Controlled stereochemistry of polyamides derived from cis/trans-1,4-cyclohexanedicarboxylic acid

A series of copolyamides 12.y was synthesized either with y = 6, or 1,4-cyclohexanedicarboxylic acid (1,4-CHDA) residue, or a mixture of both. The influence of the synthetic route of 1,4-CHDA containing polyamides on the obtained cis-trans ratio of the incorporated 1,4-CHDA was investigated. The use of acid chlorides provided a synthetic route with full control of the cis-trans ratio of the 1,4-CHDA residue during synthesis, whereas synthesis at elevated pressure and temperature caused isomerization. The content and cis-trans ratio of 1,4-CHDA in the copolyamides were determined by solution C-13 NMR spectroscopy. Increasing the degree of partial substitution of the adipic acid by 1,4-CHDA resulted in an increase in T-m, even for low molar precentages of 1,4-CHDA. This phenomenon points to isomorphous crystallization of both the 12.6 and 12.CHDA repeating units. The mps of the synthesized polyamides were independent of the initial cis-trans ratio of 1,4-CHDA, provided that the samples were annealed at 300 degreesC before DSC analysis. The polyamides exhibited a different melting pattern depending on the 1,4-CHDA content. At a low a 1,4-CHDA content a net exothermic recrystallization occurred during melting, whereas at higher contents of 1,4-CHDA this recrystallization occurs to a lesser extent, and two separate melting areas are observed. (C) 2001 John Wiley & Sons, Inc.