Curing Kinetics Of Unsaturated Polyester Resin And Characterization Of Structure Of Cured UPR

Unsaturated polyester resin(UPR) is one of the most widely used thermosettingresins, and its curing process plays an important role in the structure, properties andmolding process of cured UPR. It is of great significance on deeply understanding theproperties of cured resin and improving the curing process to study the sequencestructure of crosslinked network and curing kinetics on cured resin.In this thesis, the kinetics of UPR curing initiated by methyl ethyl ketoneperoxide(MEKP) with cobalt or copper salts by dynamic DSC was studied. Firstly,2,2-dihydroperoxybutane (T4) and2,2'-dihydro-peroxy-2,2'-dibutyl peroxide (T3)was obtained by separation of reactive oxygen ingredients for commercial methylethyl ketone peroxide solution (M-50A). Secondly, kinetics of UPR curing initiatedby M-50, T4or T3with cobalt ethylhexanoate at different heating rates were studiedby dynamic DSC. Then activation energies with different initiating systems werecalculated by Kissinger method, Flynn-Wall-Ozawa methods, Friedman method andStarink method. The results indicated that activation energies of T4curing system wasclose to M-50curing system, which was less than T3curing system. According toanalyzing kinetic characteristics of radical polymerization on curing process of UPRby reduced rate method, the curing process of UPR was also affected by gelation andvitrification effects in non-isothermal curing process of UPR. In non-isothermal DSCcurves, two peaks were identified, and the first peak was due to high monomerconcentration at early curing stage, while the second peak resulted from thesynergistic effect of thermal decomposition of initiator and gelation effects atmoderate conversion rate, but the degrees of cure at both peaks were related totemperature and initiator activity. Therefore, the UPR curing rate distribution in wholeprocess could be moderated by making multi-initiator components complex. Theexperimental analysis also demonstrated that reduced rate method was more valid toexpress the macrokinetics characteristics on the non-isothermal curing process ofUPR.Then a research method of characterizing the crosslinked structure of cured UPRwas established, that is, de-crosslinking the cured UPR by alcohols, obtaining thelinear copolymers containing the main structures of crosslinked network, and thencharacterizing the sequence structure of polystyrene segments and sequencedistribution of styrene units in linear copolymers by13C NMR technique. Experimental results showed that, in the process of UPR curing, the conversion ofdouble bonds in UP was higher than that of styrene, and the polymerization of doublebonds in UP resin and styrene was not strictly alternating copolymerization, whichtended to random radical copolymerization.