ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Proton spin-lattice relaxation times T1 were measured for two samples of polydimethylsiloxane (PDMS), one with weight-average molecular weight Mw = 77,400 and the other with Mw = 609,000. Two T1 minima and a T1 discontinuity were observed for each compound. The high-temperature T1 minima were attributed to a stretching and flexing motion of the PDMS chain. Quantitative comparison of the relaxation data with a theoretical model developed for this motion allowed the activation energy, 2.3 kcal/mole, and the maximum angular displacement of the methyl group symmetry axis to be determined. The latter was found to be 31°, independent of sample molecular weight. The low-temperature minima were ascribed to methyl reorientation with an activation energy of 1.6 kcal/mole. The T1 discontinuities were attributed to melting and allowed the degree of crystallinity to be estimated.
Additional Material:
2 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1978.180160213
