2 O system (0.1 mol/dm 3 , 50 cm 3 ) and transferred to a separator containing chloroform (70 cm 3 ). After shaking for 5 min, two layers were obtained, a bottom polymer layer and a top layer containing water and the potassium salt. These layers were separated and the top layer was removed. After three washes with distilled water, copolyether was obtained by evaporating chloroform and water in a vacuum. In subsequent experiments, other copolymers were prepared in a similar way. The final conversion was~99% and the yields of the products were 97-99%.

Measurements
First, 100 MHz 13 C nuclear magnetic resonance (NMR) spectra were recorded in CDCl 3 at 25 • C on a BrukerAvance 400 pulsed spectrometer equipped with a 5 mm broadband probe and a Waltz16 decoupling sequence. Chemical shifts were referenced to tetramethylsilane, serving as an internal standard. To obtain a good spectrum of the polymer main chain exhibiting its microstructural details, about 3000 scans were satisfactory, but in order to observe the signals of the polymer chain ends more than 10,000 scans were necessary. Molar masses and dispersities of polymers were obtained by means of size exclusion chromatography (SEC) on a Shimadzu Prominence UFLC instrument at 40 • C on a Shodex 300 × 8 mm OHpac column, using tetrahydrofuran as a solvent. Poly(propylene glycol)s were used as calibration standards. Matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) spectra were recorded on a Shimadzu AXIMA Performance instrument. Dithranol was used as a matrix. Infrared (IR) spectra of samples were recorded on a Shimadzu IR Prestige spectrometer with an attenuated total reflectance (ATR) accessory. The diamond ATR crystal was purified prior to each measurement with isopropanol. Data were analyzed using the LabSolutions program. Each sample was scanned at a resolution of 2 cm −1 .

Homopolyether-Diols
Several macrodiols were synthesized from monosubstituted oxiranes in a homogeneous system at mild conditions according to the reaction shown in Scheme 1. The role of the 18C6 (L) ligand was the complexation of counterion in order to increase the reactivity of the initiator and the number of alkoxides in the growing polymer chain by the formation of crown ether separated ion pairs. This resulted in an increase in the initiator solubility, reaction rate, and yield of the product.
Polymers 2020, 12, x FOR PEER REVIEW 5 of 25 alkoxides in the growing polymer chain by the formation of crown ether separated ion pairs. This resulted in an increase in the initiator solubility, reaction rate, and yield of the product. Conversion curves of the monomers are shown in Figure 1. The monomers were polymerized at various rates depending on the polar and steric effects of the substituent [23]. The reaction times were relatively long, which can result from intra-and/or intermolecular proton exchange between the OH and OK groups [21].   Conversion curves of the monomers are shown in Figure 1. The monomers were polymerized at various rates depending on the polar and steric effects of the substituent [23]. The reaction times were relatively long, which can result from intra-and/or intermolecular proton exchange between the OH and OK groups [21].

OH
Polymers 2020, 12, x FOR PEER REVIEW 5 of 25 alkoxides in the growing polymer chain by the formation of crown ether separated ion pairs. This resulted in an increase in the initiator solubility, reaction rate, and yield of the product. Conversion curves of the monomers are shown in Figure 1. The monomers were polymerized at various rates depending on the polar and steric effects of the substituent [23]. The reaction times were relatively long, which can result from intra-and/or intermolecular proton exchange between the OH and OK groups [21].   Table 1 shows data concerning the average molar masses (M n ) and dispersities (M w /M n ) of the mentioned polymers, as well as the initiator efficiency (f = M calc /M n ) for complete conversion of the monomer. All polymers are unimodal and their dispersities are rather low (M w /M n = 1.08-1.16). Molar masses (M n ) of PPO-diols synthesized with K-DPG/L are higher than the calculated ones (M calc ), indicating initiator efficiency f < 1. This effect can be explained by the strong tendency of the soluble initiator to the formation of various ionic aggregates existing in equilibrium (Scheme 2). Their reactivity varies, depending on the chemical structure and the polarity of the reaction mixture, which depends on the initial monomer concentration and possible monomer participation in the formation of the aggregates. These may influence on different initiator's efficiency.

