Heats of mixing of polymers with ester and ether solvents

Abstract

AbstractHeats of mixing at infinite dilution have been obtained for polydimethylsiloxane in four series of ester solvents: the methyl and ethyl esters of the aliphatic acids, and the acetic and propionic esters derived from the normal alcohols. Heats have also been obtained in certain ethers including the dialkyl ethers. The solvent molecules are considered to be chains of two types of segments: CH2CH2 and COO, or CH2O. The heat of mixing is ascribed to two contributions: I, a difference in force fields between segments of polymer and solvent molecules, and II, a difference in the Prigogine structural factors of the molecules. Contribution II has been assumed to be approximately the same as with n‐alkane solvents of corresponding chain lengths. By subtracting heats found with n‐alkane solvents from those with esters or ethers II is eliminated and the resulting difference in I may be treated using a lattice model and assuming random mixing. This approach is successful for the ester solvents but somewhat less so for the ethers, where some departure from randomness due to steric factors may be present.