Photo‐oxydation de polyéther‐block‐polyamides

Analytical and kinetic aspects of the photooxidation in the solid state of two polyether‐block‐polyamides 1a and 1b are described. The block copolymers studied contain different fractions of polyether segments. Nevertheless, their photooxidation presents the same features and concerns mainly the ether groups. In both thermoplastic elastomers, 1a and 1b very high stationary concentrations of hydroperoxy groups CH(OOH)OCH2 are observed (0,3 to 0,7 mol · kg−1). These hydroperoxides are, however, photounstable and thermounstable above 60°C. They are converted into hemiacetals OCH(OH)OCH2, saturated esters and formates. The hemiacetal groups are thermounstable, too, and decompose into alcohol and aldehyde groups, the latter being photoxidized in the matrix. The oxygen consumption rate, the primary hydroperoxidation rate, and the rate of accumulation of final products were determined. A mechanism including the photolysis and the thermolysis of the hydroperoxides can account for the formation of the final photoproducts (hemiacetals, esters, formates and acids).