SYNTHESIS OF POLY(VINYLPYRROLIDONE)-POLYS TYRENE BLOCK-COPOLYMERS BY THE USE OF A MACRO-AZO-INITIATOR

A macro-azo-initiator (MAI) was prepared from 4,4'-azobis(4-cyanopent anoyl chloride) and 1,6-hexanediol, and two-step radical block copolym erization was carried out with MAI. Vinylpyrrolidone was first polyme rized, and then styrene was polymerized to synthesize poly(vinylpyrrol idone)-polystyrene block copolymers. The poly(vinylpyrrolidone) conten t (X) in the block copolymer was determined by NMR and it ranged from 8.2% to 16.0% depending on the feed conditions. Relationship between m onomer consumption of the 2nd step polymerization and [-N = N-]0(0.5) [St]0(1.2), and relationship between (100/X-1) and [St]0(1.2)/[-N = N- ]0(0.5) showed linearity. The block efficiency was about 80%, except f or the case of [St]0 < 3.0 mol/l. The molecular weights of the block c opolymers, M(n) = 100100 approximately 162000 and M(w) = 189300 approx imately 395000, were both proportional to [St]0(0.8)/[-N = N-]0(0.5). The values of the intercept agreed with M(n) and M(w) of poly(vinylpyr rolidone) having azo groups, suggesting that the structure of the bloc k copolymers may be an -(AB)-n or ABA type.