Phase behavior of biodegradable polymers in dimethyl ether and dimethyl ether plus carbon dioxide

Abstract

Phase behavior data are presented for biodegradable polymers in high-pressure dimethyl ether (DME) and in supercritical mixtures of DME and carbon dioxide (CO2). The cloud point curves of poly(D,L-lactide) MW = 30000) in DME were measured at polymer concentrations up to similar to 15 mass % and at temperatures to 373.15 K and pressures to 14 MPa using a variable-volume view cell apparatus. This system exhibited the characteristics of a lower critical solution temperature phase behavior and showed the pressure-polymer concentration isotherms with the maximum cloud point pressure at the polymer concentration of similar to5 mass %. The cloud point pressure increased with increasing molecular weight of the poly(D,L-lactide). For poly(D,L-lactide-co-glycolide) copolymers in DME, decreasing the D,L-lactide content in the copolymer caused the single-phase region to shrink and changed the cloud point curve from a lower critical solution temperature behavior to an upper critical solution temperature behavior. The cloud points of poly(D,L-lactide) in the solvent mixtures of DME and CO2 were measured at various CO2 Compositions up to similar to 73 mass % (on a polymer-free basis) and at temperatures up to similar to 373.15 K. As the CO2 Composition in the mixed solvent increased, the cloud point pressure at a fixed temperature increased significantly. Addition Of CO2 to DME caused a lowering of the dissolving power of the mixed solvent due to the decrease of the solvent polarity.