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Keywords:

  • ADMET;
  • functionalization of polymers;
  • metathesis;
  • polycondensation;
  • step-growth polymerization

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

Although it is well known that Acyclic Diene METathesis (ADMET) describes an olefin metathesis polymerization mode that relies on double-bond substituent interchange of a diolefin, the story behind its discovery is not. The story is divulged here. Olefin metathesis has a rich history dating to the 1950s, but the one particular metathesis mode mentioned, ADMET, has more recent historical roots. ADMET polymerization is easy to do and highlighted here are the particular reaction details for success. Additionally, the most recent advances from the past 5 years are detailed, exemplifying this reaction's wide utility from fundamental structure–property studies to multiple advanced applications. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

The ADMET Discovery

Ideas—they come from all sorts of places. In the case of Acyclic Diene METathesis (ADMET) chemistry, it started during a Ph.D. oral examination held in 1970 at the University of Florida. The oral exam document, entitled “Mechanistic Possibilities for the Skeletal Change Observed in Metal-Catalyzed Diene Rearrangement”1 invoked the four-center metathesis mechanism as an alternative to explain a skeletal rearrangement that recently had been published in JACS.2 Fortunately, the oral examination concluded on a successful note for the Ph.D. candidate (Wagener), even though the metathesis four-center mechanism itself, which formed the basis of the exam, was proven to be incorrect several years later.

Nonetheless, personal intrigue with metathesis chemistry began to grow. Wagener's joining Akzo Nobel (American Enka Company in North Carolina) in 1973 added the “missing link” in thinking about what an ADMET reaction should be. Akzo Nobel produced a variety of polyester products, and so the real nature of what is required for successful polycondensation became clear: choosing the proper catalyst, preferably used in the absence of solvent under reduced pressure leading to quantitative yields with only one mechanism operating to yield the desired polymer. All prior attempts in the literature to condense dienes to polymers via metathesis chemistry had been unsuccessful since at least one of the aforementioned conditions had not been met, attempts dating back to the 1950s.

Eleven years later upon returning to academics at the University of Florida, the research group took up metathesis polycondensation (later to be called ADMET chemistry) in earnest, with Monica Lindmark-Hamberg initiating the first experiments using the classical catalyst system WCl6/EtAlCl2 attempting to polycondense 1,6-hexdiene and 1,9-decadiene. Although metathesis indeed occurred with the evolution of ethylene, it became apparent it was not the only reaction in hand. Further model experiments showed that vinyl addition accompanied metathesis chemistry—styrene was partially converted to polystyrene rather than metathesizing to stilbene—two mechanisms operating rather than one.3 Quoting from that 1987 article, “vinyl addition reactions are important “side” reactions, which indeed become the only reaction when the monomer favors cationic polymerization.” Quoting further, “obviously catalyst selection is important, and our research has turned to the synthesis of metathesis catalysts based on molybdenum and tungsten wherein no Lewis acid cocatalysts are present.” We knew we needed clean metathesis catalysts. Further, we were actually advised not to tinker with metathesis condensation chemistry by Chemistry Department Faculty (Don't bother, the equilibrium constant for the reaction is working against you!).

Ignoring this advice, timing turned out to be on our side as Schrock and coworkers had just published the tungsten version of his homogeneous “Schrock's Catalyst” for ring-opening metathesis (ROM) polymerization.4 Choosing this catalyst turned the model compound styrene into stilbene plus ethylene; only one mechanism was operating—metathesis—and so the basic requirements for successful polycondensation had been discovered. Later in 1991, proof-of-polymerization-concept was established by Nel and coworkers who converted 1,9-decadiene into polyoctenamer,5 and from that point on, the discovery process picked up considerable speed. Since then, the reaction has been shown to have wide applicability in converting dienes to high-molecular-weight, high-strength polycondensation polymers, with proper catalyst selection always being an important consideration (Fig. 1).

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Figure 1. ADMET reaction.

