Conformational energy contribution to the heat of solution in polymer–solvent systems. Part II. Experimental results

Heats of solution (ΔH_exp) in solvents of increasing thermodynamic power have been measured for four polymers: polystyrene (PS), poly(vinyl acetate) (PVAc), polyisobutylene (PIB) and polydimethylsiloxane (PDMS). After subtraction from ΔH_exp of an interaction term (calculated by the Hildebrand treatment based on solubility parameters) and the excess volume term, the quantity remaining is interpreted as the conformational energy contribution (ΔU_conf) to the heat of solution. ΔU_conf appears to correlate well with some basic conformational properties of the chain, such as the sign of the temperature coefficient of unperturbed dimensions derived from solution properties, and shows a monotonic behavior with α, the expansion coefficient of the polymer coil in the final solution. Numerical values of ΔU_conf, at least for those cases in which polymer solubility parameters are known with some certainty, are much larger than those evaluated from rubber elasticity experiments (through the experimentally accessible value of the energy component of the force of retraction im simple elongation).