Interpenetrating Chemical (Polyepoxide) and Physical (Poly(vinyl chloride)) Gels

Abstract

Low-concentration solutions of poly(vinyl chloride) (PVC) in (diglycydyl ether of bisphenol A/4,4'-diamino-3,3'-dimethyldicyclohexyl methane) monomers were observed to have the ability to form chemically reactive physical gels. The changes in rheological and optical properties were monitored as a function of time by the use of dynamic shear rheometry and light transmission, respectively. For a given PVC concentration, the isothermal behavior of these solutions is governed by the competition between physical gelation rate and reaction-induced phase separation rate. The temperature, pgTll, at which physical gelation and liquid−liquid demixing occur simultaneously, was then defined. When curing temperature, Ti, is higher than pgTll, the blend behaves like a classical amorphous thermoplastic-thermoset blend and the final heterogeneous structure consists of PVC-rich particles dispersed in a polyepoxide-rich matrix. When Ti is lower than pgTll, the physical gelation rate is high enough to ensure the formation of a macroscopic PVC gel before any phase separation phenomenon. True interpenetrating chemical (polyepoxide) and physical (PVC) gels are then generated. The usual temperature-dependent function of the crystallization-induced physical gelation rate was found to be affected by the extent of the epoxy−diamine polycondensation reaction. The evolution of pgTll with PVC concentration is mainly governed by the concentration-dependent function of the physical gelation rate, resulting in an increase of pgTll with PVC concentration.