1. Field of the Invention
The present invention relates to a novel thermoplastic polyimide, aromatic diamine compound useful for the raw material monomer of the polyimide, and a process for preparating the polyimide. More particularly, the invention relates to a novel polyimide having excellent processability and a molecular structure useful for providing the polyimide with low dielectric characteristics, a process for preparing the polyimide and novel compounds 3,3'-diamino-4,4'-difluorobenzophenone and 1,3- or 1,4-bis(3-amino-4-fluorobenzoyl)benzene which are used for the raw material monomers of the polyimide.
The novel 3,3'-diamino-4,4'-difluorobenzophenone and 1,3- or 1,4-bis(3-amino-4-fluorobenzoyl)benzene are useful for the raw material monomers of the polyimide and additionally can be utilized as the raw materials of polyamide, polyamidimide, bismaleimide and epoxy resin, and can also be applied to hardeners of other maleimide compounds and epoxy compounds.
2. Related Art of the Invention
Recently, heat-resistant resin materials have been required to satisfy various performance such as flexibility as an ingredient of a composite and processability in addition to thermal and mechanical properties. Polyimide has focused attention as a material having these properties.
Polyimide is prepared by reaction of tetracarboxylic dianhydride with diamine. Conventionally known polyimide is excellent in mechanical strengths and dimensional stability in addition to substantially high heat-resistance and also has flame retardance and electrical insulation properties. Consequently, polyimide has already been widely used in the field where heat resistance is required, particularly in the field of electric and electronic equipment and is expected to be used in greater amounts and in other fields.
Various kinds of polyimide which exhibit excellent properties have already been developed. Conventionally known polyimide, however, has no distinct glass transition temperature, though excellent in heat resistance, and must be processed by such means as sinter molding in the case of being used as a molding material.
Other conventional polyimides are dissolved in halogenated hydrocarbon solvents, though excellent in processability, which leads to problems in solvent resistance. Thus, both merits and drawbacks have been simultaneously found in the properties of conventional polyimides. In order to extend the field of use for polyimides, disadvantages of polyimides have been improved or new properties have been provided for polyimides.
For example, a typical aromatic polyimide (Vespel) (Trade mark; E.I. Du Pont de Nemours & Co.) which is obtained by reacting 4,4'-diaminodiphenyl ether with pyromellitic dianhydride is insoluble and infusible and hence has the disadvantage that processing is difficult. Vespel powder is processed by a special method, sinter molding. Sinter molding, however, is difficult to provide molded articles having a complex shape and further requires a finishing operation of the molded articles in order to obtain precise products, which leads to a great disadvantage of an increase in processing cost.
On the other hand, a polyimide resin having a benzophenone skeleton in the molecular structure has been known to have excellent heat resistance, mechanical characteristics and adhesive strength. For example, polyimide resin (LARC-TPI) which is prepared from 3,3-diaminobenzophenone is thermoplastic in addition to these excellent properties. However, processability of the resin is not good in spite of its thermoplastic property. Recently, a method for increasing the molecular chain length has been employed as a means for improving such processability. Consequently, it is expected to obtain high performance polyimide resin having good processability by applying the method to the benzophenone skeleton. On the other hand, a polyimide structure derived from a monomer diamine compound having meta-located amino and carbonyl groups such as the above 3,3'-diaminobenzophenone is also effective as another means for improving the processability.
For example, Proga et al. have described thermoplastic polyimide for use in a heat resistant adhesive in U.S. Pat. No. 4,065,345. Ohta et al. have disclosed thermoplastic polyimide represented by the formula (VI): ##STR4## (Japanese Laid-Open Patent Hei 2-018419).
The polyimide has a obtained a novel property, injection molding ability, by controlling the molecular weight of the polymer and blocking the reactive ends of the polymer chain. The polyimide is further required to have improved electrical properties such as low dielectric characteristics.
Introduction of a halogen radical into the aromatic ring has been known as an effective means for improving low dielectric characteristics of polyimide. Further, introduction of a halogen radical into the ortho position of an amino radical has been described in Chemical Abstracts, 70, 116221X. However, a diamine compound having a large halogen atom at the ortho position of an amino radical has a disadvantage that high molecular weight polymer is difficult to obtain because of steric hindrance. Thus, such kind of polyimide has not yet been developed.