Anionic polymerization of ferulic acid-derived, substituted styrene monomers

Abstract

Ferulic acid, a natural cinnamic acid derivative with hydroxyl and methoxy group, was quantitatively converted into protected functional styrene monomers via 4–vinylguaiacol (VG) as an intermediate. In a facile and scalable two-step reaction including decarboxylation followed by protection reactions, the monomers 1-ethoxy ethoxy-VG and tert-butyldimethylsilyl-VG were obtained in high yields. Living anionic polymerization of the acetal (1-ethoxy ethoxy-) and silyl (tert-butyldimethylsilyl-) protected styrenes proceeded to well-defined polymers with narrow MWD, although the reaction temperatures in THF were dependent on the protecting groups of the monomers. Deprotection of the acetal and silyl groups was conveniently attained under acidic conditions both in THF and water, resulting in well-defined poly(vinylguaiacol). In addition, demethylation with boron tribromide was performed to obtain poly(vinylcatechol) copolymers, which were used to complex Fe(III). Random copolymerization was observed for the statistical EE-VG and styrene copolymerization in THF at –95 °C. Aiming at a fully biobased approach, 4-isopropylstyrene was synthesized from cuminaldehyde by Wittig reaction, and the copolymerization of the latter with EE-VG was also performed, resulting in multi-hydroxyl functional macroinitiators after deprotection, which were employed for subsequent L-lactide and 4-methyl-ε-caprolactone grafting.