Effect of Disyndiotacticity on the Glass Transition Temperature of Poly(ethyl crotonate)s Synthesized by Group-Transfer Polymerization Catalyzed by Organic Acids

Abstract

Poly(ethyl crotonate)s (PECs), possessing various disyndiotacticities, were synthesized by group-transfer polymerization using several silicon Lewis acid catalysts like N-(trialkylsilyl)bis(trifluoromethanesulfonyl)imides (trialkylsilyl = trimethylsilyl, triethylsilyl, tert-butyldimethylsilyl, and triisopropylsilyl) and silyl ketene acetals with a corresponding trialkylsilyl moiety as an initiator. Disyndiotacticity of PECs was greatly enhanced by steric hindrance from the silyl moiety of the catalyst and initiator and also by low polymerization temperature. Dynamic mechanical analysis of the obtained PECs revealed that high disyndiotacticity improves heat resistance. The glass transition temperature (Tg) measured by DMA was 201 °C at 92% disyndiotacticity and 82 °C at 53% disyndiotacticity. The Tg enhancement at high tacticity was sufficiently large when compared to syndiotactic poly(methyl methacrylate). This is attributed to the regular arrangement of polymer chains derived from highly controlled ditacticity, as supported by analysis of polarizing optical micrographs and X-ray diffraction patterns.