The synthesis of poly(butylene succinate) (PBS) of Mw ranging from 4000 to 180,000 g mol−1 is realized with molar ratios [COOH]0/[OH]0 of 1 and 0.98, and varying amounts of titanium (IV) tetrabutoxide (TBT) catalyst. Polycondensation kinetics are followed by chemical titration of carboxylic groups, and the kinetic rate constants of self-catalyzed and external-catalyzed reactions are calculated. The synthesis of PBS with high molar mass follows the classical Flory theory. The effect of molar mass on PBS thermal properties is also studied. A faster crystallization rate and a higher temperature of crystallization are observed, for very high molar masses. This behavior could be due to a memory effect of the polymer. Complex melting behavior of PBS is induced by a continuous reorganization of the crystalline phase, as observed by MTDSC. DSC measurements also reveal that the crystallinity—and so the amorphous phase—is limited to about 35% when the molar mass Mn is higher than 40,000 g mol−1. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40639.