Linear and three-arm star hydroxytelechelic poly(benzyl β-malolactonate)s: a straightforward one-step synthesis through ring-opening polymerization

Abstract

Ring-opening polymerization (ROP) of racemic-benzyl β-malolactonate (MLA^Be) initiated by an alcohol such as 1,3-propanediol (PPD) or 2-hydroxymethyl-1,3-propanediol (TMM), and catalyzed by a metal triflate M(OTf)₃ with M = Nd, Bi, proceeded under mild operating conditions (in bulk at 60 °C). The functionality of the alcohol dictates the topology of the resulting hydroxy telechelic PMLA^Be. The ROP promoted by the neodymium-based catalytic system afforded a satisfactory activity and control in terms of molar mass and dispersity values (M_n,NMR up to 7000 g mol⁻¹, Đ_M < 1.35). Mechanistic insights revealed that ring-opening of MLA^Be took place through the selective oxygen–acyl bond cleavage without undesirable side reactions such as transesterification or crotonisation, as evidenced by NMR and mass spectrometry analyses of the recovered polyesters. The structure of the corresponding α,ω-hydroxy telechelic PMLA^Bes was ascertained by ¹H and ¹³C{¹H} NMR, SEC, and MALDI-ToF mass spectrometry analyses. In comparison, methane and trifluoromethane sulfonic acids did not allow the formation of well-defined PMLA^Be diols. Differences in the behavior of MLA^Be and the related β-butyrolactone are highlighted. The present Nd(OTf)₃/PPD or TMM catalytic ROP of MLA^Be thus represents a valuable direct synthesis of PMLA^Be diols and triols, respectively, without requiring chemical modification of a preformed PMLA^Be precursor.