engleski

Radiation and Postirradiation Crosslinking and Structure of Two Unsaturated Polyester Resins

Radiation and post-irradiation crosslinking of two unsaturated polyester (UP) resins was monitored and substantial differences in the reaction course and extents observed. DSC thermograms of one of the resins showed double peaks and significantly lower residual reaction heats. Extraction revealed that gelation dose of the resin with double peak was twice the gelation dose of the other resin that had single peaks in DSC thermograms. Although other components of the polyesters were identical, NMR spectra of the resin with a single peak revealed iso-phthalic units while in the polyester of the resin having double DSC peaks ortho-phthalic units were detected. Ortho-phthalate reduced compatibility of polyester and styrene and caused reaction induced phase separation, influencing gel structure what was visible in SEM micrographs. Previously the double peaks in crosslinking thermograms of UP resins were usually attributed to initiator effects but here no initiator was used and in the literature we found that double peaks are almost exclusively present in the thermograms of UP resins containing ortho-phthalates, while in resins with iso-phthalates double peaks appear almost never. Crosslinking extents were significantly higher in the resin containing iso-phthalate and in both cases enhanced by post-irradiation reaction that is often neglected.

Unsaturated polyester resin; Phthalates; Ionizing radiation; Crosslinking; Reaction induced phase separation; DSC; NMR; SEM

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