ADMET functional group tolerance

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. 

Recent developments in ADMET polymerization and its use in materials preparation have been presented. Due to the mild nature of the polymerization and the ease of monomer synthesis, ADMET polymers have been incorporated into various materials and functionaUzed hydrocarbon polymers. Modeling industrial polymers has proven successful, and continues to be appUed in order to study polyethylene structure-property relationships. Ethylene copolymers have also been modeled with a wide range of comonomer contents and absolutely no branching. Increased metathesis catalyst activity and functional group tolerance has allowed polymer chemists to incorporate amino acids, peptides, and various chiral materials into metathesis polymers. Sihcon incorporation into hydrocarbon-based polymers has been achieved, and work continues toward the application of latent reactive ADMET polymers in low-temperature resistant coatings. 

Olefin metathesis has been extensively written on in both books and journals [1-10]. This chapter will focus on ADMET. Of particular interest are the issues of catalysis, mainly functional group tolerance, kinetics, and mechanistic details. The development of late-transition metal catalysts has enormously expanded the scope of ADMET, so particular attention will be given to the well-defined ruthenium-based olefin metathesis catalysts. Pertinent information pertaining to catalysts of Group VI metals will also be provided. Important procedural aspects of ADMET will be presented in conclusion. 

In conclusion, the expanded scope of ADMET is largely due to the development of well-defined late-transition metal catalysts that are functional group-tolerant and easy to handle and synthesize. The potential for ADMET is very great, in that it is a mild method of forming useful linear condensation polymers and copolymers. The apphcation of ADMET in modeling polyolefins and other polymers is just being discovered, and this aspect of ADMET is expected to further the understanding of these enormously important polymers. 

In this case, ADMET was chosen based on the mild reaction conditions involved and the functional group tolerance of the ruthenium metathesis catalyst. The results of this study highlighted the use of the many forms of olefin metathesis in the fabrication of complex structures that previously were synthetically unobtainable. 

ADMET has been used to polymerize an incredible variety of functionalized dienes. With the advent of the more functional-group-tolerant Grubbs catalysts, monomers containing electron-rich functional groups could be utilized. While... 

Monomers derived from 10-undecenoic acid with amide functional groups have been polymerized via ADMET as well [133]. However, the low tolerance of... 

ADMET offers a synthetic route to strictly linear, fimctionalized polyethyl-enes through the polymerization of a,co-dienes followed by exhaustive hydrogenation. Researchers have been able to use metathesis catalysts in conjimction with the functionalized monomers to produce statistical or sequenced copolymers of ethylene with various polar monomers. With the improved tolerance and reactivity of [ Ru], the broadening of ADMET methodology will allow the syntheses of numerous functionalized systems [4]. However, due to the well known olefin isomerization that occurs during the metathesis polymerization with [Ru], monomer sequence control is lost and the methylene run length between functional groups varies widely. 

ADMET polymerization of dienes containing functional groups has been explored to some extent. It appears that diene ethers such as 36 are tolerant of Schrock s W-alkylidene catalysts when undergoing ADMET polymerization, but Grubbs first-generation catalyst is required to successfully polymerize diene alcohol 37,61 because the OH group is too Lewis basic for catalysis by W- and Mo-alkylidenes.62... 

Complex 2 is still regarded as the best catalyst for the polymerization of hydrocarbon ADMET monomers and monomers containing oflier tolerated functional groups, if the monomers can be rendered rigorously dry and oxygen-free. The ac-... 

Schrock catalysts 22 are highly active, effective catalysts, not only for ROMP and ADMET, but also other useful types of olefin-metathesis reactions. However, due to their relatively high electrophilicity, they do not tolerate polar functions well. Nonetheless, they have been effectively employed in complex organic synthetic applications, and have been modified to effect enantioselective reactions with high selectivity. Ruthenium-based Grubbs catalysts were developed to increase the range of functional groups in which metathesis could be performed. 

This has been referred to as the negative neighboring group effecf and has been proposed to be responsible for the slower kinetics of ADMET of ether dienes compared to hydrocarbon dienes [35]. Three carbons between the olefin and a carbon bearing coordinating functionahty are usually sufficient to allow polymerization, although there are exceptions to this trend [33]. Intense catalyst development efforts are producing catalysts that are more and more tolerant to functionality closer to the olefin. 

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