Theory for the Plasticity of Glassy Polymers

Abstract

We present a theory for how a shear stress alone can induce structural changes in a glassy polymer to break up the rigidity of the glass and allow flow. We consider a molecular model in which the shear-stress field is introduced as a bias on the rotational conformation of backbone bonds. It is argued that the fraction of flexed bonds is transiently increased from that in the glass and that this, additionally causing a volume increase, produces a polymer structure resembling the liquid at some temperature above the glass transition. Using these considerations along with several well-known empirical relations, we have calculated the plastic properties of polystyrene and polymethyl methacrylate. These calculated properties correspond reasonable well with the cold-drawing data available.