Polyalkylene glycol alkyl polyphosphites

A polyphosphorous mixed phosphite-phosphonate polymer flame retardant having an OH number less than one and containing both alkyl phosphite and haloalkyl phosphonate linkages, said polyphosphorus polymer represented by the formula:

• ##STR4## where R.sub.1 is alkyl;
• R is a polyalkylene glycol residue defined as that portion derived from a polyalkylene glycol having the formula:
• HO--R"O).sub.m H
• wherein R" is an alkylene group of from 2 to about 20 carbon atoms, and m designates the number of repeating alkylene ether units and is from 2 to 20;
• X is a halogen;
• and n' and n" are numbers such that the sum of n' and n" is an integer in the range from about 4 to about 50.