The radical homopolymerization of N-phenylmaleimide, N-n-hexylmaleimide and N-cyclohexylmaleimide in tetrahydrofuran

The kinetics and mechanisms of thermally initiated (using 2,2′-azobisisoburyronitrile (AIBN) as initiator) radical homopolymerizations of a series of maleimides, including N-phenymaleimide (PHMI) [1-phenyl-1H-pyrrole-2,5-dione]; N-n-hexylmaleimide (nHMI) [1-(n-hexyl)-1H-pyrrole-2,5-dione]; and N-cyclohexylmaleimide (CHMI) [1-cyclohexyl-1H-pyrrole-2,5-dione] have been investigated in THF solution by an on-line FT-NIR technique. It was found that the order of the activation energies for the three N-sub-MIs is: Ea PHMI<Ea nHMI<Ea CHMI. The overall polymerization rate parameter k and the pre-exponential factor A were calculated. The kinetic order with respect to the N-sub-MIs was in the range of 0.71<m<0.75 for the initiator and n=1.0 for the monomer. Radical transfer to solvent was found to be the key factor in determining the apparent order with respect to the initiator. the homopolymers had a relatively low molecular weight. The end groups of the polymer chains were characterized by MALDI-TOF, GPC and NMR methods and the results clearly indicate that the polymerization was initiated by THF radicals, and that the termination reaction is mainly controlled by chain transfer to solvent through an hydrogen abstraction mechanism.