A. Ueda et al., SYNTHESIS OF POLY(VINYLPYRROLIDONE)-POLYS TYRENE BLOCK-COPOLYMERS BY THE USE OF A MACRO-AZO-INITIATOR, Kobunshi ronbunshu, 51(7), 1994, pp. 453-458
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.