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The controlled synthesis of low molecular weight (Mn from 700 to 10 000 g/mol) poly(lactic acid) (PLA) telechelic oligomers end-capped with acrylate groups by a one-step reaction was investigated. A transesterification reaction was carried out in solution with a Lewis acid titanium catalyst using a high molecular weight PLA and a low molar mass diacrylate. End-functionalization was demonstrated by proton NMR spectroscopy which was also used for quantitative analysis and number average molecular weight determination using the ratio between the acrylic chain ends to the main groups of poly(D,L-lactic acid). The formation of low molar mass oligomers from high molecular weight poly(lactic acid) was verified by gel permeation chromatography. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry showed that the above oligomerization was accompanied by the formation of cyclic compounds. By these means the feasability of a simple transesterification for a controlled synthesis of telechelic oligomers with molecular mass being a function of the added amount of diacrylate has been demonstrated. The glass transition temperatures of the elaborated oligomers varied from -35 to -5 degrees C. Subsequent thermal crosslinking was performed using benzoyl peroxide which enabled the formation of amorphous networks with Tg's close to the body temperature of 40 degrees C. Upon storage in a humid atmosphere the initially fairly hard and brittle networks became, due to hydrolysis, progressively more flexible thus demonstrating the potential biodegradability of these materials., (Copyright 2000 Kluwer Academic Publishers)

Biomer is generally processed by repeated deposition of layers by solution casting onto a preshaped former. The precise nature of this processing route may influence the mechanical response and surface properties of the finished article and, as a result, its subsequent in vivo behaviour. Here we have studied the influence of a range of processing parameter: the type of former, the initial concentration of the solution from which the layers are cast and the time interval between casting of successive layers. The subsequent variation of physico-chemical properties on vitro ageing in isotonic saline solution has also been considered and, in particular, the possibility of cross-linking during long-term exposure.