EFFECT OF INTERCHANGE REACTIONS ON THE MOLECULAR-WEIGHT DISTRIBUTION OF POLY(ETHYLENE-TEREPHTHALATE) - A MONTE-CARLO SIMULATION

The effect of the interchange reactions of poly(ethylene terephthalate ) (PET) on its molecular weight distribution (MWD) was analyzed using a Monte Carlo simulation method. Three kinds of motions, which corresp ond to the direct ester-ester interchange reaction, alcoholysis, and i nternal alcoholysis in polyester, were performed in this simulation: b ond flip, end attack, and backbite. Two systems with two different typ es of nonequilibrium distribution (monodisperse and bimodal distributi on) were initially prepared. The initial biases from equilibrium MWD a re rapidly relaxed to an equilibrium MWD as the reaction progresses. T he MWD at equilibrium is well described by the most probable MWD propo sed by Flory. From the polydispersity data, it is concluded that about 0.3 interchanges per segment are sufficient to equilibrate the nonequ ilibrium system. For the validity of the simulation, the variation of MWD of the mixtures of two PETs having different molecular weights wer e monitored using gel permeation chromatography. The agreement between simulation and experiment is remarkably good. (C) 1996 John Wiley & S ons, Inc.