Degradation of Aliphatic Polyesters by Vacuum Ultraviolet Irradiation

Abstract

The photon energy of vacuum ultraviolet (VUV) light is higher than the binding energy of some chemical bonds in organic molecules, such as C–C, C–H, or C–O. Therefore, VUV light is able to cause the scission of various bonds in polymer molecules, which can lead to the decomposition of the polymeric molecules. Degradation of polymers by VUV has been studied with the purpose of investigating damage to polymeric materials by VUV, developing new photoresist materials, revealing the degradation mechanism, and modifying polymer surfaces, etc. The degradation mechanism of poly(methyl methacrylate) (PMMA) has been extensively studied for evaluation as a new photoresist material. It was found that the side chain ester group is decomposed by VUV irradiation, leading to a polymer containing carboncarbon double bonds. In addition, scission of the main chain also occurred. If an ester group is easily cleaved by VUV, it may be expected that aliphatic polyesters, which contain ester groups in the main chain, will be degraded to small volatile molecules and may function as good photoresist materials. Aliphatic polyesters are soluble in common organic solvents, which enables good thin films to be easily formed. It is well known that aliphatic polyesters are easily degraded by biological reactions, and although many studies have been performed regarding the biodegradation of aliphatic polyesters, only a few studies have investigated degradation by irradiation with UV or VUV light. In this report, the degradation of aliphatic polyesters by VUV was investigated and compared with that of PMMA. The study concentrated on the reaction mechanism, the effect of oxygen and application of an external electric field during irradiation. EXPERIMENTAL