| abstract |
Copolyimides are prepared from benzophenone-3,3'',4,4''tetracarboxylic acid dianhydride and a mixture of 4,4''methylenebis(phenyl isocyanate) and toluene diisocyanate (2,4- or 2,6-isomer or mixtures thereof). The mixture of isocyanates is used in a molar percent ratio from about 10/90 to 90/10, respectively. The copolyimides so obtained show markedly improved mold flow properties and higher glass transition temperature as compared with polyimides made from 4,4''-methylenebis(phenyl isocyanate) alone. The improvement in mold flow properties in the copolyimides is achieved without any significant loss in structural strength properties; this is contrary to expectation based on the known properties of the corresponding polyimide made from toluene diisocyanate alone. The copolyimides which are obtained from the isocyanate mixtures in which the toluene diisocyanate is the major component have the additional advantage of being soluble in polar solvents and, accordingly, find use in coating compositions and the like. All the copolyimides prepared as described above can be used in the preparation of high temperature resistant polymer articles and in the various applications for which polyimides are known to be especially adapted. |