The effect of diamine length on the direct solid state polycondensation of semi‐aromatic nylon salts

In the current paper, a comparative study on the direct solid state polycondensation (DSSP) reaction of different terephthalate based semi‐aromatic salts ( X T salts, X = 4–18) in the TGA micro‐reactor is reported. High purity X T salts were prepared in solution and were used as starting materials for DSSP. The reaction temperature ( T DSSP ) for each salt was suitably selected as 20 °C–30 °C below the melting point T m of the respective salt. The PA X T products were characterized by TGA/DSC, liquid 1 H‐NMR, and SEM. In the DSSP of X T salts, some diamine is always lost to the gas phase and as a consequence, the attainable molecular weight of the polymer formed gets limited by the unbalance of acid and amine end‐groups. The TGA curves show that as the diamine length increases and its volatility decreases, higher molecular weights are obtained. SEM pictures of the products reveal true solid character during the polymerization reaction up to and including PA10T, whereas PA5T, PA12T, and PA18T reveal stickiness and agglomeration during reaction. A possible mechanism explaining such behaviour is also provided.