NOVELTY - Liquid resin system, comprises: a liquid monobenzoxazine monomer (I); and at least one non-glycidyl epoxy compound, where the weight ratio of (I) to non-glycidyl epoxy compound is 25:75-60:40.    USE - The liquid resin system is useful: in producing flame retarded composite article (claimed), which is used as fuel cell for supplying power in conventional automobiles, hybrid cars, small boats, small-scale local power generation, household power generation, simple power supplies for isolated facilities e.g. camp sites, as power supplies for satellites, space development or computers; and as resin transfer molding resin, vacuum assisted resin transfer molding resin, pultrusion resin, adhesive, or prepreg resin.    ADVANTAGE - The liquid resin system: exhibits low viscosity at room temperature thus making it highly suitable for the use in the production of high performance composites; exhibits storage stability for a extent period of time; and provides the cured product having an excellent balance of mechanical and chemical properties e.g. high glass transition temperature, decomposition temperature, high tensile strength, low coefficient of thermal expansion, and good flexibility.    DETAILED DESCRIPTION - Liquid resin system comprises: a liquid monobenzoxazine monomer of formula (I); and at least one non-glycidyl epoxy compound, where the weight ratio of (I) to non-glycidyl epoxy compound is 25:75-60:40.    R = phenyl, 1-8C alkyl, 3-8C cycloalkyl (all optionally substituted) or allyl.    INDEPENDENT CLAIMS are also included for:    (1) producing a flame retarded composite article in a resin transfer molding system, comprising (a) introducing a fiber preform comprising reinforcement fibers into a mold, (b) injecting a thermosetting resin matrix comprising the liquid resin system into the mold, (c) allowing the thermosetting resin matrix to impregnate the fiber perform, (d) heating the resin impregnated preform at a temperature of at least 90? degrees C for a period of time to produce an at least a partially cured solid article, and (e) optionally, subjecting the partially cured solid article to post curing operations to produce the flame retarded composite article; and    (2) forming a flame retarded composite article in a vacuum assisted resin transfer molding system, comprising (a) as above per se, (b) as above per se, (f) reducing the pressure within the mold, (g) maintaining the mold at the reduced pressure, and (c)-(e) as above per se;    (3) preparing a flame retarded composite article, comprising thermally curing a thermosetting resin mixture comprising the liquid resin system above 90? degrees C;    (4) a flame retarded composite article;    (5) a thermosetting resin matrix, comprising at least 30 wt.% of the liquid resin system and at least one of a solvent, a catalyst, a flame retardant and/or fillers; and    (6) a liquid resin system, comprising (I) (obtained by the reaction of a monohydric phenol compound, an aldehyde and a primary amine, where the molar ratio of monohydric phenol compound to aldehyde is 1:22 -1:2.35, and the molar ratio of monohydric phenol compound to primary amine is 1:1), and the non-glycidyl epoxy compound.