OH
Polymers 2020, 12, x FOR PEER REVIEW 6 of 25 Table 1 shows data concerning the average molar masses (Mn) and dispersities (Mw/Mn) of the mentioned polymers, as well as the initiator efficiency (f = Mcalc/Mn) for complete conversion of the monomer. All polymers are unimodal and their dispersities are rather low (Mw/Mn = 1.08-1.16). Molar masses (Mn) of PPO-diols synthesized with K-DPG/L are higher than the calculated ones (Mcalc), indicating initiator efficiency f < 1. This effect can be explained by the strong tendency of the soluble initiator to the formation of various ionic aggregates existing in equilibrium (Scheme 2). Their reactivity varies, depending on the chemical structure and the polarity of the reaction mixture, which depends on the initial monomer concentration and possible monomer participation in the formation of the aggregates. These may influence on different initiator's efficiency.  It was observed by the 13 C NMR technique that the unsaturation of PPO-diols obtained with K-DPG is represented exclusively by allyloxy groups, CH2=CHCH2O-(116.71 ppm and 134.88 ppm, respectively), resulting from monomer deprotonation by-O -K + L groups of initiator and polymer chains ( Figure 2). It is relatively low (1-4%) and increases with the initial monomer concentration. The presence of -OH end groups in macromolecules during the polymerization avoids the isomerization of allyloxy groups to cis-propenyloxy ones. It was observed by the 13 C NMR technique that the unsaturation of PPO-diols obtained with K-DPG is represented exclusively by allyloxy groups, CH 2 =CHCH 2 O-(116.71 ppm and 134.88 ppm, respectively), resulting from monomer deprotonation by -O − K + L groups of initiator and polymer chains ( Figure 2). It is relatively low (1-4%) and increases with the initial monomer concentration. The presence of -OH end groups in macromolecules during the polymerization avoids the isomerization of allyloxy groups to cis-propenyloxy ones. In comparison, the unsaturation of polyethers was markedly higher when powdered anhydrous KOH was used as an initiator (~83%) at [M]0 and [I] 0 equal to 2.0 and 0.1 mol/dm 3 [11]. In the last case, mainly macromolecules containing isomeric cis-propenyloxy starting groups were formed. Moreover, the average molar mass of the polymer is much higher (Mn = 6000). The low unsaturation of the currently studied system results from the presence of OH groups in macromolecules. Evidently, the deprotonation of the latter by alkoxide end groups is faster than the deprotonation of the CH3 group in the monomer molecule, which markedly reduces the number of unsaturated groups (Scheme 3).  In comparison, the unsaturation of polyethers was markedly higher when powdered anhydrous KOH was used as an initiator (~83%) at [M] o and [I] o equal to 2.0 and 0.1 mol/dm 3 [11]. In the last case, mainly macromolecules containing isomeric cis-propenyloxy starting groups were formed. Moreover, the average molar mass of the polymer is much higher (M n = 6000). The low unsaturation of the currently studied system results from the presence of OH groups in macromolecules. Evidently, the deprotonation of the latter by alkoxide end groups is faster than the deprotonation of the CH 3 group in the monomer molecule, which markedly reduces the number of unsaturated groups (Scheme 3). In comparison, the unsaturation of polyethers was markedly higher when powdered anhydrous KOH was used as an initiator (~83%) at [M]0 and [I] 0 equal to 2.0 and 0.1 mol/dm 3 [11]. In the last case, mainly macromolecules containing isomeric cis-propenyloxy starting groups were formed. Moreover, the average molar mass of the polymer is much higher (Mn = 6000). The low unsaturation of the currently studied system results from the presence of OH groups in macromolecules. Evidently, the deprotonation of the latter by alkoxide end groups is faster than the deprotonation of the CH3 group in the monomer molecule, which markedly reduces the number of unsaturated groups (Scheme 3).
Cation exchange between potassium alkoxide and hydroxyl group and deprotonation of the CH3 group in the monomer.
