An investigation into the effects of residual water on the glass transition temperature of polylactide microspheres using modulated temperature DSC

The objective of the study was to ascertain residual water levels in polyla ctide and polylactide-co-glycolide microspheres prepared using the solvent evaporation technique and to investigate the effects of that water on the g lass transitional behaviour of the microspheres. Microspheres were prepared from polylactic acid (PLA) and polylactide-co-glycolide (PLGA) 50:50 and 7 5:25 using a standard solvent evaporation technique. The glass transition w as measured as a function of drying conditions using modulated temperature DSC. The microspheres were found to contain very low levels of dichlorometh ane, while residual water levels of up to circa 3% w/w were noted after fre eze or oven drying, these levels being higher for microspheres containing h igher glycolic acid levels. The residual water was found to lower the T-g f ollowing the Gordon-Taylor relationship. The data indicate that the micropa rticles may retain significant water levels following standard preparation and drying protocols and that this drying may markedly lower the T-g of the spheres. (C) 2001 Elsevier Science B.V. All rights reserved.