SYNERESIS AND CRYSTALLINITY IN PLASTICIZED RUBBERY NETWORKS AND COMPOSITES

We prepared polycaprolactone networks plasticized. (60 wt %) with tria cetin, with and without filler particles to model high-energy solid ro cket propellants. Under strain and at lower temperatures these materia ls partially crystallize but also undesirably exude plasticizer (syner esis). We measured both properties isothermally (30-degrees-C) on the basis of molecular mobility: crystallinity with rapid-passage cw proto n nuclear magnetic resonance (NMR), and syneresis with pulsed-gradient spin-echo NMR diffusion techniques, as a function of strain and time. In the gumstocks crystallinity and syneresis increase monotonically w ith strain and asymptotically with time. In a given specimen syneresis lags behind crystallinity but they approach the same value, suggestin g that syneresis originates in expulsion of plasticizer from crystalli zing regions. In the composites, crystallinity results resemble those in gum, but our diffusion data suggest that most syneresis is internal , with plasticizer accumulating in strain-debonded void regions near f iller particles. (C) 1994 John Wiley & Sons, Inc.