Segmental and crosslink point motion in networks

Abstract

Abstract13C‐ and 31P‐NMR spin lattice relaxation in the rotating frame have been measured on a series of networks prepared from monodisperse and deliberately bimodal poly(propylene glycols) (PPG) crosslinked with tris(4‐isocyanatophenyl) thiophosphate. The T1pC minima correspond to loss maxima in the DMTA (Dynamic Mechanical Testing) measured at 10Hz. The T1pP minima fall at higher temperatures than those of T1pC for the same network indicating that these crosslinks lag the segments in frequency of motion at a given temperature. The carbon relaxation is biphasic below Tg of the segments indicating two relaxation domains which we assign to bulklike PPG segments and PPG segments proximal to he crosslink. Lineshape analysis by a diffusional model indicates crosslink reorientation is not isotropic until well above Tg. Relaxation and lineshapes for the bimodal networks indicate that junctions are not uniformly plasticized by the segments.