Syntheses and Properties of Hyperbranched Aromatic Polyimides with Various End-groups.

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  • Yamanaka Kazuhiro
    Department of Organic and Polymeric Materials, Tokyo Institute of Technology
  • Jikei Mitsutoshi
    Department of Organic and Polymeric Materials, Tokyo Institute of Technology
  • Kakimoto Masa-aki
    Department of Organic and Polymeric Materials, Tokyo Institute of Technology

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A hyperbranched poly(amic acid methyl ester) precursor was prepared from self-polycondensation of an AB2 type monomer (1) in the presence of (2, 3-dihydro-2-thioxo-3-benzoxazolyl)phosphonic acid diphenyl ester (DBOP) as a condensing agent. End-capping reactions of free amine end groups of the precursor with acetyl, n-heptanoyl chloride, 4-methylphthalic anhydride and 3, 5-bis(4- nitrophenoxy)diphenyl ether-3′, 4′-dicarboxylic anhydride (10) were carried out. By chemical imidization of these precursors in the presence of acetic anhydride and pyridine, hyperbranched aromatic polyimides, which were soluble in NMP, DMF, DMSO and THF, were successfully prepared. By gel permeation chromatography (GPC) measurement, weight-average molecular weights (MW) of hyperbranched aromatic polyimides were found to be 50000-98000. From IR and 1H-NMR analyses, it was found that both end-capping and subsequent chemical imidization reactions proceeded quantitatively. The degree of branching (DB) of hyperbranched aromatic polyimides was 0.49 for 4, and 1.0 for 9. By thermogravimetric (TG) and differential scanning calorimetry (DSC) measurements of the hyperbranched aromatic polyimides, 5wt% thermal loss temperatures (T5) were observed to be above 370°C, and Tg values were 189, 138, 186 and 174°C for polyimides 4, 5, 7 and 9, respectively. The densities of the transparent films of the hyperbranched polyimides having acetoamide end-groups were found to be less than 1.35, which were lower than those of their linear analogues. The film, prepared from the hyperbranched polyimide with 4-methylphthalimide end-groups (7), had lower dielectric constant, birefringence, and shorter cut-off wavelength than the film of poly(4, 4′-oxydiphenylene pyromellitimide).

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