Effects of diamine isomers on the properties of colorless and transparent copoly(amide imide)s.

To fully understand the structure-property relationship of aromatic copoly(amide-imide)s (Co-PAIs) and determine which factors lead to chain rigidity, we prepared two series of Co-PAIs. They were synthesized from two types of amine monomers containing m - and p -isomers and different ratios of 4,4'-(hexafluoroiso-propylidene)diphthalic anhydride (6FDA) and 4,4'-biphthalic anhydride (BPA). m -Substituted and p -substituted N , N '-[2,2'-bis(trifluoromethyl)-4,4'-biphenylene]bis(aminobenzamide) (MPAB) diamine isomers were synthesized from 3- and 4-nitrobenzoyl chloride and 2,2'-bis(trifluoromethyl) benzidine (TFB), respectively. The Co-PAI films were synthesized from poly(amic acid) (PAA), via solution-casting, followed by thermal imidizations. The thermal- and mechanical-properties and optical transparency of the Co-PAI films with different BPA monomer contents were investigated. We also investigated the effects of the different MPAB isomers on the Co-PAI structures. Compared with the m -substituted MPAB Co-PAI films, the p -substituted MPAB Co-PAI films have superior thermo-mechanical properties at the same monomer content. However, the optical transparencies of the m -MPAB Co-PAIs are slightly better than those of the p -MPAB Co-PAIs.