Monomers with a three-member ring structure - such as epoxide, aziridine, and episulfide - undergo anionic ROP.
Cationic initiators and intermediates characterize cationic ring-opening polymerization (CROP).
Synthesis of polypeptides which has the oldest history of ROP, dates back to the work in 1906 by Leuchs.
Subsequently, the ROP of anhydro sugars provided polysaccharides, including synthetic dextran, xanthan gum, welan gum, gellan gum, diutan gum, and pullulan.
Ring-opening of cyclic monomers is often driven by the relief of bond-angle strain.
Thus, as is the case for other types of polymerization, the enthalpy change in ring-opening is negative.
Following Flory–Huggins solution theory that the reactivity of an active center, located at a macromolecule of a sufficiently long macromolecular chain, does not depend on its degree of polymerization (DPi), and taking in to account that ΔG, for polymerization in the bulk, are well above or below the operable polymerization temperatures, respectively.
The polymerization of a majority of monomers is accompanied by an entropy decrease, due mostly to the loss in the translational degrees of freedom.
For instance, radical ROP can produce polymers with ethers, esters, amides, and carbonates as functional groups along the main chain.
The general mechanism for anionic ring-opening polymerization.