Ring-opening metathesis polymerization of cycloolefins

Article By:

Khosravi, Ezat Department of Chemistry, Durham University, Durham, United Kingdom.

Rogan, Yulia Department of Chemistry, Durham University, Durham, United Kingdom.

Dean, Barry Department of Chemistry, Durham University, Durham, United Kingdom.

Last reviewed:2012

DOI:https://doi.org/10.1036/1097-8542.YB120311

Although a relatively new tool in the field of polymer chemistry, ring-opening metathesis polymerization (ROMP) has emerged as a powerful and broadly applicable polymerization method for synthesizing macromolecular materials with tunable sizes, shapes, and functions. The technique has found tremendous utility in preparing materials with interesting biological, electronic, and mechanical properties. ROMP is a chain-growth polymerization process in which a cyclic olefin is converted to a polymeric material. The mechanism of the polymerization, proposed by Y. Chauvin, is based on olefin metathesis and involves a unique metal-mediated carbon–carbon double-bond exchange process, leading to an unsaturated polymer. Initiation begins with the coordination of a cyclic olefin to a transition-metal alkylidene complex, forming a four-membered metallacyclobutane intermediate that breaks up productively to generate a new metal alkylidene (propagating alkylidene). Analogous steps are repeated during the propagation stage until polymerization ceases (that is, all the monomer is consumed or the reaction is terminated). The use of well-defined initiators combines rapid initiation with high propagation rates and often enables living polymerizations (that is, reactions for which there is no termination step to stop chain growth). Thus, precise adjustment of the molecular weight can be accomplished by simply varying the ratio of monomer to initiator. Polydispersity indices (PDI; molecular-weight distributions) of the obtained polymers are, in general, low (PDI<1.5) and block-copolymer synthesis is feasible. The living character of ROMP enables the synthesis of well-defined, end-functionalized polymers as well as block and graft copolymers with complex architectures and useful functions. Living ROMP reactions are commonly quenched deliberately through the addition of specific reagents, depending on the type of the initiators used.

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