Abstract
Various new fluorinated heterocyclic copolyimides have been synthesized by a polycondensation reaction of a diacid chloride containing imide, hexafluoroisopropylidene and methylene groups with aromatic or heteroaromatic diamines containing preformed phenylquinoxaline or 1,3,4-oxadiazole rings. Other fluorinated heterocyclic copolyimides have been prepared by a polycondensation reaction of the same diacid chloride with aromatic dihydrazides, bis(o-hydroxy-amine)s or a bis(o-carboxy-amine), resulting in intermediate polyhydrazides, poly(o-hydroxy-amide)s or poly(o-carboxy-amide), respectively, which were futher cyclodehydrated to the corresponding polyoxadia zole-imide, polybenzoxazole-imide or polybenzoxazinone-imide structure. These polymers showed good solubility in polar amidic solvents, such as N-methylpyrrolidinone (NMP) and dimethylformamide (DMF), and even in less polar liquids, like tetrahydrofurane or pyridine, except for those compounds containing benzoxazole rings which were less soluble, only on heating in NMP or DMF. The weight average molecular weight measured for tetrahydrofurane-fully-soluble polymers are in the range of 12800–26700 and the polydispersity is in the range of 2–5. All these polymers exhibited good thermal stability, with decomposition temperature being above 350°C, although somewhat lower than that of related polymers prepared by using fully aromatic diacid chlorides instead of the present ones containing methylene units. The glass transition temperature is in the range of 200–300°C. The dielectric constant measured for polymer films is in the range of 3.3–3.7. Tensile strength is in the range of 35–70 MPa, elongation to break between 30–40% and tensile modulus in the range of 170–330 MPa. A study of the relation between conformational parameters and properties of some of these polymers has been carried out by using the Monte Carlo method with an allowance for hindered rotation, and the values were compared with the experimental data and discussed in relation with the rigidity of the chains. The present polymers are potential candidates for use as high performance materials.
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