All PPO-diols (1-3) contain the same starting and ending -CH2CH(CH3)OH groups after quenching with HCl/H2O. For example, the 13  The splitting of the signal of the last units in the chain ends has already been discussed in our previous paper [11].
MALDI-TOF analysis of the polymer confirmed its structure ( Figure 4). Two series of signals The splitting of the signal of the last units in the chain ends has already been discussed in our previous paper [11].
MALDI-TOF analysis of the polymer confirmed its structure ( Figure 4). Two series of signals were observed in the spectrum. The first one at m/z 620.9 to 2593.5 represents macromolecules possessing the central part (-OC 3 H 6 OC 3 H 6 O-) derived from the initiator and two terminal OH groups. For example, signals at m/z 736.9, 1317.7, and 2130.1 represent macromolecules containing 10, 20, and 30 mers of propylene oxide (M calc = 738.0, 1318.8, and 2132.9, respectively). They exist as adducts with sodium ions. The second series at m/z 637.0 to 2609.6 represents macromolecules with the same structure forming adducts with potassium ions. For example, signals at m/z 1043.3, 1681.8, and 2436.2 belong to macromolecules with 15, 26, and 39 mers of propylene oxide (M calc = 1044.5, 1683.3, and 2438.4, respectively). However, signals of macromolecules with allyloxy starting groups were not detected in the spectrum. It is worth noting that, in PBO-diols (4-6) and other polyether-diols, unsaturation was not observed using 13 C NMR and MALDI-TOF techniques due to the effect of the substituent on the acidity of CH protons in the monomer molecule. In the 13 C NMR spectrum of PBO-diol (4), a signal of the CH 3 group of the initiator was observed at 17.10 ppm. The signals of the -CH 2 CH(CH 2 CH 3 )OH end group were at 73.46 and 73.70 ppm. However, signals at 65.55 and 67.10 pm derived from the initiator were not observed. This indicated that propagation occurred in two directions. The splitting of the signal of the last units in the chain ends has already been discussed in our previous paper [11].
MALDI-TOF analysis of the polymer confirmed its structure ( Figure 4). Two series of signals were observed in the spectrum. The first one at m/z 620.9 to 2593.5 represents macromolecules possessing the central part (-OC3H6OC3H6O-) derived from the initiator and two terminal OH groups. For example, signals at m/z 736.9, 1317.7, and 2130.1 represent macromolecules containing 10, 20, and 30 mers of propylene oxide (Mcalc = 738.0, 1318.8, and 2132.9, respectively). They exist as adducts with sodium ions. The second series at m/z 637.0 to 2609.6 represents macromolecules with the same structure forming adducts with potassium ions. For example, signals at m/z 1043.3, 1681.8, and 2436.2 belong to macromolecules with 15, 26, and 39 mers of propylene oxide (Mcalc = 1044.5, 1683.3, and 2438.4, respectively). However, signals of macromolecules with allyloxy starting groups were not detected in the spectrum. It is worth noting that, in PBO-diols (4-6) and other polyetherdiols, unsaturation was not observed using 13 C NMR and MALDI-TOF techniques due to the effect of the substituent on the acidity of CH protons in the monomer molecule. In the 13 C NMR spectrum of PBO-diol (4), a signal of the CH3 group of the initiator was observed at 17.10 ppm. The signals of the -CH2CH(CH2CH3)OH end group were at 73.46 and 73.70 ppm. However, signals at 65.55 and 67.10 pm derived from the initiator were not observed. This indicated that propagation occurred in two directions. In order to determine the chemical structure of PBO-diols, the MALDI-TOF technique was applied. The spectrum of the appropriate polymer is shown in Figure 5.
