Flame retardant compositions, masterbatches, glass fiber-nylon compositions and preparation methods thereof

A flame retardant composition, comprising 40-60 parts by weight of phosphonate, 5-15 parts by weight of an organosilicon flame retardant, and 2-8 parts by weight of an inorganic silicon synergist,

• wherein the phosphonate is prepared by a method comprising:
• (1) condensing a compound represented by formula (I) such that some of the compounds form a polymer, giving a partially condensed product
• wherein R is selected one from the group consisting of a C1-C6 alkyl group, and a substituted or unsubstituted phenyl group;
• and
• (2) reacting a rare earth inorganic salt with the partially condensed product to form the phosphonate.