The belief has developed that polymer molecules, in dilute solution a t least, are always molecularly dispersed, because of the lack of refuting evidence and the attractive simplicity of the assumption. I t is the purpose of this paper, however, to show that stable association of polymer molecules in solution exists under certain conditions. The work is essentially divided into two parts: in the first part the association of polyvinyl chloride in different solvent media is studied in detail by several different methods; in the second part there are described much less detailed experiments, mostly concerned with demonstrating that the stable association of polymer molecules is a general phenomenon when the system is near the point of phase separation.Wisconsin, May 28-29, 1946. England.' Presented a t the Twentieth National Colloid Symposium, which was he Id a t Madison,

Solvent activities of seven organic solvents in mixtures with PDMS (Polydimethylsiloxane) of different molecular weights have been measured at 298.15 and 313.15 K using the vapor sorption technique. The results have been used for testing the thermodynamic consistency of an extended version of Flory's theory. In this theoretical approach a more detailed expression of the combinatorial entropy is used and found to be superior to the common Flory‐Huggins expression.

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Experimental results of the composition dependence of the molar excess enthalpy HE of ten mixtures of cyclohexane with saturated and unsaturated hydrocarbons at 298.15 K and 1 bar are reported. The results of the mixtures With the saturated hydrocarbons confirm the systematic behaviour of HE with respect to the chain length and the degree of branching deduced from already existing data. The results of the mixtures with unsaturated components allow to extend the systematics taking into account the number and the location of multiple bonds within the molecules.

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