Pendant cyanate functional vinyl polymers and imido-phenolic-triazines thereof: synthesis and thermal properties

Maleimide-incorporated vinyl polymers, based on butyl acrylate (BuA), methyl methacrylate (MMA) and styrene (STY) with pendant phenol functions were synthesised by free radical copolymerization of respective monomers with N-(4-hydroxy phenyl) maleimide. The phenol functions of the linear polymers were transformed to the corresponding cyanato phenyl derivatives. Thermal curing of these polymers through the cyclotrimerization of the pendant cyanate groups led to crosslinked imido-phenolic-triazines. The thermal stabilities of the phenol precursors depended on the backbone structure. Presence of maleimide improved the thermal stability of BuA- and STY-based copolymers, whereas, it was detrimental for MMA-based ones. The early chain unzipping in the case of the latter has been attributed to the steric interaction between the α-methyl group of MMA and maleimide moiety. Although the presence of imide and triazine groups in the crosslinked network was conducive for decreasing the rate of thermal degradation at higher temperatures, they triggered an early onset of decomposition because of steric factors. The nonisothermal kinetics of thermal decomposition was studied and the relevant kinetic parameters like activation energy (E) and pre-exponential factor (A) have been calculated for various phenol-functional precursors and the corresponding imidophenolic triazines. Although the trend in values of E with composition was not indicative of the thermal stability of the triazine-network polymers due to the prevalence of kinetic compensation effect, the values served to estimate the rate constant for decomposition of various polymers, which exhibited a direct correlation with their thermogravimetric behaviour.