Synthesis and thermal properties of vinyl copolymers with phenyl vinylethylene carbonate and N-substituted maleimides undergoing color change with acid–base switching

The radical copolymerization of phenyl vinylethylene carbonate (PVEC) with various vinyl and cyclic monomers successfully proceeded through selective vinyl polymerization. In particular, compared with that of the other vinyl and cyclic comonomers, the copolymerization with the N-substituted maleimides (NMI) exhibited high yield and molecular weight without dependence on the N-substituents, due to construction of a charge-transfer complex between PVEC (electron-donor) and NMI monomers (electron-acceptors). IR and UV-vis spectra of these copolymers suggested that the alternating polymerization proceeded between PVEC and NMI monomers, and also indicated that the malemide moiety formed an enolate tautomer in the presence of sufficiently strong basic reagents. The solution of these copolymers was red in color in basic solvents due to the formation of the enolate tautomer, and the solution color changed with a high sensitivity to acid–base switching. These copolymers also exhibited high thermal stability resulting from the maleimide moiety contained within the main-chain.