Process for preparing poly(glycolide-co-lactide) copolymer microparticles

A process for preparing poly(lactide-co-glycolide) copolymer particles with an average particle size in the range of 50-800 nm, the process comprising:

• a) transferring ethanol and a poly(lactide-co-glycolide) copolymer with a content of polymerized monomer units of 55-80 mol % lactide and 20 to 45 mol % of glycolide and a molecular weight Mw of 1,000-25,000 into a first reactor with a stirring equipment,
• b) feeding carbon dioxide into the first reactor so that carbon dioxide is from 65 to 85% by weight and the ethanol is 15 to 35% by weight whereby carbon dioxide and ethanol add up to 100%,
• c) mixing the poly(lactide-co-glycolide) copolymer, the ethanol, and the carbon dioxide by stirring and adjusting or maintaining the mixture in the first reactor to a temperature of at least 31 and up to 70° C. and a pressure of from 7.38 MPa to 50 MPa, where carbon dioxide enters the supercritical stage with ethanol as a co-solvent,
• d) stirring the mixture from c) for 1 to 5 hours, whereby at least a part of the poly(glycolide-co-lactide) copolymer becomes dissolved in the mixture of carbon dioxide and ethanol,
• e) transferring the mixture from d) into a second reactor under rapid reduction of the pressure and expansion with phase separation into a gas phase, an ethanol aerosol and an ethanolic suspension containing poly(lactide-co-glycolide) copolymer particles,
• f) removing the carbon dioxide gas and the ethanol aerosol from the second reactor, and
• g) obtaining the poly(glycolide-co-lactide) copolymer particles with an average particle size in the range of 50-800 nm in the form of an ethanolic suspension or in dry form from the second reactor.