Polyamides with a Choice of Structure and Crystal Surface Chemistry. Studies of Chain-Folded Lamellae of Nylons 8 10 and 10 12 and Comparison with the Other 2N 2(N + 1) Nylons 4 6 and 6 8

Abstract

Nylons 8 10 and 10 12 have been synthesized and crystallized as chain-folded lamellae from 1,4-butanediol and the results compared with previous studies on Nylons 4 6 and 6 8. In 2N 2(N + 1) Nylons, the lengths of the two alkane segments are equal and two different hydrogen-bonded sheet schemes are possible: progressive or alternating shear. At room temperature, Nylons 8 10 and 10 12 adopt the progressive scheme and the adjacent re-entry folds in the crystals must be in the alkane chain segments. In contrast, Nylons 4 6 and 6 8 lamellae, crystallized from the same solvent, exhibit the alternating hydrogen bonding scheme and each adjacent re-entry fold must contain an amide group. The transition in the chemical nature of the lamellar surface, from the amide fold to the alkane fold, occurs in passing from Nylon 6 8 to 8 10. Thus, the progressive hydrogen-bonded sheet/alkane fold structure is energetically more favorable, provided the alkane-folding geometry is sufficiently relaxed; this comes with increasing alkane segment length. For each hydrogen-bonded sheet structure there are still two principal intersheet stacking modes in lamellar crystals: the progressively sheared R-phase or the alternatingly sheared β-phase, both of which have been found in the 8 10 and 10 12 Nylons. The 2N 2(N + 1) Nylons have the choice of four possible structures. The melting points of solution grown crystals of Nylons 4 6, 6 8, 8 10, and 10 12 decrease with decreasing intrachain amide density. When lamellar crystals of these Nylons are heated, the two characteristic interchain diffraction signals move together and meet at their Brill temperature; for Nylon 10 12 it appears to be close to the melting point.

Bio-polyamides based on renewable raw materials

“…The melting point (T m ) increases with increasing amide/ methylene ratio in the polymer backbone (0.17 for PA 4.10 and 0.1 for PA 10.12). This is consistent with the increasing linear density of hydrogen bonds and was found also for other PAs [19,48,49].…”

“…The peak positions of the fitting procedure and the spacings as calculated by Bragg's law are reported in Table 3. Within the experimental inaccuracy, the spacings do not show any significant differences according to the literature for PAs [18,19,24,40]. The amorphous regions are reflected on the smectic peak at 2h between 18°and 20°and the amorphous halo at ca.…”

“…In polyamides 2N 2(N ? 1), both types of sheet stacking were found, which gives four possible crystal structures [19]. The XRD pattern for these polyamides shows characteristic diffraction peaks related to the interchain and intersheet distance.…”

“…However, it was found for polyamides 2N (2 N ? 1) that as a length of alkane segments increases, the change in the sheet structure occurs, resulting in change in the chemical nature of lamellar surface [19]. Thus, the crystallinity degree will be affected by the consecutive alkane segments and the CONH/CH 2 ratio.…”

Polymorphism of poly(nonamethyleneoxamide) crystal

“…The crystal structures for aliphatic nylons have been widely investigated [1][2][3][4][5]. Generally, the  form appears in the crystals of even-even nylons [1,6].…”