Introduction

Group-transfer polymerization (GTP) was developed as a controlled living-polymerization method of (meth)acrylates by Webster et al. in the 1980s [1]. The first-generation GTP system used fluoride ions and silyl ketene acetals (SKAs) as the catalyst and the initiator, respectively. Since then, numerous improvements have been made to the GTP system to control the living-polymerization fashion and expand the range of available monomer substrates. Hertler et al. reported that Lewis acids, such as zinc halides, organo aluminum, and HgI2, can be applied to the controlled GTP of acrylates [2,3,4,5,6]. In addition, Kakuchi et al. developed a highly efficient organo-catalyzed GTP system using a silicon-based Lewis acid catalyst [7, 8].

Crotonic acid, cinnamic acid, and their derivatives are β-substituted acrylic compounds possessing a methyl or phenyl group at the β-position of the α,β-unsaturated carbonyl compound [9, 10]. The addition polymerization of these compounds is challenging because of the steric hindrance and/or electrical factor of the β-substituent [11,12,13,14,15,16,17,18,19,20,21]. In this context, Chen et al. recently developed a frustrated Lewis pair-catalyzed polymerization system for methyl crotonate (MC) and indenone, which used an N-heterocyclic carbene or hydrosilane as a Lewis base and an aluminum or boron compound as a Lewis acid [22,23,24]. In addition, Ute et al. developed a GTP system for the homopolymerization of various alkyl crotonates using an inorganic Lewis acid (HgI2 or CdI2) as the catalyst and iodotrialkylsilane as the cocatalyst [25,26,27,28]. Furthermore, our group reported that the organo-catalyzed GTP system using N-(trimethylsilyl)bis(trifluoromethanesulfonyl)imide (Tf2NSiMe3) and 1-trimethylsiloxyl-1-methoxy-2-methyl-1-propene (MTS), as described by Kakuchi et al., is applicable to the efficient homopolymerization of various alkyl crotonates and cinnamates [29, 30]. These studies also demonstrated that the homopolymers synthesized from β-substituted acrylates exhibit relatively high thermal stabilities, likely due to the contribution of the stiff polymer main chain bearing substituents at the α- and β positions.

Because copolymerization can greatly enhance the extent of currently attainable polymeric properties, investigations into the copolymerizability and the applicable comonomer range of β-substituted acrylates could expand the potential polymer applications [31,32,33,34]. However, our GTP system did not guarantee copolymerization because the living chain end was frequently deactivated via cyclization termination reactions [29, 30, 35, 36]. Recently, we demonstrated that changing the silyl groups of Tf2NSiMe3 and MTS to a bulkier group, such as a tert-butyldimethylsilyl moiety, is an effective means for suppressing termination reactions in the GTP system [37]. Thus, we herein report our investigation into the copolymerization of β-substituted acrylates (i.e., crotonates and cinnamate) using an organo-catalyzed GTP system with N-(tert-butyldimethylsilyl)bis(trifluoromethanesulfonyl)imide (Tf2NSitBuMe2) and 1-methoxy-1-(tert-butyldimethylsiloxy)-2-methyl-1-propene (tBuMe2SKA). Two types of copolymerization strategies are evaluated based on different monomer feed methods. More specifically, a one-stage copolymerization is conducted to obtain a random copolymer, where two types of monomers are added simultaneously to the polymerization system. In addition, two-stage polymerization is conducted to obtain a block copolymer, where one monomer is homopolymerized in the first stage, and a second feed of comonomer is subsequently added to the system. The series of copolymers prepared via this one-stage copolymerization approach incorporate two types of β-substituted acrylates selected from MC: ethyl crotonate (EC), isopropyl crotonate (iPC), n-butyl crotonate (nBC), and methyl cinnamate (MCin). Moreover, block copolymers of β-substituted acrylates with common methacrylates, such as methyl methacrylate (MMA) and n-butyl methacrylate (nBMA), are prepared by the two-stage copolymerization approach using the living-polymerization characteristics of the GTP system (Scheme 1). To the best of our knowledge, examples of addition copolymerization strategies incorporating cinnamates into the polymer backbone are limited [38,39,40]. We also investigated the thermal stabilities of a series of obtained copolymers by dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA).

