The photochemical degradation of polyamides and related model N-alkylamides

Abstract

Analogous products to those obtained from exposure of simple model N-alkylamides to u.v. light, in oxygen or under anaerobic conditions, have been sought in a concurrent investigation of the photodegradation of polyamides (chiefly 6.6 nylon) in u.v. light and sunlight. The polymer degradation has been characterized by measurement of yarn tenacity losses under different conditions, and correlation of these with changes in intrinsic viscosity, u.v. absorption and end-groups. Chemical changes occurring, detected by analysis of the hydrolysed polymer, indicate the formation of aldehyde and primary amide end-groups, and a smaller number of n-pentylamino and n-pentanoyl end-groups. The results for both N-alkylamides and polyamides, can be interpreted by postulating two types of reaction: a photolysis into both free radicals and smaller molecules, occurring at short wavelengths and independent of oxygen, and a photosensitized autoxidation, occurring at longer wavelengths, involving oxidative attack predominantly at the methylene group adjacent to the N atom of the molecule, and subsequent decomposition of the derived radical R.CO.NH.CH(O·).R′. The more rapid loss of tenacity observed with titanium dioxide delustered yarns containing no oxidation inhibitors is due to increased photodegradation around the delustrant particles; the same products result as with bright yarns.