Synthesis and properties of α,ω-diaminoalkane based poly(amide-imide)s

Several regular thermoplastic poly(amide-imide)s (PAIs) were synthesized from the diacid chloride derivatives of N,N′-alkane-α,ω-diylbis(trimellitimide)s and α,ω-diaminoalkanes. The PAI synthesized from the 1,4-diaminobutane (DAB) based bis(trimellitimide) and 1,4-diaminobutane (PAI[4,4]) yielded semi-crystalline testbars upon injection moulding, but the high melting point of ca. 346°C caused degradation during processing. Surprisingly, all 1,6-diaminohexane (DAH) based PAI[6,6], prepared from the DAH based bis(trimellitimide) and DAH, with a first heating Tm of 257°C, did not even crystallize from the melt at a cooling rate of 20°C/min in the DSC. The same lack of crystallizability from the melt was observed for all 1,3-diaminopropane and for all 1,9-diaminononane based (odd) poly(amide-imide)s PAI[3,3] and PAI[9,9]. The PAI[6,4], based on N,N′-butane-α,ω-bis(trimellitimide) and DAH, with an attractive Tm of 289°C, shows an intermediate crystallization behaviour from the melt: amorphous after injection moulding, but limited crystallization from the melt at a cooling rate of 20°C/min. Copoly(amide-imide)s, from the DAB based bis(trimellitimide) and mixtures of DAB and DAH, showed intermediate melting points of 290°C (for 50 mol% DAB) to 317°C (for 75 mol% DAB) and a better crystallizability with increasing mole percentage DAB, which is ascribed to the wider crystallization window (Tm−Tg) with increasing DAB content and to the more linear (‘all-trans’) configuration of DAB with respect to DAH. In spite of their amorphous character the injection moulded PAIs show some attractive physical properties.