The solvent action of organic substances on polyacrylonitrile

Abstract

AbstractThe facts concerning the solvent action of organic substances on polyacrylonitrile have been collected from diverse sources and new observations have been made. A new relationship between the boiling points of organic compounds and their latent heats of evaporation has been devised which is more accurate than the Hildebrand function, and this, together with new calculations and measurements of latent heats of evaporation, has been used to elucidate the relationship between the cohesive energy densities (C.E.D.) of organic compounds and their solvent power for polyacrylonitrile.All solvents for polyacrylonitrile are highly polar in character. Most of the best solvents have very high C.E.D.s in the neighbourhood of 220 to 230 cal./c.c. A separate calculation shows that this is approximately the C.E.D. of the polymer. It is believed that the molecules of such solvents have no greater attraction for the polymer molecules than they have for their own kind, solution being brought about by the increase in entropy. N‐Disubstituted amides, and probably cyclic sulphones possess strong solvent action at lower C.E.D.s (116–170 cal./c.c.), and this is probably because the molecules of these substances have a slightly greater attraction for the polymer molecules than they have for their own kind. Most strongly hydrogen‐bonded substances, such as alcohols, phenols, carboxylic acids, unsubstituted amides, and monosubstituted open‐chain amides are non‐solvents at all levels of C.E.D. The powerful attraction of the molecules of such substances for each other is not matched by an equally powerful attraction for the polymer molecules, and solution cannot therefore take place. In some cases these hydrogen‐bonded substances make a strong contribution to the solvent power of mixtures.If the C.E.D. of the polyacrylonitrile is reduced by interpolymerization with a polymerizable hydrocarbon, solvents such as open‐chain esters, ketones, and mono‐reactive nitriles possessing lower C.E.D.s will attack it. This shows that ketones, open‐chain esters, and mono‐reactive nitriles fail to dissolve polyacrylonitrile because none of these substances possesses the necessary high C.E.D. The failure is not due to their polar groups having less attraction for the nitrile groups of the polymer than they have for their own kind.A modified equation for linking solvent power with the C.E.D. of the solvent in a semi‐quantitative manner has been devised. This contains an arbitrary constant K, but the value of this varies only within narrow limits.