Synthesis of triblock stabilizers with and without end-capped for dispersion polymerization in supercritical carbon dioxide

Abstract

Supercritical carbon dioxide (ScCO2) has been more and more widely applied for polymerization to replace organic solvents. For the dispersion polymerization, especially for the powder products used in the medical fields, the stabilizer plays a role key. The hydroxylpropyl-terminated polydimethylsiloxane (HTPDMS) was used as the CO2-philic chain and poly (L- lactide) (PLLA) was selected as the hydrophilic chain. The triblock stabilizer PLLA-PDMS-PLLA and AcO-PLLA-PDMS-PLLA-OAc with end-capped were prepared by ring-opening dispersion polymerization of L-lactide initiated by hydroxyl terminated polydimethylsiloxane (PDMS) and stannous octanoate ((Sn(Oct)2). Their synthesis methods and procedures were presented, and their structures and the thermal properties were characterized by fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectrometers (NMR), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG) respectively. The size and size distribution and molecular weight of the powders prepared were characterized by laser particle size analyzer and gel permeation chromatography (GPC) respectively. The effects of synthesis conditions on the molecular weight and yield of the stabilizer prepared were studied. The optimum synthesis conditions were obtained. The effects of the stabilizer with and without end-capped on the characters of product PLLA prepared by the dispersion polymerization in ScCO2 were investigated. The reaction conditions were easy to control. The results inferred that the terminal hydroxyl stabilizer PLLA-PDMS-PLLA did play a role in the initiation for the dispersion polymerization of PLLA in ScCO2.