Structural Changes in Phase Transitions of Nylon Model Compounds. 1. Transition Behavior of Model Compounds of R-NHCO-R‘ Type

Abstract

To clarify the essential features of Brill transition of aliphatic nylons, structural changes have been investigated by X-ray diffraction and infrared spectroscopic methods for the compounds CH 3 (CH 2 ) 10 NHCO(CH 2 ) 9 CH 3 (designated as N11) and CH 3 (CH 2 ) 9 NHCO(CH 2 ) 8 CH 3 (N10) which were assumed to be the simplest models of nylons 11/11 and 10/10, respectively. Depending on the preparation conditions, N11 crystallized to the R and γ forms and N10 to the R form at room temperature. Infrared and X-ray diffraction data clarified that the R form took essentially the same chain packing structure as that of the R form of parent nylons, in which the all-trans methylene segments were packed in a triclinic subcell and the amide groups were connected by intermolecular hydrogen bonds to form a sheet structure and these sheets were stacked by a weak van der Waals force. In the DSC thermograms, the R form of N10 and N11 showed two main endothermic peaks in the Brill transition (ca. 50°C) and melting regions. The temperature region was divided into three (I, II, and III). In region I below 50°C, the crystal was of the R type. In region III (above 58°C for N10 and above 65°C for N11), the crystal transferred to the high-temperature γ form (γ h ), in which the molecular chains had disordered conformation, as speculated from the change in methylene progression bands and the broad amide bands, and these chains were packed in a pseudohexagonal mode. During the transition from region I to III, another phase was observed to appear discontinuously in region II. This intermediate phase showed the infrared spectra composed of the characteristic patterns of the R and γ h forms but the X-ray diffraction pattern was quite unique and different from those of the latter two forms, indicating that the molecules with a hybrid conformation between the R and γ h forms were packed in a unique crystal lattice. In case of the γ form of N11 compound, the molecular chains took the conformation built by skewed amide groups and partially disordered trans methylene segments even at room temperature. The crystal transferred apparently continuously to the γ h form above 70°C.

Preparation and characterization of electrospun fibers of Nylon 11

“…The crystalline structure and polymorphism of Nylon 11 has been studied by several researchers [23][24][25][26][27][28]. It has been reported that the α form of Nylon 11 exhibits two characteristic reflections at 2θ = 20.2 and 23.01° [23] whereas the γ form of Nylon 11 exhibits a characteristic reflection at 2θ = 21.34° [24].…”

Reversible changes induced by temperature in the spherulitic birefringence of nylon 6 9

“…Recent works based on FTIR data suggest that high temperature pseudohexagonal arrangements are a result of the conformational disorder of polymethylene segments rather than of disruption of hydrogen bonds [35][36][37].…”

Morphology and local chain structure of polyamide 6 modified in the solid state with a semi-aromatic nylon salt

“…As melting starts around 193 • C, the narrowing and sharpening of the peaks as well as the disappearance of the C1 ␣ and the carbonyl peak at 173.2 ppm are observed. The twisting motion and the weakening of intermolecular hydrogen bonding are accelerated for these carbon sites and become even more pronounced compared to other carbon sites in the repeat unit [23]. Close to the melting temperature of the PA6 (212 • C as the highest temperature applied during the measurements) only the trans and gauche transformers of the rigid amorphous phase are visible.…”

“…The bands at 1477, 1417, 1294, 1237 and 1201 cm −1 can be qualified as Brill bands and the disappearance of these peaks indicate the Brill transition of the copolyamides at around 160-180 • C [20,23]. During this transition, the interchain and intersheet distances of the PA6 chains become equal and the triclinic structure transforms into a pseudohexagonal structure [43].…”

“…X-ray diffraction gives direct information about the crystalline forms of the polymers. On the other hand, with FT-IR spectroscopy the crystalline and amorphous phases of the polymer and the structural changes upon heating can be investigated [19][20][21][22][23]. Solid-state NMR spectroscopy is another very useful tool to study the molecular conformations and structures of polymers [24,25].…”