engleski

POSTIRRADIATION CROSSLINKING AND STRUCTURE OF UNSATURATED POLYESTER RESIN

Initiation of unsaturated polyester (UP) resin crosslinking by ionizing radiation offers initiator-free reaction what is a great advantage in studying that complex reaction. Partially crosslinked UP resins exhibited substantial post-irradiation crosslinking, the extent increase was detected for more than five days after irradiation. Two different commercial UP resins were irradiated to a number of chosen doses and reaction extents were monitored on the selected days after the irradiation. One of the resins showed pronounced reaction induced phase separation caused by the formation of polyester rich spherical entities, microgels, at the beginning of crosslinking disrupting already limited miscibility of the styrene and polyester. NMR spectra revealed that separation occurred in the resin containing phtalic acid in the polyester chain while the polyester of the other resin included isophtalic acid. The greatest part of information on the radiation crosslinking extents was gathered by extraction analysis, it also offered some data on post-reaction, especially on different behavior of the gel and the free styrene content. Most interesting data were acquired by differential scanning calorimetry (DSC) that enabled us to determine residual reactivity. The shape of DSC traces revealed significant differences in the crosslinking course of the two UP resins, reaction induced phase separation was detected and the residual reaction heats at same total doses greatly differed. The reaction periods (initiation, propagation, gel effect and vitrification) have been determined for both resins, but the total dose of theirs appearances greatly differed because the resin containing isophtalic acid in the polyester had better compatibility with styrene resulting in almost no phase separation and higher radiation and post-irradiation conversion.

microgels; reaction induced phase separation; extraction; DSC; NMR

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