Thermoresponsive Property of Poly(N,N-bis(2-methoxyethyl)acrylamide) and Its Copolymers with Water-Soluble Poly(N,N-disubstituted acrylamide) Prepared Using Hydrosilylation-Promoted Group Transfer Polymerization

The group-transfer polymerization (GTP) of N,N-bis(2-methoxyethyl)acrylamide (MOEAm) initiated by Me2EtSiH in the hydrosilylation-promoted method and by silylketene acetal (SKA) in the conventional method proceeded in a controlled/living manner to provide poly(N,N-bis(2-methoxyethyl)acrylamide) (PMOEAm) and PMOEAm with the SKA residue at the α-chain end (MCIP-PMOEAm), respectively. PMOEAm-b-poly(N,N-dimethylacrylamide) (PDMAm) and PMOEAm-s-PDMAm and PMOEAm-b-poly(N,N-bis(2-ethoxyethyl)acrylamide) (PEOEAm) and PMOEAm-s-PEOEAm were synthesized by the block and random group-transfer copolymerization of MOEAm and N,N-dimethylacrylamide or N,N-bis(2-ethoxyethyl)acrylamide. The homo- and copolymer structures affected the thermoresponsive properties; the cloud point temperature (Tcp) increasing by decreasing the degree of polymerization (x). The chain-end group in PMOEAm affected the Tcp with PMOEAmx > MCIP-PMOEAmx. The Tcp of statistical copolymers was higher than that of block copolymers, with PMOEAmx-s-PDMAmy > PMOEAmx-b-PDMAmy and PMOEAmx-s-PEOEAmy > PMOEAmx-b-PEOEAmy.

Group-transfer polymerization (GTP) is a reliable living polymerization method for polar monomers such as (meth)acrylate, which can be performed using conventional catalysts to produce well-defined polymers [55].For instance, Taton et al., Waymouth et al., and our group reported that organocatalysts could effectively promote the controlled/living GTP of (meth)acrylate [56,57], alkyl sorbate [58], alkyl crotonate [59], methacrylonitrile [60], and N,N-disubstituted acrylamide (DSAm) [61].These conventional GTP systems require the use of silyl ketene acetal (SKA) or silyl ketene aminal (SKAm) as an initiator, resulting in the attachment of residual groups derived from SKA or SKAm at the α-chain end of the obtained polymers.Recently, we developed a new GTP method that does not require adding SKA or SKAm beforehand, i.e., the polymerization of (meth)acrylate and acrylamide monomers with hydrosilane (R 3 SiH) using tris(pentafluorophenyl)borane (B(C 6 F 5 ) 3 ) as the catalyst, which proceeded through a controlled/living GTP mechanism to produce well-defined polymers without α-chain-end groups derived from SKA or SKAm [62,63].In this GTP method, SKA or SKAm was formed via the B(C 6 F 5 ) 3 -catalyzed hydrosilylation of a monomer and R 3 SiH in the polymerization system prior to the polymerization.We applied the hydrosilylation-promoted GTP method to the synthesis of thermoresponsive polymers capped with hydrogen atoms in both chain ends, such as PDEAm and poly(Nmethyl,N-n-propylacrylamide) [64].

Materials
Dichloromethane (CH2Cl2, >99.5%; water content < 0.001%), methyl alcohol (MeOH), and calcium hydride (CaH2) were purchased from Kanto Chemicals Co., Inc. (Tokyo, Japan).Bis(2-methoxyethyl)amine, DMAm, and Me2EtSiH were obtained from Tokyo Kasei Kogyo Co., Ltd.(Tokyo, Japan).B(C6F5)3 was procured from Wako Pure Chemical Industries, Ltd. (Tokyo, Japan) and utilized after recrystallization from n-hexane at −30 °C.DMAm and CH2Cl2 were distilled using CaH2 and degassed through three freeze-pumpthaw cycles before being stored under an Ar atmosphere for future use.All other chemicals were purchased from suppliers and used without purification.Polymerizations were carried out in a glove box under Ar atmosphere at 25 °C.

Measurements
1 H NMR spectra were obtained using a Bruker Avance III HD 500 spectrometer from Bruker Corporation (Billerica, MA, USA).Polymerization solutions were prepared in a Mikrouna glove box with a gas purification system consisting of molecular sieves and a copper catalyst and were filled with a dry Ar atmosphere (with H2O and O2 contents of less than 1 ppm).The water and oxygen levels inside the glove box were monitored using the MK-XTR-100 and MK-OX-SEN-1 sensors from Mikarona Industrial Intelligent Tech-

Materials
Dichloromethane (CH 2 Cl 2 , >99.5%; water content < 0.001%), methyl alcohol (MeOH), and calcium hydride (CaH 2 ) were purchased from Kanto Chemicals Co., Inc. (Tokyo, Japan).Bis(2-methoxyethyl)amine, DMAm, and Me 2 EtSiH were obtained from Tokyo Kasei Kogyo Co., Ltd.(Tokyo, Japan).B(C 6 F 5 ) 3 was procured from Wako Pure Chemical Industries, Ltd. (Tokyo, Japan) and utilized after recrystallization from n-hexane at −30 • C. DMAm and CH 2 Cl 2 were distilled using CaH 2 and degassed through three freeze-pump-thaw cycles before being stored under an Ar atmosphere for future use.All other chemicals were purchased from suppliers and used without purification.Polymerizations were carried out in a glove box under Ar atmosphere at 25 • C.

