Robust and Transparent Polyamide 1012 Membranes for Biogas Purification Controlled by the Degree of Hydrogen Bonding Order

Crystal Polymorphism and Phase Transition of Isodimorphic Copolyamides Based on Even–Even and Odd–Even Comonomer Units: Synergistic Effects of Copolymer Composition and Crystallization Temperature

“…Notably, the crystallization and Brill transition of aliphatic polyamides are strongly influenced by the even or odd CH 2 unit numbers in the methylene sequences of the polyamides. Previous studies have found that most of the even–even aliphatic polyamides (e.g., PA4,6, PA6,6, and PA10,10) experience reversible γ–α phase transition during cooling. − However, the odd–even polyamides (e.g., PA5,6, PA9,2, PA5,10) merely keep as the γ phase and do not convert back into the α phase upon cooling, − because their α and γ phases have the different H-bonding directions. , This phase transition can result in the formation of different crystal polymorphs (α phase for even–even polyamides and γ phase for odd–even polyamides) with distinct mechanical properties after melt processing …”

“…22,23 This phase transition can result in the formation of different crystal polymorphs (α phase for even−even polyamides and γ phase for odd−even polyamides) with distinct mechanical properties after melt processing. 3 Random copolymerization is a practical way to modulate the physical properties and develop new materials for polyamides. Also, the crystallization kinetics, crystal polymorph, and phase transition of polyamides can vary significantly with the incorporation of comonomer units.…”

“…Aliphatic polyamides have gained significant attention across various industries, including electronics, textiles, and aerospace, due to their excellent mechanical properties and chemical resistance. , Polyamides are typical polymorphic polymers, and most of them can form a triclinic or monoclinic α phase and a pseudohexagonal γ phase under different crystallization conditions. The α phase of polyamides generally possesses higher density and modulus, while the γ phase usually exhibits good transparency and toughness. − Furthermore, the α phase of polyamide can gradually transform into the γ phase during the heating process, termed as Brill transition . Two main mechanisms have been proposed to explain the Brill transition of polyamides: (1) conformational changes in the methylene sequences of polyamides induced by thermal expansion − and (2) reorganization of hydrogen bonding (H-bonding) between amide groups .…”

Structural and Morphological Evolution upon Heating of Quenched Polyamide 1012

“…Pepin et al pointed out that the H-bonded sheets of the α form in PA6 and PA11 were an obstacle to biaxial orientation due to high anisotropy, while the ductility of the mesophase became significantly better due to the disordered H-bonds. Our previous research has found that the γ′ form of PA1012 obtained by melt quenching has better toughness, transparency, and gas-selective properties compared to melt slow-cooled samples …”

“…PA1012 is a kind of typical AABB-type even–even LCPA, and it has been developed in recent decades. PA1012 has been reported to display four crystalline forms, the triclinic α and α′, the pseudohexagonal γ′ form at room temperature, and the pseudohexagonal γ form at high temperatures . The α form is the most thermodynamically stable crystal form of PA1012, which is characterized by the organization of H-bonded sheets held together by van der Waals interactions between sheets.…”