Interpenetrating chemical (polyepoxide) and physical (poly(vinyl chloride)) gels

Low-concentration solutions of poly(vinyl chloride) (PVC) in (diglycydyl et her of bisphenol A/4,4'-diamino-3,3'-dimethyldicyclohexyl methane) monomers were observed to have the ability to form chemically reactive physical gel s. The changes in rheological and optical properties were monitored as a fu nction of time by the use of dynamic shear rheometry and light transmission , respectively. For a given PVC concentration, the isothermal behavior of t hese solutions is governed by the competition between physical gelation rat e and reaction-induced phase separation rate. The temperature, pgT(parallel to), at which physical gelation and liquid-liquid demixing occur simultane ously, was then defined. When curing temperature, T-i, is higher than pgT(p arallel to), the blend behaves like a classical amorphous thermoplastic-the rmoset blend and the final heterogeneous structure consists of PVC-rich par ticles dispersed in a polyepoxide-rich matrix. When T-i is lower than pgT(p arallel to), the physical gelation rate is high enough to ensure the format ion of a macroscopic PVC gel before any phase separation phenomenon. True i nterpenetrating chemical (polyepoxide) and physical (PVC) gels are then gen erated. The usual temperature-dependent function of the crystallization-ind uced physical gelation rate was found to be affected by the extent of the e poxy-diamine polycondensation reaction. The evolution of pgT(parallel to) w ith PVC concentration is mainly governed by the concentration-dependent fun ction of the physical gelation rate, resulting in an increase of pgT(parall el to) with PVC concentration.