Radical-initiated copolymers of N-vinyl pyrrolidone and N-acryloxy succinimide: Kinetic and microstructure studies

Kinetics of solution (co)polymerization of N-vinyl pyrrolidone (NVP, or V) and N-acryloxy succinimide (NAS, or A) have been investigated at 60 degrees C in N, N-dimethylformamide with 4,4'-azobis(4-cyanopentanoic acid) as initiator. First, the k(p)/root k(t) value for homopolymerization of A monomer was estimated as 0.871(0.5) mol(-0.5) s(-0.5). The comonomer feed composition was observed to have a strong effect on the overall copolymerization rate. Reactivity ratios of the binary system were determined to be r(NAS) = 0.27 +/- 0.04 and r(NVP) = 0.01 +/- 0.01, indicating a strong alternating tendency in the formed copolymer. Copolymers were then characterized as regards to composition (by ultraviolet spectrophotometry) and monomer sequence distribution (by C-13 nuclear magnetic resonance spectroscopy). The presence of a small fraction of WA triads was clearly evidenced which was not expected from simulation based on a terminal kinetic model; the occurrence of a more complex model has been discussed.