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Again, with the history of metathesis dating to the 1950s, the ADMET polymerization discovery in 1987 was reliant on choosing an appropriate catalyst mixture from the vast library of available metathesis catalysts to drive the previously hypothetical reaction and expanded using well-defined catalysts still today. Although it is well known that ADMET describes an olefin metathesis polymerization mode that relies on double-bond substituent interchange of a diolefin, the story behind its discovery is fragmented in the literature. Now, all of the implications stemming from this particular olefin metathesis mode are detailed.

METATHESIS FEATURES AND EVOLUTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

Olefin Metathesis

Olefin metathesis is a powerful synthetic technique in forming carbon–carbon bonds.6, 7 The developments in mechanism and useful catalysts collectively earned Robert H. Grubbs, Richard R. Schrock, and Yves Chauvin the 2005 Nobel prize in Chemistry.8

Using this mild reaction in forming carbon–carbon double bonds, complex reaction modes (Fig. 2) have developed beyond the simplest olefin metathesis mode involving the cross metathesis (CM) highlighted above.7 CM involves two different olefins and heterointerchange, whereas self-metathesis (SM) involves two of the same olefins and homointerchange as a result.9 Furthermore, rings may be opened using ROM10 with a selected opening species or closed using ring-closing metathesis (RCM)11, 12 releasing ethylene. A combination of metathesis modes coupled with understanding reactivity has even allowed for metathesis polymerization modes involving either chain polymerization (ROMP)10, 13 or step polymerization (ADMET). ROMP, the chain polymerization, relies on releasing ring strain by ring opening via a cyclic alkene monomer in an addition chain polymerization.

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Figure 2. Modes of metathesis.

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Alternately, the step polymerization, ADMET chemistry, relies on CM with ethylene removal driving the reaction in a step-growth condensation polymerization. ADMET has more recent historical roots as this polymerization was not discovered until 1987,3 which coincided with choosing an appropriate catalyst mixture from the vast library of available metathesis catalysts to drive the previously hypothetical reaction. Controlling relevant aspects of this reaction results in high-molecular-weight polymer structures, with the most ADMET work emphasizing functionalization and precision placement of substituents along the polymer chain.

The Olefin Metathesis Discovery

Industrial pursuits in metathesis chemistry can be traced to reports in the 1950s and 1960s during a time when synthetic polyolefin advances centered around catalyst mixtures of high oxidation metal salts and an activating agent. Such is the case with reaction observations by DuPont chemist William Truett that something different was occurring during a ring-opening reaction of norbornene resulting in unusual stereospecificity of cyclopentane rings linked by cis-1,3 linkages to trans backbone double bonds, a coordination-type polymerization.14 Truett's former laboratory partner Otto Vogl more clearly defines this part of history as the first example of metathesis polymerization.15 Indeed, additive reports during this time included patents by fellow DuPont chemist Herbert Eleuterio.16, 17 Additionally, a few other reports also surfaced independently on exchange reactions along with ring-opening polymerization using Zieglar-Natta-type catalyst MoCl5/Et3Al, but little mechanistic support was offered.18

The connection that these reactions were in fact the same reaction (metathesis) became apparent in 1967 when Goodyear chemist Nissim Caulderon noted rapid polymerization of cyclic alkene monomers and disproportionation of 2-pentene using WCl6/EtAlCl2/EtOH.19–22 Hence, the term “olefin metathesis” was coined by Caulderon as he released further articles explaining a mechanism involving a three-step process with the first involving bisolefin–metal coordination.

The accepted mechanism first proposed by Chauvin in 1971 begins through metallocyclobutane formation (Fig. 3).23, 24 The mechanism debate continued, and although the mechanism was not confirmed until 1975 by Katz and McGinnis,25 Chauvin's proposal took time before it gained acceptance and was distinguished from the numerous incorrect proposals of the 1970s. Katz compared several of the other proposed mechanisms and compared the statistical distribution of different products based on starting olefin structural and electronic variations expected in the intermediate stability within the metal–carbene mechanism.26, 27

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Figure 3. Metal–carbene metallocyclobutane formation.

