Investigation of solution-grown, chain-folded lamellar crystals of the even-even nylons: 6 6, 8 6, 8 8, 10 6, 10 8, 10 10, 12 6, 12 8, 12 10, and 12 12

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

“…Crystalline structures of all solution-crystallized polyamides (crystallization from ethylene glycol at 110 °C and then washed and dried) were first analyzed by WAXS and FTIR spectroscopy, and the corresponding results are shown in Figure . Figure a shows that all of the solution-crystallized polyamides form the α or α-like phase, which is consistent with the previous reports. , All polyamides exhibit sharp diffraction peaks in the entire composition range, indicating the high crystallinities of random copolyamides. The crystallinities of all polyamides were determined by the peak fitting method (Figure S3) and vary from 31.0% to 41.7% (Table ), displaying the minimum value for the sample with the intermediate composition (e.g., f 56 -0.5).…”

“…The α phase of PA6,6 (denoted as α 66 ) is reported to have the triclinic unit cell with the lattice parameters of a = 0.49 nm, b = 0.53 nm, c = 1.73 nm, α = 50°, β = 77°, and γ = 64°. 43,45 The α-like phase of PA5,6 (denoted as α 56 ) has the monoclinic unit cell with the lattice parameters of a = 0.51 nm, b = 0.86 nm, c = 3.13 nm, α = 90°, β = 125.7°, and γ = 90°. 44 Note that both the (002) plane of α 66 phase and (004) plane of α 56 phase represent the lamellar stacking periodicity, which is calculated to be ∼3.5 chemical repeats per lamellar thickness for both PA6,6 and PA5,6.…”

“…44 Note that both the (002) plane of α 66 phase and (004) plane of α 56 phase represent the lamellar stacking periodicity, which is calculated to be ∼3.5 chemical repeats per lamellar thickness for both PA6,6 and PA5,6. 43,44 The lattice spacing (i.e., d 002 and d 004 ) could be calculated from the corresponding q values in WAXS curves by Bragg's law. The d 002 of the α 66 phase (0.67 nm) is larger than the d 004 of the α 56 phase (0.63 nm), which is expected because the repeat unit length of PA6,6 is longer than that of PA5,6.…”

“…Figure 2a shows that all of the solution-crystallized polyamides form the α or α-like phase, which is consistent with the previous reports. 43,44 All polyamides exhibit sharp diffraction peaks in the entire composition range, indicating the high crystallinities of random copolyamides. The crystallinities of all polyamides were determined by the peak fitting method (Figure S3) and vary from 31.0% to 41.7% (Table 1), displaying the minimum value for the sample with the intermediate composition (e.g., f 56 -0.5).…”

Structural and Morphological Evolution upon Heating of Quenched Polyamide 1012

“…During melt cooling, the thermodynamically driven methylene segments preferentially adopt the lowest-energy trans conformation. Therefore, the methylene segments in the thermodynamically stable α form of PA1012 (usually prepared by slow cooling from the melt) adopt an almost all- trans conformation at room temperature. , The WAXS result showed that the average chain periodicity of the γ′ form of PA1012 is c = 2.508 nm, close to that value of the all- trans α form (Figure ). Moreover, the progression bands at 986 and 1063 cm –1 , which are assigned to the long zigzag methylene sequences (10 methylene groups), were observed in the FTIR spectra of the γ′ form (Figure S3).…”