Structure and molecular dynamics in renewable polyamides from dideoxy-diamino isohexide

The chemical structure, the conformation, and the flexibility of the polymer chain fragments present in the polyamides synthesized from 2,5-diamino-2,5-dideoxy-1,4;3,6-dianhydrosorbitol, 1,4-diaminobutane, and either sebacic or brassylic acid have been studied by liquid-state 2D NMR spectroscopy viz. correlation spectra (COSY) and heteronuclear multiple-bond correlation spectra (gHMBC), by 13C cross-polarization/magic-angle spinning (CP/MAS) NMR, by X-ray scattering, and by FT-IR spectroscopy. The presence of 2,5-diamino-2,5-dideoxy-1,4;3,6-dianhydrosorbitol in the crystal phase of the polyamides was probed by wide-angle X-ray diffraction (WAXD), FT-IR, and solid-state 13C NMR. The incorporation of dideoxy–diamino isohexide into the backbone of PA 4.10 or PA 4.13 induces formation of gauche type conformers and gives rise to pseudohexagonal packing of the polymer chains in these semicrystalline copolymers. The experimental determination of the polymer chain structure combined with ab initio calculations revealed the presence of three most abundant diaminoisosorbide (DAIS) conformers. The combination of the 13C chemical shifts of these three conformers could explain all experimental resonances in the region of 50–90 ppm. WAXD and DSC analysis show that the crystallinity, and hence the physical properties of the investigated compositions, can be tailored by the content of the bicyclic diamine in the backbone of the polyamides