The photodegradation of polystyrene (PS) in deoxygenated solutions of CCb and CHCl, by irradiation with ultraviolet light of wavelengths 1 2 270 nm is investigated by quasielastic and integral light scatte_ring techniques. Molar mass distributions w (M), number-and weight-average molar masses % and M , as well as the average number of chain scissions per macromolecule x ( t ) as a function of the time of irradiation t were determined. The results obtained prove that efficient photodegradation occurs in CCb-and CHC1,-solutions of PS, although measurable changes in molar mass of irradiated PS starts to occur only after several hours of irradiation.

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SynopsisStatic and dynamic molecular properties are obtained from simultaneous elastic and quasielastic light scattering experiments for nine narrowly distributed polystyrene fractions in nine solvents covering the cross-over region from theta to good-solvent conditions. This set of consistent experimental data is compared with theoretical predictions of two renormalization group theories: the first-order c-expansion calculations of Oono et al. and second-order calculations within the "renormalized two-parameter" theory of Douglas and Freed. Static properties (the penetration function) are found to be exactly described by the c2-order model, while dynamic behavior seems to be in better accord with Oono's d-order calculations. No evidence of draining effects is detected. Solutions with benzene (and partially with toluene) exhibited atypical, nonuniversal behavior. Some features of static and dynamic exponents behavior in the crossover region are also discussed and compared with previously published theoretical predictions.

Several methods for the treatment of experimental data (including 3 different parameter-fitting procedures, histograms, and Provencher's constrained regularization) are considered which allow to obtain molecular weight distributions w ( M ) from quasielastic light scattering measurements. As a result of the introduction of a few improvements to these methods described in the literature, we were able to use more severe criteria for the quality of the distribution functions obtained, based on the mean-square deviation rather than on the coincidence of a few first moments. The quality of five investigated inversion methods was compared on the basis of simulated and experimental data for flexible chain polymers (polystyrene standards) in dilute solution. a) This work was carried out under The Research Project CPBP 01.12 of the Polish Academy of Sciences.0025-1 16)