2H-NMR measurements of deuterated poly(dimethylsiloxane) [PDMS(d)] elastomers with systematically varied elastic and swelling properties are presented. 2H-NMR transverse dephasing data are compared to the predictions of a model describing elastomer deuterium transverse dephasing data as a linear superposition of contributions from elastic and pendant chains. Structural parameters obtained from the model for 2H-NMR transverse dephasing are compared to structural parameters inferred from swelling measurements using statistical and thermodynamic models. As predicted by the model for transverse dephasing data, dephasing time constants for elastic chains are directly proportional to number-average molecular weights of elastic chains obtained from swelling measurements.

2 H-NMR spectroscopy is applied to measure strain-induced orientational anisotropy of polymer segments in three environments in poly(dimethylsiloxane) (PDMS) elastomers: elastic chains, pendant chains, and PDMS(d) chains dissolved in the network. The elastomers were prepared with systematically-varied structures and selective deuterium labeling. Network features were inferred from macroscopic measurements using statistical and thermodynamic models. The segment order parameter, S, was found to be proportional to λ 2 -λ -1 , where λ is the compression ratio, for the three environments in uniaxially-compressed PDMS networks: elastic chains, pendant chains, and dissolved probe chains. Furthermore, all three environments show the same dependence of the ratio S/(λ 2 -λ -1 ) on the elastic modulus, in the range 0.089-0.29 MPa. These results agree with the recent theoretical predictions of Brereton and Ries (Macromolecules 1996, 29, 2644) and thus support the premise that the excluded volume (entropic) interactions between segments subjected to deformation cause anisotropic averaging of the quadrupolar interaction and thus cause a 2 H-NMR line splitting.