Measurements
1 H NMR spectra were obtained using a Bruker Avance III HD 500 spectrometer from Bruker Corporation (Billerica, MA, USA).Polymerization solutions were prepared in a Mikrouna glove box with a gas purification system consisting of molecular sieves and a copper catalyst and were filled with a dry Ar atmosphere (with H 2 O and O 2 contents of less than 1 ppm).The water and oxygen levels inside the glove box were monitored using the MK-XTR-100 and MK-OX-SEN-1 sensors from Mikarona Industrial Intelligent Technology Co., Ltd.(Shanghai, China), respectively.The polymers' number-average molecular mass (M n,SEC ) and polydispersity index (Ð) were measured through size exclusion chromatography (SEC) at 40 • C. The Agilent high-performance liquid chromatography system (1260 Infinity II) was utilized in N,N-dimethylformamide (DMF) containing 0.01% lithium chloride.A solution of 1.0 mol L −1 was flowed through Agilent Polar Gel-M columns (exclusion limit, 2 × 10 4 g mol −1 ) and Polar Gel-M columns (exclusion limit, 4 × 10 6 g mol −1 ) (7.5 × 300 mm; average bead size, 5 µm) (Agilent Technologies Inc. Shanghai, China) at a rate of 1.0 mL min −1 .Cloud-point measurements were taken on a Jasco V-770 ultraviolet-visible (UV-vis) spectrophotometer (Tokyo, Japan), which was equipped with a Jasco CTU-100 temperature controller.The temperature was then increased at a rate of 1 • C min −1 while the path length was 10 mm.Changes in transmission were recorded at 500 nm with varying temperatures.The hydrodynamic radius (R h ) of the produced polymers was analyzed through a Dyna Pro Nanostar ® instrument from Wyatt Technology in Santa Barbara, CA, USA.

Synthesis of PMOEAm
A solution of MOEAm (749.0 mg, 4 mmol), Me 2 EtSiH (5.28 µL, 40 µmol), and B(C 6 F 5 ) 3 (2.1 mg, 4.0 µmol) in CH 2 Cl 2 (3.96 mL) was stirred for 12 h at room temperature in a glove box under an Ar atmosphere.To terminate the polymerization, a small amount of MeOH was added, and then the crude product was purified by dialysis against acetone to obtain a white solid product.The yield was 408.7 mg (54.6%).

Synthesis of PMOEAm-s-PDMAm
A solution containing MOEAm (375.5 mg, 2 mmol), DMAm (198.4 mg, 2 mmol), Me 2 EtSiH (5.28 µL, 40 µmol), and B(C 6 F 5 ) 3 (2.1 mg, 4.0 µmol) in CH 2 Cl 2 (3.96 mL) was stirred for 12 h at room temperature in a glove box under an Ar atmosphere.To terminate the polymerization, a small amount of MeOH was added, and the crude product was then purified by dialysis against acetone to obtain a white solid product.The yield was 369.1 mg (50%).

Synthesis of PMOEAm-b-PDMAm
A solution containing MOEAm (375.5 mg, 2 mmol), Me 2 EtSiH (5.28 µL, 40 µmol), and B(C 6 F 5 ) 3 (2.1 mg, 4.0 µmol) in CH 2 Cl 2 (3.96 mL) was stirred under an Ar atmosphere at room temperature in a glove box for 12 h.A sample of the reaction solution was taken to confirm the complete MOEAm consumption via 1 H NMR spectroscopy.Afterward, DMAm (198.4 mg, 2 mmol) was introduced to the polymerization mixture and stirred for 36 h.The crude product was then purified following the same procedure used in the synthesis of PEOEAm.The result was a white solid polymer with a yield of 345.9 mg (47%).

