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

A combination of an alkyl chloride (R–Cl) as an initiator and MtCln 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) (Mw/Mn = 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 (Mw/Mn = 1.1–1.2) in CH3CN without protecting the phenol and catechol groups.