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

Phase behavior data are presented for biodegradable polymers in high-pressu re dimethyl ether (DME) and in supercritical mixtures of DME and carbon dio xide (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 t emperatures to 373.15 K and pressures to 14 MPa using a variable-volume vie w cell apparatus. This system exhibited the characteristics of a lower crit ical solution temperature phase behavior and showed the pressure-polymer co ncentration isotherms with the maximum cloud point pressure at the polymer concentration of similar to5 mass %. The cloud point pressure increased wit h increasing molecular weight of the poly(D,L-lactide). For poly(D,L-lactid e-co-glycolide) copolymers in DME, decreasing the D,L-lactide content in th e 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-lacti de) in the solvent mixtures of DME and CO2 were measured at various CO2 Com positions up to similar to 73 mass % (on a polymer-free basis) and at tempe ratures up to similar to 373.15 K. As the CO2 Composition in the mixed solv ent increased, the cloud point pressure at a fixed temperature increased si gnificantly. Addition Of CO2 to DME caused a lowering of the dissolving pow er of the mixed solvent due to the decrease of the solvent polarity.