Effect of solvent proton affinity on the kinetics of michael addition polymerization of n , n ′‐bismaleimide‐4,4′‐diphenylmethane with barbituric acid

The effect of solvent proton affinity on the kinetics of the Michael addition polymerizations of N , N ′‐bismaleimide‐4,4′‐diphenylmethane (BMI) and barbituric acid (BTA) in different solvents [ N ‐methyl‐2‐pyrrolidone (NMP), N , N ′‐dimethylacetamide (DMAC), and N , N ′‐dimethylformamide (DMF)] were investigated. This was achieved by the complete suppression of the competitive free radical polymerization via the addition of a sufficient amount of hydroquinone (HQ). A mechanistic model was developed to adequately predict the polymerization kinetics before a critical conversion, at which point the diffusion‐controlled polymerization become the predominant factor during the latter stage of polymerization, was achieved. The activation energy ( E a ) of the Michael addition polymerization of BMI with BTA in the presence of HQ in increasing order was: NMP < DMAC < DMF, which was correlated quite well with the solvent proton affinity (NMP > DMAC > DMF). By contrast, the frequency factor ( A ) in increasing order is: NMP < DMAC < DMF. As a result of the compensation effect between E a and A , at constant temperature, the Michael addition rate constant decreased with increasing solvent proton affinity. POLYM. ENG. SCI., 54:559–568, 2014. © 2013 Society of Plastics Engineers