Segmental orientation in plastically deformed glassy PMMA

In this study, spatial orientational distribution functions of labeled chain segments of cross-linked and linear PMMA were obtained by solid-state NMR as a function of finite deformation (far) below and (far) above the glass transition temperature T_g. The applied data analysis allows comparison of theoretical predictions and experimental data, both in terms of the orientational probability distributions as a function of two polar angles, as well as in terms of moments of the distribution. Orientation-strain relationships of chain segments agreed above and below T_g with predictions from the rubber-elastic affine network model, but suggests a much denser network below T_g than given by the cross-link density or the entanglement density in the melt. This suggested network structure is believed to be the generator of segmental orientation during plastic deformation in the glassy state, independent of the range of applied cross-link densities and deformation rates used in this study.