Intermolecular forces and chain flexibility in linear polymers

Intermolecular forces in a fluid can be measured by the internal pressure, obtained most directly from the coefficient (∂P/∂T)v. Results are reported for a fluid polyisobutene over the temperature range −20.9°C. to +38.9°C. (Pi = 76 to 71.7 cal./cc.). Flexibility is assessed by comparing the activation volume for viscous flow (ΔV) with the molar volume (Vm). ΔV is obtained from measurements of the pressure coefficient of viscosity and for polyisobutene of Vm = 500 is ca. 100 cc./mole at low tmperatures. Above 20°C., ΔV begins to fall sharply; this is ascribed to the onset of flexibility, permitting segmental flow.