Synthesis of Polymers with Complex Architectures

Several other research works on the synthesis of bottlebrush polymers and copolymers have also been reported [127-134], including dendronized 

The synthesis of block copolymers via ROMP of conventional monomers has been the focus in the last 10 years. This has included making block copolymers via sequential polymerization of different ROMP monomers as well as those made from a combination of ROMP with other polymerization techniques [74, 141] A metathesis approach has been reported involving ROMP combined with the polymerization of 1,6-heptadiynes by molybdenum or ruthenium initiators [142,143], or with monomers allowing enyne metathesis polymerization [144]. Choi et al. [145] prepared block copolymers of NBE derivatives with a 6-heptadiyne derivative leading to an in situ crosslinking of the conjugated segment and in turn to nanoparticle formation. Moreover, a combination of ROMP and insertion polymerization of ethylene has also been reported [146]. 

Trimmel et al. prepared a series of amphiphilic block copolymers with different lengths of apolar and polar segments, and studied the micellization of these block copolymers in alcohol. The size of the micelles, as well as those of the core and shell could be nicely tuned [147]. In a follow-up paper, they studied the self-assembly of the block copolymers in the solid state and demonstrated how the composition polymers translates into different solid-state structures [148]. The approach was used to seU-assemble platinum dyes on the nanoscale [149]. Although the syntheses of most block copolymers have been successfully accomplished, some restrictions have also been reported [89]. Particularly, monomers with the ability to strongly interact with the initiator have been shown to cause problems, which could be circumvented by polymerizing them as the second monomer [150, 23]. 

Grubbs et al. [151] reported a pulsed-addition protocol involving the use of a chain transfer agent, for example, a symmetrical internal cis-olefin, for terminating the ROMP and regenerating the initiator for further homo or block copolymer preparation runs. 

The ruthenium initiators have also been used to conduct hydrogenations after the polymerization process. Polymers obtained from G1 or G3 have been shown to be readily hydrogenated upon addition of a base and hydrogen gas. This resulted in the decomposition of initiators and the formation of products acting as hydrogenation catalysts [152-155]. 

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Active species of CROP of THF are long-living, which makes possible their quantitative conversion to a variety of functional polymers that may be used for synthesis of polymers with complex architectures, such as star polymers or block copolymers. 

Reversible addition-fragmentation chain transfer (RAFT) polymerization has proven to be a powerful tool for the synthesis of polymers with predetermined molecular weight and low polydispersity [11, 12], In recent years, synthesis of polymers with complex molecular architecture, e.g. block and star copolymers, via the RAFT process have been reported [13],... 

Dr. Alain Deffieux, bom in Liboume, France, did his PhD in polymer science in the group of Pierre Sigwalt at the Univereity Pierre and Marie Curie, Paris VI, and then spent 2 years as associate researcher in the laboratory of professor Vivian Stannett at North Carolina University. He joined the Centre National de la Recherche Sdentifique (CNRS) in 1974 at Paris VI University and then moved to Bordeaux University in 1986 in the newly created Laboratoire de Chimie des Polymd s Organiques where he became a Research Professor. His research activities are focused on precision polymer synthesis, from studying the mechanisms of elementary reaction processes and reactivity control to the design and characterization of polymers with complex chain architecture. 

Chemoenzymatic polymerizations have the potential to further increase macro-molecular complexity by overcoming these limitations. Their combination with other polymerization techniques can give access to such structures. Depending on the mutual compatibility, multistep reactions as well as cascade reactions have been reported for the synthesis of polymer architectures and will be reviewed in the first part of this article. A unique feature of enzymes is their selectivity, such as regio-, chemo-, and in particular enantioselectivity. This offers oppormnities to synthesize novel chiral polymers and polymer architectures when combined with chemical catalysis. This will be discussed in the second part of this article. Generally, we will focus on the developments of the last 5-8 years. Unless otherwise noted, the term enzyme or lipase in this chapter refers to Candida antarctica Lipase B (CALB) or Novozym 435 (CALB immobilized on macroporous resin). 

This paper has provided, we believe, a comprehensive, up-to-date, critical, and objective review on the discovery and the subsequent fast development of living radical polymerizations catalyzed by transition-metal complexes in the period from 1994 to early 2001. These metal-catalyzed living radical polymerizations have rapidly been developing since their discovery in 1994, and the scope of applicable monomers, metal catalysts, and initiators has been expanding. Their advantages include versatility toward a variety of monomers, feasibility in a wide range of reaction conditions, and relatively easy access to the materials. This permits many researchers to use the systems for the precision synthesis of various polymers with controlled architectures. 

