Influence of stereochemistry on the thermal properties of partially cycloaliphatic polyamides

The effects of the partial substitution of 1,4-disubstituted cyclohexane monomers for linear aliph. monomers in polyamides are discussed. More specifically, the relation between the stereochem. of the cycloaliph. residues and the thermal properties [melting temp. (Tm) and crystn. temp. (Tcr)] was investigated. For this purpose, two different types of copolyamides were synthesized: in nylon 12-6, the adipic acid residues were partially replaced by cis/trans-1,4-cyclohexanedicarboxylic acid (1,4-CHDA), whereas in nylon 4-14, the 1,4-diaminobutane residues were partially substituted with cis/trans-1,4-diaminocyclohexane (1,4-DACH). For both systems, increasing the degree of substitution of cycloaliph. residues for linear aliph. residues resulted in a rise of both Tm and Tcr. This points to the isomorphous crystn. of the linear and cycloaliph. residues. In contrast to the use of 1,4-DACH as a comonomer, 1,4-CHDA residues showed isomerization upon thermal treatment of the polyamides. This isomerization of the cyclohexane residues influenced the thermal properties of the copolyamides. The use of a nonisomerizing cis-trans mixt. of 1,4-DACH showed the large influence of the stereochem. of the cycloaliph. residues on the Tm of the copolyamides. For both the 1,4-CHDA- and 1,4-DACH-based copolyamides, differential scanning calorimetry anal. revealed that recrystn. occurs during melting. This exothermal effect becomes less pronounced with an increasing content of rigid cycloaliph. residues. [on SciFinder (R)