Functionalized Polycarbonate Derived from Tartaric Acid: Enzymatic Ring-Opening Polymerization of a Seven-Membered Cyclic Carbonate

Enantiomerically pure functional polycarbonate was synthesized from a novel seven-membered cyclic carbonate monomer derived from naturally occurring l-tartaric acid. The monomer was synthesized in three steps and screened for polymerization with four commercially available lipases from different sources at 80 °C, in bulk. The ring-opening polymerization (ROP) was affected by the source of the enzyme; the highest number-average molecular weight, M_n = 15500 g/mol (PDI = 1.7; [α]_D²⁰ = +77.8, T_m = 58.8 °C) optically active polycarbonate was obtained with lipase Novozyme-435. The relationship between monomer conversion, reaction time, molecular weight, and molecular weight distribution were investigated for Novozyme-435 catalyzed ROP. Deprotection of the ketal groups was achieved with minimal polymer chain cleavage (M_n = 10000 g/mol, PDI = 2.0) and resulted in optically pure polycarbonate ([α]_D²⁰ = +56) bearing hydroxy functional groups. Deprotected poly(ITC) shows T_m of 60.2 °C and ΔH_f = 69.56 J/g and similar to that of the poly(ITC), a glass transition temperature was not found. The availability of the pendant hydroxyl group is expected to enhance the biodegradability of the polymer and serves in a variety of potential biomedical applications such as polymeric drug delivery systems.