Synthesis of PMOEAm
We reported preliminary results for the GTP of MOEAm with SKA Et or Me 2 EtSiH using B(C 6 F 5 ) 3 as the catalyst, i.e., the conventional and hydrosilylation-promoted methods, respectively [72].In order to clarify the effect of the chain end group, it is necessary to use polymers synthesized under similar polymerization conditions for both GTPs.For the hydrosilylation-promoted GTP of MOEAm with Me 2 EtSiH, the polymerization was performed at a [MOEAm] 0 /[Me 2 EtSiH] 0 /[B(C 6 F 5 ) 3 ] 0 ratio of 25/1/0.1.The M n,SEC of the obtained polymer was 4.5 kg mol −1 , which was in good agreement with the calculated molecular mass (M n,calcd ) of 4.7 kg mol −1 (Table 1, run 1).The polydispersity index (Ð) of the obtained polymer was as low as 1.13 (Figure 1a).Similarly, the conventional GTP of MOEAm was performed at a [MOEAm] 0 /[SKA Et ] 0 /[B(C 6 F 5 ) 3 ] 0 ratio of 25/1/0.1 to obtain a polymer with a M n,SEC of 5.1 kg mol −1 , which was close to the M n,calcd of 4.9 kg mol −1 (Table S1).The SEC trace of the resulting polymer was unimodal with a low Ð of 1.11 (Figure 1b).tained polymer was 4.5 kg mol , which was in good agreement with the calculated mo-lecular mass (Mn,calcd) of 4.7 kg mol −1 (Table 1, run 1).The polydispersity index (Đ) of the obtained polymer was as low as 1.13 (Figure 1a).Similarly, the conventional GTP of MOEAm was performed at a [MOEAm]0/[SKA Et ]0/[B(C6F5)3]0 ratio of 25/1/0.1 to obtain a polymer with a Mn,SEC of 5.1 kg mol −1 , which was close to the Mn,calcd of 4.9 kg mol −1 (Table S1).The SEC trace of the resulting polymer was unimodal with a low Đ of 1.11 (Figure 1b).The 1 H NMR spectra of the polymers obtained using the two initiation methods were almost identical, showing signals due to the -NCH2CH2O-, -OCH3, -CH2CH-, and -CH2CHgroups at 3.83-3.88,3.31-3.38,0.99-2.01,and 2.45-2.75ppm, respectively.In addition, signals due to the -C(CH3)2 group as a residue of SKA Et were observed at 1.26 ppm for the polymer prepared using the conventional initiation method (Figure 2).More detailed information on the resulting polymer structures was obtained via matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) measurements.The 1 H NMR spectra of the polymers obtained using the two initiation methods were almost identical, showing signals due to the -NCH 2 CH 2 O-, -OCH 3 , -CH 2 CH-, and -CH 2 CH-groups at 3.83-3.88,3.31-3.38,0.99-2.01,and 2.45-2.75ppm, respectively.In addition, signals due to the -C(CH 3 ) 2 group as a residue of SKA Et were observed at 1.26 ppm for the polymer prepared using the conventional initiation method (Figure 2).More detailed information on the resulting polymer structures was obtained via matrixassisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) measurements.
The MALDI-TOF MS spectrum depicted in Figure 3a   The MALDI-TOF MS spectrum depicted in Figure 3a reveals a sole set of molecular ion peaks with an adjacent peak distance of 187.24 Da, consistent with the molecular mass prediction of MOEAm as the constitutional repeat unit.Moreover, the m/z values of each molecular ion peak were in accordance with the sodium-cationized polymer composition of [H-MOEAmn-H + Na] + (molecular formula: C9nH17n + 2H2NnO3nNa).For example, an m/z value of 4705.82Da corresponds to a sodium-cationized 25-unit polymer structure of [H-MOEAm25-H + Na] + , with a theoretical monoisotopic value of 4705.03Da for the molecular formula C225H427N25O75Na.
Similarly, for the polymer obtained using the conventional GTP with SKA Et , only one series of molecular ion peaks is observed in Figure 3b, and the difference in the m/z values between each peak is consistent with the molecular mass predicted for MOEAm.In addition, the m/z value of each molecular ion peak can be attributed to the sodium-cationized polymer with the MCIP group, the desilylated SKA Et , at the α-chain end and a hydrogen atom at the ω-chain end of [CH3O2CC(CH3)2-MOEAmn-H + Na] + (C9n+5H17n+9NnO3n+2Na).For example, an m/z of 4805.52 Da for a specific peak corresponds to a [CH3O2CC(CH3)2-MOEAm25-H + Na] + with a theoretical monoisotopic value of 4806.09 for C230H436N25O77Na.In the conventional and hydrosilylation-promoted GTP reactions, the resulting polymers consisted only of monomeric units, although the difference between Me2EtSiH and SKA Et used in the initiation reaction was reflected in the structure of the initiating end of the polymer, i.e., PMOEAm25 and CH3O2CC(CH3)2-MOEAm25, respectively.S1, run 1).
Similarly, for the polymer obtained using the conventional GTP with SKA Et , only one series of molecular ion peaks is observed in Figure 3b, and the difference in the m/z values between each peak is consistent with the molecular mass predicted for MOEAm.In addition, the m/z value of each molecular ion peak can be attributed to the sodium-cationized polymer with the MCIP group, the desilylated SKA Et   4, both GTP systems exhibited induction times (t i ), with the t i for Me 2 EtSiH (13.1 min) being smaller than that for SKA Et (55.0 min) due to the difference in both initiation reactions.In the kinetic plot of MOEAm with Me 2 EtSiH and SKA Et , a clear zero-order relationship between polymerization time and monomer conversion was observed, with M n , SEC increasing linearly with increasing monomer conversion and Ð remaining at low values.The polymerization rates of both GTP reactions of MOEAm were almost the same with k p,obs values of 0.35 min −1 for Me 2 EtSiH and 0.33 min −1 for SKA Et .These results confirmed that the difference in the initiation method affected only the induction time in the early stages of the polymerization but had no effect on the propagation rate.  1, run 1) and (b) MCIP-PMOEAm25 with a Mn,SEC of 5.1 kg mol −1 and a Đ of 1.11 (Table S1, run 1).
Furthermore, the polymerization features of the GTP of MOEAm initiated using two different methods were compared by evaluating the polymerization kinetics.The GTP of MOEAm was performed at a [MOEAm]0/[Me2EtSiH or SKA Et ]0/[B(C6F5)3]0 ratio of 100/1/0.1 and a [MOEAm]0 of 1.0 mol L −1 in CH2Cl2 at 25 °C.Although Et3SiH should be used for an accurate comparison with SKA Et , the hydrosilylation-promoted GTP of DSAm with Et3SiH did not proceed in a controlled/living manner; therefore, Me2EtSiH was used instead of Et3SiH.As shown in Figure 4, both GTP systems exhibited induction times (ti), with the ti for Me2EtSiH (13.1 min) being smaller than that for SKA Et (55.0 min) due to the difference in both initiation reactions.In the kinetic plot of MOEAm with Me2EtSiH and SKA Et , a clear zero-order relationship between polymerization time and monomer conversion was observed, with Mn,SEC increasing linearly with increasing monomer conversion and Đ remaining at low values.The polymerization rates of both GTP reactions of MOEAm were almost the same with kp,obs values of 0.35 min −1 for Me2EtSiH and 0.33 min −1 for SKA Et .These results confirmed that the difference in the initiation method affected only the induction time in the early stages of the polymerization but had no effect on the propagation rate.