The spectrum in Figure 5 reveals two series of signals at m/z 600 to 4000. The first series at m/z 661.9 to 3762.7 represents macromolecules containing a central part derived from the initiator, several BO mers, and two end OH groups. For example, signals at m/z 1239.5, 2465. For polyether-diols, FTIR ATR spectra were recorded to confirm their chemical structure based on selected mer units. The spectrum of PBO-diol (4) is shown in Figure 6.  In order to determine the chemical structure of PBO-diols, the MALDI-TOF technique was applied. The spectrum of the appropriate polymer is shown in Figure 5. For polyether-diols, FTIR ATR spectra were recorded to confirm their chemical structure based on selected mer units. The spectrum of PBO-diol (4) is shown in Figure 6.   For polyether-diols, FTIR ATR spectra were recorded to confirm their chemical structure based on selected mer units. The spectrum of PBO-diol (4) is shown in Figure 6.  Hydroxyl characteristic bands might also be identified at 1060 cm −1 for primary hydroxyl stretching [24]. For all polyethers, a strong C-O stretching band located in the 1200-1050 cm −1 wave number range is visible, but it is overlaid with an ether C-O-C band located at 1095 cm −1 , characteristic of alkyl-substituted ether [25].
MALDI-TOF mass spectrometry was also used for the determination of the chemical structure of poly(glycidyl ether)s. The spectrum of PAGE-diol is presented in Figure 7.
Hydroxyl characteristic bands might also be identified at 1060 cm for primary hydroxyl stretching [24]. For all polyethers, a strong C-O stretching band located in the 1200-1050 cm −1 wave number range is visible, but it is overlaid with an ether C-O-C band located at 1095 cm −1 , characteristic of alkyl-substituted ether [25].
MALDI-TOF mass spectrometry was also used for the determination of the chemical structure of poly(glycidyl ether)s. The spectrum of PAGE-diol is presented in Figure 7.  Figure 8 presents the 13 C NMR spectrum of PAGE-diol (7). The signal of the CH3 group of the initiator was observed at 17.10 ppm. The signals at 68.62 and 69.01 ppm can be attributed to the methine carbon of -OCH2CH(CH2OCH2CH=CH2)OH end group. It can also be stated that the alternative structure of the end group, i.e., -OCH(CH2OCH2CH=CH2)CH2OH, is highly improbable since in this case the signals of CH and CH2 carbons in the vicinity of the OH group should arrive at about 81.3 and 62.9 ppm, respectively, and there are no signals in these regions. This indicates regular chain propagation, and hence the opening of oxirane ring only in the β position.  Figure 8 presents the 13 C NMR spectrum of PAGE-diol (7). The signal of the CH 3 group of the initiator was observed at 17.10 ppm. The signals at 68.62 and 69.01 ppm can be attributed to the methine carbon of -OCH 2 CH(CH 2 OCH 2 CH=CH 2 )OH end group. It can also be stated that the alternative structure of the end group, i.e., -OCH(CH 2 OCH 2 CH=CH 2 )CH 2 OH, is highly improbable since in this case the signals of CH and CH 2 carbons in the vicinity of the OH group should arrive at about 81.3 and 62.9 ppm, respectively, and there are no signals in these regions. This indicates regular chain propagation, and hence the opening of oxirane ring only in the β position.
