SPECTROSCOPIC INVESTIGATION OF THE PHOTODEGRADATION OF POLYDIACETYLENE SOLUTIONS

The degradation of chloroform solutions of nBCMU-polydiacetylenes [nBC MU = (BuO2CCH2NHCO2)-O-n(CH2)(n)], and related polymers with chiral ur ethane sidegroups, stored in Pyrex glassware under normal laboratory a tmosphere and lighting was studied by the measurement of changes in th e optical absorption spectrum. Both the magnitude and wavelength of th e absorbance maximum decrease as the mean molecular weight is reduced by degradation. Measurements made on a reference sample stored in the dark showed that thermal degradation was negligible. Comparison with t he spectra of a sample degraded by UV radiation (lambda < 300 nm) show s that the degradation behaviour of white light exposed samples is dis tinctly different. While the precise temporal dependence of the degrad ation varies from polymer to polymer there is a discernible generic be haviour. This is also true for the shift in the energy of the absorpti on maximum when plotted against the decrease in absorption strength. A model based on the known dependence of the absorption maximum on poly mer chain length is developed to describe the observed generic behavio ur. Degradation by random scission followed by depolymerization is sho wn to be consistent with the experimental data The measurements show t hat polydiacetylene solutions can be stored in the dark for up to four years but that solutions left open to the light can have shelf lives as short as ten days.