Synthesis of Block and Statistical Copolymers of PMOEAm
The response performance of thermoresponsive polymers is controlled by adjusting the degree of polymerization and introducing polymer chain-end groups.The use of block and statistical copolymer systems based on thermoresponsive polymers is an additional approach to controlling the thermoresponsive property.In this study, DMAm as a simple DSAm and EOEAm as an analog of MOEAm were used as comonomers.The block GTcoP reactions of MOEAm and DMAm or EOEAm with Me 2 EtSiH using B(C 6 F 5 ) 3 as the catalyst were performed using a sequential monomer addition method by varying the molar ratio of [MOEAm] 0 and [DMAm or EOEAm] 0 .The copolymerization results are listed in Tables 2 and 3, respectively.The molecular mass of the polymers was determined using size exclusion chromatography equipped with a refractive index detector in dimethylformamide (DMF) containing 0.01 mol L −1 of lithium chloride and using polymethylmethacrylate (PMMA) as standards.c Determined by UV-vis measurements in water (10 g L −1 ).d Water-soluble but no T cp under 95 • C. e Not determined due to insoluble in water.
In the hydrosilylation-promoted GTcoP of MOEAm and DMAm with a [MOEAm] 0 /[DMAm] 0 /[Me 2 EtSiH] 0 molar ratio of 50/50/1 (Table 2, run 9), after confirming the quantitative consumption of MOEAm in the first GTP, DMAm was added to the living PMOEAm system to perform the second GTP.The progress of GTcoP was verified through the shift in the SEC traces of the resulting polymers between the first and second GTPs while maintaining a Ð value below 1.13, as illustrated in Figure S1.The M n,SEC of the resulting polymer increased from 9.6 kg mol −1 at the first GTP to 14.4 kg mol −1 at the second GTP, consistent with the M n,calcd values of 9.4 and 14.3 kg mol −1 , respectively.Furthermore, the block GTcoP of MOEAm and EOEAm performed with a [MOEAm] 0 /[DMAm] 0 /[Me 2 EtSiH] 0 molar ratio of 50/50/1 gave similar results to the block GTcoP of MOEAm and DMAm; the M n,SEC and Ð values of the resulting polymers were 9.1 kg mol −1 and 1.12 for the first GTP and 20.2 kg mol −1 and 1.11 for the second GTP.Note that the M n,SEC values were close to the M n,calcd values of 9.4 and 20.1 kg mol −1 , respectively.In the 1 H NMR spectrum of the resulting copolymer (Figure S3a), signals due to the -NCH 2 CH 2 O-and -OCH 3 groups were observed at 3.39-3.87and 3.31-3.39ppm, respectively, and a signal appearing at 2.79-3.22ppm can be attributed to the -NCH 3 group of the MOEAm and DMAm units incorporated in the polymer.Similarly, signals due to the -OCH 3 group of PMOEAm and the -OCH 2 CH 3 group of PEOEAm were observed at 3.31-3.39and 1.12-1.23 ppm, respectively (Figure S4a), which correspond to the MOEAm and EOEAm units incorporated in the copolymer.These results support the copolymer structures of PMOEAm 50 -b-PDMAm 50 and PMOEAm 50 -b-PEOEAm 50 .The polymerization results of the synthesis of PMOEAm x -b-PDMAm y and PMOEAm x -b-PEOEAm y with other x/y ratios are summarized in Table 2.
Statistical copolymers of PMOEAm-s-PDMAm and PMOEAm-s-PEOEAm were prepared via the hydrosilation-promoted GTcoP of MOEAm and DMAm or EOEAm, respectively.Table 3 lists the copolymerization results.For example, random GTcoP reactions were performed with a [MOEAm + DMAm or EOEAm] 0 /[Me 2 EtSiH] 0 molar ratio of (50 + 50)/1 (runs 21 and 26, respectively).The M n,SEC and Ð values of the resulting polymers were 14.5 kg mol −1 and 1.14 (run 21) and 20.5 kg mol −1 and 1.13 (run 26), with the M n,SEC values agreeing with the M n,calcd of 14.3 and 20.1 kg mol −1 , respectively.The 1 H NMR spectra of both polymers with an x/y ratio of 50/50 were essentially identical to those of PMOEAm 50 -b-PDMAm 50 and PMOEAm 50 -b-PEOEAm 50 (Figures S3b and S4b, respectively).Similar to PMOEAm 50 -s-PDMAm 50 and PMOEAm 50 -s-PEOEAm 50 , other statistical copolymers with different x/y ratios were synthesized via the corresponding random GTcoP; the M n,SEC values of the obtained copolymers were consistent with the M n,calcd values, and the SEC traces were unimodal with low Ð values (Figure S2).
The thermal phase transition behavior of a copolymer depends on the type of monomer sequence, i.e., alternating, block, or random sequence, which can be estimated by the monomer reactivity ratio (r).Therefore, the r values of the random GTcoP of MOEAm (r MOEAm ) and DMAm (r DMAm ) and those of MOEAm (r MOEAm ) and EOEAm (r EOEAm ) were determined using the Kelen-Tüdös method (see Supporting Information).The obtained r MOEAm and r DMAm values of 0.39 and 0.94, respectively, indicate that the sequence of the two monomers is relatively alternating-rich, whereas the r MOEAm of 1.45 and the r EOEAm of 1.03 suggest that the sequence of the two monomers is slightly block-rich.Furthermore, the number-average sequence length of the MOEAm unit (l MOEAm ) determined using the r values reflects the isolation tendency of the MOEAm-MOEAm diad.When x increased from 30 to 90 (x + y = 100) for PMOEAm x -s-PDMAm y and PMOEAm x -s-PEOEAm y , l MOEAm increased from 1.17 to 2.56, and l DMAm decreased from 3.19 to 1.27, while l MOEAm increased from 1.62 to 6.80 and l DMAm decreased from 3.40 to 1.26.These results indicate that the random GTcoP of MOEAm and DMAm or EOEAm produced PMOEAm-s-PDMAm with an alternating-rich sequence of both monomer units and PMOEAm-s-PEOEAm with a block-rich sequence of both monomer units, respectively.