It is also worth noting that the isomerization of allyloxy groups does not occur under the influence of -O − K + L active centers. The signals of cis-propenyloxy groups CH 3 CH=CHO previously observed at 9.2, 101.1 and 145.9 ppm in the polymerization of AGE initiated with anhydrous KOH (12%) [20] are very weak (0.1%). This is caused by the influence of the OH group derived from the initiator. Figure 9 shows the MALDI-TOF spectrum of PPGE-diol. Two series of signals were observed in the spectrum (Figure 9). The first series at m/z 924.0 to 5873.0 represents macromolecules possessing a central part derived from the initiator and two terminal OH groups. For example, signals at m/z 1225. It is also worth noting that the isomerization of allyloxy groups does not occur under the influence of-O -K + L active centers. The signals of cis-propenyloxy groups CH3CH=CHO previously observed at 9.2, 101.1 and 145.9 ppm in the polymerization of AGE initiated with anhydrous KOH (12%) [20] are very weak (0.1%). This is caused by the influence of the OH group derived from the initiator. Figure 9 shows the MALDI-TOF spectrum of PPGE-diol. Two series of signals were observed in the spectrum (Figure 9)   Similar results were obtained for other polyether-diols synthesized in this work. This means that, during the polymerization, fast counterion exchange occurs between two macromolecules, which causes the propagation in two directions (Scheme 4).  Similar results were obtained for other polyether-diols synthesized in this work. This means that, during the polymerization, fast counterion exchange occurs between two macromolecules, which causes the propagation in two directions (Scheme 4). Similar results were obtained for other polyether-diols synthesized in this work. This means that, during the polymerization, fast counterion exchange occurs between two macromolecules, which causes the propagation in two directions (Scheme 4  When comparing the average molecular weight determined by MALDI-TOF and SEC, it can be seen that the results obtained by both methods are comparable but still show some discrepancies. For the samples with lower dispersities (M w /M n < 1.10), the SEC-derived values are slightly lower (e.g., for sample 1: M n = 1500 (SEC), M n = 1600 (MALDI-TOF)), while for samples with higher dispersities (M w /M n > 1.10), the SEC-derived values are slightly higher (e.g., for sample 7: M n = 2700 (SEC), M n = 2450 (MALDI-TOF)). This discrepancy is connected with the fact that the dispersity of the samples is a well-known factor that influences the MALDI-TOF spectra [26,27] and standards used for SEC calibration.
Summarizing, the application of potassium hydroxyalkoxide for the polymerization of monosubstituted oxiranes allows us to prepare several new linear polyether-polyols in mild conditions. Especially interesting for the synthesis of new polyurethane elastomers are macrodiols (Table 1, no 4-14) due to their unimodality and relatively high molar masses. The preparation of rigid crosslinked polyurethanes can also be possible in the reaction of macrodiols with poly(diisocyanates). They also appear to be useful as macroinitiators for the synthesis of new triblock copolyether-diols.

Triblock Copolyether-Diols
Several triblock copolyether-diols were synthesized using three macroinitiators based on PO(1), BO(4), and AGE (7). In each experiment, a macroinitiator was prepared by the ring-opening polymerization of the chosen monosubstituted oxirane (A) at [A] o = 2.0 mol/dm 3 , initiated with monopotassium dipropylene glycoxide at [I] o = 0.1 mol/dm 3 in the presence of macrocyclic ligand 18-crown-6 (K-DPG/L). After complete conversion of the monomer, the second oxirane (B) was added to the reaction mixture and underwent quantitative copolymerization. Six triblock copolyether-diols were obtained after neutralization with HCl/H 2 O. The products were analyzed by several techniques. The SEC method indicated that all copolymers are unimodal. Their full characterization by this technique was shown in Table 2. In order to confirm the structure of macromolecules formed in the copolymerization, 13 C NMR spectroscopy was applied. Figure 10 shows, for example, the spectrum of PAGE/PPO/PAGE copolymer (1). It reveals strong signals of carbons present in polymer chains, i.e., CH2 and CH (at 70-80 ppm), as well as substituents, i.e., CH3 (at 17.3 ppm) and OCH2CH=CH2 (at 116.6 and 134.9 ppm). The signal of terminal carbon of the CH(CH2OCH2CH=CH2)OH group was identified at 68.62 and 69.01 ppm. However, signals of terminal carbon of CH(CH3)OH group (at 65.55 and 67.10 ppm) were not found in the spectrum. Scheme 5. Preparation of triblock copolyether-diols by ring-opening polymerization of monosubstituted oxiranes, where: R 1 : CH 3 and R 2 : CH 2 OCH 2 CH=CH 2 or CH 2 OPh (for copolymer 15 or 16), R 1 : CH 2 CH 3 and R 2 : CH 2 OCH 2 CH=CH 2 or CH 2 OCH(CH 3 ) 2 (for copolymer 17 or 18), R 1 : CH 2 OCH 2 CH=CH 2 and R 2 : CH 2 OCH(CH 3 ) 2 or CH 2 OCH 2 Ph (for copolymer 19 or 20).
