DYNAMICS OF THE JUNCTION POINT IN MODEL NETWORK POLYMERS BY P-31 NUCLEAR MAGNETIC-RELAXATION

Solid-state P-31 NMR spin-lattice relaxation times (T1P) have been mea sured over a wide range of temperatures for a series of network polyme rs with molecular weights between cross-links (M(c)) ranging from 250 to 2900. The networks were formed from poly(tetrahydrofuran) and tris( 4-isocyanatophenyl) thiophosphate. The chain length dependence of the glass transition temperature obeys the Fox-Loshaek relation. The domin ant mechanism for P-31 spin-lattice relaxation was found to be chemica l shift anisotropy. The data fitted equally well to the Cole-Cole or t he Williams-Watts relaxation functions. The apparent and microscopic a ctivation energies for the motion of junction points are 44-73 and 23- 30 kJ/mol, respectively, for different M(c) samples. The degree of mot ional correlation can be described quantitatively by the coupling para meters. The effect of increasing M(c) is to reduce the width of the di stributions and the cooperative motional mode in the cross-link point.