Abstract
AbstractSignificant drift in the compositions of copolymer and of unreacted monomer mixture is predicted to occur during the bulk copolymerization of N‐vinyl‐2‐pyrrolidone (VP) with butyl acrylate (BA), when the inital feed mixture contains 75 wt.‐% VP. The drift in copolymer composition has been confirmed by 1 the optical appearance and glass transition (Tg) behaviour of the products of the γ‐ray initiated copolymerization at various fractional conversions (C) and 2 the Tg behaviour of low‐conversion samples of poly(VP‐co‐BA) blended in propertions so as to simulate the overall composition of material that would be present cumulatively at selected values of C during an actual copolymerization. The compositions of unreacted monomer mixtures co‐existing with copolymer at selected conversions have been calculated and intrinsic viscosities [η] of blends dissolved in these VP/BA mixtures have been measured. Theta conditions for the blends have been established turbidimetrically in chloroform/heptane and the corresponding values of [η]Θ measured. The chain expansion factors thereby derived from [η] and [η]Θ show a decreasing affinity of copolymer for residual monomer during the course of copolymerization.
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