Abstract
A soluble fluorine-containing polyimide derived from 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA) and 3,3′-dihydroxy-4,4′-diaminobiphenyl (DHBP) was prepared and successfully crosslinked via the reaction between hexamethylene diisocyanate (HMDI) and the hydroxyl groups on the phenylene rings, leading to the formation of a soft polyimide gel. The gelation times vary according to the amount of crosslinker. Higher concentration of the crosslinker and catalyst accelerates the gelation reaction. We found that the crosslinker, HMDI, not only reacts with hydroxyl groups on the phenylene rings but also forms an oligomeric chain through the reaction with moisture. The conversion of the crosslinker was estimated from NMR. The volume changes of the gels against solvent composition were also studied. The polyimide gels swell when the N-methyl-2-pyrrolidone (NMP) weight fraction is larger than 0.80 in the mixed solvent NMP/water at 20°C. During the swelling process less time is needed for the gels to reach the equilibrium in NMP richer solvents. This is the first report as far as we know on the synthesis of a polyimide gel and the study of its properties.
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