Lewis acid–base complexation of polyamide 66 to control hydrogen bonding, extensibility and crystallinity

Polyamide 66 (PA66) has been complexed with the Lewis acid GaCl3 for the purpose of disrupting the interchain hydrogen bonded network. FTIR and 13C-NMR observations indicate that Ga metal cations form a 1:1 complex with the carbonyl oxygens of the PA66 amide groups. PA66–GaCl3 films are amorphous and rubbery with a single relaxation, attributable to the glass transition temperature, at ∼−32 °C and a structure that appears by X-ray diffraction to be thermally stable to at least 200 °C. The complexed films could be drawn at room temperature to draw ratios (DR) up to ∼30, and could then be decomplexed, or regenerated, by soaking in water. GaCl3 complexation and subsequent regeneration of PA66 was accomplished without changing its molecular weight, and all but ∼5 mol% of the amide groups in the regenerated PA66 were uncomplexed. The undrawn regenerated films regain levels of crystallinity much lower than possessed by the uncomplexed PA66 reference film. However, up to a DR of 8, drawing prior to regeneration increases the crystallinity, reaching crystallinity levels that are high for PA66, that has not been heat treated, and that are almost twice higher than in the uncomplexed (undrawn) reference film. It is intriguing that, in this DR regime, crystallinity increases quite sharply as the film is extended, despite the fact that molecular orientation does not appear to be increasing. For DR>8, the crystallinity decreases, but remains above that of the reference film. The level of crystallinity in PA66 can be controlled over a much wider range by the complexation-drawing-regeneration process than by conventional drawing processes.