NOTES Degradation of Aliphatic Polyesters by Vacuum Ultraviolet Irradiation Yabin LI, Akiko HAYASHI, Mizuho SAITO, Martin VACHA, Shigemitsu MURASE, and Hisaya SATO y Graduate School of Bio-Application Systems and Engineering, Tokyo University of Agriculture & Technology, 2-4-16 Naka-cho, Koganei 184-8588, Japan (Received September 27, 2005; Accepted November 17, 2005; Published April 15, 2006) KEY WORDS Aliphatic Polyesters / Vacuum Ultraviolet Irradiation / Degradation / Negatively Charged Oxygen / [DOI 10.1295/polymj.38.395] The photon energy of vacuum ultraviolet (VUV) light is higher than the binding energy of some chemi- cal bonds in organic molecules, such as C–C, C–H, or C–O. Therefore, VUV light is able to cause the scis- sion of various bonds in polymer molecules, which can lead to the decomposition of the polymeric mole- cules. Degradation of polymers by VUV has been studied with the purpose of investigating damage to polymeric materials by VUV, developing new photo- resist materials, revealing the degradation mecha- nism, and modifying polymer surfaces, etc. 1–9 The degradation mechanism of poly(methyl methacrylate) (PMMA) has been extensively studied for evaluation as a new photoresist material. 10–13 It was found that the side chain ester group is decomposed by VUV irradiation, leading to a polymer containing carbon- carbon 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 func- tion as good photoresist materials. Aliphatic poly- esters 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 ali- phatic 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 mech- anism, the effect of oxygen and application of an external electric field during irradiation. EXPERIMENTAL Materials Poly(methyl methacrylate) (PMMA), poly(L-lactic acid) (PLA), and poly(butylene succinate) (PBS) were obtained commercially and used without further puri- fication. Methods Polymer thin films were prepared by spin coating a chloroform solution of the respective polymer (0.010 g mL 1 ) on a germanium or quartz glass substrate at a spin rate of 500 rpm. The film thickness was in the order of 0.2 mm. For the patterning experiment the film was heated at 80  C for 10 min. VUV was generated using a Xe excimer lamp (Harrison Toshiba Lighting) with a center wavelength of 172 nm. The light intensity was 0.23 mW cm 2 as measured at the sample position with a power meter (Ushio, UIT-150) and a detector (Ushio, UVD-C254). IR spectra were measured for the samples on germani- um substrates using a Jasco FT-IR-460 spectrometer. UV spectra were measured for the samples on quartz glass substrates using a Jasco V-570 spectrometer. Surface profiles were observed using a contact profil- ometer (Dektak). Micrographs were obtained using a digital microscope (Keyence, VH-Z450). RESULTS AND DISCUSSION The degradation of the polymers upon irradiation with the Xe excimer lamp was characterized by IR spectroscopy. Figure 1 shows an example of the IR spectral change of PBS film with the thickness of 0.4 mm. The intensities of all the peaks decreased uni- y To whom correspondence should be addressed (Tel: +81-42-388-7050, Fax: +81-42-388-7050, E-mail: h-sato@cc.tuat.ac.jp). 395 Polymer Journal, Vol. 38, No. 4, pp. 395–399 (2006)