Dependence of association in polyacrylonitrile solutions on the molecular volume of the nonsolvent

Abstract

synopsisAn examination of data obtained from viscometric measurements of the association occurring in solutions of polyacrylonitrile in dimethylformamide, 7-butyrolactone, and dimethylacetamide has shown that the solubility parameter of the solvent-nonsolvent liquid mixture at the aggregation point is closely related to the molecular volume of the nonsolvent used to bring about association.The kinetic features of the association occurring in solutions of polyacrylonitrile in N,N'-dimethylformamide (DMF) have been examined in some detail.' Viscometric measurements made over a range of temperatures2 and with a variety of nonsolvents3 have established that association occurs through dipolar interaction between CN groups along the polymer molecule. It has been shown1 that large changes occur in the viscosity number of the solution over a narrow range of nonsolvent composition. It has been found convenient to characterize the association by determining the vol-% nonsolvent P at which the association rate constant has a value of 1 X sec-'. Although qualitatively the association of the various solvent-nonsolvent systems so far examined is similar, the primary effect of the nonsolvent is to determine the volume concentration at which association occurs. It has been shown3 that a relationship exists between the solubility parameter SNS of the nonsolvent and P as follows:where A and B are constants. Calculations carried out subsequently as a result of an examination of the effect of variation of the solvent on the associa.tion in polyacrylonitrile solutions has shown that the solubility parameter of the liquid mixture 6 , at a composition corresponding to P showed much less variation than the values of SNS. Initially it was considered that 6, had a constant value for a particular solvent or nonsolvent system, but since association can be observed in systems for which SS 2 SNS, then clearly this supposition was unrealistic. Subscripts S and NS are here taken to denote the solvent and nonsolvent components, respectively. A misplaced parameter led to calculations being made of the molecular volumes of the nonsolvents used, and it was found that variation in S , , although subjected