CATALYTIC SYNTHESIS OF POLY(ETHYLENE TEREPHTHALATE-CO-OXYBENZOATE) SYSTEMS VIA THE MELT POLYESTERIFICATION ROUTE - COPOLYESTERIFICATION KINETICS

Kinetics of copolyesterification between poly(ethylene terephthalate) and 4-acetoxybenzoic acid (PET/ABA) in the melt has been analyzed usin g a phenomenological approach. A parallel second-order reaction sequen ce neatly summarizes catalyzed and uncatalyzed homopolyesterifications of 4-acetoxy benzoic acid (ABA) as well as the PET/ABA copolyesterifi cation. Single stage kinetics fits the data reasonably well since the length of oxybenzoate sequences in the copolyester chain seldom exceed 5. Close correspondence exists between the kinetic parameters determi ned for the first stage of 4-acetoxybenzoic acid homopolyesterificatio n, prior to oligomer precipitation, and those obtained in the present study through a least squares procedure. A Gauss-Legendre quadrature n umerical procedure, used to compute the amount of acetic acid produced , is very efficient for comparison with experiments. Rate constants fo r copolyesterification are found to be several times lower than those of ABA polyesterification. The kinetics data support the formation of randomized blocks in the PET/oxybenzoate chain. The thermal data give support to this as well as to liquid crystallinity in a specific copol yester composition range. We also fitted a more elaborate complex kine tic model in which all the possible reaction sequences of importance h ave been explicitly accounted for. The complex rate model deviates fro m the simplified model by a marginal correction term. The simplified r ate model directly results when we truncate the number of reaction eve nts to only those few significant ones.