Heats of Mixing of Polyisobutylene With Some Organic Solvents

The heats of mixing of four fractions of polyisobutylene with five organic solvents have been measured at 25 °C with the use of a Tian–Calvet microcalorimeter. The maximum concentrations attained were of the order of 3% in polymer. It has been found that the enthalpy parameter k 0 is independent of the molecular weight of the polymer sample in the investigated molecular weight range. All the values for k 0 calculated from the Van Laar–Scatchard equation for the different polymer–solvent pairs are different from the values estimated from the partial molal quantities. This is explained with the use of new theories on the thermodynamics of high polymer solutions by Orofino and Flory and by Huggins.