Synthesis using ADMET chemistry

ADMET is quite possibly the most flexible transition-metal-catalyzed polymerization route known to date. With the introduction of new, functionality-tolerant robust catalysts, the primary limitation of this chemistry involves the synthesis and cost of the diene monomer that is used. ADMET gives the chemist a powerful tool for the synthesis of polymers not easily accessible via other means, and in this chapter, we designate the key elements of ADMET. We detail the synthetic techniques required to perform this reaction and discuss the wide range of properties observed from the variety of polymers that can be synthesized. For example, branched and functionalized polymers produced by this route provide excellent models (after quantitative hydrogenation) for the study of many large-volume commercial copolymers, and the synthesis of reactive carbosilane polymers provides a flexible route to solvent-resistant elastomers with variable properties. Telechelic oligomers can also be made which offer an excellent means for polymer modification or incorporation into block copolymers. All of these examples illustrate the versatility of ADMET. 

It became clear even in the initial report of ADMET that this reaction could have wide utility in the fabrication of unique structures [51, 52] indeed, virtually any compound that can be functionalized with two olefins could, potentially, become an ADMET monomer. Not surprisingly, early efforts in this area involved the synthesis of a wide variety of functionalized polymers using this chemistry. Consequently, as the metathesis catalysts became increasingly robust and tolerant of functional... 

The Synthesis of Polycarhosilanes. Silicon-based polycarbosilanes do not exist naturally. A number of synthetic methods have been used to prepare them, but only now can the synthesis of polycarbosilanes, via ADMET chemistry, be realized (72). Our initial work began with the monomers, dimethyldivinylsilane and diphenyldivinylsilane. The attempted condensation of these monomers in a typical ADMET scheme did not lead to the formation of polymer. The explanation for the nonreactivity of these monomers can be attributed to steric interactions which preclude the formation of the required metallacyclobutane as illustrated in the polymerization cycle shown in Figure 3. This observation has precedence considering Schrock s work with vinyltrimethylsilane as illustrated in Figure 7 (13). Here it becomes evident that the steric interaction required to form the metallacyclobutane is inhibited by the... 

Olefin metathesis has quickly become one of the most widely used methods for mild carbon-carbon bond formation in organic synthesis [1,2]. With the development of highly active, fimctional group-tolerant catalysts, like Grubbs second generation catalyst ([Ru] ), metathesis has been successfully applied across many areas of research, and some reviews already exist that deal with metathesis catalysis and applications [1-5]. This review focuses on recent developments in acycUc diene metathesis (ADMET) polymerization chemistry and methodology that have been published over the past five years, starting with a short discussion on the history of olefin metathesis and ADMET polymerization. 

More industrial polyethylene copolymers were modeled using the same method of ADMET polymerization followed by hydrogenation using catalyst residue. Copolymers of ethylene-styrene, ethylene-vinyl chloride, and ethylene-acrylate were prepared to examine the effect of incorporation of available vinyl monomer feed stocks into polyethylene [81]. Previously prepared ADMET model copolymers include ethylene-co-carbon monoxide, ethylene-co-carbon dioxide, and ethylene-co-vinyl alcohol [82,83]. In most cases,these copolymers are unattainable by traditional chain polymerization chemistry, but a recent report has revealed a highly active Ni catalyst that can successfully copolymerize ethylene with some functionalized monomers [84]. Although catalyst advances are proving more and more useful in novel polymer synthesis, poor structure control and reactivity ratio considerations are still problematic in chain polymerization chemistry. 

This chapter will cover both the synthesis and basic principles of modern, well-defined metal alkyhdenes related to their use in ROMP, ADMET-polymerization and alkyne metathesis polymerization. The term well-defined is limited to catalytic systems, usually metal alkyhdenes, that are characterized by a uniform and stoichiometric composition and for which the actual propagating species is well known and characterized. Consequently, the entire chemistry of standard binary or ternary systems such as WCl6/AlEt2Cl/ethanol has been neglected. Where ap-phcable, general aspects of the preparation of advanced materials via ROMP and alkyne-polymerization will be mentioned briefly. 

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