Thermoresponsive Property of PMOEAm and Its Copolymers
The thermal phase transition behavior of PMOEAm and its copolymers were assessed at T cp , which is the point where the transmittance attains 50% of the transmittancetemperature curve plotted by monitoring an aqueous polymer solution (10 g L −1 ) using UV-vis spectroscopy at a wavelength of 500 nm. Figure S7 illustrates the findings.The thermoresponsive property of PMOEAm was compared with that of PMOEAm with the SKA residue at the α-chain end and block and statistical copolymers of PMOEAm and PDMAm or PEOEAm to investigate the effect of the chain-end group of the homopolymer and the monomer sequence of block and statistical copolymers on the thermoresponsive property.The dependence of T cp on the degree of polymerization (DP x ) for PMOEAm x and MCIP-PMOEAm x is shown in Figure 5a.The T cp of both polymers decreased as DP x increased, from 56.5 • C to 48.0 • C for PMOEAm x and from 41.5 • C to 34.5 • C for MCIP-PMOEAmx.The relationship between DP x and T cp for both polymers was very similar, but the T cp of MCIP-PMOEAm x was, on average, 13.4 • C lower than that of PMOEAm x , regardless of the DP x .These results indicate that the -C(CH 3 ) 2 group acted as a hydrophobic group, reducing the T cp of PMOEAm x .Therefore, a polymer without substituents at the chain ends should be used to determine whether the polymer exhibits thermoresponsive properties.The thermal phase transition should be accompanied by a change in the aggregate size of the copolymers, which was confirmed by measuring their hydrodynamic radius (R h ) in water before and after the T cp .The R h values increased drastically from 15.2 nm at 20 • C to 425.6 nm at 60 • C for the PMOEAm 50 polymer with a T cp of 53.9

