VISCOELASTICITY OF POLYMERIC SYSTEMS IN FLUID AND RUBBERY STATES IN UNIAXIAL EXTENSION AND SHEAR

Relaxation transition of linear polymers from fluid to rubbery state under the effect of deformation at temperatures far above Tgare considered. The transi-tion is accompanied by loss of polymer fluidity that makes it impossible to obtain the rheological characteristics in simple shear experiments at shear stresses exceeding approximately (1—5) 106 dyne/cm2. Based on shear experi-ments, predictions are made and some fundamental problems are stated con-cerning viscoelastic properties of polymers in uniaxial extension. Particular attention is drawn to the phenomenon of fracture and especially to durability— time to fracture of uncüred polymers. The importance of dividing total deforma-tion into reversible and irreversible components is demonstrated. The fast decrease of irreversible deformation, with tensile stresses and deformation rates exceeding the critical values, gives the best indication of loss of polymer fluidity. The master curves of dependence on temperature and molecular weight of tensile stress total deformation and its reversible and irreversible components for narrow distribution polyisoprenes in a very broad range of deformation rates have been obtained. It has been revealed experimentally that high-molecular narrow distribution polymers behave as linear bodies up to fracture. Fundamental peculiarities of the process of fracture of uncured polymers are established. Correlation of reversible deformation of broad distribution polymers in the rubbery state and their tensile strength in the frozen state is discussed