Polymerization of phosphorus containing cyclic monomers: Synthesis of polymers related to biopolymers

The mechanism of polymerization is discussed, in which cyclic esters of phosphoric acid, and related compounds are converted into linear macromolecules, modelling nucleic and teichoic acid backbones. Structures like deoxyribose polyphosphate and glycerol polyphosphate were prepared from the corresponding cyclic compounds. These polymerizations involve heterolytic breaking of the P‐O bond in the cyclic monomer and proceed by ionic mechanism. Both 5‐ and 6‐membered monomers have been polymerized. The thermodynamic parameters of the ring‐chain interconversion were determined; the 5‐membered rings polymerization is driven by the exothermicity of the ring‐opening, whereas polymerization of several 6‐membered rings is endothermic and allowed because of the positive change of entropy. Anionic polymerization, and particularly the pseudo(coordinate)anionic polymerization provides, in contrast to the cationic process, high‐molecular‐weight polymers with more uniform structure. Anionic polymerization proceeds mostly (at the applied conditions) on the macroion – ‐pairs. The elementary reactions consist of the nucleophilic attack of the paired macroanions on the phosphorus atom in the cyclic monomer molecule. Rate constants of the elementary reactions for the model monomers will be presented. Stereochemistry of the propagation steps is shown to be governed by the statistical ring‐opening, leading to the three kinds of polymer units (head‐to‐tail and two symmetrical units). Apart from the ring‐opening, the polyaddition of diepoxides to phosphorous and phosphoric acids is described. Finally, a few examples of preparation of models of biopolymers are given, namely poly(deoxyribose phosphate) and poly(glycerol phosphate).