Free‐radical copolymerization of styrene with N‐phenyl maleimide initiated by thiol

Abstract 2‐Methyl–2‐undecanethiol was found efficient to initiate the free‐radical copolymerization of styrene (St) with N‐phenyl maleimide (NPMI) at 40°C. The initial copolymerization rate increases with the increasing of thiol concentration at first, then keeps constant with the further increasing of the thiol concentration. The charge‐transfer complex (CTC) formed between St and NPMI was investigated in different solvents by using 1H‐NMR. There is no definite correlation between CTC equilibrium constant, K, and the polarity of the solvent. With the increasing of CTC concentration, both the copolymerization rate and NPMI content in copolymer enhances, indicating the participation of CTC in both initiation and propagation. The monomer reactivity ratios were calculated to be rNPMI = 0.052 and rSt − 0.166, showing an alternating tendency for the copolymerization of St with NPMI. The molecular weight approach has shown again the effect of CTC. The function of thiol as a regulator is mitigated due to the involvement of CTC.