Conclusions
Using the conventional method with SKA Et and the hydrosilylation-promoted method with Me2EtSiH, we proceeded in a controlled/living manner to produce PMOEAm and MCIP-PMOEAm, respectively.Using a different initiation method affected only the induction time in the early stages of the polymerization, whereas it had no effect on the propagation rate.The relationship between DPx and Tcp for PMOEAmx and MCIP-PMOEAmx was very similar, but the Tcp of MCIP-PMOEAmx was lower than that of PMOEAmx, regardless of the DPx value.Poly(N,N-disubstituted acrylamide), a polymer

Conclusions
Using the conventional method with SKA Et and the hydrosilylation-promoted method with Me2EtSiH, we proceeded in a controlled/living manner to produce PMOEAm and MCIP-PMOEAm, respectively.Using a different initiation method affected only the induction time in the early stages of the polymerization, whereas it had no effect on the propagation rate.The relationship between DPx and Tcp for PMOEAmx and MCIP-PMOEAmx was very similar, but the Tcp of MCIP-PMOEAmx was lower than that of PMOEAmx, regardless of the DPx value.Poly(N,N-disubstituted acrylamide), a polymer segment combined in copolymers of PMOEAm, affected the thermoresponsive properties, with the Tcp of the block and statistical copolymers consisting of PMOEAm, and nonthermoresponsive and highly water-soluble PDMAm being higher than that of copolymers with thermoresponsive and less water-soluble PEOEAm.For PMOEAm and its block and statistical copolymers, the Tcp was slightly higher for PMOEAm-b-PDMAm than for PMOEAm and considerably higher for PMOEAm-s-PDMAm due to the alternating-rich nature of the monomer sequence.Meanwhile, the difference in Tcp was small between PMOEAm, PMOEAm-b-PEOEAm, and PMOEAm-s-PEOEAm, and the DP dependence on Tcp was small for these (co)polymers.These thermoresponsive features are most likely caused by the low Tcp of PEOEAm.To determine whether a polymer exhibits thermoresponsive properties and the type of comonomers that are appropriate to obtain thermoresponsive copolymers, polymers without substituents at the chain ends should be used.Hydrosilylation-promoted GTP is a reliable tool for resolving these issues and will

Conclusions
Using the conventional method with SKA Et and the hydrosilylation-promoted method with Me 2 EtSiH, we proceeded in a controlled/living manner to produce PMOEAm and MCIP-PMOEAm, respectively.Using a different initiation method affected only the induction time in the early stages of the polymerization, whereas it had no effect on the propagation rate.The relationship between DP x and T cp for PMOEAm x and MCIP-PMOEAm x was very similar, but the T cp of MCIP-PMOEAmx was lower than that of PMOEAm x, regardless of the DP x value.Poly(N,N-disubstituted acrylamide), a polymer segment combined in copolymers of PMOEAm, affected the thermoresponsive properties, with the T cp of the block and statistical copolymers consisting of PMOEAm, and nonthermoresponsive and highly water-soluble PDMAm being higher than that of copolymers with thermoresponsive and less water-soluble PEOEAm.For PMOEAm and its block and statistical copolymers, the T cp was slightly higher for PMOEAm-b-PDMAm than for PMOEAm and considerably higher for PMOEAm-s-PDMAm due to the alternating-rich nature of the monomer sequence.Meanwhile, the difference in T cp was small between PMOEAm, PMOEAmb-PEOEAm, and PMOEAm-s-PEOEAm, and the DP dependence on T cp was small for these (co)polymers.These thermoresponsive features are most likely caused by the low T cp of PEOEAm.To determine whether a polymer exhibits thermoresponsive properties and the type of comonomers that are appropriate to obtain thermoresponsive copolymers, polymers without substituents at the chain ends should be used.Hydrosilylation-promoted GTP is a reliable tool for resolving these issues and will contribute to the molecular design, synthesis, and application of thermoresponsive polymer materials.

