There are two types of polycondensation reactions in the solid-state polymerization (SSP) of poly(ethylene terephthalate) (PET), namely, transesterification and esterification. Transesterification is the reaction between two hydroxyl ends with ethylene glycol as the byproduct, and esterification is the reaction between a carboxyl end and a hydroxyl end with water as the byproduct. The SSP of powdered PET in a fluid bed is practically a reaction-controlled process because of negligible or very small diffusion resistance. It can be proved mathematically that an optimal carboxyl concentration for reaction-controlled SSP exists only if k(2)/k(1) > 2, where k(2) and k(1) are the forward reaction rate constants of esterification and transesterification, respectively. Several interesting observations were made in fluid-bed SSP experiments of powdered PET: (1) the SSP rate increases monotonously with decreasing carboxyl concentration, (2) k(2)

Keywords:poly(ethylene terephthalate) (PET);solid-state polymerization (SSP);diffusion;reaction rate constants;catalysts