STRUCTURAL CHARACTERIZATION OF THE CROSS-POLYMERIZATION OF A DIACETYLENE-FUNCTIONALIZED POLYAMIDE

The molecular structural changes caused by the radiation-induced cross-polymerization of diacetylene units across host chains of a diacetylene-functionalized polyamide have been studied by solid-state C-13 NMR and wide-angle X-ray diffraction. By measuring C-13 NMR spin-lattice relaxation times of poly(hexamethylene-10,12-docosadiyne-1,22-diamide) before and after diacetylene cross-polymerization, it was found that cross-linking occurred primarily within the crystallites, as evidenced by the complete retention of amorphous-phase segmental mobility and constant rigid-component mass fractions. Cross-linking was also found to be accompanied by an increase in the local segmental mobility within the crystallites which was shown to result from a trans to gauche conformational transition of the methylene carbons pendant to the newly formed polydiacetylene chains. Wide-angle X-ray diffraction revealed that the diacetylene-functionalized polyamide crystallizes in a manner similar to that of conventional polyamides. Upon cross-polymerization, the formation of gauche conformers expanded the interplanar spacing between the hydrogen-bonded sheets while the spacing between the hydrogen-bonded chains remained constant, at least adjacent to the amide groups. Thus, the full hydrogen-bonding strength is retained since any lattice strains imposed by polymerization of the diacetylene units to polydiacetylene chains are accommodated by the conformational changes of the methylene segments connecting the amide groups to the polydiacetylene cross-links.