An Intrinsically Transparent Polyamide Film with Superior Toughness and Great Optical Performance.

Polyamide 66 was extensively utilized in various applications contributed by its excellent mechanical performance and outstanding durability. However, its high crystallinity renders it to have low transparency, which seriously limits its application in optical devices. Herein, a highly transparent polyamide (PA) 66-based copolymer was reported using 4,4'-diaminodicyclohexylmethane (PACM), adipic acid, and polyamide 66 salt as the reaction monomers. Wide-angle X-ray diffraction (WAXD) analysis revealed that the crystal phase of the synthesized PA66/PACM6 displayed a clear transition from α to γ as the PACM6 increased accompanied by a decreased intensity in the diffraction peak of the copolymer, whose transmittance was successfully adjusted reaching as high as 92.5% (at 550 nm) when the PACM6 was 40 wt%. Moreover, the copolymer with a higher content of PACM6 exhibited larger toughness. On the other hand, the biaxially oriented films of PA66/PACM6 (20 wt%) were also prepared, and it was found that the transparency of the PA66/PACM6 copolymer could be further enhanced via adjusting the stretching ratio of the film. Furthermore, the mechanical strength of the biaxially oriented PA66/PACM6 was also improved with the increase in the orientation degree in the stretching process, indicating that the physical properties of the transparent PA66 were significantly influenced by its alicyclic structure, and the introduction of PACM into PA66 was capable of effectively improving the optical and crystalline characteristics of PA66, revealing that the synthetic strategy has great potential for guiding the design and development of transparent polyamide materials.