In order to confirm the structure of macromolecules formed in the copolymerization, 13 C NMR spectroscopy was applied. Figure 10 shows, for example, the spectrum of PAGE/PPO/PAGE copolymer (1). It reveals strong signals of carbons present in polymer chains, i.e., CH 2 and CH (at 70-80 ppm), as well as substituents, i.e., CH 3 (at 17.3 ppm) and OCH 2 CH=CH 2 (at 116.6 and 134.9 ppm). The signal of terminal carbon of the CH(CH 2 OCH 2 CH=CH 2 )OH group was identified at 68.62 and 69.01 ppm. However, signals of terminal carbon of CH(CH 3 )OH group (at 65.55 and 67.10 ppm) were not found in the spectrum. The lack of 13 C NMR spectrum carbon signals of the end group derived from the macroinitiator indicated that, during the copolymerization, rapid cation exchange takes place. This allows polymer chains to grow in two directions. A similar phenomenon was observed in the copolymerization of other oxiranes.
It is also worth noting that, for systems containing AGE as a comonomer, 13 C NMR analysis of copolymers ( Figure 11) indicated weak signals of cis-propenyloxy groups, i.e., OCH=CHCH3 (at 101.1 and 145.9 ppm). This resulted from the isomerization of allyl groups under the influence of active centers of growing polymer chains (Table 3). This effect was observed, before now, in the homopolymerization of AGE mediated with anhydrous KOH-activated cation complexing agents [19]. The lack of 13 C NMR spectrum carbon signals of the end group derived from the macroinitiator indicated that, during the copolymerization, rapid cation exchange takes place. This allows polymer chains to grow in two directions. A similar phenomenon was observed in the copolymerization of other oxiranes.
It is also worth noting that, for systems containing AGE as a comonomer, 13 C NMR analysis of copolymers ( Figure 11) indicated weak signals of cis-propenyloxy groups, i.e., OCH=CHCH 3 (at 101.1 and 145.9 ppm). This resulted from the isomerization of allyl groups under the influence of active centers of growing polymer chains (Table 3). This effect was observed, before now, in the homopolymerization of AGE mediated with anhydrous KOH-activated cation complexing agents [19]. The lack of 13 C NMR spectrum carbon signals of the end group derived from the macroinitiator indicated that, during the copolymerization, rapid cation exchange takes place. This allows polymer chains to grow in two directions. A similar phenomenon was observed in the copolymerization of other oxiranes.
It is also worth noting that, for systems containing AGE as a comonomer, 13 C NMR analysis of copolymers ( Figure 11) indicated weak signals of cis-propenyloxy groups, i.e., OCH=CHCH3 (at 101.1 and 145.9 ppm). This resulted from the isomerization of allyl groups under the influence of active centers of growing polymer chains (Table 3). This effect was observed, before now, in the homopolymerization of AGE mediated with anhydrous KOH-activated cation complexing agents [19].  Employing MALDI-TOF mass spectrometry for the analysis of copolymers allows us to obtain additional data about the structure of macromolecules formed during the process. Figure 12 presents, for example, the MALDI-TOF spectrum of PIPGE/PBO/PIPGE-diol (18).  Employing MALDI-TOF mass spectrometry for the analysis of copolymers allows us to obtain additional data about the structure of macromolecules formed during the process. Figure 12 presents, for example, the MALDI-TOF spectrum of PIPGE/PBO/PIPGE-diol (18). Several signals revealed in the spectrum represent macromolecules containing a block of PBO and two blocks of PIPGE, which possess a central fragment -OC3H6OC3H6O-derived from the initiator and two end OH groups. They form adducts with sodium ions. Characterization data of this copolymer involving the main macromolecules at m/z 1301.3 to 4802.9 are shown in Table 4. Signals of the highest intensities (>40%) represent macromolecules containing 3-29 mers of BO and 7-28 mers of IPGE. Macromolecules (1-12) possessing 3, 4, 7, 14, 17, and 20 mers of BO contain ≥50 mol % of IPGE mers. On the other hand, macromolecules with 21, 22, and 26-29 mers of BO contain ≤50 mol % of IPGE mers. The average ratio of BO/IPGE is 40/60.  Several signals revealed in the spectrum represent macromolecules containing a block of PBO and two blocks of PIPGE, which possess a central fragment -OC 3 H 6 OC 3 H 6 O-derived from the initiator and two end OH groups. They form adducts with sodium ions. Characterization data of this copolymer involving the main macromolecules at m/z 1301.3 to 4802.9 are shown in Table 4. Signals of the highest intensities (>40%) represent macromolecules containing 3-29 mers of BO and 7-28 mers of IPGE. Macromolecules (1-12) possessing 3, 4, 7, 14, 17, and 20 mers of BO contain ≥50 mol % of IPGE mers. On the other hand, macromolecules with 21, 22, and 26-29 mers of BO contain ≤50 mol % of IPGE mers. The average ratio of BO/IPGE is 40/60.
