Structural change in the Brill transition of Nylon m/n (1) Nylon 10/10 and its model compounds

The crystal structures of poly(nonamethyleneoxamide) (nylon-9,2) were investigated by wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry. Nylon-9,2 shows a polymorphism with two different structures depending on the conditions of sample preparation.Monoclinic form I is the dominant crystalline phase for the solution-crystallized sample. For melt-crystallized samples, form I and new monoclinic form I′ coexist. Variable-temperature WAXD measurements were used to investigate the stability of each crystal form and the phase transition. Form I does not undergo any phase transitions prior to melting, although the orthorhombic molecular chain packing in form I at low temperature comes close to the quasihexagonal one during the heating process. Form I′ shows no phase transition on heating until its melting, too. The crystal lattice simply expands due to the thermal expansion. Form I is believed to be more stable, because the melting temperature of form I is higher than that of form I′.

Section: Temperature Variation Of the Crystal Structure In The Scsmentioning

confidence: 99%

Polymorphism of poly(nonamethyleneoxamide) crystal

Nakagawa

Nozaki

Maeda

et al. 2015

“…The 13 C-NMR apparatus used here was a Bruker Biospin ADVANCE500 spectrometer operating at 125 MHz. To evaluate the position of the methyl group in the MOMD segments, the model compounds shown in Figure 4 were synthesized and then analyzed by 13 C-NMR under the same conditions as those for nylon-MOMD-2.…”

Section: Nuclear Magnetic Resonancementioning

confidence: 99%

“…Hence, the Brill transition no longer occurs in the nylon-MOMD-2 crystal. We have investigated the crystal structure of nylon-MOMD-2, and the temperature variation of the crystal structure by 13 C NMR, molecular mechanics, X-ray diffraction, and DSC.…”

Section: Temperature Variation Of the Crystal Structurementioning

confidence: 99%

“…We are interested in the crystallization of nylon-MOMD-2 and the effect that methyl groups at the -sites have on the crystal structure. In this study, the crystal structure of nylon-MOMD-2 is investigated by 13 C nuclear magnetic resonance, molecular mechanics calculations, and X-ray diffraction. The temperature dependence of the crystal structure is also studied.…”

Section: Introductionmentioning

confidence: 99%

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Crystal structure of an aliphatic polyoxamide containing methyl side-groups: Poly(2-methyl-1,8-octamethyleneoxamide)

Nakagawa

Maeda

Nozaki

et al. 2014

Poly (2-methyl-1,8-octametyleneoxamide) (nylon-MOMD-2) was prepared from dibutyl oxalate and 2-methyl-1,8-octamethylenediamine. The chemical structure was investigated by 13 C nuclear magnetic resonance ( 13 C NMR). The 13 C NMR spectrum revealed that the methyl groups distribute among the four -sites at random. The crystal structure and its temperature dependence were also investigated by molecular mechanics calculations, X-ray diffraction, and differential scanning calorimetry. The structure was determined to be monoclinic and a = 6.26 Å, b = 8.80 Å, c = 14.7 Å, and  = 50.7°. The torsion angle of the NH-CH 2 bonds has a skew conformation and there are the two distinct torsion angles in the crystal structure. The crystal structure of nylon-MOMD-2 has a disordered and statistical structure. The crystal structure shows no phase transition on heating until its melting point, although the unit cell expands in the a and b axis directions.

“…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].…”

Section: Introductionmentioning

confidence: 99%

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

Murase

Casas

Martínez

et al. 2015

Spherulitic morphologies of nylon 6 9 as an example of an even-odd nylon were studied by optical microscopy. A well-defined dependence on crystallization temperature was found. In particular, positively birefringent spherulites were characteristic for temperatures higher than 232 ºC, low birefringence spherulites developed between 232 and 225 ºC, positive ringed spherulites were found between 225 and 220 ºC, and finally negative fibrillar spherulites were formed at temperatures lower than 220 ºC. These optical properties were clearly different from those observed with even-even nylons (e.g., negative and positive birefringence for high and low temperatures, respectively), and may derive from the peculiar crystalline structures determined for even-odd nylons.Furthermore, low birefringence spherulites were characterized by a flat-on lamellar disposition and reversibility of the birefringence sign in the 80-120 ºC temperature interval (positive and negative values at high and low temperatures, respectively).Real time WAXD profiles taken during heating and cooling processes demonstrated that different crystalline structures (named I, II and III) developed depending on the temperature and crystallization procedure of samples (e.g., from solution or from the melt state). Crystalline structures were characterized by the formation of hydrogen bonds along two crystalline directions in all cases, a peculiar arrangement that may account for the development of positive and negative spherulites in a more simple way than formulated for conventional polyamides having a single hydrogen bonding direction. DSC and FTIR data also showed a complex structural behavior with structural transitions in the 80-120 ºC range, a region that corresponds to birefringence sign reversibility.