Recent advances in ring-opening metathesis polymerization, and application to synthesis of functional materials

Abstract

This article reviews the development of catalysts for ring-opening metathesis polymerization (ROMP), synthesis of polymers bearing amino acids and peptides by ROMP of functionalized norbornenes, formation of aggregates and micelles, and applications of the polymers to medical materials. It also describes the control of monomer unit sequences, that is, living polymerization to synthesize block copolymers, and alternating copolymerization that is achieved on the basis of acid-base interactions. Polymer Journal (2010) 42, 905-915; doi:10.1038/pj.2010.94; published online 13 October 2010Keywords: alternating copolymerization; amino acid; block copolymerization; living polymerization; metathesis catalyst; peptide; ROMP INTRODUCTIONOlefin metathesis reactions are metal-mediated carbon-carbon (C-C) double bond exchange processes, 1,2 which were discovered in the mid 1950s. Chauvin proposed the commonly accepted mechanism for metathesis involving a metallacyclobutane, as illustrated in Scheme 1. 3 Initially, olefin metathesis was regarded as an odd reaction, but now it has undoubtedly established the position as one of the most important C-C bond formation reactions applicable to synthesis of a wide variety of useful products. In the early stages, transition metal chlorides were used as catalysts for the reaction, but the transition metal carbene complex catalysts designed by Schrock and Grubbs have remarkably advanced mechanistic analysis and control of catalytic activity by the choice of ligands. In 2005, Chauvin, Grubbs and Schrock were awarded the Nobel Prize in chemistry for development of the metathesis method in organic synthesis.Olefin metathesis polymerization is an application of metathesis reactions to polymer synthesis and includes ring-opening metathesis polymerization (ROMP) and acyclic diene metathesis (ADMET) polycondensation (Scheme 2). ADMET has been extensively developed by Wagener since 1987 4 for the synthesis of polyolefins having regularly spaced functional group branches and high thermal stability and crystallinity. 5,6 ADMET is also useful for synthesizing polymeric materials containing in-chain functionality. Although the general structures of the polymers obtained by ROMP and ADMET are illustratable in the same fashion as shown in Scheme 2, a completely different treatment is necessary from the viewpoint of polymerization kinetics. The former involves chain polymerization, whereas the latter is a step-growth polymerization process.

Effects of Grafting Density on Block Polymer Self-Assembly: From Linear to Bottlebrush

“…Ring-opening metathesis polymerization (ROMP) is a powerful strategy to 6 synthesize well-defined bottlebrush polymers in a controlled and living manner. [49][50][51][52] We targeted poly(D,L-lactide)-b-polystyrene (PLA-b-PS) graft diblock polymers to permit comparisons with brush PLA-b-PS systems previously investigated in the context of self-assembly. [21][22][23][24][25] All polymerizations were carried out in CH2Cl2 at room temperature under an inert atmosphere.…”

Design, Synthesis, and Self-Assembly of Polymers with Tailored Graft Distributions

“…Graftingthrough ring-opening metathesis polymerization (ROMP) closes this gap by affording wide functional group tolerance and enabling simultaneous control over side chain and backbone lengths. [35][36][37] We recently introduced a ROMP strategy that provides access to polymers with uniform grafting densities spanning the linear to bottlebrush regimes. 38 In this report, we further expand the scope of architectural design by demonstrating that ROMP can be exploited to further tune "molecular shapes.…”

Metathesis Polymerization Reactions Induced by the Bimetallic Complex (Ph4P)2[W2(μ-Br)3Br6]

“…In toluene, traces of polymer were obtained even after 23 h (entries 7 and 8). Interestingly, with 1/NBD molar ratio equal to 1/1000, without adding AgBF 4 , and under reflux, PNBD was obtained in high yield (80%; entry 9). Under similar conditions, but at room temperature, the reaction provided traces of PNBD (entry 10).…”

“…(Ph 4 P)[W(CO) 5 Br] [21] and (Ph 4 P) 2 [W 2 (µ-Br) 3 Br 6 ] (1) [22] were prepared according to literature procedures. For the synthesis of both compounds, Ph 4 PBr was used instead of n Pr 4 NBr. PA was passed through an Al 2 O 3 column and was distilled under vacuum.…”

“…Among them, metathesis polymerization of alkynes [1][2][3] and ring opening metathesis polymerization (ROMP) of cycloolefins [4][5][6] yield unsaturated polymeric materials and are considered as two of the most important tools in polymer chemistry, leading to the synthesis of novel materials (Scheme 1). The properties of these polymers sensitively depend on their microstructure.…”