Quantitative studies of the radiation chemical behaviour of PMMA and poly(lactides)

Abstract Polymers irradiated with synchrotron radiation undergo various radiation chemical reactions. Some of them are favourable to the fabrication of mechanical microstructures from a partially irradiated polymeric resist by subsequent selective development of either the irradiated or the non-irradiated parts in an appropriate chemical mixture. To have a measure for the radiation sensitivity of such a resist, we analyzed quantitatively the different reactions occurring in poly(lactides), which have recently shown to be a convenient material for the LIGA microfabrication process from which the first step, the X-ray lithography, was described above. The standard resist/developer system, PMMA/GG, was also analyzed to detect the differences in radiation chemistry and developer function. Molecular weight reduction of both materials was studied by size exclusion chromatography, giving the radiation chemical effectiveness of main chain scissions. Subsequent carboxylic acid generation in both polymers was observed via semi-quantitative FT-IR spectroscopy and titrimetric measurements. Side chain reactions and a certain main chain scission mechanism in poly(lactides) leading to the production of gaseous fragments were analyzed by in situ semi-quantitative mass spectroscopy. All methods together give a rather complete radiation chemical reaction scheme for PMMA and poly(lactides) that explains the improved performance of the new lactide system over the standard PMMA/GG used so far.