Covalent polymer grafting

Polymer grafting can be used to alter chemical and physical properties of a homopolymer. For example, Sawhney and Hubbell [18] grafted polyethyleneoxide to poly L-lysine to enhance biocompatibility of polylysine and improve the polylysine-alginate capsules. Stevenson and Sefton [19] modified alginate by grafting it with hydroxyalkyl methacrylate, again to improve the biocompatibility and to allow for polymerization by means of y-irradiation. Covalently modified (co)-polymers have not been evaluated in this study. 

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. 

Fig. 5.8 Examples of polymers grafted from nanocarbons, (a) An ATRP initiator covalently attached to RGO via nitrene and carbodiimide chemistry was used for the growth of poly(2-(ethyl (phenyl)amino)ethyl-methacrylate). (b) A RAFT chain transfer agent is covalently attached to GO prior to polymerization of vinylcarbozole.

Polymer Grafting of Carbon Nanotubes by Con-trolled/Living Radical Polymerization Polymer grafting techniques that use direct covalent functionalization methods, such as radical reactions, have been developed in order to avoid the problems associated with the functionalization of CNTs using acids. These grafting techniques eliminate the need for nanotube pretreatment before the functionalization and allow attachment of polymer molecules to pristine tubes without altering their original structure. 

The presence of appropriate active functional groups such as carboxylic acids or amines on the CNT surface allows for further covalent functionalisation with polymer molecules (polymer grafting). Two main approaches for the covalent functionalisation of CNTs with polymers have been reported grafting from and grafting The main differences, advantages... 

More recently, the importance of introducing supramolecular interactions between macromolecular chains has become evident, and many new options have been introduced. The final step in this development would be to develop polymers based on reversible, noncovalent interactions. Rather than linking the monomers in the desired arrangement via a series of polymerization reactions, the monomers could be designed in such a way that they self-assemble autonomously into the desired stracture. As with covalent polymers, a variety of structures of these so-called supramolecular polymers are possible, with block-copolymers or graft copolymers - as well as polymer networks - being created in this way. 

The advantages of ceramic UF and MF membranes discussed earher in the chapter are often offset by their low selectivity, which makes their use economically unfeasible for many applications. These membranes separate solutes from solvents primarily by site exclusion, and to a lesser extent, by interactions with the membrane surface. The selectivity of ceramic membranes can be improved by modification of the membrane surface either by polymer grafting or graft polymerisation. The latter has the advantage of providing a covalently bonded brush layer of high surface coverage with minimal difiusional limitations and steric hindrance effects. 

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