Synthesis of acrylate functional telechelic poly(lactic acid) oligomer by transesterification

The controlled synthesis of low molecular weight (Mn from 700 to 10 000 g/m ol) poly(lactic acid) (PLA) telechelic oligomers end-capped with acrylate g roups by a one step reaction was investigated. A transesterification reacti on was carried out in solution with a Lewis acid titanium catalyst using a high molecular weight PLA and a low molar mass diacrylate. End-functionaliz ation was demonstrated by proton NMR spectroscopy which was also used for q uantitative analysis and number average molecular weight determination usin g the ratio between the acrylic chain ends to the main groups of poly(D,L-l actic acid). The formation of low molar mass oligomers from high molecular weight poly(lactic acid) was verified by gel permeation chromatography. Mat rix-assisted laser desorption ionization time-of-flight mass spectrometry s howed that the above oligomerization was accompanied by the formation of cy clic compounds. By these means the feasability of a simple transesterificat ion for a controlled synthesis of telechelic oligomers with molecular mass being a function of the added amount of diacrylate has been demonstrated. T he glass transition temperatures of the elaborated oligomers varied from -3 5 to -5 degrees C. Subsequent thermal crosslinking was performed using benz oyl peroxide which enabled the formation of amorphous networks with Tg's cl ose to the body temperature of 40 degrees C. Upon storage in a humid atmosp here the initially fairly hard and brittle networks became, due to hydrolys is, progressively more flexible thus demonstrating the potential biodegrada bility of these materials. (C) 2000 Kluwer Academic Publishers.