Copolymers incorporated with β-substituted acrylate synthesized by organo-catalyzed group-transfer polymerization

Various copolymers incorporated with β-substituted acrylates, such as alkyl crotonates (e.g., methyl crotonate (MC), ethyl crotonate (EC), isopropyl crotonate (iPC), and n-butyl crotonate (nBC)) and methyl cinnamate (MCin), were synthesized by group-transfer polymerization (GTP) using a silicon-based Lewis acid catalyst. In addition to β-substituted acrylates, α-substituted acrylates (e.g., methyl methacrylate (MMA) and n-butyl methacrylate (nBMA)) were examined as comonomers. Proton nuclear magnetic resonance (1H NMR) spectroscopy and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) characterizations of the obtained copolymers revealed that each monomer component was incorporated sufficiently. The thermal stabilities of the resulting copolymers were investigated by dynamic mechanical analysis (DMA), indicating that the glass-transition temperature (Tg) of the copolymers can be widely varied over a relatively high-temperature range by selecting the optimal comonomer. More specifically, the Tg values of poly(MC-random-EC) (MC/EC molar ratio = 50/50), poly(MC-random-nBC) (MC/nBC molar ratio = 50/50), poly(MC-random-MCin) (MC/MCin molar ratio = 54/46), and poly(nBC-random-MCin) (nBC/MCin molar ratio = 56/44) were 173, 130, 216, and 167 °C, respectively. The copolymerization of β-substituted acrylates (i.e., crotonates and a cinnamate) using an organo-catalyzed group-transfer polymerization system with N-(tert-butyldimethylsilyl)bis(trifluoromethanesulfonyl)imide (Tf2NSitBuMe2) and 1-methoxy-1-(tert-butyldimethylsiloxy)-2-methyl-1-propene (tBuMe2SKA) was investigated. The tert-butyldimethylsilyl moiety served as an effective means for suppressing the termination reactions of the GTP system. One-stage and two-stage copolymerization strategies employing different monomer feed methods were evaluated and gave random and block copolymers, respectively. The glass-transition temperatures of the prepared copolymers varied significantly depending on the comonomer used during the synthesis.