Brill Transition in Nylons: The Structural Scenario()

Pleated and rippled sheet crystal structures of even–even nylons that feature twisted amide group–aliphatic part links were introduced in the previous contribution (Macromolecules, 2021, 54, DOI: 10.1021/acs.macromol.0c02404). sheets are made isochiral conformational isomeric stems, racemic stereocomplexes enantiomeric stem conformations. These models used to reanalyze various puzzling manifestations Brill transition first reported 1942. The is generally considered result from generation gauche bonds aliphatic parts nylon α phase which travel junctions with groups. Recognition pleated/rippled suggests a different scenario takes into account, but challenges, this analysis. place chain It dynamic interconversion between two possible conformers (mirror images) stems lattice. timescale ≈100 picosecond range, as determined by NMR. During interconversion, C–C–C plane flips ≈120° (from + −60°). intrasheet H preserved, transitory intersheet may be formed, accounts for frequent not systematic pseudo-hexagonal cell structure. This fully consistent (and more so than earlier models) wide body experimental data available on transition. generic all types (even, even–even, etc.) therefore valid their transitions well. On basis, should defined molecular process (the conformation interconversion) rather an criterion lacks general validity merging equatorial reflections).