Synthetic polyamides, nylons, especially those having relatively simple repeating units, are generally hard to be decomposed under natural environmental conditions either through biological or through hydrolytic processes. This research is concerned with the degradability of three kinds of polyamides prepared from 2-pyrrolidone (1), epsilon-caprolactam, and a bicyclic lactam, 8-oxa-6-azabicyclo[3,2,1]octan-7-one (2). The anionic polymerization of 1 catalyzed by potassium t-butoxide at 30ﾟC gave high molecular weight nylon 4. The bicyclic lactam 2 has both of five- and seven-membered lactam-rings and its quasi-living anionic polymerization in dimethylsulfoxide gives a monodisperse and well-dified polyamide having a tetrahydropyran ring in the repeating unit (3). Films of nylon4, nylon6, and polyamide 3 were supplied to soil burial tests in several kinds of soils, the soil composted for more than 10 years in university farm (pH,7.5 ; Soil 1), the noncomposted soil in the same farm (pH,5.
9 ; Soil 2), the soil in the campus of the university (pH,4.5 ; Soil 3), and its sterilized soil (pH,4.5 ; Soil 4). Among them, the film of nylon4 was found to be decomposedin Soil and disappeared with 4 months. The solution viscosity of nylon4 recovered during the tests did not irrespective of their weight loss. In a phosphate buffer (pH,7.5) both of weight and solution viscosty of the recovered nylon4 film did not change. Therefore it was degraded probably through biological processes by microorganisms in Soil 1. On the other hand, the molecular weight of polyamide 3 decreased in all the burial tests, and its weight also duced during the tests in the acid soils for 6 months. The decrease rate of the molecular weight in Soil 1 was similar to that in the phosphate buffer (pH,7.5). This suggests that the degradation of 3 in the soils proceeded through the hydrolysis. The solution viscosity of nylon 6 recovered after the soil burial tests l the acid soils (Soil 2, Soil 3, Soil 4) was found to decreases slightly. But in the neutral conditions not only its solution viscosity but also its weight did not change. In the soil burial tests of the nylon6 film blended with nylon4, only the nylon4 phase was degraded and its residual part was formed with nylon6. From these results, nylon4 is inferred to be biodegradable in the farm soil and polyamide 3 to be hydrolyzable. In fact, one of actinimetes was found to degrade nylon4 film. Less