ISSN:
0098-1273
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
Proton spin relaxation time measurements are reported for a series of liquid polydimethylsiloxanes covering the temperature range from -50 to 200°C. These include fractionated and whole polymer samples (Mw from 104 to 106), binary mixtures, and crosslinked material. This paper is mainly devoted to the behavior of the spin-spin relaxation (T2) which is sensitive to the low-frequency long-range configurational motions occurring in the liquid phase. These motions determine the time scale over which final motional averaging of the nuclear dipolar interactions occur, prior to the onset of normal liquid-like behavior of T2. When these motions are too slow (e.g., at low temperatures of high molecular weight) to lead to appreciable averaging of the small residual static dipolar interactions present in the liquid phase, the spin-spin relaxation exhibits pseudo-solid-like behavior. A further aspect of this work concerns the observed sensitivity of T2 to network formation which considerably restricts the long-range motions that determine T2. It is possible to determine the fraction of material present in the form of a network from the relative proportions of network and non-network T2 components. This is not only true for a permanent crosslinked network but also for a network arising from transient entanglement couplings. The dynamic nature of the latter type of a network is clearly revealed in the proton nuclear magnetic resonance measurements reported here.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1978.180160611