Anionic polymerization has proven to be a very powerful tool for the synthesis of well-defined macromolecules with complex architectures. Although, until now, only a relatively limited number of such structures with two or thee different components (star block, miktoarm star, graft, a,to-branched, cyclic, hyperbranched, etc. (co)polymers) have been synthesized, the potential of anionic polymerization is unlimited. Fantasy, nature, and other disciplines (i.e., polymer physics, materials science, molecular biology) will direct polymer chemists to novel structures, which will help polymer science to achieve its ultimate goal to design and synthesize polymeric materials with predetermined properties. 

The synthesis of polyelectrolytes with well-defined architectures, however, has imposed many challenges to the polymer chemists. Many polymerization techniques are not tolerable to the ionic functional groups. In most cases, preparation of polyelectrolytes involves the protection and deprotection of the ionic groups in the monomer. For polyelectrolytes with different architectures, various synthetic strategies are required. Recently, we have synthesized various complex architectures containing polyelectrolytes with different nonlinear topologies, such as combshaped [22], hyperbranched [23-25], Janus-type [26], stars [27, 28] and brushes [29-31],... 

While not related exclusively to block copolymer synthesis, the formation of many of the more complex architectures available through RAFT polymerization - including those based on a single monomer - shares the characteristics and caveats of linear block copolymer formation. One technique to obtain such structures (aldn to the triblock synthesis mentioned above) is the use of higher-level, multifunctional RAFT agents. A synthetic approach with a multifunctional core or a RAFT agent-functionalized polymer backbone allows... 

Past and recent polymerization procedures, their combinations, and the contribution of click chemistry serve as powerful tools for the synthesis of novel well-defined star polymers with different architectures and chemistry. The study of these polymers, the simplest branched stmctures, in bulk or solution, has broadened our knowledge/understanding of the properties and behavior of more complex stmctures. Hopefully the commercialized applications of star polymers will be expanded in the future as the fruits of the intense research on these materials. 

Since Yokozawa and coworkers published in 2007 the first example of chain-growth Suzuki-Miyaura polymerization for the synthesis of poly(9,9-dioctyl-2,7-fluorene) using PhPd[P Bu3]Br as an initiator [90], different methods have been developed for synthesizing Jt-conjugated polymers with specific architectures. IPr-Pd-PEPPSI complex was found to mediate hving, chain-growth homo- and... 

Further progress in the field of IPECs has been associated with involvement of more complex polyionic architectures, such as branched ionic (co)polymers (polyelectrolyte stars and cylindrical polyelectrolyte brushes) as well as self-assemblies of linear ionic diblock copolymers (polymeric micelles) (Fig. 6a-c), into interpolyelectrolyte complexation. Synthesis of well-defined polymeric architectures with nonlinear topology has become possible only recently due to considerable developments in living and controlled polymerizations. In this section, we briefly... 

Nikos Hadjichristidis has dedicated his career primarily to the synthesis of model polymers with complex macromolecular architectures and has published more than 370 papers and 23 reviews in refereed scientific journals, 6 patents, two books (as editor), and is the author of Block Copolymers Synthetic Strategies, Physical Properties, and Applications (2003). 

The development of PPE synthetic chemistry makes the synthesis of PPEs with various structures possible. Recently, PPE-based polymers with different topological structures including linear random copolymers, block copolymers, star polymers, miktoarm polymers, and brush and hyperbranched polymers have been synthesized. Among them, linear homopolymers or random copolymers of PPEs are perhaps the most studied. Different block copolymers with AB, ABA, and ABC architectures have been synthesized by controlled ROP. By the combination of ROP of PPE with other controlled polymerization methods, such as living radical polymerization, or click chemistry, more complex architectures including miktoarm, comb, or graft copolymers can be synthesized. The richness of structures has allowed the convenient adjustment of material properties of PPE for biomedical applications. 

The design and synthesis of supramolecular architectures with parallel control over shape and dimensions is a challenging task in current organic chemistry [13, 14], The information stored at a molecular level plays a key role in the process of self-assembly. Recent examples of nanoscopic supramolecular complexes from outside the dendrimer held include hydrogen-bonded rosettes [15,16], polymers [17], sandwiches [18, 19] and other complexes [20-22], helicates [23], grids [24], mushrooms [25], capsules [26] and spheres [27]. 

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