Copolyesters of Poly(ethylene terephthalate), Hydroquinone Diacetate, and Terephthalic Acid: A Simple Rate Model for Catalyzed Synthesis in the Melt

Abstract

The kinetics of melt transesterification between poly(ethylene terephthalate) (PET), hydroquinone diacetate (HQDA), and terephthalic acid (TA) is examined. The considerably complex system is treated by methods analogous to solution kinetics. A number of assumptions are proposed and validated to simplify the kinetics and to make the analysis tractable. A key postulation is that the reaction originates between HQDA and TA to form a dimer which slices the PET chain. The subsequent coupling of segments re-forms the PET chain with random incorporation of HQDA−TA units. The steady−state approximation is invoked for the rate of generation of dimer. The number of moles of acetic acid, generated in both homopolyesterification (HQDA−TA) and copolyesterification (coupling of segments) channels, is monitored to follow the overall rate of the reaction and to evaluate the individual rate constants. The rate constants obtained for a majority of compositions conform to that predicted theoretically. The kinetic analysis r...