Scheme 1
scheme 1

Copolymerization strategies toward β-substituted acrylates via GTP using Tf2NSitBuMe2 and tBuMe2SKA

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Experimental

Materials

MC, EC, iPC, nBC, MCin, MMA, nBMA, methyl isobutyrate, tert-butyldimethylchlorosilane, N,N’-dimethylpropyleneurea, lithium(diisopropylamide) (1.5 M in THF), and bis(trifluoromethanesulfonyl)imide (Tf2NH) were obtained from Tokyo Chemical Industry Co., Ltd. CH2Cl2 and tetrahydrofuran (THF) (Kanto Chemical Co., superdehydrated grade) were purified using an SPS 800 system (MBraun). Argon and nitrogen were purified before use by passing through a dry clean column (4 Å molecular sieves) and a gas clean CC-XR column purchased from Nikka Seiko. All monomers, except MCin, were distilled using CaH2 and stored in a glovebox. MCin was purified using 3 and 4 Å molecular sieves in CH2Cl2 and stored in a glovebox.

Synthesis of 1-methoxy-1-(tert-butyldimethylsiloxy)-2-methyl-1-propene) (tBuMe2SKA)

1-Methoxy-1-(tert-butyldimethylsiloxy)-2-methyl-1-propene (tBuMe2SKA) was synthesized by the reaction of methyl isobutyrate and tert-butyldimethylchlorosilane, in accord with the literature [41]. More specifically, a solution of methyl isobutyrate (14.0 g, 137 mmol) in THF (200 mL) was charged to a flask filled with dry nitrogen gas, after which a 1.5 M lithium(diisopropylamide) THF solution (100 mL, 150 mmol) was added dropwise with vigorous stirring at −78 °C over 30 min. Subsequently, a solution of N,N′-dimethylpropyleneurea (200 mmol) and tert-butyldimethylchlorosilane (22.6 g, 150 mmol) in THF (50 mL) was added, and stirring continued at −78 °C for 60 min. Next, the reaction mixture was warmed to room temperature and stirred for 24 h before concentration. The resulting mixture was taken up in hexane (500 mL), washed with water (3 × 100 mL), saturated aqueous NaHCO3 (100 mL), and brine (100 mL), and then dried over anhydrous MgSO4. After filtration, the organic layer was concentrated. Distillation under vacuum conditions gave the desired tBuMe2SKA as a clear, colorless liquid (54% yield) with a purity of >99%, as determined by proton nuclear magnetic resonance (1H NMR) spectroscopy.

Measurements

All molecular weight data for the polymer samples were obtained by gel permeation chromatography (GPC) at 40 °C using a Shimadzu GPC system equipped with an RID-10A refractive index detector, a Shodex GPC K-802 column, and a Shodex GPC K-806 M column. CHCl3 was used as the eluent at a flow rate of 0.8 mL min−1. Polystyrene standards with a low polydispersity were used to obtain a calibration curve.

1H NMR and 13C NMR measurements were performed on a Varian NMR system. The samples were dissolved in CDCl3, and 500 MHz 1H NMR spectra were recorded at room temperature. The 125 MHz 13C NMR spectra were recorded at room temperature in a CDCl3 solution. The data were calibrated against tetramethylsilane (TMS, δ 0.00) and analyzed using Mnova NMR software.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) was conducted on an ultrafleXtreme MALDI-TOF spectrometer (Bruker Daltonics, Billerica, MA) operating in linear mode at an accelerating voltage of 20 kV. Samples for MALDI-TOF-MS comprised combinations of the polymer (2 μL), the matrix (1,8-dihydroxy-9(10H)-anthracenone (dithranol), 10 mg mL−1, 8 μL), and the ionizing agent (sodium trifluoroacetate, 10 mg mL−1, 2 μL) in THF. Samples were deposited on an MTP 384 ground steel target plate. External calibration was conducted before data acquisition. The detected mass list was extracted using FlexAnalysis software (Bruker Daltonics).

TGA was performed on an SII Nano Technology TG/DTA7200 thermal analyzer from room temperature to 500 °C in a nitrogen atmosphere at a heating rate of 10 °C min−1. Td5 and Td50 were defined as the temperature at which the weight loss reached 5% and 50%, respectively, of the total weight.

The Tg of each polymer sample was measured by DMA (Perkin Elmer DMA800) under a nitrogen atmosphere by cooling the sample to −50 °C at a rate of 10 °C min−1 and then recording the DMA scan from −50 to +250 °C at a heating rate of 5 °C min−1 and a frequency of 1 Hz.

