A model for photodegradation of transparent thermoplastics has been developed and tested using data from polystyrene samples. The proportionality between incident energy and amount of degradation is calculated at each wavelength to yield the "wavelength sensitivity spectrum" for degradation of the polymer. The formal derivation of the wavelength sensitivity spectrum is described. The model was tested by exposing polystyrene samples containing several different stabilizers at various loadings to two different sources of xenon arc ultraviolet radiation. The degradation rates predicted by the model correlated well with the experimentally observed rates over all the different conditions. The model systematically underestimates the absolute degradation. Measurement of stabilizer concentration as a function of depth into the molded test specimens showed that the stabilizer was distributed uniformly before exposure to the light source. After exposure, the stabilizer was largely depleted from the surface layer, but the concentration was unchanged in the bulk of the specimens.

The wavelength sensitivity of unpigmented 100 mil thick ABS exposed to sunlight and filtered xenon are radiation was determined by the sharp cut filter technique based on three types of photochemical changes: bleaching, yellowing and loss in impact strength. Bleaching of the yellow‐colored species formed in the processed material is caused by wavelengths between 380 and 525 nm with maximum color change by the 475–485 nm region. Photochemical yellowing is due to wavelengths between 300 and 380 nm with all wavelengths being almost equally effective. The spectral sensitivity based on change in impact strength shifts from the UV to the visible region as photochemical yellowing progresses. Addition of two stabilizers, a benzotriazole ultraviolet absorber and a hindered amine stabilizer, shifts the wavelength sensitivity based on yellowing to wavelengths shorter than 330 nm, but has no influence on the spectral effects based on impact strength. It is postulated that the rate of yellowing is reduced mainly by the ultraviolet absorber and stabilization against loss in impact strength is due largely to the hindered amine. Differences in rates and spectral response of the three types of photochemical changes indicate that they are due to different initiating mechanisms and thus require different types of stabilization. The significance to stability testing is discussed.

Additives are commonly formulated into polymers to stabilize them against thermo‐oxidative and photo‐oxidative degradation. However, the additives themselves undergo degradation in the polymers, especially when the polymers are placed in hostile environments. This study focuses on the degradation of additives in chemical and photo‐oxidizing environments; i.e., spas and xenon arc, respectively. HPLC‐UV/vis, FT‐IR, and GC‐MS techniques were utilized to follow the degradation chemistry of the additives. The chemistry was determined for additive degradation by spa chemicals, but the degradation chemistry of benzotriazoles remains elusive due to the insolubility of the resinous degradation products. © 1994 John Wiley & Sons, Inc.

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The infrared spectra for a series of random styrene-acrylonitrile (SAN) copolymers of various compositions were analyzed to determine the dependence of the individual spectral peaks on the copolymer composition. Correlations were established to relate changes in the peak positions and intensities to changes in the copolymer composition and monomer sequence distribution. It was found that a number of peaks shift to higher frequencies as the amount of acrylonitrile in the SAN copolymer is increased while others shift to lower frequencies. It was also found that some peak positions are unaffected by changes in the copolymer composition. The intensities of the spectral peaks were also analyzed as a function of the copolymer content by plotting changes in the intensity values against the number fraction of each of the possible monad, dyad, and triad structures. A peak was then determined to result from a given microstructure if there exists a positive linear relationship between the peak intensity and the number fraction of this microstructure.