Abstract: | The molecular motion of crosslinked polyepichlorohydrin (PECH) is studied qualitatively by NMR techniques. The results of temperature dependence of 1H T2 and T1 indicate that the crosslinking (crosslink density < 3%) restricts molecular motions of the polymer even far above its Tg. The 1H T1 minimum, corresponding to the large-scale chain-motion of crosslinked PECH, shifts to higher temperatures with increasing crosslink density. 1H T2 data also show that the crosslinking hinders free chain motions of the polymer above its Tg. The 13C T1 relaxation time is sensitive to such motional changes as well. 13C linewidths of crosslinked PECHs vary with the crosslink density in both the swollen state and the solid state. The mechanism of 13C linewidth broadening of crosslinked polymers is discussed in detail. In the case of PECH, the linewidth broadening is caused by changing molecular environment due to crosslinking (such as presence of various chemical shift structures and freezing effects in conformational environment as chain mobility decreases), rather than increasing correlation times, which shorten the relaxation time (T2) of polymer chains. © 1994 John Wiley & Sons, Inc. |