Preparation and characterization of the molecular weight controllable poly(lactide-co-glycolide)

A series of poly(d,l-lactide-co-glycolide) (PLGA) polymers with various molecular weight were synthesized by a ring-opening polymerization method using stannous 2-ethyl hexanoate (Sn(Oct)(2)) as the catalyst. The molecular weight of these polymers was controlled in a novel way, using t-butyldimethylsilanol (TBDS) or triphenylsilanol (TPS). The silicon-end group attached to the PLGA copolymer was removed at room temperature using either hydrochloric acid (HCl) or trifluoroacetic acid (TFA). The structures of these polymers before and after end group removal were characterized by (1)HNMR spectroscopy, while the molecular weight and polydispersity index (PDI) were determined by viscosity method and gel permeation chromatography (GPC). The residual amounts of stannum in PLGA and the glass transition temperature (T (g)) of copolymer before and after end group removal were determined by the atomic absorption spectrum (AAS) and differential scanning calorimetry (DSC), respectively. The results showed that the removal method was effective. This study demonstrated that the molecular weight of PLGA could be easily controlled by altering the monomers/silanol molar ratio and the molecular weight and the purity of PLGA copolymer materials after silicon-end group removal could meet the demand of drug release.