Interactions between unlike Polymers versus Dilute Solution Properties of Copolymers

Solution properties of the copolymers and polymer blends which are under the influence of an unfavorable heteropolymer interaction are described. A body of experimental and computer simulation data indicates that the overall effects of the interaction on the conformational properties of copolymers are strongly dependent on their chain architecture. Typically, block copolymers are surprisingly insensitive to such an interaction. Even among the statisti— cal class of copolymers, the effects are different for different arrangements of comonomer units along the chain. Moreover, the apparent effects of the interaction vary from solvent to solvent. These phenomena are comprehensively interpreted by postulating that the solubility parameter of a copolymer slightly deviates from the composition average of those of the pareDt polymers, due to the presence of alternating chemical bonds. Based on this idea, the interaction parameter X12 between polystyrene (PS) and poly(methyl methacrylate) (PNNA) has been extracted from the viscometric data on the copolymers. The parameter X12 in a ternary solution can be fairly accurately determined by the light scattering method which utilizes the optical cancellation among the scattering components. Application of this technique to PS/PMMA systems has disclosed several facts: For a given pair of the polymers, there exists a characteristic concentration * below which X12 is approximately constant but above which it increases rather sharply. The value of X12 below * is dependent on molecular weight, which can be interpreted according to the dilute solution theory. The value of X12 above * is a function of concentration only. These dilute and concentrated solution studies offer another two estimates of X12 between PS and PMMA, which are in favorable agreement with each other and also with the copolymer value. These results suggest that solution data could be, at least in certain cases, used to provide quantitative information on polymer— polymer interactions.