N-vinylimidazole-N-vinyl-2-pyrrolidone copolymers. Part I. Reactivity ratios, solubility and viscosimetric study

Copolymers of N-vinylimidazole (VI) with N-vinyl-2-pyrrolidone (VP), (VI-co-VP) were obtained by radical polymerization using α,α′-azobisisobutyronitrile as initiator. The copolymers were characterized by ¹H NMR and viscosimetric measurements. The monomer reactivity ratios were estimated to be r₁ = 100 ·for VP and r₂ = 0·07 for VI by the Fineman-Ross and Kelen-Tüdos linear procedures. These parameters were also estimated using a computer program based on a non-linear minimization algorithm (NLMA) starting from the values of r₁ and r₂ obtained by the linear procedures. All copolymers could be considered as random. The solubility in chloroform, n-butanol and n-propanol depends on the copolymer composition. Water, methanol and ethanol are solvents, irrespective of the copolymer compositions. The viscosimetric behaviour of unfractionated copolymers of one composition was studied in dilute solution in water (pH 2·0 and 6·0) at 0·01 M (NaCl) ionic strength and in methanol.