Wavelength Sensitivity in the Photo-Degradation of Polymethyl Methacrylate:Accelerated Degradation and Gel Formation

Abstract

We have been investigating the wavelength effect on polymer degradation using Okazaki Large Spectrograph(OLS) which was built at the National Institute for Basic Biology in Okazaki Japan. Such studies contribute to identify the spectral region which causes damage on polymer materials. Polymethylmethacrylate(PMMA) is known to be a degradation type polymer to photoirradiation. On irradiating PMMA at ambient temperature in the presence of oxygen, the threshold wavelength of main-chain scission in PMMA was found to be below 320 nm in our previous study¹. If we introduce some chromophore having the absorption at longer wavelength than 320 nm, the threshold wavelength of main-chain scission of PMMA would shift to the longer wavelength. This means that photodegradation of PMMA is easily take place in the wavelength region of the terrestrial sunlight. Benzophenone(BP) and β-carotene have one of their absorption maxima at around 340 nm and 450 nm, respectively. So, in photoirradiation of PMMA films containing BP or β-carotene with radiation of longer wavelength than 320 nm, we can expect the accelerated degradation of PMMA under the terrestrial sunlight. Under these considerations, we have investigated the wavelength sensitivity in the photodegradation of PMMA containing BP or β-carotene.