Preparation And Characterization Of Polyimides With Alkyl Side Chains

For recent 40 years, polyimides have been developing rapidly and are finding a certain range of applications in many high performance fields, such as aerospace, microelectronics, and elsewhere. Owing to their excellent heat-resistant property, mechanical and dielectric properties, polyimides are one of the most valuable engineering plastics. Introduction of functional side chains to polyimides can effectively achieve outstanding performance. Three series of polyimides with alkyl side chains were prepared and characterized.Firstly, 3,5-diaminobenzoic acid-4?-alkyloxybenzene ester was synthesized from hydroquinone, 1-bromoalkane and 3,5-dinitrobenzoyl chloride via mono-etherealization reaction, esterification and reduction reaction. Three series of polyimides with alkyl side chains were prepared from 3,5-diaminobenzoic acid-4?-alkyloxybenzene ester with three kinds of dianhydride, pyromellitic dianhydride(PMDA), 3,3',4,4'-Benzophenonetetracarboxylic acid dianhydride(BTDA) and 2,2-bis[4-(3',4'-dicarboxyphenoxy)-phenyl]propane dianhydride(BASS). The polyimides were characterized by FTIR, UV-Vis, TGA, DSC, XRD, AFM, et al. With the increase of alkyl length, the surface tension and optical transparency of three series of polyimides declines. Because of flexible main chain and introduction of methyl to main chain in polyimides derived from BASS, the value of surface tension and effect of alkyl length on optical transparency are lowest. Intrinsic viscosities of polyimides derived from BASS decline with the increase of alkyl length and range from 0.35 to 0.53 dL/g in N-methyl-2-pyrrolidone (NMP). The decomposition temperature of polyimides with side chains decreases with the increase of the alkyl length. The decomposition of polyimides begins with alkyl side chains. The glass transition temperatures of polyimides derived from PMDA and BTDA are higher than the decomposition temperature. Introduction of alkyl group to polyimide derived from BASS makes glass transition temperature shift to lower temperature.Secondly, XRD analysis indicates that all the polyimides with side chains are amorphous polymers. The regulation of polyimides derived from PMDA and BTDA decreases with the increase of the alkyl length. Also because of flexible main chain, the alkyl length has little effect to the regulation of polyimides derived from BASS. The equilibrium geometries for the polyimides with side chains are optimized, using hyperchem program. Computational studies demonstrate that the regulation of polyimides decreases when the main chains of polyimides transform from stiffness to flexibility. The microstructures of the polyimide film surface are not smooth. The parallel microgrooves generate during rubbing the polyimide films surface with cotton cloth.