Another example is PIPGE/PAGE/PIPGE-diol (19), for which the MALDI-TOF spectrum is shown in Figure 13.

Random Copolyether-Diols
Additional, three new random copolyether-diols were synthesized in this study by using monopotassium salt of dipropylene glycol as an initiator, which was activated by macrocyclic ligand 18-crown-6 (K-DPG/L). In all systems, the initial concentration of each monomer was 2.0 and the initial concentration of each initiator was 0.1 mol/dm 3 . Two monosubstituted oxiranes as comonomers were mixed and added to the initiator solution in tetrahydrofuran. After several hours at room temperature, this results in copolyether-diols after protonation (Scheme 6).

Random Copolyether-Diols
Additional, three new random copolyether-diols were synthesized in this study by using monopotassium salt of dipropylene glycol as an initiator, which was activated by macrocyclic ligand 18-crown-6 (K-DPG/L). In all systems, the initial concentration of each monomer was 2.0 and the initial concentration of each initiator was 0.1 mol/dm 3 . Two monosubstituted oxiranes as comonomers were mixed and added to the initiator solution in tetrahydrofuran. After several hours at room temperature, this results in copolyether-diols after protonation (Scheme 6). The products obtained were analyzed by several methods. The SEC method indicated that all copolymers are unimodal. Their characterization is shown in Table 6. In general, the 13 C NMR spectra of copolymers reveal strong signals of carbons present in polymer chains (CH2 and CH) and substituents, as well as weak signals in carbons' terminal groups (Table 7). Scheme 6. Preparation of initiator and random copolyether-diols by ring-opening copolymerization of monosubstituted oxiranes.
The products obtained were analyzed by several methods. The SEC method indicated that all copolymers are unimodal. Their characterization is shown in Table 6. In general, the 13 C NMR spectra of copolymers reveal strong signals of carbons present in polymer chains (CH 2 and CH) and substituents, as well as weak signals in carbons' terminal groups (Table 7). Weak signals of CH 3 carbons derived from initiator were observed in the 13 C NMR spectrum at 17.3 ppm of copolymers (21) and (23). The lack of signals from the terminal carbon of the CH(CH 3 )OH group from the initiator at 65.0 and 67.1 ppm indicated that propagation occurs in two directions. This is possible due to cation exchange reaction. In the spectrum of copolymer (22), carbon signals of the allyl group (at 117.0 and 136.0 ppm) were not found, which indicated that the chain transfer reaction to PO did not occur. However, in the spectrum of copolymer (23), weak signals of cis-propenyloxy groups were shown (at 101.0 and 146.0 ppm), resulting from isomerization of the allyloxy groups in the substituent.
Analysis of copolymers by MALDI-TOF mass spectrometry provided additional data concerning their structure. The spectrum of the BO/BGE copolymer is shown in Figure 14.  Weak signals of CH3 carbons derived from initiator were observed in the 13 C NMR spectrum at 17.3 ppm of copolymers (21) and (23). The lack of signals from the terminal carbon of the CH(CH3)OH group from the initiator at 65.0 and 67.1 ppm indicated that propagation occurs in two directions. This is possible due to cation exchange reaction. In the spectrum of copolymer (22), carbon signals of the allyl group (at 117.0 and 136.0 ppm) were not found, which indicated that the chain transfer reaction to PO did not occur. However, in the spectrum of copolymer (23), weak signals of cispropenyloxy groups were shown (at 101.0 and 146.0 ppm), resulting from isomerization of the allyloxy groups in the substituent.
