The synthesis and characterization of a new family of cyclic carbonate monomers, poly(ester-carbonates), and tin-based macroinitiators
A number of cyclic carbonate monomers were synthesized to generate a family of novel poly(ester-carbonates) that contain pendent functional groups along the polymer backbone. The six-membered cyclic carbonate monomers were derived from the starting material, 2,2- bis (hydroxymethyl)propionic acid (bis -MPA). After preparation of the cyclic carbonates, each was copolymerized with lactides (rac -lactide or L-lactide) and/or [varepsilon]-caprolactone via metal-catalyzed ring opening polymerization (ROP). The structural, thermal, and degradative characteristics of the copolymers were studied in great detail. New tin-based macroinitiators for ROP were produced from the reaction of either L-lactide (LLA) or rac -lactide ( rac -LA) with Sn(OEt)2 (monomer concentration/initiator concentration ≤20). These tin(II) macroinitiators were dissolved in toluene and stored in a stoppered-flask for the subsequent ROP of cyclic esters and carbonates. The soluble tin alkoxide macroinitiators yielded predictable and quantitative initiation of polymerization for up to 1-month storage time at room temperature. The resulting polymers displayed relatively narrow polydispersities (PDI ≤ 1.5), and high monomer conversions (>95%) were obtained within relatively short polymerization times (≤2 h). The kinetics of ROP for rac -LA was studied using FT-IR spectroscopy. The polymerizations were conducted in toluene and were initiated by either new tin(II) macroinitiator adducts or a tetra-functional alcohol/Sn(Oct) 2 system. The progress of polymerization in real-time was studied by monitoring the -C-CO-O- ring vibration from rac -LA at 1240 cm-1 . The FT-IR method proved to be accurate and convenient, and it was used to study the effect of different experimental variables, e.g., temperature, initiator concentration, or catalyst concentration, on the rate of polymerization, ratio effectively controlled the molecular weight of the polymers.