PARAMETERS OF EQUATION OF STATE OF POLYURETHANES FROM ACOUSTIC-RESONANCE AND ISOBARIC EXPANSIVITY

A series of polyurethanes was synthesized, varying the length of the soft sequences in the chain. Linear isobaric expansitivities, alpha-L, were measured as a function of temperature, T, from -100 to +100-degrees-C. Volumetric isobaric expansivities, alpha, and characteristic parameters upsilon and T* in the Hartmann equation of state23 were computed from alpha-L values. For these polymers, upsilon goes symbatically with the length of the soft segment. T* decreases at the same time, showing that longer soft segments weaken intersegmental interactions. When the Hartmann equation was used in the opposite way, specific volumes, upsilon(T), were obtained, which agree well with the experimental ones. Dynamic mechanical tests were performed on the same materials by using a resonance method; temperature shift factors, a(T), were obtained from the data. When a formula for a(T) in terms of the reduced volume upsilon-approximately-15,17 and the Hartmann equation again were used, characteristic temperatures, T*, were obtained also from the resonance data. For each polymer, the T* value from expansivity is close to the value derived from dynamic mechanical testing. Hence, the Hartmann equation provides reliable results not only for the equation of state data but also for prediction of temperature shift factors via the a(T)(upsilon-approximately) equation.