A copolymer is formed by reacting a composition I, which includes (a) a first epoxy compound having a chemical structure of

##STR00001##

wherein R.sup.1 is single bond, —O—,

##STR00002##

(b) a second epoxy compound that is different from (a) the first epoxy compound, and (c) a curing agent. The copolymer can be mixed with inorganic powder to form a composite material.

Provided are a fiber-reinforced composite material excellent in heat resistance and strength properties, an epoxy resin composition to obtain the fiber-reinforced composite material, and a prepreg obtained by using the epoxy resin composition. Further provided are a fiber-reinforced composite material having less volatile matters during the curing time, and having excellent heat resistance and strength properties, an epoxy resin composition to obtain the fiber-reinforced composite material, and a prepreg obtained by using the epoxy resin composition. Provided are: an epoxy resin composition for a fiber-reinforced composite material, comprising an amine type epoxy resin [A], an aromatic amine curing agent [B], and a block copolymer [C] having a reactive group capable of reacting with an epoxy resin; a prepreg obtained by impregnating a reinforced fiber with the epoxy resin composition; and a fiber-reinforced composite material obtained by curing the prepreg. Further provided are: an epoxy resin composition comprising an epoxy resin [A] having two or more of four- or more-membered ring structures, and having either one of a glycidyl amino group directly bonded to the ring structure or a glycidyl ether group directly bonded to the ring structure, epoxy resin [B] having three or more of functional groups, a curing agent [C], and an elastomer component [D]; a prepreg obtained by impregnating a reinforced fiber with the epoxy resin composition; and a fiber-reinforced composite material obtained by curing the prepreg.

Provided are a fiber-reinforced composite material excellent in heat resistance and strength properties, an epoxy resin composition to obtain the fiber-reinforced composite material, and a prepreg obtained by using the epoxy resin composition. Further provided are a fiber-reinforced composite material having less volatile matters during the curing time, and having excellent heat resistance and strength properties, an epoxy resin composition to obtain the fiber-reinforced composite material, and a prepreg obtained by using the epoxy resin composition. Provided are: an epoxy resin composition for a fiber-reinforced composite material, comprising an amine type epoxy resin [A], an aromatic amine curing agent [B], and a block copolymer [C] having a reactive group capable of reacting with an epoxy resin; a prepreg obtained by impregnating a reinforced fiber with the epoxy resin composition; and a fiber-reinforced composite material obtained by curing the prepreg. Further provided are: an epoxy resin composition comprising an epoxy resin [A] having two or more of four- or more-membered ring structures, and having either one of a glycidyl amino group directly bonded to the ring structure or a glycidyl ether group directly bonded to the ring structure, epoxy resin [B] having three or more of functional groups, a curing agent [C], and an elastomer component [D]; a prepreg obtained by impregnating a reinforced fiber with the epoxy resin composition; and a fiber-reinforced composite material obtained by curing the prepreg.

A curable epoxy resin composition including: (a) a cycloaliphatic epoxy resin, (b) an oxazolidone ring-containing epoxy resin, (c) a reaction product of (i) an anhydride compound and (ii) a polyol, and (d) an anhydride hardener; a process for preparing the curable epoxy resin composition; and a composite including a reinforcing fiber embedded in a thermoset resin, wherein the thermoset resin is a reaction product of the curable epoxy resin composition.

The present invention provides a curable composition comprising a urethane-modified epoxy resin (A) as an essential component of a main material, and an acid anhydride (B) as an essential component of a curing agent, wherein the urethane-modified epoxy resin (A) is a reaction product of a polyisocyanate compound (a1), a polyester polyol (a2), and a hydroxyl group-containing epoxy resin (a3) as essential reaction raw materials. The curable composition of the invention is advantageous in that a cured product having excellent fracture toughness and excellent tensile strength can be formed from the composition.

The present invention provides a curable composition comprising a urethane-modified epoxy resin (A) as an essential component of a main material, and an acid anhydride (B) as an essential component of a curing agent, wherein the urethane-modified epoxy resin (A) is a reaction product of a polyisocyanate compound (a1), a polyester polyol (a2), and a hydroxyl group-containing epoxy resin (a3) as essential reaction raw materials. The curable composition of the invention is advantageous in that a cured product having excellent fracture toughness and excellent tensile strength can be formed from the composition.

Provided is an epoxy resin composition with improved heat resistance and resin elongation. Further provided is a fiber-reinforced composite material which uses the epoxy resin composition and thereby excels in compression strength in high-temperature environments and interlaminar toughness. The epoxy resin composition comprises the constituents [A], [B] and [C], 8-40 mass % of [B] is contained in the epoxy resin composition. The number of moles of active hydrogen contained in [C] is 1.05-2.0 times the number of moles of epoxy groups contained in the entire epoxy resin composition, in a cured resin formed by curing the epoxy resin composition and having a degree of curing of at least 90% obtained by DSC (differential scanning catorimetry), [A], [B] and [C] form a monolayer structure, or a phase separation structure of less than 500 nm. The rubber state modulus of elasticity Y (MPa) and glass transition temperature X (° C.) obtained by DMA (dynamic mechanical analysis) of the cured resin satisfy formula (1). [A] amine type epoxy resin [B] thermoplastic resin [C] aromatic amine

0.19X/° C.-31.5≦Y/MPa≦0.19X/° C.-27   (1)

Liquid crystalline network compositions comprising azo-containing aromatic epoxy units cross-linked with alkylene diacid units having alkylene segments containing at least one methylene unit, wherein the azo-containing aromatic epoxy units and alkylene diacid units are connected by ester linkages resulting from ring-opening esterification between the epoxy units and alkylene diacids, and wherein the azo-containing aromatic epoxy units and alkylene diacid units are in a molar ratio that results in the liquid crystalline network composition exhibiting a glass transition temperature (T.sub.g) of at least 25° C. Methods for producing these compositions and their use in light- or thermal-activated physical deformation, shape memory applications, and self-healing, as well as their ability to be recycled and used in additive manufacturing processes are also described.

Liquid crystalline network compositions comprising azo-containing aromatic epoxy units cross-linked with alkylene diacid units having alkylene segments containing at least one methylene unit, wherein the azo-containing aromatic epoxy units and alkylene diacid units are connected by ester linkages resulting from ring-opening esterification between the epoxy units and alkylene diacids, and wherein the azo-containing aromatic epoxy units and alkylene diacid units are in a molar ratio that results in the liquid crystalline network composition exhibiting a glass transition temperature (T.sub.g) of at least 25° C. Methods for producing these compositions and their use in light- or thermal-activated physical deformation, shape memory applications, and self-healing, as well as their ability to be recycled and used in additive manufacturing processes are also described.

Disclosed is a polyurethane-modified epoxy resin composition capable of satisfying both high toughness and high elasticity. This epoxy resin composition is an epoxy resin composition, in which (A) a polyurethane-modified epoxy resin having a polycarbonate structure in the molecule and having a urethane modification rate of 20 to 60% by weight, (B) a non-polyurethane-modified epoxy resin that is liquid at 30° C., (C) a solid epoxy resin having a glass transition temperature or melting point of 50° C. or higher and (D) an amine-based curing agent that is dicyandiamide or a derivative thereof are as essential components, and 20.0 to 50.0% by weight of (A), 0.1 to 50.0% by weight of (B) and 0.1 to 50.0% by weight of (C) are contained relative to the total of (A) to (D).