Polymerization of Cyclic Esters of Phosphoric Acid

Abstract—Highmolecularweightpolyestersof phosphoric acid,havebeenpreparedwithasequenceof atoms inthe main chain similar to that in naturally occuring polymers, teichoic acid or nucleic acids. Although the five and six-membered cyclic esters of phosphoric acid polymerize readily, such as with anionic or cationic initiation, the polymerization degrees are low because of an extensive chain transfer to monomer which competes successfully with chain propagation. Polymerization of the six-membered esters is highly reversible. The corresponding thermodynamic equilibrium parameters have been determined for several monomers (differing in structure of the exocyclic group) and the lineai isoequilibrium dependence (AH,, as a function of iS,) has been found. For a model monomer, 2-methyl-2-oxo-1,3,2-dioxaphosphorinane) the kinetics of anionic and cationic polymerization is described and the corresponding activation parameters are discussed. Structure of the polymer chain has been determined by 'H, 31P and 13C—NMR and it is shown subsequently that cyclic end-groups are present, formed in the chain transfer reaction. In order to avoid the chain transfer, involving the exocyclic ester group, 2-hydro-2-oxo-l,3,2-dioxaphosphorinane was used as a monomer. High molecular weight polymers have been prepared and subsequently oxidized the corresponding acidic polyesters. The five-membered 2-alkyl-2-oxo-1,3,2-dioxaphospholanes have been polymerized with organometallic initiators. The use of these initiators eliminates the chain transfer and leads to the high-molecular weight polymers (M> 10). The conversion of the neutral polyesters into the acidic polyesters is described.