Group-transfer polymerization

All manipulations were performed in a dry and oxygen-free argon atmosphere using standard high-vacuum Schlenk techniques or a glovebox. A typical procedure for the one-stage polymerization process (entry 3, Table 1) was as follows: MC (501 mg, 5 mmol), nBC (711 mg, 5 mmol), tBuMe2SKA (10.8 mg, 0.050 mmol), and CH2Cl2 (6.0 mL) were charged to a Schlenk tube in a glovebox. A CH2Cl2 solution (2.7 mL) of Tf2NH (7.0 mg, 0.025 mmol) was added to initiate the polymerization reaction at 0 °C. After 48 h, methanol (10 mL) was added to the reaction mixture, after which the solvents were removed by evaporation under reduced pressure. The residue was then dissolved in CHCl3, and the solution was poured into a large volume of hexane. The precipitated polymer was collected as the hexane-insoluble component by filtration, washed several times with hexane, and dried under vacuum for 24 h. For the two-stage polymerization process (entry 8, Table 1), the procedure was as follows: MC (501 mg, 5 mmol), tBuMe2SKA (10.8 mg, 0.050 mmol), and CH2Cl2 (4.0 mL) were charged to a Schlenk tube in a glovebox. A CH2Cl2 solution (2.7 mL) of Tf2NH (7.0 mg, 0.025 mmol) was added to initiate the polymerization reaction at 0 °C. After 24 h, a CH2Cl2 solution (2.0 mL) of nBC (711 mg, 5 mmol) was added dropwise, and the polymerization reaction was allowed to continue for an additional 24 h. The second monomer feed was introduced without sampling from the first step because this manipulation may deactivate the living polymers by introducing trace amounts of water. Finally, the reaction was worked up using the same process that was employed for the one-stage polymerization.

Table 1 Summarized data for the copolymerization of two types of β-substituted acrylatesa
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Results and discussion

Copolymerization using two types of β-substituted acrylates

Initially, the preparation of a series of copolymers incorporating two types of β-substituted acrylates (M1 and M2) selected from the MC, EC, iPC, nBC, and MCin groups was attempted by GTP using Tf2NSitBuMe2 (generated via the in situ reaction between tBuMe2SKA and Tf2NH (Scheme S1, Supporting Information)) as the catalyst and tBuMe2SKA as the initiator in CH2Cl2 at 0 °C at a molar feed ratio of M1:M2 = 1:1. Table 1 summarizes the conversions of M1 and M2 (x1 and x2, respectively), the polymer yields, the number-average molecular weights (Mn), and the dispersities (Đ) of the obtained polymers. Figure 1 shows the GPC curves for the synthesized polymers.

Fig. 1
figure 1

GPC curves of the obtained polymers for the reaction presented in entries 1–9 (Table 1)

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When the polymerization reaction was conducted using a simultaneous feed of M1 and M2 (one-stage polymerization) (entries 1–7, Table 1), the consumption of both monomers was observed. In the cases of entries 1–3, the use of MC as M1 and an alkyl crotonate (EC, iPC, or nBC) as M2, where the molar feed ratio of the sum of M1 and M2 versus the initiator was 400, polymers possessing a high molecular weight (Mn > 76 kg mol−1) and a relatively narrow dispersity (Ð < 1.2) were obtained. In particular, the polymer obtained by the reaction outlined in entry 3 (i.e., from MC and nBC) exhibited a high molecular weight of >107 kg mol−1. In terms of entries 4–7, the use of alkyl crotonates (MC, EC, iPC, or nBC) as M1 and MCin as M2, where the molar feed ratio of the sum of M1 and M2 versus the initiator was 100, gave polymers possessing a relatively high molecular weight (Mn > 24 kg mol−1) and a relatively narrow dispersity (Ð < 1.3). The exception to this rule was entry 6, where the reactivity of iPC was low, which was likely due to the steric hindrance of the ester group.

In the case of the two-stage polymerization process (entries 8 and 9, Table 1), where M1 was homopolymerized for 24 h in the first stage, followed by a second feed of M2 and polymerization for an additional 24 h, the consumption of M2 was barely observed. The molecular weights of the obtained polymers (Mn = 53 100 g mol−1 in entry 8 and 63 900 g mol−1 in entry 9) were clearly smaller than that obtained for the reaction of entry 3 (Mn = 107 600 g mol−1), where the polymerization process was conducted under conditions identical to those for entries 8 and 9, with the exception of the monomer feeding method. This result suggests that in the two-stage polymerization of β-substituted acrylates, the amount of living polymer derived from M1 was low during the additional M2 feed. This deactivation of a living polymer is thought to be caused by a side reaction, such as an intramolecular termination reaction (e.g., terminal cyclization of the propagating chain-end groups), as proposed for the GTP system [35, 36].

