NOVELTY - A solvent-free thermosetting resin composition comprises benzoxazine component containing difunctional benzoxazine and monofunctional benzoxazine; liquid epoxy compound; and toughening agent having phenol-terminated polyurethane, polyurea, or polyurea-urethane.    USE - For forming resin coated substrate such as plastic, glass, alloy, metal, ceramic, wood, cement, concrete, rubber, or reinforcement fiber material; for forming cured product; and for producing flame retarded composite article (claimed) used in aerospace applications such as aircraft primary structural materials (including main wings, tail wing and floor beam), secondary structural materials (including flap, aileron, cowl, fairing and interior trim), rocket motor cases, structural materials for artificial satellites, castings, prepregs, bonding sheets, laminates and metal-foil clad laminates; and also used in moving bodies such as cars, boats and railway carriages, drive shafts, fuel cells, plate springs, wind turbine blades, pressure vessels, fly-wheels, papermaking rollers, civil engineering and building materials (including roofing materials, cables, reinforcing bars and retrofitting materials).    ADVANTAGE - The solvent-free thermosetting resin composition exhibits improved thermal and physical properties, such as a high glass temperature, flexibility and toughness, so as to be suitable for use in applications where service temperatures may range from ambient temperature to greater than or equal to 175 degrees C; and benzoxazine-based thermosetting resin composition is able to perform both thermally and physically at high temperatures for long periods of time, making it useful in high temperature applications in various industries. The solvent-free thermosetting resin composition has glass transition temperature (Tg) of greater than 170 degrees C; a lap shear strength of at least 3500 (preferably at least 4000) psi, when cured for 2 hours at 195-205 degrees C and tested at ambient temperature; lap shear strength of at least 700 (preferably at least 900) psi, when cured for 2 hours at 195-205 degrees C and tested at 177 degrees C; and flame retardancy in terms of a UL94 ranking of at least V1, preferably V0.    DETAILED DESCRIPTION - A solvent-free thermosetting resin composition (C1) comprises benzoxazine component containing difunctional benzoxazine and monofunctional benzoxazine; liquid epoxy compound; and toughening agent having phenol-terminated polyurethane, polyurea, or polyurea-urethane of formula R'o-(X-C(O)-Y'-R2-(OH)m)n (I).    m=1 or 2;    n=2-6;    R'o=n-valent radical of an elastomeric prepolymer after the removal of terminal isocyanate, amino or hydroxyl groups, the elastomeric prepolymer being soluble or dispersible in epoxy resin;    X and Y'=-O- or -NR3-;    R2=m+1-valent radical of a polyphenol or aminophenol after the removal of the phenolic hydroxy group(s) and/or the amino group;and    R3=H, 1-6C alkyl or phenol.    At least one X or Y' is -NR3-. INDEPENDENT CLAIMS are included for the following:    (1) preparing (M1) solvent-free thermosetting resin composition involving mixing together from benzoxazine component (0.5-90 parts by weight) containing difunctional benzoxazine and monobenzoxazine; liquid epoxy compound (0.1-30 parts by weight); and toughening agent (0.1-40 parts by weight) having phenol-terminated polyurethane, polyurea, or polyurea-urethane of the formula (I);    (2) process (M2) for forming a resin coated substrate involving contacting a substrate with the solvent-free thermosetting resin composition (C1);    (3) process (M3) for forming cured product involving contacting substrate with the solvent-free thermosetting resin composition (C1) and curing the resin coated substrate by applying thermal and/or radiation energy to the resin coated substrate;    (4) process (M4) for producing flame retarded composite article involving providing a layer or bundle of reinforcement fibers; providing the solvent-free thermosetting resin composition (C1); contacting the reinforcement fibers with the solvent-free thermosetting resin composition to coat and/or impregnate the reinforcement fibers; and curing the coated and/or impregnated reinforcement fibers at 195-205 degrees C.