To address the issues of diamine volatilization

low yield

and difficulty in increasing molecular weight during the direct solid state polymerization (DSSP) of high-temperature-resistant polyamides

this study first used dimethyl terephthalate (DMT) to react with excess 1

5-pentanediamine (PDA) and 1

6-hexanediamine (HMDA) to prepare diamides diamines 5T5 and 6T6. Then

5T5 and 6T6 were reacted with terephthalic acid (PTA) to form different compositions of 5T5T/6T6T mixed salts. Finally

a series of high-viscosity

high-temperature-resistant copolyamides PA56T were successfully synthesized through direct solid state polymerization from the mixed salts. The structure and properties of PA56T were systematically investigated using FTIR

NMR

DSC

and TGA. The results indicate that using diamides diamines as amide salts can effectively prevent the volatilization of diamines during the direct solid-state polymerization process

thereby significantly improving the yield

molecular weight

and quality of the high-temperature-resistant copolyamides. By changing the composition

the comprehensive properties of the copolyamide PA56T can be effectively regulated. Its melting point (Tm) first decreases and then increases with the increase in 6T content. Copolymerization enhances the thermal stability of the high-temperature-resistant polyamides. The copolymer PA56T-40

with 40 mol% 6T content exhibits excellent comprehensive properties

with a melting point (Tm) of 310 °C

a 5 wt% weight loss temperature (Td5) of 440 °C

and a tensile strength of 95.2 MPa.