Structural analyses of the obtained polymers

To confirm the structures of the obtained polymers, 1H NMR analyses were conducted. Figure 2a shows the 1H NMR spectrum of the polymer synthesized using MC as M1 and EC as M2 (entry 1, Table 1), in addition to those of poly(MC) and poly(EC), which were synthesized via a similar GTP route for comparison (Table S3, Supporting Information). Furthermore, Fig. 2b shows the 1H NMR spectrum of the polymer synthesized using EC as M1 and MCin as M2 (entry 5, Table 1), in addition to those of the prepared poly(EC) and poly(MCin) (Table S3, Supporting Information). As shown in Fig. 2a, the 1H NMR spectrum of entry 1 agrees well with the overlap of the spectra of poly(MC) and poly(EC). Similarly, as shown in Fig. 2b, the 1H NMR spectrum of entry 5 is comparable to the superposition of the spectra of poly(EC) and poly(MCin). These results suggest that the consumed monomers (M1 and M2) were successfully introduced into the polymer backbone.

Fig. 2
figure 2

1H NMR spectra (red lines) of the polymers synthesized from a MC as M1 and EC as M2 (entry 1, Table 1) and b EC as M1 and MCin as M2 (entry 5, Table 1), measured at 500 MHz in CDCl3 at room temperature. The blue and green lines represent the 1H NMR spectra of the homopolymers synthesized from M1 and M2, respectively

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The molecular structures of the obtained polymers were investigated in greater detail by MALDI-TOF-MS analysis. Figure 3a shows the mass spectrum of the polymer synthesized using MC as M1 and iPC as M2 (entry 2, Table 1), while Fig. 3b shows the mass spectrum of the polymer synthesized using EC as M1 and MCin as M2 (entry 5 in Table 1).

Fig. 3
figure 3

MALDI-TOF-MS spectra of the polymers synthesized from a MC as M1 and iPC as M2 (entry 2, Table 1) and b EC as M1 and MCin as M2 (entry 5, Table 1), measured using dithranol as a matrix and CF3COONa as an ionizing agent

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From the detailed analysis, it was confirmed that the observed peaks correspond to the sum of the masses of the copolymers containing M1 and M2 generated by GTP using tBuMe2SKA and Na+ (derived from CF3COONa added as an ionizing agent in the MALDI-TOF-MS measurements). The polymer shown in Fig. 3a was therefore determined to have the structural formula (CH3)2[CH3OC(=O)]C–(MC)m(iPC)n–H, where the (CH3)2[CH3OC(=O)]C moiety at the initiation chain-end was derived from tBuMe2SKA, and the methylene group at the termination chain-end was generated by acid treatment of the terminal silyl ether group in the living polymer (Scheme S2, Supporting Information). Similarly, the polymer shown in Fig. 3b was determined to have the structural formula (CH3)2[CH3OC(=O)]C–(EC)m(MCin)n–H. Therefore, MALDI-TOF-MS structural analyses of the obtained polymers afforded clear evidence that copolymerization using a simultaneous feed of two types of β-substituted acrylates proceeded smoothly.

Time–conversion curve

Subsequently, we attained the time–conversion curve data to obtain information regarding the monomer unit arrangement in the copolymer backbone. Figure 4a shows the time–conversion curve for the copolymerization reaction using MC as M1 and EC as M2 (entry 1, Table 1), while Fig. 4b shows the time–conversion curve for the copolymerization reaction using EC as M1 and MCin as M2 (entry 5, Table 1).

Fig. 4
figure 4

Time–conversion curves for the copolymerization of a MC with EC and b EC with MCin. Copolymerization was conducted using tBuMe2SKA as the initiator and Tf2NSitBuMe2 (generated via the in situ reaction between tBuMe2SKA and Tf2NH (Scheme S1, Supporting Information)) as the catalyst in CH2Cl2 at 0 °C. The polymerization conditions were as follows: a [MC]0 = [EC]0 = 0.50 M, [tBuMe2SKA]0 = 0.0025 M, and [Tf2NSitBuMe2]0 = 0.0025 M, b [EC]0 = [MCin]0 = 0.64 M, [tBuMe2SKA]0 = 0.013 M, and [Tf2NSitBuMe2]0 = 0.013 M

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As shown in Fig. 4a, the conversion ratio of M1 (MC) versus M2 (EC) was within the range of 0.5–1 from the initial term to the end term of the copolymerization process, suggesting that the polymerization rate of EC was only slightly faster than that of MC. This result indicates that in the case of the copolymer obtained for the reaction outlined in entry 1 (Table 1), the MC and EC monomer units were incorporated throughout the polymer backbone.

