PHOTODEGRADATION OF POLY(METHYL METHACRYLATE) BY MONOCHROMATIC LIGHT - QUANTUM YIELD, EFFECT OF WAVELENGTHS, AND LIGHT-INTENSITY

Poly(methyl methacrylate) (PMMA) was photolyzed with monochromatic light of wavelengths 260, 280, and 300 nm by the use of the Okazaki large spectrograph. The quantum yield of mainchain scission (ϕcs), effects of wavelength, and incident photon intensity on the photodegradation were investigated. It turned out that photodegradation of PMMA took place by the irradiation of 260–300 nm light, but did not by the irradiation at λ ⩾ 320 nm. The number of main‐chain scission (Ncs) has a maximum value in the case of the irradiation with 280 nm light. Under the same conditions of wavelength and total photon intensity, a longer‐term irradiation with a weaker incident photon intensity tends to yield a greater amount of main‐chain scission. A linear relationship was found between the number of main‐chain scission and the incident photon intensity. The average values of ϕcs obtained in this work were 2.1 × 10−4, 2.4 × 10−4, and 4.1 × 10−4, respectively, for the irradiations at 260, 280, and 300 nm. It was found that the photoinduced side‐chain scission initiates the main‐chain scission of PMMA. Copyright © 1990 John Wiley & Sons, Inc.