The formation of ether linkages in polyethylene terephthalate was investigated using three different metal acetates as catalysts. The zinc salt was found to produce more ether bonds than either lead(II) or manganese(II) acetate. The amount of diethylene glycol detected in the fibers increased with rising catalyst concentration as well as with increasing polycondensation time. Negligible at the reesterification temperature of 195°C, ether formation became more important during the preheating period during which the polycondensation temperature was achieved (280°C). Most of the ether linkages were formed during the first 30 min of polycondensation and only a slow increase was observed thereafter. Model experiments conducted by heating pure ethylene glycol with the catalysts were in agreement with the polycondensation results.