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Although not all considerations could be explained, Katz envisioned applications forthcoming along with initiator and catalyst developments. Just after Katz's mechanistic report, Grubbs and Hoppin released support for the metal–carbene mechanism including vigorous isotopic labeling and isolation of the various metathesis pathway products.28 Katz proceeded in developing low oxidation state electrophilic Fischer carbenes promoting ROMP but unsuccessful in promoting olefin metathesis.

Metathesis Catalyst and Initiator Evolution

It was the developments of the 1970s by Richard Schrock, then a researcher at DuPont, toward homogenous metathesis catalysts that eventually led to the isolation of a high oxidation state nucleophilic carbenes, termed “Schrock carbenes,” including tantalum carbene complexes.29 Schrock carbene ligands are viewed as X2 ligands with +2 charge in contrast to the neutral Fischer carbene L ligands. With tantalum catalyst activity too low, further catalyst developments using tungsten30, 31 and molybdenum32, 33 followed (Fig. 4).

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Figure 4. Schrocks' tungsten (W1) and molybdenum (Mo1) ADMET active catalysts.

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The multitude of highly active early-transition metal catalysts allowed for diverse applications that were limited by the electrophilic and oxophilic metal centers sensitive to air, moisture, and functional groups. Late-transition metals remained desirable as they are less electrophilic and moving toward that direction. Schrock and Toreki eventually also created olefin metathesis active rhenium complexes.34 From Schrock's work, numerous achievements in small molecules and polymers were possible.

Simultaneous discoveries by Grubbs and coworkers throughout the 1980s led to spectroscopically characterizable titanacyclobutanes from titanium/Lewis acid mixtures,35–37 which brought the understanding of olefin metathesis to a more complete level. Incidentally, the Wagener research group was just being established at this time in 1984. Grubbs and coworkers also found success on moving from the titanium/Lewis acid mixtures to well-defined homogenous catalysts with rhenium and the more successful ruthenium centers such with Grubbs' first-generation catalyst (Ru1) and second-generation catalyst (Ru2) (Fig. 5).38–40

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Figure 5. Grubbs' ruthenium catalysts, first (Ru1) and second (Ru2) generation.

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Although ruthenium has proven to be the most successful late-transition metal in reducing air, moisture, and coordinating functionality sensitivity, the first-generation catalysts were less active than early-transition metal catalysts. In particular, structures such as those shown in Figure 6 were interesting in that they exhibited features of Fischer and Schrock carbenes, but not exclusively classified as either. This allowed for a continuum between early- and late-transition metals, dependent on metal and ligand selection in altering electronics and/or sterics for particular metathesis modes.

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Figure 6. Productive ADMET polymerization cycle.

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Certainly, all of these developments have established a huge library of catalysts from which a number of synthetic challenges in pharmaceuticals, petrochemicals, and polymers have been met. These catalyst developments have also allowed for a multitude of developments in the more specialized ADMET polymerization reaction since the early 1990s. The focus on polymerization requirements resulting from the ADMET mechanism and a survey of the most recent developments of the evolution of ADMET since 2005 will be presented.

ADMET FEATURES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

Although the commonalities of the metathesis modes include an exchange of double-bond substituents, ADMET polymerization is a step, condensation polymerization and thus has numerous features differentiating the polymerization from the more commonly used ROMP chain technique.41

ADMET Mechanism

The polymerization cycle proceeds through the same basic metal–carbene mechanism as in CM with features optimized to enhance polymerization through productive metathesis (Fig. 6).5, 42–44

The precatalyst involves a metal species with associated ligands [M], which reacts reversibly to form a metal methylidene carbine, which is the true catalyst in this step polymerization. The open coordination site allows for olefin coordination, and 2 + 2 cycloaddition forming a metallocyclobutane, which decomposes by a 2 + 2 cycloreversion, releasing ethylene condensate and resulting in an α-substituted metal alkylidene with an open coordination site.

