Introduction
(BAA-BPDA/PPD) and 3,3 ,4,4-biphenyl tetracarboxylic acid (BPA) is used as a PI-BPDA/PPD precursor.
Similarly, as a PI-PMDA/ODA precursor, an equimolar Because aromatic polyimides have outstanding thermixture of BAA-PMDA/ODA and pyromellitic acid mal, mechanical, and electrical properties as well as (PMA) is used. [BAA denotes amine-terminated bissolvent resistance, they have been used for interlayer (amic acid), which is synthesized from 1 mol of tetradielectric for semiconductor devices, wire coating matecarboxylic dianhydride and 2 mol of diamine in solrials, or as substrates for flexible printed circuits.
vents. Chemical structures of BAAs are shown in Fig. Among aromatic polyimides, 1 poly(4,4 -phenylene-
2.] These components are not high molecular weight 3,3,4,4-biphenyltetracarboxyimide) (PI-BPDA/PPD), 2 polymers so that the resulting PI precursor solutions and poly(4,4-oxydiphenylenepyromellitimide) (PIcontaining them show low viscosity even in high solid PMDA/ODA) 3 exhibiting excellent heat resistance and contents. From these precursor solutions, correspondmechanical strength are the most important polyiming PI films showing good mechanical properties are ides. (Chemical structures are shown in Fig. ). These produced through the cast process involving thermal PI films are usually prepared by casting corresponding cure. poly(amic acid) solutions and thermal curing of the In this article, PI precursor solutions utilizing this resulting films. The poly(amic acid) solution can be binary system will be presented. produced by reaction of 3,3 ,4,4-biphenyl tetracarboxylic dianhydride (BPDA) or pyromellitic dianhydride (PMDA) with an equimolar amount of p-phenylenediamine (PPD) or 4,4-oxydianiline (ODA), respectively, EXPERIMENTAL in aprotic polar solvents such as N,N-dimethylacetamide (DMAc), N,N-Dimethylformamide (DMF) and N-Polymerization grade BPDA, BPA, PMDA, PMA, PPD, methyl-2-pyrrolidone (NMP). Thus, prepared polyand ODA were purchased from commercial sources and (amic acid) is high molecular weight linear polymer were used as received. DMAc, DMF, and NMP were so that solutions containing this polymer show high reagent grade materials and were used as received and viscosity. Therefore, as long as poly(amic acid)s are were dried over molecular sieves prior to use. used as a precursor, it seems difficult to increase solid Into a three-neck flask fitted with a mechanical stircontents significantly in the precursor solution.
rer, cooling bath and thermometer were charged 98.0 In the course of our R&D activities related to arog of DMAc under a nitrogen atmosphere. After 10.81 g matic polyimides, 4 a high solid precursor solution of (100 mmol) of PPD were added and suspended with PI-BPDA/PPD or PI-PMDA/ODA has been developed stirring, 15.00 g (51 mmol) of BPDA was added gradunewly using a binary component system. In this system, ally to the stirring PPD solution at 8ะC over 40 min. an equimolar mixture of specially designed diamine
The resulting mixture was stirred for 2 h at 8ะC to yield a BAA-BPDA/PPD solution. To this solution, 16.18 g (49 mmol) of BPA was added gradually and the mixture