Thermodynamics and kinetics of ring‐opening polymerization of cyclic alkylene phosphates

Polymerization of cyclic compounds containing phosphorus has been used to prepare models of chains of nucleic acids and teichoic acids. Polymers of high molecular weight (Mn≥105) have been prepared in the past in this laboratory by ring-opening polymerization. These processes have a number of particular features, related to the low ring strain of the involved monomers (the majority of six-membered esters are strainless) and to the presence of the labile exocyclic groups. Results of the studies of these polymerizations contributed to the understanding of general phenomena of ring-opening polymerizations related to these features. In this review paper the thermodynamics of strainless rings is discussed. It is shown that for the same monomer, polymerization can either be exothermic (δHSS 0, δSSS>0). The presence of the labile exocyclic groups introduce a potential possibility of chain transfer. It is shown that in the cyclic, non-strained six-membered monomers kP/ktr is relatively low for cyclic triesters but much higher (≈300) in the polymerization of cyclic amides, since the alcoholate is a better leaving group then the amide group. The importance of these findings for other classes of monomers (cyclic amines, siloxanes, orthoesters) having also labile exocyclic groups is discussed.

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