The metal alkylidene species may be monomer or polymer, and coordination of another monomer or polymer molecule productively results in a α,β-substituted metallocyclobutane. The cycloreversion results in the release of two linearly coupled molecules and regenerates the metal methylidene carbene.

Additionally, regiochemical considerations of metallocyclobutane formation are more complicated in achieving productive metathesis with this step-growth process. The regiochemical cycloreversion results in a nonproductive pathway if the starting materials are simply regenerated and productive pathway if the alternate regiochemical cycloreversion results in a new olefin and new metal–carbene as was previously shown in Figure 4. The regiochemical requirements for productive metathesis are twofold including metallocyclobutane sterics and metallocyclobutane reversion breaking the original bonds generating the interchange of double-bond substituents. Metallocyclobutane formation can proceed forming either α,α′ substitution or α,β substitution (Fig. 7).

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Figure 7. Regiochemical productive and nonproductive routes.

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Sterics favor α,α′ substitution but lead to nonproductive metathesis and more specifically degenerate metathesis. To favor α,β substitution, the least sterically demanding monomers are generally used—α,ω-dienes.

The cis:trans stereochemical outcome of productive ADMET with Grubbs catalysts has implications on the overall polymer properties yet is rooted in the mechanism. With cis:trans ratios of 3:7 and 1:4 with more time, the preference of trans can be rationalized with the lesser sterically favored approach and resulting α,β-metallocyclobutane conformation (Fig. 8).45 The trans microstructure is a consequence of the kinetic product formed by olefin approach and resulting metallocyclobutane conformation with equatorial substituents as well as the thermodynamic equilibration to the thermodynamically preferred trans-olefins.

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Figure 8. Stereochemical trans outcome rationale.

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Condensation Polymerization

As ADMET is classified as a condensation polymerization, and as with most condensation polymerizations, this equilibrium process requires desired functional groups reacting in a step-wise fashion allowing for molecular weight increase proceeding stepwise from monomer, dimer, trimer, and so on to high polymer.41 This stepwise event occurs as the linearly coupled molecules are released during the metathesis catalytic cycle. To drive the equilibrium, ethylene is removed from the reaction. At high conversion, each coupling between polymer chains reduces the number of polymer molecules in the sample significantly. This stark contrast to the situation at low conversions, which results in only a small reduction of polymer molecules, results in a low polymerization rate until high conversions are realized. Implications on catalysis include necessitating a highly active catalyst that remains active throughout the polymerization cycle.

High conversions are achieved by removing the condensate, driving the equilibrium. Using the least sterically demanding monomers, α,ω-dienes, the ethylene condensate is removed, thus preventing the reverse reaction regenerating monomer. Despite the high conversion required for high molecular weight as with typical condensation polymers, several commercially important condensation polymers are used successfully including polyesters and polyamides.

Molecular weight distributions in ADMET polymers are also typical of other condensation polymers. The polydispersity index (PDI) is defined as the weight-average molecular weight, Xw, divided by the number-average molecular weight, Xn, and describes the molecular weight distribution. Statistically, condensation polymers typically have PDIs approaching 2.0, the most probable distribution, as conversion reaches 1 or 100%.

Considerations

Equilibrium along with regiochemical considerations allows for productive and nonproductive pathways upon coordination of a disubstituted olefin in forming high polymer described previously. Other typical well-known equilibrium that occurs in polycondensation chemistry has effects on ADMET polymers including cyclization and metathesis interchange.41

Cyclization is favored under high dilution and occurs in metathesis chemistry by backbiting of an oligomeric or polymeric metal–carbene with a double bond on the backbone of that polymer (Fig. 9). Indeed, very low concentrations of cyclics have been observed in ADMET polymerization, which is typical of any polycondensation.46 As the mechanisms in cyclic formation of ADMET polymerization and ROMP are similar, the backbiting has actually been optimized via a Ru2 modification to form wholly cyclic polymers.47 Similarly, RCM has seen utility in yielding rings of more than 20 atoms.48 To avoid cyclizations, bulk or high concentrations favoring intermolecular reactions are typical along with monomers incapable of forming favored ring sizes.

