Adiabatic Compressibilities of Polymer Solutions. II. Dilute Solutions of Cellulose Acetates

Abstract

Adiabatic conipressibilitias of solutions of a secondary ccllrilose acetate and cellulose triacetate in representative solverits are obtained from measurements of sound velocity and density at 25°C. By assuming solvent molecules concerned in solvation to be incompressible etfectively, degrees of solvation are estimated from the adiabatic compressibilities of the solntioiis arid solvents. Where comparison is possible degrees of solvation for the secondary acetate are in general agreement with the results of some other methods of estimation. Those for the triacetate agree with degrees of solvation estimated by use of other methods. Degrees of solvation for the secondary acetate generally show a marked decrease with iiicreasing molar volume of solvent. The degree of solvation obtained with acetonitrile is an exception and it is suggested that the mode of interaction of acetonitrile with the polymer differs from that of the other solvents. The degrees of solvation of the secondary acetate do not generally siiggest a stoichiometric association of solveiit molecules and functional groups of the polymer and with solvents of smaller molecalar size the degrees of solvation exceed one solvent molecule per functional group of polymer. In the case of the triacetate one molecule of chloroform or methylene chloride seems to be associated with each acetyl group.