Cocrystallization phenomena in piperazine-based copolyamides as examined by differential scanning calorimetry, wide-angle X-ray diffraction, and solid-state NMR

Copolyamides 2.14/piperazine.14 with variable built-in ratios of 1,2-ethylenediamine (1,2-EDA) and piperazine (pip) were synthesized by solution polycondensation. The built-in ratio of both diamine comonomers was determined with solution ¹³C NMR analysis. The gradual replacement of 1,2-EDA units by cycloaliphatic pip units in polyamide 2.14 resulted in a progressively decreased melting (T<INF>m</INF>) and crystallization temperature of the obtained copolyamides. Apparently, the T<INF>m</INF> raising effect of the incorporation of rigid cycloaliphatic moieties is overruled by the simultaneous T<INF>m</INF> reduction caused by a decreasing hydrogen-bond density. Indications for cocrystallization of 2.14 and pip.14 repeating units were obtained by the thermal analysis of copolyamides 2.14/pip.14 and of a blend of both homopolyamides. A preliminary wide-angle X-ray diffraction study pointed to the same conclusion. Solid-state NMR spectroscopy was used to investigate the influence of the composition on the percentage of the rigid phase of the copolyamides and delivered additional indications for cocrystallization. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2082–2094, 2003