New poly(P-malic acid alkyl esters) with two stereogenic centers have been synthesized by anionic ring-opening polymerization of racemic and optically active 2-butyl and 3,3-dimethyl-2-butyl malolactonates. The configurational structure of these racemic and optically active polyesters has been determined by C-13 NMR analysis. Comparison between polydiastereisomers structures has been possible by using this spectroscopic method. Several main-chain and side-chain carbon atoms were stereosensitive, and polystereoisomers composition has been deduced from C-13 NMR spectra. Thermal properties of the different polystereoisomers have been correlated with the configuration of both chiral sites in the macromolecular chains. It has been shown, crystallinity rate was dependent on main-chain configurational structure. The lateral stereogenic center is important to increase the organization of macromolecular chains in crystallites and therefore their regularity. Moreover, the presence of the 3,3-dimethyl-2-butyl group led to a semi-crystalline racemic polymer, that confirms the particular behaviour of this bulky group in a macromolecular architecture. Comparison has been done with poly(benzyl 3-alkylmalates) containing two stereogenic centers in the main-chain. (C) 2000 Elsevier Science Ltd. All rights reserved.