The Ring‐Opening Polymerization–Polycondensation (ROPPOC) Approach to Cyclic Polymers

Abstract

A new concept called ring‐opening polymerization–polycondensation (ROPPOC) is presented and discussed. This synthetic strategy is based on the intermediate formation of chains having two end groups that can react with each other. The ROPPOC syntheses are subdivided into three groups according to the nature of the chain ends: two ionic end groups, one ionic and one covalent chain end, and a combination of two reactive covalent end groups may be involved, depending on the catalyst. The usefulness for the preparation of cyclic polymers is discussed with a review of numerous previously published examples. These examples concern the following classes of cyclic polymers: polypeptides, polyamides, and polyesters, including polycarbonates and cyclic polysiloxanes. It is demonstrated that the results of certain ROPPOC syntheses are in contradiction to the Jacobson–Stockmayer theory. Finally, the usefulness of ROPPOCs for the detection of polydisperse catenanes is discussed.

What Does Conversion Mean in Polymer Science?

“…Based on the covalent or ionic nature of the end groups, ROPPOCs may be subdivided into three categories. First, both chain ends are ions and the entire polymerization pro cess is a zwitterionic polymerization as illustrated exemplarily in Scheme 10 [31][32][33] Second, one chain end is covalent (e.g., an activated COgroup) and the other chain end is ionic (e.g. an anion).…”

“…The oligopeptides of almost all natural amino acids can adopt the βsheet structure which, due to intermolecular Hbonds, causes insolubility in all inert solvents useful for a clean polymerization of the NCAs. [31] When precipitation of the growing chains more is rapid than cyclization, linear chains having two active end groups will be fixed in the βsheet crystals and cyclization is prevented as long as these crystals exist. In the case of soluble αhelix forming polypeptides (e.g., poly(benzyl Lglutamate)) chain growth to DPs above 10 may result in the formation of αhelices prior to cyclization.…”

“…In the case of soluble αhelix forming polypeptides (e.g., poly(benzyl Lglutamate)) chain growth to DPs above 10 may result in the formation of αhelices prior to cyclization. [31] The chain growth may continue at the end of the helices, but the helices are too stiff for cyclization. The CCpolymerization of γ-GluNCA initiated by imidazole (Scheme 12, In summary it may be said, that regardless, if the conversion of polycondensation/ cyclization part of the ROPPOC process is complete or not, a simple correlation between conversion and DP does not exist.…”

ROP of L‐lactide and ε‐caprolactone catalyzed by tin(ii) and tin(iv) acetates–switching from COOH terminated linear chains to cycles

“…ROPPOC means ring-opening polymerization combined with simultaneous polycondensation, a new concept recently discussed and reviewed. 37 Hence, the observed phenomena defy a straightforward explanation on the basis of the mechanisms outlined in Scheme 1.…”

Synthesis of Dendrimer‐Like Helical Poly(Phenyl Isocyanide)s Using Air‐Stable Palladium Complexes with Double Arms

“…In order to mimic natural products, polymer chemists have developed a variety of polymers with different topological structures, such as linear, [ 32 ] cyclic, [ 33,34 ] star, [ 35,36 ] graft, [ 37,38 ] branched, [ 39,40 ] dendritic, [ 41,42 ] and so on. Among them, dendrimer‐like polymers are a special type of macromolecules with unusual structural and transport properties.…”