In contrast, as shown in Fig. 4(b), the conversion of M1 (EC) was approximately tenfold greater than that of M2 (MCin) in the initial stage of copolymerization. This result indicates that in the case of entry 5 (Table 1), EC monomer units were primarily incorporated at the head part of the polymer backbone, while MCin monomer units were mainly incorporated at the tail end. Thus, copolymerization using two types of β-substituted acrylates with greatly different polymerizabilities leads to the generation of a gradient-like random copolymer.

Copolymer of α-substituted acrylate and β-substituted acrylate

Subsequently, the preparation of a series of copolymers from an α-substituted acrylate (M1, MMA or nBMA) and a β-substituted acrylate (M2, MC, nBC, or MCin) was attempted using the GTP protocol with Tf2NSitBuMe2 as the catalyst and tBuMe2SKA as the initiator in CH2Cl2 at 0 °C, using a molar feed ratio of M1:M2 = 1:1. Table 2 summarizes the conversions of M1 and M2 (x1 and x2, respectively), the polymer yields, and the Mn and Đ values of the obtained polymers, while Fig. 5 shows their GPC curves.

Table 2 Summarized data for the copolymerization reactions of α-substituted acrylates with β-substituted acrylatesa
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Fig. 5
figure 5

GPC curves of the polymers obtained from the reactions outlined in entries 10–17 (Table 2). The blue and red inverted triangles represent lower- and higher-molecular-weight polymers, respectively

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In the case of the two-stage polymerization reactions, where the α-substituted acrylate was homopolymerized in the first stage, followed by a second feed of the β-substituted acrylate and an additional polymerization phase (entries 10–15, Table 2), sufficient consumption of both monomers was observed. When MMA or nBMA was employed as M1 and an alkyl crotonate (MC or nBC) was used as M2, where the molar feed ratio of the sum of M1 and M2 versus the initiator was 400 (entries 10–14, Table 2), polymers possessing a relatively high molecular weight (Mn > 56 kg mol−1) were obtained. In contrast, (entry 15, Table 2), when nBMA was used as M1 and MCin was employed as M2, where the molar feed ratio of the sum of M1 and M2 versus the initiator was 100, a polymer possessing a relatively low molecular weight of 16,800 g mol−1 was obtained.

On the other hand, in the case of entry 16 (Table 2), where the first feed monomer was a β-substituted acrylate (MC) and the second feed monomer was an α-substituted acrylate (nBMA), the conversion of nBMA was particularly low (x2 < 10%). In addition, in the case of entry 17, where one-stage copolymerization was conducted, the conversion of the α-substituted acrylate (nBMA) was low (<10%). The molecular weights of the obtained polymers (Mn = 49 300 g mol−1 for entry 16, Mn = 46 700 g mol−1 for entry 17) were smaller than that of entry 12 (Mn = 57 600 g mol−1), despite the polymerization process being conducted under conditions identical to those used for entries 16 and 17 (with the exception of the monomer feeding method). These results suggest that the living chain end derived from the β-substituted acrylate exhibits poor reactivity toward the α-substituted acrylate monomer. In addition, it was suggested that the living chain end derived from a β-substituted acrylate is more susceptible to a termination reaction, such as a cyclization reaction, than that derived from an α-substituted acrylate [29, 35, 36] (Table S1 and Fig. S35, Supporting Information).

As shown in Fig. 5, the polymers obtained from the reactions outlined in entries 10–13 (Table 2) exhibit bimodal peaks in their GPC curves that correspond to lower- and higher molecular weight polymers. The peaks corresponding to a lower molecular weight were attributed to the homopolymers of the α-substituted acrylate generated by a termination reaction (e.g., cyclization reaction) of the living chain end in the first stage. On the other hand, the peaks corresponding to a higher-molecular weight were attributed to the block copolymers of M1 and M2, which propagated from the living homopolymers of the α-substituted acrylate that were alive during the second feed of the β-substituted acrylate monomer (Table S2, Supporting Information).

The polymer corresponding to entry 14 was obtained by shortening the time of the first-stage polymerization of nBMA with respect to entry 12 (12 h for entry 14 c.f. 24 h for entry 12). As shown in Fig. 5, the polymer obtained by the reaction presented in entry 14 gave an almost unimodal peak by GPC. This result confirms the hypothesis that the observed bimodal peaks for entry 12 were caused by the terminated homopolymers of nBMA. In addition, this result indicates that the block copolymer content can be enhanced by optimizing the polymerization time in the first stage.

