ADMET polymerization

Overall, ADMET polymerization is an advantageous strategy for synthesizing transition metal-containing polymers because of the functional group tolerance of the metathesis catalysts employed, the mild conditions under which it operates, the wide range of accessible architectures, and the precise structural control afforded by the method. 

One strategy to obtain organometallic a,gj-dienes for ADMET is to substitute phosphine ligands containing terminal alkene substituents onto metal-metal bonded dimers.42 An example of one such dimer is shown in equation 14. 

Cp-substituted reactants. It is not clear why such long chain lengths are required to alleviate steric interactions in the Humphrey-Lucas molecules, but similar steric effects may be acting in the polymerizations of complex 3, where two molecules of 3 and a catalyst molecule all need to interact to carry out the polymerization. Nevertheless, despite this one setback, ADMET remains an attractive method for synthesizing new polymers with metal-metal bonds along their backbones. 

Handbook of Metathesis Vol 3 Polymer Synthesis, Second Edition. 

This hypothesis was supported by the reaction of WCl5/EtAlCl2 with styrene, which yielded polystyrene, presumably by cationic polymerization, rather than stilbene, the expected product of metathesis. The realization that vinyl addition competes with olefin metathesis in reactions using these classical catalyst systems was the key. This work serendipitously coincided with Schrock and coworkers report of their Lewis acid-free metathesis catalyst. These two advances, taken together, allowed ADMET to be realized as a method of forming a high polymer. 

The development of an olefin metathesis catalyst based on late transition metals was a logical step because they are usually less sensitive to air, moisture, and polar or protic functional groups. Schrock and Toreki [11] created well-defined rhenium 

ADMET is a step-growth polymerization, a process very different from ring-opening metathesis polymerization (ROMP), which is a chain-growth polymerization process [19]. 

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Acyclic diene molecules are capable of undergoing intramolecular and intermolec-ular reactions in the presence of certain transition metal catalysts molybdenum alkylidene and ruthenium carbene complexes, for example [50, 51]. The intramolecular reaction, called ring-closing olefin metathesis (RCM), affords cyclic compounds, while the intermolecular reaction, called acyclic diene metathesis (ADMET) polymerization, provides oligomers and polymers. Alteration of the dilution of the reaction mixture can to some extent control the intrinsic competition between RCM and ADMET. 

X(A1C13) = 0.5) to immobilize a ruthenium carbene complex for biphasic ADMET polymerization of an acyclic diene ester (Figure 7.4-2). The reaction is an equilibrium processes, and so removal of ethylene drives the equilibrium towards the products. The reaction proceeds readily at ambient temperatures, producing mostly polymeric materials but also 10 % dimeric material. 

Nearly all of the polymers produced by step-growth polymerization contain heteroatoms and/or aromatic rings in the backbone. One exception is polymers produced from acyclic diene metathesis (ADMET) polymerization.22 Hydrocarbon polymers with carbon-carbon double bonds are readily produced using ADMET polymerization techniques. Polyesters, polycarbonates, polyamides, and polyurethanes can be produced from aliphatic monomers with appropriate functional groups (Fig. 1.1). In these aliphatic polymers, the concentration of the linking groups (ester, carbonate, amide, or urethane) in the backbone greatly influences the physical properties. 

Olefin metathesis, an expression coined by Calderon in 1967,1 has been accurately described in Ivin and Mol s seminal text Olefin Metathesis and Metathesis Polymerization as the (apparent) interchange of carbon atoms between a pair of double bonds (ref. 2, p. 1). This remarkable conversion can be divided into three types of reactions, as illustrated in Fig. 8.1. These reactions have been used extensively in the synthesis of a broad range of both macromolecules and small molecules3 this chapter focuses on acyclic diene metathesis (ADMET) polymerization as a versatile route for the production of a wide range of functionalized polymers. 

ADMET of av j-dicncs has been a focus of research in the Wagener laboratories for many years now, where we have studied this chemistry to explore its viability in synthesizing polymers possessing both precisely designed microstructures as well as a variety of functionalities. The requirements for this reaction, such as steric and electronic factors, functionalities allowed, appropriate choice of catalyst, and necessary length or structure of the diene, have been examined.3,12-14 A detailed discussion will be presented later in this chapter with a brief synopsis of general rules for successful ADMET polymerization presented here. 

Shorter chain dienes have an increased propensity to form stable five-, six-, and seven-membered rings. This thermodynamically controlled phenomenon is known as the Thorpe-Ingold effect.15 Since ADMET polymerization is performed over extended time periods under equilibrium conditions, it is ultimately thermodynamics rather than kinetics that determine the choice between a selected diene monomer undergoing either polycondensation or cyclization. 

At this point it is appropriate to discuss the mechanism for ADMET, because ADMET polymerization is more involved than its chain polymerization counterpart— ROMP. Figure 8.6 illustrates the accepted mechanistic pathway which leads to productive metathesis polymerization, as first described by Wagener et al.14a A general model reaction between an a,o>-diene with a metal alkylidene... 

Figure 8.7 Second generation of ADMET polymerization glassware.

Usually ADMET polymerizations are conducted in the bulk state (neat) to maximize the molar concentration of the olefin, and so the examples discussed in this chapter describe bulk polymerization conditions. 

Figure 8.8 ADMET polymerization of (a) 1,9-decadiene and (b) 6-methyl-1,10-undecadiene.

K. B. Wagener, Acyclic Diene Metathesis (ADMET) Polymerization, in Synthesis of Polymers, A. D. Schluter (Ed.), Materials Science and Technology Series, Wiley, Weinheim, 1999. 

ADMET polymerization. See Acyclic diene metathesis (ADMET) polymerization... 

Methyl-l,10-undecadiene, ADMET polymerization of, 442 Michaelis-Menten enzymatic kinetics, 84 Microbial hydrolysis, 43 Microcellular elastomers, 204-205 Microphase-separated block copolymers, 6-7... 

Wolfe and Wagener have developed main-chain boronate polymers (59) (Fig. 38) by the acyclic diene metathesis (ADMET) polymerization of symmetrical ,oj-dienes, containing both methyl- and phenyl-substituted boronate functionalities using Mo and Ru catalysts.84 The ring-opening metathesis polymerization (ROMP) of several norbornene monomers containing methyl- and phenyl-substituted boronates into... 

Lehman, S. E., Jr. and K. B. Wagener, Macromolecules, 35, 702 (2002) Catalysis in ADMET Polymerizations, Chap. 6 in Late Transition Metal Polymerization Catalysis, B. Rieger, L. Baugh, S. Kacker, and S. Striegler, eds., Wiley-VCH, New York, 2003. 

In the field of alkene metathesis ruthenium-allenylidene precursors have made, since 1998, an important contribution to catalysis [12, 31, 32], for the formation of cycles and macrocycles via RCM, ROMP and acyclic diene metathesis (ADMET) polymerization. 

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