Copolymerizations involving N-vinyl-2-pyrrolidone

Low conversion copolymerizations have been conducted with N-vinyl-pyrrolidone (VP) as monomer-1 and the following reagents were used as monomer-2: acryloxymethylpentamethyldisiloxane (AMS), methacryloxymethylpentamethyl disiloxane (MMS), n-butyl acrylate (BA) and 2-hydroxyethylmethacrylate (HEMA). In the same order the derived monomer reactivity ratios (r₁, r₂) were (0.34, 1.57); (0.04, 4.92); (0.02, 0.80) and (0.05, 3.12). For a range of different feed compositions within each system integral curves were thereby computed for the instantaneous copolymer composition throughout all stages of conversion. These gave predictions on compositional heterogeneity which compared satisfactorily with the clear, translucent or opaque appearance of copolymers prepared to very high conversion via γ-irradiation. However, the VP-HEMA system, for which there is no azeotropic composition, yielded optically clear copolymers at all feed compositions. This finding is explained on the basis of the almost iso-refractive nature of the two homopolymers and/or strong thermodynamic compatibility among copolymers and homopolymers as evidenced by a single T_g observed on cast films.