Enhanced Case-II diffusion of diluents into glassy polymers undergoing plastic flow

Abstract

Dramatic enhancement of diluent conductance in glassy polymers actively undergoing plastic flow has long been suspected. We report observations of this phenomenon in a glassy poly(ether imide) (Ultem)™ in the presence of resorcinol bis(diphenyl phosphate) (RDP) by means of the limited-supply diffusion experiment developed earlier by Nealey et al. In this experiment it is demonstrated that RDP uptake in plastically deforming Ultem is nearly identical at 113°C, ie. 102°C below Tg, as it is at 215°C, at Tg, without concurrent plastic flow. While the characteristic profiles of penetrating Case-II fronts are present in experiments at 130°C without plastic flow, they are absent in experiments above Tg without plastic flow and in those at 113°C undergoing concurrent plastic flow. This demonstrates that in the plastically deforming polymer, well below Tg, a steady dilated flow state exists, which resembles in its molecular level conformational rearrangements that at Tg without deformation, where in both the resistance to diluent penetration has been radically reduced. Based on the measured diffusion constant of RDP in Ultem, the structural correspondence of the thermally dilated state at Tg and the flow dilated state at 113°C is equivalent to an increase of the diffusion constant by a factor of 1.9×104 in the latter.