Effect of Initiator Concentration on the Bulk Free-Radical Copolymerization of N-Vinylcaprolactam and N-Vinylimidazole

The bulk radical copolymerization of N-vinylcaprolactam (VCL) and N-vinylimidazole (VI) initiated by 2,2′-azobisisobutyronitrile (AIBN) was investigated. The composition of the resulting amphiphilic copolymers is always enriched in VI units and is independent of the initiator concentration in the range from 0.001 to 0.1 mol L−1. The reactivity ratios calculated at an AIBN concentration of 0.005 mol L−1 (rVI = 5.33 ± 0.58 and rVCL = 0.21 ± 0.01) are practically identical to those previously obtained at 0.01 mol L−1. The independence of the copolymer composition from the initiator concentration is due to the self-assembly of amphiphilic macromolecules formed during copolymerization.