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Phosphorus trichloride and oxygen react readily with polyethylene to introduce phosphonic dichloride (—POCl2) groups into the polymer (chlorophosphonation). Treatment of the resulting intermediate with water, alcohols, and amines yields polymeric alkylphosphonic acids, esters and amides, respectively. Derivatives containing as much as 16% phosphorus have been prepared. With increasing degree of phosphonation, polyethylene crystallinity is reduced, the acid and amide derivatives become stiffer, less extensible, and less soluble in nonpolar solvents, and internal plasticization is observed in the ester derivatives. No significant decrease in flammability is effected by phosphonation unless chlorine is introduced also. The ester and amide derivatives crosslink under mild conditions by an unknown mechanism, the acid derivative will crosslink on heating with litharge. The chlorophosphonation reaction is sensitive to inhibitors and no highly active catalyst was found. The rate appears to be governed by the rate at which oxygen dissolves in the mixture. Substitution of air or chlorine for oxygen, phenyldichlorophosphine or diphenylchlorophosphine for phosphorus trichloride results in introduction of phosphorus‐containing groups into polyethylene, also, but at reduced rates. In sharp contrast to polyethylene's apparent stability toward the phosphonation conditions, polystyrene, poly(methyl methacrylate), and polyisobutylene undergo a rapid decrease in molecular weight on treatment with phosphorus trichloride and oxygen. The fact that these four polymers exhibit the same relative behavior, i.e., polyethylene is stable whereas the other three polymers are unstable, in various free radical processes argues for a free radical mechanism in the chlorophosphonation reaction.

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