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

The kinetics and mechanisms of thermally initiated (using 2,2'-azobisisobur yronitrile (AIBN) as initiator) radical homopolymerizations of a series of maleimides, including N-phenymaleimide (PHMI) [l-phenyl-1H-pyrrole-2,5-dion e]; N-n-hexylmaleimide (nHMI) [l-(n-hexyI)-1H-pyrrole-2,5-dione]; and N-cyc lohexylmaIeimide (CHMI) [l-cyclohexyl- 1H-pyrrole-2,5-dione] have been inve stigated 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: E-a PHMI < E-a (PHMI) < E-a (CHMI). The overall polymerization rate parameter k and t he 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 k ey factor in determining the apparent order with respect to the initiator. All of the homopolymers had a relatively low molecular weight. The end grou ps of the polymer chains were characterized by MALDI-TOF, GPC and NMR metho ds and the results clearly indicate that the polymerization was initiated b y THF radicals, and that the termination reaction is mainly controlled by c hain transfer to solvent through an hydrogen abstraction mechanism. (C) 200 1 Elsevier Science Ltd. All rights reserved.