PHASE-SEPARATION IN HEXAMETHYLENETETRAMINE CROSS-LINKED NOVOLAC POLY(ETHYLENE-CO-VINYL ACETATE) BLENDS/

Phase separation during curing reaction in the system of Novolac/poly( ethylene-co-vinyl acetate) (EVA) loaded with hexamethylenetetramine (H exa) was investigated by time-resolved light scattering (TRLS), optica l microscopy and scanning electron micrograph (SEM). Novolac/EVA mixtu res showed a lower critical solution temperature (LCST) phase diagram with a high asymmetry in which the immiscible region emerges at high t emperature and high Novolac contents. Hydrogen-bonding interaction bet ween Novolac and EVA was verified by FTi.r. measurement as well. As th e curing reaction proceeded, an initially homogeneous Novolac/EVA/Hexa mixture underwent phase separation via spinodal decomposition (SD), w hich was induced by depression of LCST with the increase of the molecu lar weight of Novolac. A regular and cocontinuous phase-separated stru cture was finally formed for the cured Novolac/EVA mixture. Time-resol ved light scattering investigation showed that the process of SD durin g curing was different from that in ordinary thermally induced SD, i.e . q(m), the wavenumber q at the peak position of the scattering profil e, increases with time in the early stage of curing. The structure for mation process was discussed in terms of the SD mechanism based on the investigation of TRLS and SEM observation. The scaling structure func tions analysis and SEM observation show that the final morphology of t he cured mixture may be yielded through the route of the cluster to th e cocontinuous structure. (C) 1998 Elsevier Science Ltd. All rights re served.