Solvent-resistant polyetherimide network systems via phenylethynylphthalic anhydride endcapping

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Abstract
The synthesis and characterization of a highly processable thermosetting polyimide system based on 22'-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane dianhydride or bisphenol A dianhydride (BPA-DA) endcapped with 4-phenylethynylphthalic anhydride is described. The system afforded oligomers that were readily melt processable at high curing temperatures (380-420 CC). Imide oligomers ranging from MR = 2000 to 40 000 g molI and copolyimides were synthesized using the ester acid of the dianhydrides and either meta- and/or para-phenylene diamines as comonomers via solution imidization techniques. The oligomers were shown to display low melt viscosity values and to flow under low pressure during compression moulding. The thermally cured polymers formed tough creasable films and displayed excellent solvent resistance which was correlated to their high gel fractions (>95%). Very significant increases in glass transition temperatures were observed after cure of a 3000., oligomer. The mera-phenylene diamine-based polymer exhibited a cured Ts approximately 30C lower (233C) than the para:meta (70:30) system (267C). The all para-phenylene diamine-based homopolymers could be completely cyclized in solution but crystallized at room temperature to produce fine insoluble powders. The resulting moderately semicrystalline homopolymer showed a TM of up to 321 'C which was not observed on the second heating. These polyimides also show excellent thermal stability as judged by thermogravimetric analysis (TGA) and are being examined as structural adhesives and matrix resins.