MACRORADICAL CONFORMATIONS IN IRRADIATED POLYAMIDES

ENDOR spectra of middle-chain radicals formed in irradiated PA-6,6, PA -6, and PA-12 polyamides were measured. The constants of hyperfine int el action between unpaired electron and protons of the beta- and delta -methylene groups in the -CH2-CO-NH-CH-CH-(2)- macroradicals were dete rmined. In all the polyamides studied, the rotation about the C-alpha- C-beta bond relative to the ideal flat trans-zigzag conformation was 9 -12 degrees. Variations of the angle of internal rotation about the C( 0)-C-delta bond in polyamides with a-crystalline structure (PA-6 and P A-6,6) are relatively small (10-13 degrees), while in the case of gamm a-crystalline structure (PA-12 and iodine-treated PA-6), the rotation angle can reach up to 60 degrees.