Sized carbon fibers capable of use with polyimide matrix

A carbon fiber having a flexible coating on the surface thereof in a concentration of approximately 0.3 to 5.0 percent by weight based upon the weight of the carbon fiber of a sizing composition which comprises a polyamic acid oligomer, and is capable of yielding a rigid polyimide at elevated temperatures which is derived from the reaction of approximately 47.5 mole percent of p-phenylenediamine, approximately 2.5 mole percent of m-phenylenediamine, approximately 35 mole percent of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and approximately 15 mole percent of the 3,3'-diethylester of 3,3',4,4'-benzophenonetetracarboxylic acid wherein said polyamic acid oligomer is an intermediate in the formation of said rigid polyimide.

A carbon fiber having a flexible coating on the surface thereof in a concentration of approximately 0.5 to 1.3 percent by weight based upon the weight of the carbon fiber.

A composite structure comprising a rigid polyimide matrix having carbon fibers incorporated therein which are coated on the surface thereof with approximately 0.3 to 5.0 percent by weight based upon the weight of the carbon fibers of a sizing composition comprising a rigid polyimide coating which is derived from the reaction of at least one aromatic diamine, at least one aromatic dianhydride, and at least one aromatic tetracarboxylic acid diester in which the carboxylic acid groups and ester groups are ortho disposed, wherein a polyamic acid oligomer is formed as an intermediate during the formation of said rigid polyimide coating and is present within a flexible coating comprising said reactants which facilitates impregnation of said coated carbon fibers with said matrix during the formation of said composite structure.

A composite structure comprising a rigid polyimide matrix having carbon fibers incorporated therein which are coated on the surface thereof with approximately 0.3 to 5.0 percent by weight based upon the weight of the carbon fibers of a sizing composition comprising a rigid polyimide coating which is derived from the reaction of approximately 47.5 mole percent of p-phenylenediamine, approximately 2.5 mole percent of m-phenylenediamine, approximately 35 mole percent of 3,3',4,4'-benzophenonetetracarboxylic dianhydride, and approximately 15 mole percent of the 3,3'-diethylester of 3,3',4,4'-benzophenonetetracarboxylic acid, wherein a polyamic acid oligomer is formed as an intermediate during the formation of said rigid polyimide coating and is present within a flexible coating comprising said reactants which facilitates impregnation of said coated carbon fibers with said matrix during the formation of said composite structure.