2H nmr study of a deformed poly(dimethylsiloxane) rubber network below and above the crystallization temperature

Deuterium n.m.r. is used to observe the change in segmental dynamics and orientation at the crystallization temperature T-c in a uniaxially stretched poly(dimethylsiloxane) (PDMS) network. Experiments are performed over a wide temperature range (235-294 K). The amorphous parts of the chains are probed via perdeuterated n-octane probe molecules dissolved in the network. H-2 n.m.r. spectra change drastically within a small temperature interval of 4 K in the vicinity of T-c. Above T-c, the spectra reflect the uniaxial dynamics of the octane probes. In the vicinity of T-c, the spectra are sensitive to the internal dynamics of the octane probe and indicate a heterogeneity in the mobility of the network chains. The isotropic lines obtained for T less than or equal to T-c confirm that the local constraints introduced by the external deformation disappear in the amorphous part of the sample in the presence of the crystalline phase. (C) 1998 Elsevier Science Ltd. All rights reserved.