Graft copolymerization conventional method

Radiation-induced modification or processing of a polymer is a relatively sophisticated method than conventional thermal and chemical processes. The radiation-induced changes in polymer materials such as plastics or elastomers provide some desirable combinations of physical and chemical properties in the end product. Radiation can be applied to various industrial processes involving polymerization, cross-linking, graft copolymerization, curing of paints and coatings, etc. 

A number of methods have been used to prepare graft copolymers in the past few decades including both conventional chemical and radiation-chemical methods [20,86,87]. In the latter case, graft copolymerization is usually initiated by creating active radical sites on existing polymer chains. The advantages of radiation-chemical methods are (i) ease of preparation as compared to... 

Conventional copolymerizations yield macromolecules mostly with random distribution and only very seldom with alternating distribution of the monomer units. In order to synthesize block or graft polymers, special methods must be used, of which some are described in the following sections. 

Microwave-assisted synthesis of a guar-g-polyactylamide (G-g-PAA) has also been reported [80]. The reactions were performed in a domestic microwave oven. Graft copolymerization of the guar gum (GG) with acrylamide (AA) under the action of microwave irradiation in the absence of any radical initiators and catalyst resulted in grafting yields comparable with redox (potassium persulfate-ascorbic acid) initiated by conventional heating but in a very short reaction time. Grafting efficiency up to 20% was further increased when initiators and catalyst were used under microwave irradiation conditions. Maximum grafting efficiency achieved under MW conditions was 66.66% in 0.22 min, compared with 49.12% in 90 min by the conventional method. 

The most widely used method for chemical initiation for graft copolymerization on polysaccharides has been with ceric salts such as CAN or ceric ammonium sulfate. Free radical sites are generated on a polymeric backbone by direct oxidation through ceric metal ions (e.g., Ce "). The ceric ion with low oxidation potential is the proper choice for the reaction. The proposed mechanism for such processes has been depicted by an intermediate formation of metal ion polymer complex (chelate type) [17, 21-24]. Such a complex formation is not restricted to all polymers. The plausible mechanism for ceric ion induced graft copolymerization by direct oxidation method is shown in Scheme 3.1. A series of four grades of Ag-g-PAM copolymers have been synthesized by the conventional method. 

The first attempts to produce a graft copolymer of poly(amino acids) onto the natural polymers, such as cellulose, starch, and their derivatives, were carried out by Zilka and Avny in 1965. Sodium methoxide was known to be an initiator of NCA polymerization. Therefore, they proposed to use alkoxide derivatives of polysaccharides as macroinitiators for the graft copolymerization of NCA s of a-amino acids. All known methods for production of alkoxide derivatives of natural polymers, such as the reaction of polyhydroxy polymers with sodium metal in liquid ammonia, or exchange reactions between lower alkoxides and polyhydroxy polymers, - were unsatisfactory for the subsequent graft copolymerization of NCAs, because any residual base would lead to homopolymerization. In addition, alkoxide derivatives of cellulose acetate and nitrocellulose could not be obtained by these conventional methods due to chemical degradation. Zilka et al., finally found that the reaction of alkali metal naphthalenes [20] with polyhydroxy polymers in either... 

Thus the use amphiphilic macromonomers is another method to achieve the particle formation and their subsequent stabilization. Macromonomers can be pre-reacted to form graft copolymers, which are be introduced into the reaction medium afterwards. Macromonomers can also be copolymerized with classical monomers in situ to form graft copolymers. This is a simple and flexible method for producing monodisperse micron-sized polymer particles. Macromonomers can produce ion-free acrylic lattices with superior stability and film forming properties compared to conventional charge stabilized lattices. These non-con-... 

The composition distribution of the graft copolymers obtained by the macromonomer method has been shown theoretically to be statistically broader than in the corresponding conventional linear copolymer, due to the high MW of the macromonomer branches [45, 46]. This has been experimentally confirmed by Teramachi et al. with PSt macromonomers, 23 or 24, copolymerized with MMA [47-49]. The chemical composition distribution was found to broad-... 

Grafting through , involving the copolymerization of macromonomers (made either from other living methods or from conventional radical methods using other small monomers)... 

Synthesis of graft copolymers resembles that of block copolymers with an increased number of reactive sites per macromolecule. There are two techniques similar to those used in block copolymer preparation, namely grafting from and grafting onto preformed chains. Another method, grafting through, is similar to that used in conventional random copolymerization, where in-chain units function as comonomers. 

When specific functionalities are desired, copolymerization or grafting reactions are common ways to add functionalities to polystyrenes. Other techniques used to chemically modify polystyrenes are grafting reactions, ionic polymerization, alkylation, amination, condensation reactions and ctosdinking reactions. Copolymerization sometimes involves the laborious synthesis of functionalized styrene molecules through conventional oiganic synthetic methods. In future years it will be difficult and expensive for companies to introduce new monomers due to tougher n ulations. 

Graft copolymers containing styrene in the main chain and other monomers in their side chains are available by numerous methods, including conventional radical [171], controlled radical, anionic [174], and cationic [175] polymerization and by copolymerization of macromonomers [80,174], Grafting methods via conventional radical polymerization are reviewed by Nuyken and Weidner [171], The following reaction scheme demonstrates the principles and universality of the methods applying polymeric initiators ... 

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