Poly(l-lactide) microspheres with controlled crystallinity

Biodegradable polyester microspheres were synthesized directly from l-lactide by ring-opening dispersion polymerization. Diameter distributions of these particles were narrow (Dw/Dn<1.27), molecular weight of polymer constituting microspheres ranged from 7 to 270 kDa, and its molecular weight polydispersity was low (Mw/Mn<1.2). Degree of crystallinity of poly(l-lactide) in microspheres was controlled in the range from 0 to 60%, by the appropriate thermal treatment of suspensions of microspheres. This procedure did not affect diameters of microspheres, their colloidal stability, and molecular weight of poly(l-lactide) in polymer particles. It has been established that the determination of the degree of crystallinity of poly(l-lactide) in microspheres by 13C CP-MAS NMR yielded results more reproducible than determined by DSC.