SYNTHESIS AND PROPERTIES OF POLYAMIDES AND COPOLYAMIDES BASED ON 2,6-NAPHTHALENE DICARBOXYLIC-ACID

A number of polyamides based on 2,6-naphthalene dicarboxylic acid (NDA ) and various aromatic diamines were synthesized in N-methyl pyrrolido ne (NMP) containing lithium chloride (LiCl) or calcium chloride (CaCl2 ) by direct polycondensation using triphenyl phosphite and pyridine. T he best reaction conditions for polycondensation were determined in te rms of factors such as the amount of the solvency-promoting reagent su ch as LiCl or CaCl2 and the initial reactant concentration. Thus, almo st all polyamides were obtained with inherent viscosities above 1.0 an d up to 3.28 dL/g. Similarly, high molecular weight copolyamides with inherent viscosities of 1.76-3.61 dL/g were prepared from 4,4'-oxydian iline (ODA) and mixed dicarboxylic acids of NDA/terephthalic acid (TPA ) or NDA/isophthalic acid (IPA). The solubility of NDA homopolyamides depended on the diamine components. The polyamides derived from meta-, sulfone-, or alkylene-linked diamine showed increased solubility. Cop olymerization of ODA with NDA/IPA led to a significant increase in sol ubility, whereas with NDA/TPA, it gave a limited improvement. All the homopolyamides and copolyamides showed an amorphous X-ray diffraction pattern. Almost all the polymers soluble in aprotic solvents can be so lution-cast into strong and tough films. Glass transition shifts of so me NDA polyamides can be observed in the differential scanning calorim etry (DSC) curves ranging from 243 to 345-degrees-C. Most NDA/IPA-ODA copolyamides also showed clear transitions in the range of 255-268-deg rees-C. In nitrogen, all the polymers showed no significant weight los s up to 400-degrees-C, and their 10% weight loss temperatures were rec orded in the range of 434-541-degrees-C. (C) 1994 John Wiley & Sons, I nc.