AN ELECTRON-SPIN-RESONANCE STUDY ON GAMMA-IRRADIATED POLY(L-LACTIC ACID) AND POLY(D,L-LACTIC ACID)

The effect of gamma irradiation on poly(L-lactic acid) (L-PLA) and pol y(D,L-lactic acid) (D,L-PLA), has been examined using ESR spectroscopy and through analysis of the changes in molecular weight. The G values for radical formation of both polylactic acids have been calculated a t 77 and 300 K; G(R) = 2.0 at 77 K and G(R) = 1.5 at 300 K for L-PLA a nd G(R) = 2.4 at 77 K and G(R) = 1.2 at 300 K for D,L-PLA. The ESR spe ctrum at 300 K for the polymers was assigned to one radical, resulting from H atom abstraction from the quaternary carbon atom. The G values for crosslinking and scission have also been determined for the polym ers at 300 K; G(S) = 2.3 and G(X) = 0.0 for D,L-PLA, G(S) = 2.4 and G( X) = 0.28 for L-PLA.