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Figure 9. Cyclization of a linear metal alkylidene chain end by backbiting.

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Once high-molecular-weight polymer is achieved, interchange reactions can occur when the chain end or backbone is still active toward condensation chemistry as with polyesters, polyamides, and polysulfides. This is true of internal double bonds in ADMET polymers and as with interchange reactions on condensation polymers, another pathway resulting in degenerate reactions without altering the average molecular weight. There is no change in average molecular weight, but interchange does, however, allow depolymerization with ethylene or random incorporation with other olefins.49, 50 For this reason, monomer purity is critical. Introduction of a monofunctional olefin will reduce the number-average molecular weight with varying effects based on conversion.

Limiting molecular weight or end capping the polymer chains may prove beneficial to processing. In fact, ADMET polymerizations are commonly quenched by addition of monofunctional ethyl vinyl ether dissolved in toluene, replacing a metal alkylidene active chain end with a well-defined terminal olefin CH2 group (Fig. 10) while also forming a stable Fischer carbene, which is fairly metathesis inactive.51, 52 This technique has been developed in preparing various copolymers and telechelic functional polymers as will be discussed with the evolution of ADMET.

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Figure 10. ADMET polymerization quenching.

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ADMET EVOLUTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

From the discovery of ADMET using the WCl6/EtAlCl2 catalyst system in the simplest and model cases, to the most recent advances using well-defined catalysts, many advances and application areas have seen success. Along with significant progress in catalysis in the past several years, significant utility has also been pursued. The most recent active areas from the past 5 years will be described including functional polyolefins and advanced applications.

Functional Polyolefins

ADMET remains a choice polymerization technique, generating a continuum of high-molecular-weight functional polymers, which may be hydrogenated to yield analogous polyethylene (PE) copolymers, except linear with exact functional group placement (Fig. 11). PE is commercially sought after for its cost effectiveness, production ease, and range of properties.53, 54 For these reasons, PE is produced in the greatest amounts by weight and simple manipulations of structure to improve the properties have been under investigation for the past several decades. Polymers unattainable by other techniques and exact models of commercially produced PEs by less controlled techniques have continued to be developed using ADMET polymerization.

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Figure 11. ADMET polymerization/hydrogenation route to linear precise polymers.

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Following pivotal work of early 2000,55–57 several alkyl-branched PEs have been synthesized and studied since 2005 showing further dramatic effects on thermal behavior and crystallinity.57–63 By choosing an appropriate monomer both the branch identity and frequency can systematically be changed.

With exact incorporation dependent on functional group, materials deviating from orthorhombic PE are obtained beginning with the simplest methyl group modeling ethylene–propylene copolymers.64 PE bearing a methyl group on every 15th and 21st carbon showed a lamellar morphology with the thickness greater than the distance between methyl groups, indicating an inclusion of the defect into the crystalline lattice. With more frequent introduction of methyl defects, these ethylene–propylene copolymer mimics are rendered amorphous although low-temperature annealing reveals melting endotherms as well.65

In a later study comparing methyl, geminal-methyl, and ethyl groups on every 21st carbon, alternate crystal structures were proposed in accommodating the feature into the crystal structure.58, 59 To further elucidate changes in morphology including crystal structure and defect fate (included or excluded from the crystal), a series of polymers were synthesized and exhaustively characterized (Fig. 12).66 Inclusion of the methyl and ethyl branch was proposed, and certainly, the progressive convergent decrease of melting temperatures and similar degree of crystallinity of larger alkyl groups supports this finding. There is a change in crystal structure when the size is increased beyond ethyl.

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Figure 12. Summary of (a) structure, (b) melting, and (c) crystallinity of an alkyl-branched precision PE series adapted from ref.66.

