INTERPRETATION OF SEGMENTAL ORIENTATION IN DEFORMED NETWORKS IN TERMSOF CONSTRAINED JUNCTION MODEL OF RUBBER ELASTICITY

Results of Fourier transform infra-red (FTi.r.) dichroism measurements of segmental orientation in model poly(dimethylsiloxane) (PDMS) netwo rks of different molecular weights between junctions are interpreted i n terms of the constrained junction model of rubber elasticity. The th eory shows quantitative agreement with experimental data, without the necessity of adjusting any parameter. Based on this agreement, one may conclude that in PDMS networks, the dependence of orientation on defo rmation results from the non-affine transformation of junction points, and that local intermolecular contributions to segmental orientation are not significant. In the case of less flexible chains such as polyi soprene on the other hand, intermolecular contributions to segmental o rientation might be relatively more important. Correspondence between birefringence experiments and segmental orientation is formulated whic h permits direct quantitative comparison between the birefringence and FTi.r. dichroism experiments.