Flame retardants

A flame retardant phosphorus-containing condensation product wherein said condensation product is obtained by an addition reaction between acrylic, methacrylic or crotonic acid esters of a polyhydric alcohol having at least three alcoholic hydroxyl groups selected from the class consisting of glycerine, polyglycerines, trimethylol ethane, trimethylol propane, pentaerythritol, dipentaerythritol, tripentaerythritol, tetrapentaerythritol, mannite and sorbite, and an organophosphorus compound of Formula II, ##STR11## wherein X, Y and Z each is hydrogen or halogen.

A flame retardant resin composition comprising 100 parts by weight of a thermoplastic resin and 3 to 50 parts by weight of phosphorus-containing condensation products of an organophosphorus compound represented by Formula I, ##STR12## wherein X, Y and Z each is hydrogen or halogen, R.sub.1 and R.sub.2 each is hydrogen or methyl and R.sub.3 is hydrogen or an alkyl group with a polyhydric alcohol having at least three alcoholic hydroxyl groups, where said condensation products have a phosphorus content of 6.0 to 10.7% by weight and a softening point of 55.degree.-155.degree. C.

A flame retardant resin composition comprising 100 parts by weight of a thermosetting resin and 3 to 50 parts by weight of phosphorus-containing condensation products of an organophosphorus compound represented by Formula I, ##STR13## wherein X, Y and Z each is hydrogen or halogen, R.sub.1 and R.sub.2 each is hydrogen or methyl and R.sub.3 is hydrogen or an alkyl group with a polyhydric alcohol having at least three alcoholic hydroxyl groups, where said condensation products have a phosphorus content of 6.0 to 10.7% by weight and a softening point of 55.degree.-155.degree. C.