Analysis of copolymers by MALDI-TOF mass spectrometry provided additional data concerning their structure. The spectrum of the BO/BGE copolymer is shown in Figure 14. Several signals were observed in the spectrum at m/z 1500 to 4000. They represent macromolecules containing central fragment -OC3H6OC3H6O-derived from the initiator, two end H atoms, and various numbers of mers of both monomers. The composition of copolyether-diols that form adducts with sodium ions was determined and is presented in Table 8. Macromolecules containing 9-14 mers of BO and 9-16 mers of BGE were identified with an average BO/BGE ratio of 1/1. Signals of homopolymers, i.e., PBO-diols and PBGE-diols, were not found in the spectrum. Several signals were observed in the spectrum at m/z 1500 to 4000. They represent macromolecules containing central fragment -OC 3 H 6 OC 3 H 6 O-derived from the initiator, two end H atoms, and various numbers of mers of both monomers. The composition of copolyether-diols that form adducts with sodium ions was determined and is presented in Table 8. Macromolecules containing 9-14 mers of BO and 9-16 mers of BGE were identified with an average BO/BGE ratio of 1/1. Signals of homopolymers, i.e., PBO-diols and PBGE-diols, were not found in the spectrum.  Figure 15 presents the MALDI-TOF spectrum of the PO/PGE copolymer.    The spectrum of this copolymer reveals several peaks in the range of m/z 1000 to 5500. The composition of copolyether-diols that form adducts with sodium ions was determined (Table 9). Macromolecules containing 2-8 mers of PO and 16-28 mers of PGE were identified. In all macromolecules, the PO/PGE ratio is about 1/4. This means that PO indicates the tendency to homopolymerization. Indeed, several signals of PPO-diols were identified in the spectrum (Table 10). Homopolymers of PO contain a relatively high number of mers, i.e., in the range 45-81. The spectrum of this copolymer reveals several peaks in the range of m/z 1000 to 5500. The composition of copolyether-diols that form adducts with sodium ions was determined (Table 9). Macromolecules containing 2-8 mers of PO and 16-28 mers of PGE were identified. In all macromolecules, the PO/PGE ratio is about 1/4. This means that PO indicates the tendency to homopolymerization. Indeed, several signals of PPO-diols were identified in the spectrum (Table 10). Homopolymers of PO contain a relatively high number of mers, i.e., in the range 45-81.   Figure 16 shows the MALDI-TOF spectrum of the AGE/PGE copolymer. Several signals were present in the spectrum in the range of m/z 1000 to 6000 (Table 11). They represent macromolecules of copolyether-diols containing 7 or 12-14 mers of AGE and 4-24 mers of PGE were identified. For example, macromolecules containing 14 mers of AGE contain 5-23 mers of PGE. Analysis of the spectrum also indicated signals that represent homopolymers, i.e., PAGE-diols and PPGE-diols (Tables 12 and 13).
Polymers 2020, 12, x FOR PEER REVIEW 22 of 25 Figure 16 shows the MALDI-TOF spectrum of the AGE/PGE copolymer. Several signals were present in the spectrum in the range of m/z 1000 to 6000 (Table 11). They represent macromolecules of copolyether-diols containing 7 or 12-14 mers of AGE and 4-24 mers of PGE were identified. For example, macromolecules containing 14 mers of AGE contain 5-23 mers of PGE. Analysis of the spectrum also indicated signals that represent homopolymers, i.e., PAGE-diols and PPGE-diols (Tables 12 and 13).    All the results derived from the MALDI-TOF MS analysis confirmed the presence of a copolymeric structure in the studied random copolyether-diols, with a lack of homopolymeric diol macromolecules for BO/BGE, and some of them for the PO/PGE and AGE/PGE systems.