Covalent polymer

Molecularly imprinted polymers (MIPs) can be prepared according to a number of approaches that are different in the way the template is linked to the functional monomer and subsequently to the polymeric binding sites (Fig. 6-1). Thus, the template can be linked and subsequently recognized by virtually any combination of cleavable covalent bonds, metal ion co-ordination or noncovalent bonds. The first example of molecular imprinting of organic network polymers introduced by Wulff was based on a covalent attachment strategy i.e. covalent monomer-template, covalent polymer-template [12]. 

Covalent polymer networks or (Class II) crosslinked macromolecular architecture polymers rank among the largest molecules known. Their molecular weight is given by the macroscopic size of the object for instance, a car tire made of vulcanized rubber or a crosslinked layer of protective coating can be considered one crosslinked molecule. Such networks are usually called macronetworks. On the other hand, micronetworks have dimensions of several nanometers to several micrometers (e.g. siloxane cages or microgels). 

An alternative approach for covalent polymer attachment is called the grafting from method. This method is based on binding the monomer precursor to the nanotube and generating chain growth directly from the tube. By these means, several types of polymers could be grafted, such as polystyrene-sulfonate [46], polyvinylpyri-dine [47], polystyrene [48] and many others. 

M. Fang, K. G. Wang, H. B. Lu, Y. L. Yang, S. Nutt, Covalent polymer functionalization of graphene nanosheets and mechanical properties of composites, Journal of Materials Chemestry, vol. 19, pp. 7098-7105, 2009. 

Figure 16. Crosslinking reactions in bisarylazide-rubber resists. The primary photoevent is production of a nitrene which then undergoes a variety of reactions that result in covalent, polymer-polymer linkages. A schematic representation of crosslinking via nitrene insertion to form aziridine linkages is shown together with several other reaction modes available to the...

This chapter will outline the synthesis of polymeric materials pursuing structural diversity and prepared by equilibrium reactions through DCLs. In particular, the dynamic covalent polymers will be focused upon because of their high stability and processability. In addition, advanced approaches to polymeric materials in DCC will be outlined. In this chapter, the authors will only discuss covalent polymers, excluding noncovalent polymers (supramo-lecular polymers) that can be found in References 7 and 8. 

Covalent polymers with reversible properties arising from dynamic covalent bonds such as disulfide exchange reaction [47 9], transesterification [50,51], transetherification [52], and boronate ester formation [53] were reported without respect to DCC. These studies should involve DCLs in... 

Scheme 8.13 Dynamic covalent polymers based on carbine dimerization, (a) Preparation of difnnctional carbene 58 and polymerization of 58 via carbene dimerization (b) Chain transfer reaction of 59 by the agency of monofnnctional carbene 60, and (c) Formation of the organometallic copolymer 62 by the insertion of PdCl [45],...

Skene, W. G. Lehn, J.-M. Dynamers Polyacylhydrazone reversible covalent polymers, component exchange, and constitutional diversity. Proc. Natl. Acad. Sci. U.S.A. 2004,101, 8270-8275. 

Ono, T. Nobori, T. Lehn, J.-M. Dynamic polymer blends Component recombination between neat dynamic covalent polymers at room temperature. Chem. Commun. 2005,1522-1524. 

Otsuka, H. Aotani, K. Higaki, Y. Takahara, A. A dynamic (reversible) covalent polymer Radical crossover behavior of TEMPO-containing poly(alkoxyamine ester)s. Chem. Commun. 2002, 2838-2839. 

Kamplain, J. Bielawski, C. W. Dynamic covalent polymers based upon carbene dimerization. Chem. Commun. 2006, 1727-1729. 

Note 3 An example of covalent polymer gels is nei-poly(A-isopropylacrylamide) swollen in water, which shows volume phase transition during heating. 

At the most basic level, mechanical properties are necessarily a matter of action and reaction, stimulus and response. The actor—a mechanical stress—is a familiar part of everyday life, but efforts to understand its molecular consequences are only recently coming to the fore in supramolecular chemistry. We next consider examples of how covalent polymers respond to a mechanical stress, and then we extend that examination to the case of SPs. This discussion is not intended to capture all of the details of a thermodynamically rigorous treatment but is instead focused on providing a useful conceptual framework for key concepts related to the mechanics of SPs. 

The overlaps between SPs in semidilute concentrations can be thought of in very similar terms to the entanglements defined above. Supramolecular interactions create large stmctures that physically interact to determine the mechanical response (in this case, viscous flow). The primary relaxation is the diffusion of an SP that is effectively intact on the timescale of the diffusion process. Thus, at a fixed concentration, the SP properties in dilute solution are therefore quite similar to those of covalent polymers of the same molecular weight and molecular weight distribution. 

Thibault RJ, Hotchkiss PJ, Gray M, Rotello VM. Thermally reversible formation of micro-spheres through non-covalent polymer cross-linking. J Am Chem Soc 2003 125 11249-11252. 

Wilson AJ. Non-covalent polymer assembly using arrays of hydrogen-bonds. Soft Mater 2007 3 409-425. 

Such facets of dynamic metal-ligand binding offer a range of tunable properties in MSPs. We now discuss a selection of examples that reveals how these systems differ from typical covalent polymers and small molecule metal complexes yet combine the properties of both to form a new class of materials. 

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