A detailed kinetic model for the bulk styrene polymerization initiated by symmetrical diperoxyester bifunctional initiators is presented. When chain termination occurs via a combination termination mechanism, six distinct polymeric species are identified in accordance with the nature of the polymer end units. It is shown that the unequal thermal decomposition characteristics of the peroxides of the bifunctional initiator system lead to the formation of polymers having considerably higher molecular weight than those obtained by the monofunctional intiator systems. It has also been found that high monomer conversion, high molecular weight, and narrow molecular weight distribution can be obtained simultaneously by using the bifunctional initiators at high reaction temperatures. This is due to the reinitiation and propagation of inactive polymers carrying undecomposed peroxides. The molecularweight-increasing effect of the bifunctional initiator is more pronounced at high reaction temperatures. The new possibilities of increasing the monomer conversion and controlling the polymer molecular weight properties more effectively through the use of bifunctional initiators are discussed.

SynopsisThe kinetics of bulk styrene polymerization catalyzed by symmetrical bifunctional initiators [2,5-dimethyl-2,5-bis(benzoyl peroxy) hexane] is studied. Being characterized by the presence of two peroxide groups of equal thermal stabilities, this bifunctional initiator system shows complex initiation, propagation, and termination reaction pathways. The kinetic model for bulk styrene polymerization with the bifunctional initiator is presented and compared with experimental data. The experimental data indicate that the model is quite satisfactory in describing the polymerization rate and polymer molecular weights for bulk styrene polymerization catalyzed by the symmetrical bifunctional initiator.

The kinetics of a semibatch melt transesterification of dimethyl terephthalate (DMT) with ethylene glycol (EG) is studied with zinc acetate as a catalyst. This paper quantifies the effect of various reactor operating conditions on the transesterification rate and the product composition distribution. Our experiments support the assumption that the methylesters in DMT and growing oligomer chains have the same reactivities for transesterification with EG and that the reactivity of hydroxyl groups in pure EG for esterification with DMT is twice that of the hydroxyl group in oligomers. With a molecular species model in which various oligomers are identified by the type of functional end groups, the progress of the transesterification and the oligomer concentration distribution were estimated and the agreement between the model predictions and the experimental data were excellent. It has also been shown that 30 wt.

SynopsisA semibatch melt prepolymerization of poly( ethylene terephthalate) (PET) is studied. Being characterized by complex reaction pathways leading to various functional end groups and side products, PET prepolymerization process poses a challenging modeling problem. Ten distinct polymeric species have been defined in accordance with the type of functional end groups and the corresponding mass balance and moment equation are developed to estimate the progress of reaction and polymer molecular weight. The effect of various reactor operating conditions on the performance of the polymerization process has been examined through numerical simulation of the molecular species model developed. In particular, the effect of incomplete transesterification of methyl ester groups on the polymer molecular weight has been investigated in detail.

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