Evolution in Concepts Concerning the Mechanism of Plasticity in Solid Polymers after the 1950s

The evolution of fundamental concepts concerning the mechanisms of plastic deformation in solid polymers, crystals (both glassy and semicrystalline) over the recent five decades has been reviewed. The most effective approach to the description of cold plastic deformation is a gradual drift away from the chain straightening mechanism as a limiting kinetic stage of the process (or, in other words, from the picture of the rubbery character of deformation) to concepts that are characteristic of the deformation physics of nonpolymer solids, primarily metals. Various nonpolymeric mechanisms, such as nucleation and growth of dislocations in polymer crystals, formation and evolution of short-scale undeveloped shear transformations in glasses, and mutual deformation constraints of amorphous and crystalline phases in semicrystalline polymers, are introduced in polymer science. An analysis of the published data shows that deformation in solid polymers is undoubtedly accompanied by chain straightening, but, in most cases, this process does not control the overall kinetics of plasticity, at least at small and moderate strains. In glassy polymers, conformational chain rearrangements are not going directly but proceed as shape fitting of macromolecule coils to short-scale shear transformations that serve as active sites of plasticity. The chain character and flexibility of macromolecules have a slight effect on the nucleation of the above transformations. The development of local shear at the early stages of loading is the thorniest stage of deformation. Problems concerning the joint development of polymer and nonpolymer processes during deformation of macromolecular solids and the specific features related to the polymer structure of macromolecules are discussed.