Kinetics of methyl methacrylate polymerization initiated by bifunction initiator
Bifunctional initiators with two labile groups ( e g peroxides or azo groups) are frequently used in the polymer industry for the synthesis of vinyl polymers and resin curing In general, there are two types of bifunctional initiators: one is symmetrical bifunctional initiators containing two labile groups of equal structure, the other is unsymmetrical bifunctional initiators containing two labile groups of unequal structure One of the potential advantages of using bifunctional initiators is that high polymer molecular mass and high polymerization rate can be obtained simultaneously by controlling the initiator decomposition rate through optimal reaction temperature programming For free radical polymerization of methyl methacrylate (MMA) with monofunctional initiators, the kinetics is reasonably well understood in both low and high monomer conversion regimes However, the presence of an additional labile group in bifunctional initiators makes the polymerization kinetics very complicated. This is because labile groups such as peroxides become redistributed repeatedly in the growing and inactive polymers and they are engaged in further initiation, propagation, chain transfer and termination reactions during the course of polymerization. The effects of temperature and initiator concentration on the kinetics of MMA bulk polymerization initiated by 2,5 dimethyl 2,5 bis(2 ethyl hexanoyl peroxide) hexane (TX 141) were investigated.The energy of activation of MMA bulk polymerization initiated by TX 141 was about 91 kJ·mol -1 , and that of TX 141 decomposition was about 140 kJ·mol -1 , which was more close to the experimental data.The reaction order of TX 141 concentration was about 0 72,because there was mono and bi molecule termination. The kinetic comparison initiated by TX 141 and benzoyl peroxide (BPO) with the same half life period showed that the kinetics was the same when the concentration of TX 141 was half of that of BPO.But, the number average molecular mass ratio of that initiated by TX 141 to that by BPO was from 1 2 to 1 33 increasing with the conversion.There was an exothermal peak in the DSC curve of polymer initiated by TX 141 at low conversion, but there was no peak at high conversion and no peak was observed for the polymer initiated by BPO.It was shown that the two functional groups of bifunctional initiator decomposed at different times during the polymerization process.