Well-defined architecture

Over the past decade, copper-catalyzed atom transfer radical polymerization (ATRP) has had a tremendous impact on the synthesis of macromolecules with well-defined architectures, functionalities, and compositions. Structural and mechanistic... 

Such well-defined architectures could be useful for nanoscale applications in, for example, catalysis or as carrier materials for chemical transport. 

Telechelic (or a, co-difunctional) oligomers exhibit functional groups at both ends of the oligomeric backbone. These compounds are quite useful precursors for well defined architectured polymers (e.g. polycondensates, polyadducts and other fluoropolymers previously reviewed [400, 401]). As mentioned above, a... 

Fortunately, much work has still to be developed, and especially a better knowledge of the synthesis of tailor-made polymers with well-defined architecture in order to improve the properties by a better control of the regioselectivity and of the tacticity. Even if much work on the reactivity has been extensively carried out by Tedder and Walton, methods are searched for a better orientation of the sense of addition, since most fluoroalkenes are unsymmetrical. 

Asymmetric star polymers are megamolecules [1] emanating from a central core. In contrast to the symmetric stars very little was known, until recently, about the properties of the asymmetric stars. This was due to the difficulties associated with the synthesis of well-defined architectures of this class of polymeric materials. The synthesis, solution and bulk properties, experimental and theoretical, of the following categories of asymmetric stars will be considered in this review ... 

In controlled polymer synthesis, in addition, it is particularly important that the control herein implies not only the simple regulation of molecular weights, MWD, and other structural factors but also the precise introduction of functional groups into specific positions of polymers with well-defined architectures. Namely, the control of one or more of these structural factors, then, leads to a variety of polymers of synthetic interest, as some of them illustrated schematically in Fig. 2 ... 

And not only for organic synthesis the reversible addition fragmentation to the thiocarbonylthio motif found in xanthates, dithiocarbamates, dithioesters, trithiocarbonates etc., discussed in Scheme 2 for the particular case of xanthates, is now being actively exploited for the synthesis of bloc polymers. For a recent review, see [75] for the original patents on MADIX and RAFT, see [76,77]. The principle of this approach is summarised in Scheme 38 for the synthesis of a diblock polymer 66. The RAFT and MADIX processes, as they are now called, are set to revolutionise the crafting of polymers with well-defined architectures. It is an extremely effective technique that can be applied to essentially all commercial monomers and is tolerant of many functional groups. Scientific papers and patents on the subject now number in the hundreds. 

Figure 1.12 shows the timeline of discovery of various styrenic polymers and copolymers. It would be naive to suggest that the rate of invention and innovation will level off in this century. Rather, the pace of discovery of new styrenic polymers will probably increase. Advances in new catalyst technology and controlled radical polymerisation technology will undoubtedly yield new styrenic polymers with well-defined architecture, as we have recently seen with the introduction of syndiotactic PS and ethylene-styrene interpolymers. 

This picture (or more precisely the complete elaborate picture resting on the ideas presented here in a schematic way) points to the necessity to have a well-defined architecture on the surface, which constitutes a demand for the elaborate concerted mechanism in selective oxidation. 

A corresponding principle applies to controlled radical polymerisation performed in quite a number of modes such as nitroxide-mediated polymerisation (NMP), atom transfer radical polymerisation (ATRP), reversible addition fragmentation chain transfer (RAFT) or catalytic chain transfer (CCT) reactions. All of these variants of controlled radical polymerisation lead to well-defined architectures with the particular advantage that a much larger number of monomers are suitable and the reaction conditions are much less demanding than those of living ionic polymerisation reactions. 

Due to the availability of controlled polymerization routes for PFS monomers, well-defined architectures with organic and inorganic coblocks are available. The incorporation of PFS segments into self-organizing motifs, such as block copolymers, provides further possibilities for supramolecular chemistry and the development of functional nanomaterials.18-23 This section summarizes recent developments in the synthesis and self-assembly of PFS block copolymers, as well as their applications in material science. 

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],... 

The living nature of the nickel-catalyzed a-olefin polymerizations coupled with the propensity for chain straightening of longer a-olefins can be utilized to prepare block copolymers with well-defined architectures. For example, the synthesis of a-olefin A—B—A block copolymers where the semicrystalline A blocks are made up of poly(l-octadecene) and the B block is composed of a more highly branched, amorphous, random copolymer of propylene and 1-octadecene enabled the preparation of thermoplastic elastomeric polyolefins. ... 

In order to study the detailed behavior of LC block copolymers, it would be ideal to create monodispersed LC-BCP samples with well defined architecture for each block over a wide range of molecular weights. LC-BCP systems with narrow polydisper-sity should form well-ordered microdomain structures while LC-BCPs with broad molecular weight distributions would probably not. Synthesis of such materials still remains a challenge. 

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