Structure and properties of 6/6.9 copolyamide series. I. Amorphous phase

The amorphous phase of a series of random 6/6.9 copolyamides was investigated. It was characterized by the glass transition temperature (T_g) and the hydrogen bond content, as a function of the copolymer composition, compared to the corresponding homopolymers, polyamide 6 and polyamide 6.9. The hydrogen bonds in the amorphous phase have a major influence on the copolymer properties. The glass transition temperature decreases as either comonomer content increases, attaining a minimum value at about 1:1 molar composition. This is due to the decreased content of hydrogen bonds, their broader strength distribution, and the decreased degree of crystallinity. In addition to the usual effects, quenching in the present system causes the formation of a less dense and less regular hydrogen bonds network, reducing the T_g. Following room temperature aging, the usual hydrogen bond content is restored.