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Indeed, these results were confirmed in a TEM study comparing the lamella thickness and thickness distribution between a precise PE containing either an ethyl or a hexyl group on every 21st carbon.61 The 55-Å thickness of the ethyl-functional PE polymer corresponds to twice the length between ethyl branches with three branches, one of which is included in the lamella. The 25- to 26-Å thickness found for the hexyl-functional PE suggests that the lamella stem is composed of only one ethylene length between hexyl branches, and the hexyl branch excluded.

Significant progress has been accomplished in understanding these strictly alkyl functional, and similar effort has been undertaken in more functional PE polymers. As polar group incorporation into a hydrophobic backbone has shown to improve particular properties such as impact resistance and polymer adhesion, but also as chemical barriers, the catalyst developments underlying the ADMET polymerization chemistry here give rise to nearly limitless options with regard to drawing functional groups from the period table ranging from metals67–70 to halogens71–73 and various ether,74–78 ester,79–84 acid,85–87 and ionic88–90 functionality.

Advanced Applications

Drawing from the progress in highly functional polymers, using fundamental ADMET polymerization chemistry combined with various other emerging polymer developments, materials have been obtained in multiple areas including architectures of telechelic,91–94 block,80–83 crosslinked,95–97 and hyperbranched copolymers.98–101 Biological applications have also been pursued, and in addition, numerous contributions in liquid crystalline and conjugated materials have emerged with ADMET serving as the choice polymerization technique.

Using ADMET homopolymerizaiton and copolymerization, various architectures have been sought. Beyond copolymerization in synthesizing statistically random ADMET polymers, telechelic structures have been isolated by several methods including polymerizing a diolefin with a monofunctional olefin, depolymerizing an ADMET polymer, or optimizing synthetic steps (Fig. 13).91 In addition to varying molecular weight control, the resulting telechelic polymers were amorphous and precisely end-functional with 2-hydroxyl groups allowing for potential application as thermoplastic elastomers or hydrolysis and UV-resistant polyurethanes. Progress in this area has also been realized in polyesters80 and oligo(oxyethylene) carbosilanes.97

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Figure 13. A comparison of pathways to telechelic hydrocarbon diols adapted from ref.91.

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Replacing unreactive hydrocarbon with reactive silane functionality has allowed for crosslinking via chemical crosslinking and photocuring both forming thermosets.95 Crosslinking can of course be accomplished by increasing the monomer functionality from 2 to 3 by synthesizing trienes and polymerizing by using ADMET conditions98, 99, 101 or otherwise termed acyclic triene metathesis (ATMET),100 where combining trifunctional monomers with single olefins allowed for end group and molecular weight control. Further, hyperbranched pursuits have allowed for highly functional materials98, 99 while controlled self-assembly and crosslinking stabilization of nanoobjects has also been successful.102

With the same fundamental ADMET polymerization chemistry and considerations underlying the successes highlighted, biological advances have been developed. From the most recent years, advances have centered around obtaining suitable diene monomers from renewable resources including fatty acids,80–83 carbohydrates,103 amino acid dimers,104 and even bile acid105 while probing polymer interactions more typical to biological systems.102, 106, 107 Moving toward using the well-defined ADMET polymers in delivery applications108, 109 has also seen vast progress (Fig. 14).

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Figure 14. A comparison of polymer structures with variable polymer drug linkers adapted from ref.108.

