Polymer grafting chemical modification

Radiation-induced graffing is a method widely investigated for the preparation of AEMs. Nevertheless, the success of these membranes is limited. When radiation-induced grafting is practiced at a large scale, the amount of electrical power required for production is on the one hand very expensive and, on the other, physically impracticable. The introduction of cationic moieties into a polymer by chemical modification is widely investigated. Membranes based on styrene, polyfether imide), or polysulfone suffer from the problem that their preparation makes use of... 

Biodegradable polymers and plastics are readily divided into three broad classifications (/) natural, (2) synthetic, and (J) modified natural. These classes may be further subdivided for ease of discussion, as follows (/) natural polymers (2) synthetic polymers may have carbon chain backbones or heteroatom chain backbones and (J) modified natural may be blends and grafts or involve chemical modifications, oxidation, esterification, etc. 

Modification of the membranes affects the properties. Cross-linking improves mechanical properties and chemical resistivity. Fixed-charge membranes are formed by incorporating polyelectrolytes into polymer solution and cross-linking after the membrane is precipitated (6), or by substituting ionic species onto the polymer chain (eg, sulfonation). Polymer grafting alters surface properties (7). Enzymes are added to react with permeable species (8—11) and reduce fouling (12,13). 

Grafting reactions alter the physical and mechanical properties of the polymer used as a substrate. Grafting differs from normal chemical modification (e.g., functionalization of polymers) in the possibility of tailoring material properties to a specific end use. For example, cellulose derivatization improves various properties of the original cellulose, but these derivatives cannot compete with many of the petrochemically derived synthetic polymers. Thus, in order to provide a better market position for cellulose derivatives, there is little doubt that further chemical modification is required. Accordingly, grafting of vinyl monomers onto cellulose or cellulose derivatives may improve the intrinsic properties of these polymers. 

An effective method of NVF chemical modification is graft copolymerization [34,35]. This reaction is initiated by free radicals of the cellulose molecule. The cellulose is treated with an aqueous solution with selected ions and is exposed to a high-energy radiation. Then, the cellulose molecule cracks and radicals are formed. Afterwards, the radical sites of the cellulose are treated with a suitable solution (compatible with the polymer matrix), for example vinyl monomer [35] acrylonitrile [34], methyl methacrylate [47], polystyrene [41]. The resulting copolymer possesses properties characteristic of both fibrous cellulose and grafted polymer. 

The chemical modification techniques refer to the treatments used to modify the chemical compositions of polymer surfaces. Those can also be divided into two categories modification by direct chemical reaction with a given solution (wet treatment) and modification by covalent bonding of suitable macromolecular chains to the polymer surface (grafting). Among these techniques, surface grafting has been widely used to modify the surface of PDMS. 

The objective of recent DSM studies was to develop new EPM-based elastomers that have improved oil resistance. The idea was to develop such products by chemical modification of EPM copolymers using highly polar graft monomers, such as maleic anhydride (MA), and, optionally, by reacting these EPM-g-MA polymers with other chemicals as a way to (cross-Unk and) further enhance the polarity of the products. It is expected that the enhanced polarity will eventually lead to improved oil resistance of the final (cross-Unked) products, ft is noted that the EPM copolymers with extremely high MA graft levels as employed in this study are not commercially available. 

The in situ bulk polymerization of vinyl monomers in PET and the graft polymerization of vinyl monomers to PET are potential useful tools for the chemical modification of this polymer. The distinction between in situ polymerization and graft polymerization is a relatively minor one, and from a practical point of view may be of no significance. In graft polymerization, the newly formed polymer is covalently bonded to a site on the host polymer (PET), while the in situ bulk polymerization of a vinyl monomer results in a polymer that is physically entraped in the PET. The vinyl polymerization in the PET is usually carried out in the presence of the swelling solvent, thereby maintaining the swollen PET structure during polymerization. The swollen structure allows the monomer to diffuse in sufficient quantities to react at the active centers that have been produced by chemical initiation (with AIBM) before termination takes place. 

Chemical modification with a bifunctional reagent Polymer grafting, self-bonding, stability to weathering... 

Hill, C.A.S., etin, N.S., Quinney, R.F., Derbyshire, H. and Ewen, R.J. (2001). An investigation of the potential for chemical modification and subsequent polymeric grafting as a means of protecting wood against photodegradation. Polymer Degradation and Stability, 72(1), 133-139. 

This book contains papers presented at the symposium on Polymer Modification held at the National American Chemical Society Meeting in Orlando, Florida, August, 1996. The chemistry presented is broad ranging, and includes grafting and chemical oxidation reactions, and many other chemical modifications. 

The chemical modification of polymers with a view to confer them new properties presents a great interest. In this area, the activation of natural or synthetic polymers by ozone followed in a second step by grafting of monomers or reactive molecules in radical medium constitutes a field of important developments, mainly in terms of patents. We will give here the main outlines. 

Hydrosilylation is also a very useful chemical modification which leads to silane modified polymers with special properties [60-62]. Silane modified polymers have improved adhesion to fillers and better heat resistance. It also acts as a reactive substrate for grafting or moisture catalysed room temperature vulcanisation. Guo and co-workers [61] carried out catalytic hydrosilylation of BR using RhCl(PPh3)3 as the catalyst. Hydrosilylation reactions followed anti-Markovnikov rule as shown in the Scheme 4.4. 

Photochemical and photophysical processes in cellulose and related compounds have received considerable attention during the last decades, resulting in research work concerned with the improvement of cellulosic materials via physical and chemical modifications. One method was to apply a copolymer between the cellulose and a synthetic polymer which are generally grafted by free radical reactions. 

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