The acidolysis kinetics of the initial stage in the bulk polymerization of aromatic diacids (AA-type monomers) with aromatic diacetates (BB-type monomers) were investigated by a newly developed gas chromatography (GC) method. The model reactions of p-tert-butylbenzoic acid (ptBuBA) with either hydroquinone diacetate (HQD) or p-acetylaminophenol (APAP) follow second-order kinetics in these homogeneous conditions. HQD and APAP have approximately equal reactivity. The polycondensation of terephthalic acid (TA) with HQD, TA with 2-phenylhydroquinone diacetate (PhHQD), and TA with HQD and with 2,6-naphthalenedicarboxylic acid (NDA), follow pseudo-first-order kinetics. These reactions are heterogeneous. The polymerization of TA/PhHQD is the fastest, whereas the polymerization of TA/HQD is slower than that of TA/HQD/NDA. We propose that the solubility of the 1:1 dimer plays a crucial role in determining the polymerization rate, and that the mechanism changes from acidolysis to a dehydration esterification in the later stage of the AA/BB polymerization. The reaction rate constants and activation energies were obtained for all model reactions and polymerizations.