) 48. 0 a
[MOEAm] concentration of 1.0 mol L −1 was used in CH 2 Cl 2 solvent at 25 • C under an Ar atmosphere.Monomer conversion was determined to be >99.9% by 1 H NMR in CDCl 3 .b The molecular mass of the polymers was calculated using the equation [MOEAm]/[Me 2 EtSiH]0 × (conv.)× (M.W. of monomer) + (M.W. of H) × 2. c The molecular mass of polymer was determined by SEC equipped with an RI detector in DMF containing lithium chloride (0.01 mol L −1 ) using PMMA as standards.d The T cp s of [MOEAm] was determined by UV-vis measurements in water at 10 g L −1 .
) 48.0 a [MOEAm] concentration of 1.0 mol L −1 was used in CH2Cl2 solvent at 25 °C under an Ar atmosphere.Monomer conversion was determined to be >99.9% by 1 H NMR in CDCl3.b The molecular mass of the polymers was calculated using the equation [MOEAm]/[Me2EtSiH]0 × (conv.)× (M.W. of monomer) + (M.W. of H) × 2. c The molecular mass of polymer was determined by SEC equipped with an RI detector in DMF containing lithium chloride (0.01 mol L −1 ) using PMMA as standards.d The Tcps of [MOEAm] was determined by UV-vis measurements in water at 10 g L −1 .
reveals a sole set of molecular ion peaks with an adjacent peak distance of 187.24 Da, consistent with the molecular mass prediction of MOEAm as the constitutional repeat unit.Moreover, the m/z values of each molecular ion peak were in accordance with the sodium-cationized polymer composition of [H-MOEAmn-H + Na] + (molecular formula: C 9n H 17n + 2 H 2 NnO 3n Na).For example, an m/z value of 4705.82Da corresponds to a sodium-cationized 25-unit polymer structure of [H-MOEAm 25 -H + Na] + , with a theoretical monoisotopic value of 4705.03Da for the molecular formula C 225 H 427 N 25 O 75 Na.Polymers 2023, 15, 4681 6 of 15 Polymers 2023, 15, x FOR PEER REVIEW 6 of 16

Figure 3 .
Figure3.MALDI-TOF MAS spectra of (a) PMOEAm25 with a Mn,SEC of 4.5 kg mol −1 and a Đ of 1.13 (Table1, run 1) and (b) MCIP-PMOEAm25 with a Mn,SEC of 5.1 kg mol −1 and a Đ of 1.11 (TableS1, run 1).Furthermore, the polymerization features of the GTP of MOEAm initiated using two different methods were compared by evaluating the polymerization kinetics.The GTP of MOEAm was performed at a [MOEAm]0/[Me2EtSiH or SKA Et ]0/[B(C6F5)3]0 ratio of 100/1/0.1 and a [MOEAm]0 of 1.0 mol L −1 in CH2Cl2 at 25 °C.Although Et3SiH should be used for an accurate comparison with SKA Et , the hydrosilylation-promoted GTP of DSAm with Et3SiH did not proceed in a controlled/living manner; therefore, Me2EtSiH was used instead of Et3SiH.As shown in Figure4, both GTP systems exhibited induction times (ti), with the ti for Me2EtSiH (13.1 min) being smaller than that for SKA Et (55.0 min) due to the difference in both initiation reactions.In the kinetic plot of MOEAm with Me2EtSiH and SKA Et , a clear zero-order relationship between polymerization time and monomer conver-
, at the α-chain end and a hydrogen atom at the ω-chain end of [CH 3 O 2 CC(CH 3 ) 2 -MOEAm n -H + Na] + (C 9n+5 H 17n+9 N n O 3n+2 Na).For example, an m/z of 4805.52 Da for a specific peak corresponds to a [CH 3 O 2 CC(CH 3 ) 2 -MOEAm 25 -Polymers 2023, 15, 4681 7 of 15 H + Na] + with a theoretical monoisotopic value of 4806.09 for C 230 H 436 N 25 O 77 Na.In the conventional and hydrosilylation-promoted GTP reactions, the resulting polymers consisted only of monomeric units, although the difference between Me 2 EtSiH and SKA Et used in the initiation reaction was reflected in the structure of the initiating end of the polymer, i.e., PMOEAm 25 and CH 3 O 2 CC(CH 3 ) 2 -MOEAm 25 , respectively.Furthermore, the polymerization features of the GTP of MOEAm initiated using two different methods were compared by evaluating the polymerization kinetics.The GTP of MOEAm was performed at a [MOEAm] 0 /[Me 2 EtSiH or SKA Et ] 0 /[B(C 6 F 5 ) 3 ] 0 ratio of 100/1/0.1 and a [MOEAm] 0 of 1.0 mol L −1 in CH 2 Cl 2 at 25 • C.Although Et 3 SiH should be used for an accurate comparison with SKA Et , the hydrosilylation-promoted GTP of DSAm with Et 3 SiH did not proceed in a controlled/living manner; therefore, Me 2 EtSiH was used instead of Et 3 SiH.As shown in Figure

