Copolyamide based on tetramethylene terephthalamide and hexamethylene terephthalamide

The invention relates to a semi-aromatic polyamide that contains tetramethylene terephthalamide units. The invention also relates to a process for preparing a polyamide that contains at least tetramethylene terephthalamide units and to compositions and products containing said polyamide. The invention relates to a semi-aromatic polyamide containing at least tetramethylene terephthalamide units and also hexamethylene terephthalamide units.The copolyamide has a melting point higher than approximately 290° C., a high crystallinity and a good stability.Preferably the copolyamide according to the invention contains approximately 30-75 mol % hexamethylene terephthalamide units and also approximately 0.01-20 mol % other units.The invention also relates to a process for the preparation of a semi-aromatic copolyamide containing at least tetramethylene terephthalamide units and hexamethylene terephthalamide units, characterized in that, successively, a first polymerization is effected in the melt phase, followed by an post-polymerization of the low molar mass polymer thus obtained in the solid phase; and to compositions and products that contain said copolyamide.