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Multiple areas beyond those mentioned thus far include ADMET-derived liquid crystalline and conjugated systems.110 Most recently, main-chain ADMET liquid crystalline structures have been of interest in designing materials for electromechanical actuators111 and nonlinear optic in display technologies.112–114 Further research in display technologies has been accomplished in conjugated systems. Although in the minority of conjugated materials synthetic approaches, ADMET has proven a useful one.115–117 An abundance of specific experimental techniques have been optimized to produce the particular desired materials. Although bulk solution techniques were mentioned as the most desirable to preclude cyclization, the best techniques are those that achieve appropriate molecular weights and well-defined polymers. Often bulk techniques are not possible beyond the solid state, and instead solution techniques are used with conjugated monomers offering the advantage of a rigid backbone incapable of cyclization.118–121 However, solid-state ADMET polymerization has been successful in poly(phenylene vinylene) (PPV) synthesis.122 As PPV is one of the most widely studied conjugated polymers,123, 124 the synthesis has of PPV nanoparticles in aqueous emulsion has also been reported.125 Meanwhile, typical tandem ADMET-hydrogenolysis has been used in preparing polyfluorenes without a conjugated backbone.126 The more traditional bulk ADMET technique has seen utility in this area yet accompanied with formation of cyclic observed from ADMET of a flexible monomer while exploring σ–π conjugation through silyl bonds in divinyl silanes.127

OUTLOOK

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

Clearly, the ongoing success of the ADMET reaction has its roots in catalysis and optimizing particular reaction aspects. ADMET polymerization is easy to do once suitable monomers have been prepared as shown with the progress just from the past 5 years from fundamental structure–property studies to multiple advanced applications. Revisiting several commodity polymers with models has had a profound impact on studying structure–property relationships as was already mentioned. With complete primary polymer structure control comes several opportunities for tailoring polymers as models for more traditional PE and α-olefin copolymers and as novel structures that would be otherwise unattainable.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

We thank Paula Delgado for her cover artwork. We also thank the National Science Foundation, the Army Research Office, the International Max Planck Research School, and the Alexander von Humboldt Foundation for their support.

REFERENCES AND NOTES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information

Biographical Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information
Thumbnail image of

Kathleen Louise Opper

Kathleen Louise Opper was born in Massachusetts and grew up just across the border in New Lebanon, NY. After receiving the Rensselaer Medal, she moved to Troy, NY in 2001 to study biology at Rensselaer Polytechnic Institute (RPI). During her time there, she began undergraduate research under Professor Brian Benicewicz studying polymers applied to fuel cells and then added chemistry as a major. Upon graduating with her BS with a dual major in biology and chemistry in 2005, she began graduate studies in Polymer and Organic Chemistry later that year at the University of Florida under Professor Ken Wagener's guidance. In late 2008 she completed collaborative research at the Max Planck Institute for Polymer Research under the direction of Professor Dr. Klaus Müllen and Dr. Markus Klapper. Ending a successful graduate career she earned her Ph.D. in 2010 focused on fundamental structure-property-morphology polymer relationships and precision polyolefin organic synthesis. Now, a Research Investigator employed with DuPont, she resides in Wilmington, DE and has served as the 2011 ACS Delaware section chair.

Biographical Information

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. METATHESIS FEATURES AND EVOLUTION
  5. ADMET FEATURES
  6. ADMET EVOLUTION
  7. OUTLOOK
  8. Acknowledgements
  9. REFERENCES AND NOTES
  10. Biographical Information
  11. Biographical Information
Thumbnail image of

Ken Wagener

Ken Wagener is the George Bergen Butler Professor of Polymer Chemistry in the Department of Chemistry at the University of Florida. He also serves as the Director for the Center for Macromolecular Science & Engineering on campus. He completed his BS degree in Chemistry at Clemson University in 1968, followed by his Ph.D. in Organic/Polymer Chemistry with George Butler at the University of Florida in 1973. Ken's background includes 11 years as a research chemist, research department manager, and technical director with Akzo Nobel (at American Enka in Asheville, NC), followed by his return to academics in 1984. More than 115 undergraduates, MS and PhD students, postdoctorial associates, and visiting faculty have passed through his group since then. The research group is best known for its discovery and elucidation of the ADMET reaction, now using this chemistry to precisely control structure and morphology in a large number of polymers. Recent awards include the 2010 Herty Medal, the 2009 Max Planck Institute for Polymer Research Award, the 2008 University of Florida CLAS Teacher of the Year Award, and the 2007 Alexander von Humboldt Senior Research Prize.