Stereochemistry Driven Distribution of 1,4-Diaminocyclohexane Residues over the Crystalline and Amorphous Phase in Copolyamides 4.14/1,4-DACH.14. A Solid-State NMR and Temperature-Dependent WAXD Study

Abstract

Following our previous study on the stereoselective cocrystallization of linear and cyclic dicarboxylic acid residues in copolyamides 12.6/12.1,4-cyclohexanedicarboxylic acid (12.6/12.1,4-CHDA, Vanhaecht et al., Macromolecules 2004, 37, 421), we have now investigated a series of copolyamides containing trans or cis isomers of 1,4-diaminocyclohexane (1,4-DACH), viz. 4.14/1,4-DACH.14. Solidstate NMR studies and WAXD experiments demonstrate that the cis isomer is present in the amorphous regions of the copolyamide, whereas the trans isomer is located in both the crystalline and the amorphous phase. Similar to the results for the trans-1,4-CHDA-based copolyamides, trans-1,4-DACH moieties are probably built into the crystalline structure with the cycloaliphatic ring oriented perpendicular to the hydrogen-bonded crystal sheets. Temperature-dependent WAXD patterns show that, unlike in the homopolyamide 4.14, a pseudohexagonal phase is not formed at the Brill temperature in the copolyamide. Instead, crossing rather than merging of the (100) and the combined ( 010)-( 110) WAXD reflections occurs upon heating of the copolyamides containing trans-1,4-DACH. In contrast to the cis isomer, introduction of trans-1,4-DACH into polyamide 4.14 raises the melting temperature, confirming the findings by solidstate NMR and WAXD analysis. Unlike 1,4-CHDA moieties, 1,4-DACH residues do not undergo thermal isomerization. Therefore, at the same amount of initially trans isomers, the copolyamides 4.14/1,4-DACH.14 exhibit higher second heating end melting points than the corresponding isomeric copolyamides 12.6/12.1,4-1,4-CHDA.

Preparation, Solid-State NMR, and Physicochemical Characterization of Surprisingly Tough Open Cell PolyHIPEs Derived from 1-Vinyl-1,2,4-triazole Oil-in-Water Emulsions

“…However, surprisingly, it appears to have been scarcely used for polyHIPE analysis. ,, We investigated the chemical structure of the VT-MBA polyHIPE monoliths by MAS NMR spectroscopy (on sample P34VT4). In addition with the more common 1 H and 13 C MAS NMR analysis, 15 N MAS NMR spectra were also recorded as previously reported for polyamide and N-containing insoluble polymers. − Experimental results displayed in Figure were in complete agreement with the expected structure: (i) 13 C NMR spectra displayed the two signals assigned to the quaternary carbons belonging to the triazole ring (150.7 and 143.1 ppm), two lines for methylene (52.5 ppm) and methine (38.1 ppm) aliphatic carbons of the main chain, and a well-defined small peak at 173 ppm attributed to the carbonyl groups from MBA. The corresponding integration represented roughly 4% of the integration of triazole ring carbons.…”

Isodimorphic Crystallization and Tunable γ–α Phase Transition in Aliphatic Copolyamides: Critical Roles of Comonomer Defects and Conformational Evolution

“…These included comonomer units can greatly influence their Brill transition behaviors. For instance, Koning and co-workers found that incorporation of trans cyclic comonomers into polyamides inhibited the trans – gauche conformational evolution, and thus the α phase was maintained during heating. − In other cases, incorporating diaminoisoidide in aliphatic copolyamides caused conformational disorder and resulted in large amounts of gauche bonds, facilitating the formation of a γ phase. − These studies show a possible influence of comonomer inclusion on the trans / gauche conformational evolution, thus affecting the α/γ Brill transition of copolyamides. Nevertheless, an accurate conclusion about how the existence of comonomer units (i.e., the comonomer defects) in the crystalline phase affects the Brill transition behavior of copolyamides is lacking.…”

Brill Transition in Polyamide 1012 Multiblock Poly(tetramethylene oxide) Copolymers: The Effect of Composition on Hydrogen-Bonding Organization

“…According to the literature, cocrystallization can occur in PA-based copolymers with a stereochemical comonomer. Koning et al reported one non-classical Brill transition with a crossing rather than a merging of the two reflections of the α-phase in the copolyamides in the presence of trans cycloaliphatic residues in the crystalline phase. , They believed that the crossing behavior is caused by the reduced mobility of the chains, preventing the formation of the pseudohexagonal phase before the melting temperature . Based on the literature, the observed differences between PA1012 and PAE38 samples in Figure are probably caused by the accelerated mobility contributed by the PTMO SS.…”

“…29,69 They believed that the crossing behavior is caused by the reduced mobility of the chains, preventing the formation of the pseudohexagonal phase before the melting temperature. 69 Based on the literature, the observed differences between PA1012 and PAE38 samples in Figure 7 are probably caused by the accelerated mobility contributed by the PTMO SS.…”