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

Following our previous study on the stereoselective cocrystallization of linear and cyclicdicarboxylic 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 copolyamidescontaining trans or cis isomers of 1,4-diaminocyclohexane (1,4-DACH), viz. 4.14/1,4-DACH.14. SolidstateNMR studies and WAXD experiments demonstrate that the cis isomer is present in the amorphousregions of the copolyamide, whereas the trans isomer is located in both the crystalline and the amorphousphase. Similar to the results for the trans-1,4-CHDA-based copolyamides, trans-1,4-DACH moieties areprobably built into the crystalline structure with the cycloaliphatic ring oriented perpendicular to thehydrogen-bonded crystal sheets. Temperature-dependent WAXD patterns show that, unlike in thehomopolyamide 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 occursupon heating of the copolyamides containing trans-1,4-DACH. In contrast to the cis isomer, introductionof trans-1,4-DACH into polyamide 4.14 raises the melting temperature, confirming the findings by solidstateNMR and WAXD analysis. Unlike 1,4-CHDA moieties, 1,4-DACH residues do not undergo thermalisomerization. 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 copolyamides12.6/12.1,4-1,4-CHDA.