Synthesis and characterization of vinyl acetate/N-phenylmaleimide copolymers and the corresponding polyvinyl alcohol/N-phenylmaleimide with color cycle change property

N-phenylmaleimide (NPMI) has a specially five-membered ring and N-aryl substituted structure, which allows its homopolymers and copolymers to exhibit remarkable thermal resistance properties. By introducing a desired amount of NPMI into polyvinyl acetate (PVAc) and polyvinyl alcohol (PVA) main chain, their thermal resistance properties will hopefully be significantly improved. There is a very large gap in the reactivity ratios between NPMI (rNPMI = 86.12) and vinyl acetate (VAc, rVAc = 0.001) in methanol by counting experimental results. As a result, the co-polymerization of NPMI (a relatively high reactive monomer) with low-reactive VAc remains a great challenge in industrial synthesis. In this paper, VAc was copolymerized with different mole ratios NPMI by starvation feeding method. The DSC curves indicated that the introduction of 4% NPMI improved Tg of PVAc/NPMI by about 10 °C. After hydrolysis, the corresponding PVA/NPMI also exhibits higher Tg compared to that of pure PVA under identical polymerization conditions. Interestingly, a visible and rapid discoloration can be observed after the incorporation of a base catalyst during the alcoholysis of PVAc/NPMI, and such color change is reversible under acid or base conditions. The mechanism of color change has been ascribed to interconversion between keto and enol under the interplay of acid or base conditions.