The viscoelastic properties of linear polymers in the state of flow and the transition to the high elastic state. Review

Abstract

The results of experimental research on the viscoelastic properties of linear polymers with a narrow MWD, and of mixtures and solutions of these, are discussed and generalized. A rational classification of macromolecular compounds that lays down a clear boundary between oligomers and polymers is proposed. In comparison of polymers of different homologous series, their molecular weights must be standardized with respect to the number of monomer units between points of molecular entanglement, and for this the reference temperature is taken as 100° above the glass temperature. The transition of polymers from the flow state to the high elastic state, brought about by increase in deformation rate (frequency), is studied systematically. The transition of linear high polymers to the high elastic state takes place within a narrow range of critical stresses (in the region of 0·1 → 1·0 × 10 7 dyne/cm 2) and is not dependent on molecular weight, whereas the critical rates of strain (frequencies) are dependent on molecular weight and viscosity, these rates falling very rapidly with increase in these characteristics. Polydispersity affects the properties of polymeric systems to a great extent. As the rate of deformation is increased, components of higher molecular weight pass successively into the high elastic state. This gives rise to nonlinear, especially non-Newtonian, behaviour of systems comprising components with linear characteristics. The durability of raw rubbers in the high elastic state exhibits the same relationships as for vulcanized rubbers. This means that the three dimensional network of uncrosslinked macromolecules, behaves similarly to networks with chemical crosslinkages.