Thermal properties of the copolymers

We then investigated the thermal properties (i.e., Tg, Td5, and Td50) of the obtained copolymers by DMA and TGA, as summarized in Table 3. In this study, Tg was defined as the temperature corresponding to the maximum tan δ value in the DMA measurements because differential scanning calorimetry did not afford a clear Tg.

Table 3 Thermal properties of the obtained copolymers
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Table 3 shows that the Tg values of the copolymers obtained in the reactions outlined in entries 1–7 and prepared from two types of β-substituted acrylates were >130 °C, indicating a relatively high heat stability. This high Tg can be rationalized via the stiffness of the polymer main chain containing substituents at the α-position (ester group) and the β-position (methyl or phenyl group). A high Tg was also confirmed for the homopolymers of β-substituted acrylates synthesized by GTP using Tf2NSitBuMe2 and tBuMe2SKA (Table S3, Supporting Information). Comparing entry 4 (copolymer of MC with MCin) with entries 1–3 (copolymer of MC as M1 with EC, iPC, or nBC, respectively, as M2) shows that the copolymer obtained using the conditions outlined in entry 4 exhibited the highest Tg. This result suggests that cinnamate is a better comonomer than crotonate for enhancing the Tg of the resulting copolymers. Among entries 1–3, greater numbers of carbon atoms on the ester group of M2 resulted in lower Tg values for the resulting copolymers. Similarly, among entries 4–7 (copolymers synthesized using MC, EC, iPC, or nBC, respectively, as M1, and MCin as M2), the ester group of crotonate (as M1) significantly influenced the Tg value of the resulting copolymers. These results indicate that the Tg of the copolymers described herein can be varied over a relatively high-temperature range by selecting the optimal comonomer.

In terms of the block copolymers prepared from an α-substituted acrylate (MMA or nBMA) and a β-substituted acrylate (MC, nBC, or MCin), the Tg corresponding to the poly(MMA) block was detected at approximately 116–32 °C (entries 10 and 11), while the Tg corresponding to the poly(nBMA) block was detected at approximately 51–58 °C (entries 12, 13, and 15). It has been previously reported that the Tg of poly(MMA) ranges from 51–122 °C, while that of poly(nBMA) ranges from 15–50 °C [42]. In contrast, the value of Tg derived from the poly(β-substituted acrylate) block was confirmed only as an indistinguishable or a small region. Thus, the Tg values of the block copolymers in this DMA study strongly reflected the characteristics of the poly(α-substituted acrylate).

Finally, in the context of their thermal decomposition, the copolymers obtained herein were found to exhibit relatively high heat resistance, with Td5 > 325 °C and Td50 > 376 °C. The exceptions to this rule were the copolymers obtained under the conditions presented in entries 6 (Table 1) and 15 (Table 2), which had relatively low molecular weights of <20 kg mol−1.

Conclusion

We herein reported the preparation of various copolymers incorporated with β-substituted acrylates, such as alkyl crotonates (MC, EC, iPC, and nBC), and MCin, via the GTP process using a silicon-based Lewis acid catalyst and SKAs possessing a relatively bulky silyl moiety, such as the tert-butyldimethylsilyl group. Our results indicated that using this organo-catalyzed GTP system, the copolymerization of β-substituted acrylates could be achieved by selecting a suitable comonomer. When multiple β-substituted acrylates were used, a simultaneous monomer feed system was necessary to ensure smooth copolymerization. In addition, when an α-substituted acrylate was used as the comonomer, a multistage copolymerization method (where the α-substituted acrylate is homopolymerized in the first stage followed by a second feed of the β-substituted acrylate) resulted in the formation of a block copolymer incorporated with each component. This monomer feed method must consider the susceptibility of termination reactions and/or the copolymerizability of the living chain end derived from the monomers used. 1H NMR spectroscopy and MALDI-TOF-MS were used to confirm the successful copolymerization reactions, and the thermal stabilities of the resulting copolymers were investigated by DMA and TGA. These results indicated that the Tg values of the prepared copolymers can be varied by changing the comonomer. Future studies should focus on the use of additional comonomers, such as acrylamides and acrylonitriles, which are known to be suitable for application in GTP systems, to gain a better understanding of the comonomer scope and to develop high-performance polymeric materials.