Synthesis of poly (l-lactide) in supercritical carbon dioxide with PDMS based stabilizers

The dispersion polymerization of poly (L-lactide)(PLLA) in supercritical carbon dioxide (ScCO 2 ) with stannous octoate (Sn(Oct) 2 ) as a catalyst and n-butanol as an initiator was studied. An amphiphilic triblock copolymer was synthesized by the ring-opening polymerization ofε-caprolactone (ε-CL) with the hydroxylpropyl-terminated polydimethylsiloxane (HTPDMS) as the macromolecule initiator and then chosen as the stabilizer in the synthesis of PLLA. With the concentrations of 3 wt % (stabilizer/monomer), fine powder formed PLLAs were obtained. The effects of operating parameters such as pressure, temperature and stirring rate on the properties of the synthesized PLLAs were investigated. The results showed that the temperature had the greatest effect on the conversion and the stirring rate was the most important factor which determined the morphology of the products. An obvious increase of conversion was observed when the temperature increased from 80 °C to 100 °C. The influence of stirring rate on the morphology was achieved through the anchoring of the stabilizer with the growing polymer chains. The stirring rate of 300 rpm was turned out to be necessary and adequate. When the stirring rate increased or decreased out of the range of (300 ± 100)rpm, only agglomerates were obtained.