The solubility of a polymer in a non‐polymeric liquid depends mainly on the heat of mixing. When no polar forces are concerned, the cohesive energy densities of polymer and solvent must be close; a method is given for estimating the cohesive energy densities of polymers from a set of additive constants, and it is shown that good agreement is found between values so calculated and values obtained by swelling measurements. The effects of dipole interactions and hydrogen bonding are also discussed. The solubility of polyvinyl chloride in a number of solvents is considered, and correlated with both the cohesive energy density of the solvent and its ability to form hydrogen bonds.

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In part 1 the heat, entropy, and free energy changes for the (hypothetical) polymerization reactions of liquid cycloparaffins and their methyl and 1 : 1-dimethyl derivatives to condensed polymers are estimated, making use of published thermodynamic data and semi-empirical correlations based upon them. For the unsubstituted cycloparafis except cyclohexane the calculated free energy of polymerization is negative at least up to cyclo-octane ; substitution by either a single methyl group or a pair on the same carbon atom makes the free energy (algebraically) greater, in all cases. In part 2 the polymerizability of heterocyclic compounds is discussed in the light of the results obtained for homocyclic compounds in part 1. 1711The method may be seen clearly by considering the following cycle, which defines the quantities involved : VAPORIZATION OF THE MONOMERSThe standard heats and entropies of vaporization of hydrocarbons, as given in the A.P.I. Tahles,2 correlate well with their boiling points at 1 atm; however, aiicyclic and aromatic hydrocarbons, and the higher n-paraffins, have rather higher values for their boiling points than the average, and branched paraffis rather lower ones. The heats and entropies of vaporization of those cyclic hydrocarbons for which data are lacking Bave been estimated from this correlation, assuming that all the cyclo-parafis have somewhat high values like those whose heats and entropies of vaporization are known. CONDENSATION OF THE POLYMERSHeats of vaporization at 25" C are given in ref.(2) for the liquid normal p a r m s up to neicosane; a linear extrapolation of the data for the higher members of this series suggests that the standard heat of vaporization per CH2 group for liquid polymethylene would be 1.18 kcal/mole. Recent values 3 for the entropy of liquid paraEins suggest, similarly, that the entropy at 25' C of liquid polymethylene is 7.73 cal/mole deg. per CH2 group.Taken in conjunction with the entropy per CH2 in the gaseous standard stateP this figure leads to an estimate of 1.58 cal/mole deg. for the standard entropy of vaporization at 25' C per CH2 group.The branched lower paraffins have standard heats and entropies of vaporization which are rather lower than those of their normal isomers. It has been assumed that this is true of the polymers, and the difference has been estimated from the data in ref.(2); the difference due to a given type of branching varies with the chain length, and decreases as the branch is displaced away from the ends of the chain. Average values have been used.* ESTIMATION OF mgg AND ASo,, BY SEMI-EMPIRICAL METHODSA number of authors have drawn up schemes for estimating the thermodynamk properties of organic compounds based on analysis into group and structural contributions (see, for example, ref.(1), (3, (6)). In most of these the effect of molecular symmetry and isomerism has been neglected; the schemes given in ref. (5) and (6) are exceptions. It has been considered desirable to make a fresh analysis for present purposes, making explicit allowan...