R–Cl/SnCl4/n-Bu4NCl-induced direct living cationic polymerization of naturally-derived unprotected 4-vinylphenol, 4-vinylguaiacol, and 4-vinylcatechol in CH3CN

Abstract

A combination of an alkyl chloride (R–Cl) as an initiator and MtCl_n as an activator, which is a common initiating system for living cationic polymerizations, was used for the direct cationic polymerization of unprotected 4-vinylphenol or p-hydroxystyrene (pHOS), which were derived from naturally-occurring p-coumaric acid via decarboxylation, in the absence and presence of additives such as n-Bu₄NCl. The initiating system consisting of an HCl-adduct of p-methoxystyrene (pMOS–HCl), SnCl₄, and n-Bu₄NCl induced the direct living cationic polymerization of pHOS in CH₃CN at −40 °C without using any protective groups on the phenolic groups and resulted in well-defined poly(pHOS) with controlled molecular weights and narrow molecular weight distributions (MWDs) (M_w/M_n = 1.1–1.2). The pMOS–HCl/SnCl₄/n-Bu₄NCl initiating system was also effective for living cationic polymerization of pMOS in CH₃CN even in the presence of phenol, where side reactions such as proton initiation and chain-transfer reactions caused by phenol were almost completely suppressed. ¹H and ¹¹⁹Sn NMR analyses of the mixtures revealed that CH₃CN strongly interacted with both the phenol and SnCl₄ and thereby prevented the direct interaction between the phenol and SnCl₄, suppressing these side reactions. Similar direct living cationic polymerizations of 4-vinylguaiacol and 4-vinylcatechol, which were obtained via decarboxylation of naturally-occurring ferulic and caffeic acids, respectively, resulted in well-defined polymers (M_w/M_n = 1.1–1.2) in CH₃CN without protecting the phenol and catechol groups.