Experimental arguments on the conformation of molecules in molten and glassy polymers

Abstract

In molten non-crystallising polymers we find normal random coil conformations of the molecules. This is inferred from the theoretically predicted and experimentally observed relationships between the properties of solutions (relaxational modulus, viscosity, osmotic pressure and specific volume) and melts. It is also derived from the intrinsic viscosities (η) and the diffusion constants of molecules with a very high molecular weight in polymeric solvents (M = 104−105) of the same chemical constitution. Moreover the properties of melts (relaxational modulus, flow curve, viscosity) depend on chemical structure and long chain branching in the manner predicted assuming a random coil conformation. At the glass temperature Tg the conformation resembles that in the melt as the temperature dependence of the conformation at T > Tg shows ((η) in polymeric solvents, diameters of the domains in block copolymers). However, on cooling below Tg an irreversible volume shrinking process may lead to an inhomogeneous distribution of densities and possibly to an extended conformation of molecules in grain boundaries. Experiments show that only strong deviations from random coil conformations decrease the ultimate strength of a glass.