MOLECULAR-ORIENTATION IN DEFORMED BIMODAL NETWORKS .2. FOURIER-TRANSFORM INFRARED MEASUREMENTS ON POLY(DIMETHYLSILOXANE) NETWORKS AND COMPARISON WITH THEORY

Results of segmental orientation in uniaxially stretched bimodal poly(dimethylsiloxane) networks are reported. Measurements are carried out by Fourier transform infrared dichroism spectroscopy. Bimodal networks were formed by tetrafunctionally end-linking low molecular weight (M(n) = 5600) deuterated chains with high molecular weight (M(n) = 20000) hydrogenated chains. Independent measurements of segmental orientation of the short and the long chains showed that the short (long) ones orient less (more) than the corresponding chains of the unimodal networks, in conformity with the predictions of the theory developed in the preceding paper. Furthermore, the change in segmental orientation of short and/or long chains in bimodal networks relative to their unimodal counterparts, expressed by the ratios S-S/S-S degrees or S-L/S-L degrees is in reasonable quantitative agreement with the theory. Experiments show that the orientations of the short and the long chains in bimodal networks are approximately equal to each other. On the other hand,the theory based on the phantom network model theory and experiments is observed in the case of longer chains, whose behavior does ndt conform with the phantom network model underlying the theory. The differences between theory and experiments are attributed to the effects of entanglements which operate to different extents for different chain lengths.