Synthesis And Properties Of Crosslinked Polyimides Containing Aryl-s-triazine Moiety

Polyimides are well known for their utilities in the aerospace and electronic industries in the forms of films and moldings for their excellent thermo-oxidative stability, balanced mechanical and electric properties. However, they are difficult to fabricate into finished products because of their high softening temperatures associated with insolubility in commercially available solvents. To further broaden the applications of the polyimides associated with improved insolubility, our research interest has recently been focused on the preparation of soluble and curable poly(ether imide)s.In this paper, four kinds of dianhydride monomer were synthesized by a modified method starting from the nitro displacement reaction. On this base, a novel series of soluble and curable phthalonitrile-terminated poly(phthalazinone imide) oligomers with well controlled molecular weights were prepared by varying the molar ratio of dianhydrides to diamines, which can be fabricated in their organic solution or their melt and thermally crosslinked to form the heterocyclic s-triazine rings-containing thermosetting poly(ether imide)s. FT-IR,'H NMR and elemental analysis were applied to confirm the structure of the oligomers whose molecular weights were determined by FT-IR and 1H NMR analysis. The uncured polymers are soluble in several common polar aprotic solvents for the incorporation of crank, twisted and non-coplanar phthalazinone moiety, which disorders the close packing of the intermolecular chain. However, the cured samples are insoluble in all solvents because of the formation of the heterocyclic s-triazine networks during the crosslinking reaction of the cyano groups. Both the oligomers and the cured ones were characterized by FT-IR, DSC, TGA and DTG. The cured samples show no glass transition temperature from 100 to 400℃for the heterocyclic s-triazine networks decrease the flexibility of polymer backbone. And they exhibit excellent thermal stability with high 5%and 10%weight loss temperature. For the excellent thermal stability of the cured poymers, they can be used as high performance polymeric materials in the aerospace and base materials for high temperature composite matrix.