a
The cloud point temperature of [MOEAm] was determined by measuring its ultraviolet-visible spectrum in water at a concentration of 10 g L −1 .b Determined by DLS measurements in 10 g L −1 water by dynamic light scattering (DLS).c At 75 • C. For all copolymer systems, the T cp increased with a decreasing DP x from 51.4 • C to 58.0 • C for PMOEAm x -b-PDMAm y , from 55.5 • C to 73.4 • C for PMOEAm x -s-PDMAm y , from 25.0 • C to 43.5 • C for PMOEAm x -b-PEOEAm y , and from 33.7 • C to 46.2 • C for PMOEAm x -s-PEOEAm y (Figures 5 and 6b).PDMAm is nonthermoresponsive and highly water soluble, whereas PEOEAm is thermoresponsive with a low T cp and less water soluble.This is reflected in the T cp of the block and statistical copolymers of PMOEAm-b-PDMAm and PMOEAm x -s-PDMAm, which were higher than those of PMOEAm-b-PEOEAm and PMOEAm-s-PEOEAm.For PMOEAm and its block and statistical copolymers, the T cp increased slightly from 53.9 • C for PMOEAm 50 to 58.0 • C for PMOEAm 50 -b-PDMAm 50 and increased considerably to 72.1 • C for PMOEAm 50 -s-PDMAm 50 due to the alternatingrich monomer sequence.Meanwhile, the T cp decreased from 53.9 • C for PMOEAm 50 to 43.5 • C for PMOEAm 50 -b-PDMAm 50 and increased slightly to 46.2 • C for PMOEAm 50 -s-PEOEAm 50 .The slight difference in T cp between the block and statistical copolymers can be attributed to the lower degree of blockiness in the monomer sequence in the statistical copolymer.

Figure 6 . 1 H
Figure 6. 1 H NMR spectra of (a) PMOEAm 50 -b-PDMAm 50 measured in D 2 O at 30, 50, and 70 • C and (b) PMOEAm 50 -b-PEOEAm 50 measured in D 2 O at 20, 30, and 50 • C. The phase transition behavior was confirmed by measuring 1 H NMR spectra at different temperatures.In the 1 H NMR spectra of PMOEAm 50 -b-PDMAm 50 with a T cp of 58.0 • C, signals attributed to the -OCH 3 group of PMOEAm and the -NCH 3 group of PDMAm were observed at 3.19-3.30and 2.73-3.07ppm, respectively, at 30 • C.These signals shifted to a low magnetic field, and the intensity of the signal of the -OCH 3 group decreased compared with that of the -NCH 3 group at 50 • C. The signal of the -OCH 3 group completely disappeared at 75 • C. A similar thermal phase transition was observed for PMOEAm 50 -s-PDMAm 50 with a T cp of 72.1 • C (Figure S5).Furthermore, an increase in R h from 16.7 nm at 20 • C to 402.8 nm at 70 • C for PMOEAm 50 -b-PDMAm 50 and from 14.5 nm at 20 • C to 349.9 nm at 75 • C for PMOEAm 50 -s-PDMAm 50 was observed.These results indicate that PMOEAm and PDMAm acted as hydrophobic and hydrophilic moieties, respectively, resulting in the formation of aggregates comprising a PMOEAm core and a PDMAm shell.In the 1 H NMR spectra in the D 2 O of PMOEAm 50 -b-PEOEAm 50 with a T cp of 25.0 • C (Figure 5b), the signal at 1.11 ppm attributed to the -OCH 2 CH 3 groups of PEOEAm decreased at 20 • C and disappeared completely at 30 • C, which may be partly due to the low T cp of 13.9 • C for the PEOEAm 50 moiety.A signal due to the -OCH 3 of PMOEAm observed at 3.27 ppm at 20 • C decreased considerably at 30 • C and disappeared completely at 50 • C. A similar thermal phase transition was observed in the 1 H NMR spectra of PMOEAm 50 -s-PEOEAm 50 with a T cp of 46.2 • C (Figure S5).However, an increase in R h from 16.7 nm at 20 • C to 402.8 nm at 60 • C for PMOEAm 50 -b-PEOEAm 50 and from 18.9 nm at 20 • C to 551.7 nm at 60 • C for PMOEAm 50 -s-PEOEm 50 confirmed the thermal phase transition.In the block and statistical copolymers of PEOEAm and PMOEAm, the small change in T cp is due to PEOEAm with a low T cp acting as a highly hydrophobic moiety.
• C and from 16.1 nm at 20 • C to 457.2 nm at 60 • C for the MCIP-PMOEAm 50 polymer with a T cp of 40.8 • C (Table4).