COPOLYESTERS OF POLY(ETHYLENE-TEREPHTHALATE), HYDROQUINONE DIACETATE,AND TEREPHTHALIC ACID - A SIMPLE RATE MODEL FOR CATALYZED SYNTHESIS IN THE MELT

The kinetics of melt transesterification between poly(ethylene terepht halate) (PET), hydroquinone diacetate (HQDA), and terephthalic acid (T A) is examined. The considerably complex system is treated by methods analogous to solution kinetics. A number of assumptions are proposed a nd validated to simplify the kinetics and to make the analysis tractab le. A key postulation is that the reaction originates between HQDA and TA to form a dimer which slices the PET chain. The subsequent couplin g of segments re-forms the PET chain with random incorporation of HQDA -TA units. The steady-state approximation is invoked for the rate of g eneration of dimer. The number of moles of acetic acid, generated in b oth homopolyesterification (HQDA-TA) and copolyesterification (couplin g of segments) channels, is monitored to follow the overall rate of th e reaction and to evaluate the individual rate constants. The rate con stants obtained for a majority of compositions conform to that predict ed theoretically. The kinetic analysis reveals the implicit simplicity of complex systems.