Iodine reaction of vinyl acetate – vinyl propionate copolymers I. Molar absorption coefficients of the copolymer‐iodine complexes

Poly(vinyl propionate) was found to form a weak iodine‐complex in an aqueous solution of potassium iodide. The complex was colorless under usual conditions differing from the poly(vinyl acetate)iodine complex which had a red‐violet colour. Random and block copolymers of vinyl acetate (VAc) and vinyl propionate (VPr) also formed colored iodine complexes. The maximum absorption wave‐length (λmax) of the complex shifted to shorter wave‐lengths with decrease in the VAc‐fraction of copolymers and to longer wave‐lengths with increase in the concentration of added iodine. This shift of λmax was discussed in connection with the chain length of the polyiodine in the complex. The molar absorption coefficient (ϵmax) of the complex (defined as absorbance per bound iodine molecule) depended remarkably upon the polymer composition. The dependence of ϵmax upon the copolymer composition could be explained by the assumption that the complex consists of two different parts, a strongly colored and a weakly colored one.