Determination of polymer–liquid interaction by swelling measurements

The interaction of polymers and liquids can be fairly well characterized by the value of the quantity μ, commonly used in thermodynamics of polymer solutions and usually evaluated from osmotic pressure measurements. The Flory‐Rehner theory of swelling relates the amount of swelling of a slightly cross‐linked polymer in a liquid to μ and a parameter M c , the average molecular weight between cross links. M c , may be determined for a cross‐linked polymer from its swelling volume in a solvent in which osmotic pressure measurements with the noncross‐linked polymer have given the value of μ. The cross‐linked polymer, thus calibrated, can be used to obtain the μ value for other liquids by measuring its swelling volume in them. This procedure has been carried out on polyvinyl chloride which can be cross linked by heating. Calibration in three different liquids gave comparable values of M c , thus checking the Flory‐Rehner theory. The quantity μ was determined at two different temperatures for fifty liquids. The value of μ and its temperature dependence correlate well with the observed properties of the binary systems. Variation of μ with molecular weight in an homologous series is demonstrated.