TUTORIAL - THERMODYNAMICS OF RING-OPENING POLYMERIZATION

The ring-opening polymerization of cyclic monomers shows the characteristic features of any addition polymerization or any physical aggregation process, in particular a ceiling temperature above which the formation of the aggregate (long-chain polymer), under given conditions of monomer concentration, solvent and pressure, would involve a positive change of free energy and is therefore impossible. Conversely for a given temperature, pressure and solvent, there is an equilibrium monomer concentration below which long-chain polymer cannot be formed. Cyclic monomers must therefore have a negative free energy of polymerization, under given conditions, if they are to be capable of undergoing a significant extent of ring-opening polymerization. The effect of monomer structure, including ring size, on thermodynamic polymerizability is discussed, as well as the possibility of copolymerizing monomers which cannot themselves give homopolymers. Examples are given for various possible mechanisms of polymerization.