Grafting process

When 4-(mercaptoacetamido)diphenylamine [60766-26-9] (39) is added to EPDM mbber and mixed in a torque rheometer for 15 minutes at 150°C, 87% of it chemically binds to the elastomer (24). The mechanical and thermal stress placed on the polymer during mixing mptures the polymer chain, producing radicals that initiate the grafting process. 

A novel type of grafting process was developed using a new photosensitive polymer containing vanadium (V) chelates. These polymers were generally synthesized by the condensation of a VOQ2OH complex and a hydroxy-containing polymer to produce photoactive polymer (red in color) with pendant vanadium (V) chelate. 

Ionizing radiation is unselective and has its effect on the monomer, the polymer, the solvent, and any other substances present in the system. The radiation sensitivity of a substrate is measured in terms of its G value or free radical yield G(R). Since radiation-induced grafting proceeds by generation of free radicals on the polymer as well as on the monomer, the highest graft yield is obtained when the free radical yield for the polymer is much greater than that for the monomer. Hence, the free radical yield plays an important role in grafting process [85]. 

Grafting presents a means of modifying the cellulose molecule through the creation of branches of synthetic polymers, which impart to the cellulose certain desirable properties without destroying the properties of cellulose. The polymerization of vinyl monomers may be initiated by free radicals or by certain ions. Depending on the monomer, one or the other type of initiation may be preferred. The grafting process depends on the reactivity of the monomer used, the type of initiation, and cellulose accessibility [1,2]. 

This technique is based in the fact that when cellulose is oxidized by ceric salts such as ceric ammonium nitrate Ce(NH4)2(N03)6 free radicals capable of initiating vinyl polymerization are formed on the cellulose. However, the possibility remains that the radical formed is an oxygen radical or that the radical is formed on the C-2 or C-3 instead of the C-6 carbon atom. Another mechanism, proposed by Livshits and coworkers [13], involves the oxidation of the glycolic portion of the an-hydroglucose unit. Several workers [14,15], however, have found evidence for the formation of some homopolymer. In the ceric ion method free radicals are first generated and are then capable of initiating the grafting process [16-18]. 

Cotton linters and viscose grade wood pulp were grafted with acrylamide using the xanthate method. The effects of monomer concentration, reaction time, hydrogen peroxide concentration, reaction temperature, and liquor ratio on the grafting process were studied. Optimum conditions for the grafting reaction were established [26]. 

The effect of the reaction temperature on the grafting process is discussed. Upon increasing the reaction temperature from 15°C to 40°C the grafting decreases from 30.7% to 29.1% and from 30.0% to 28.5% for cotton linters and viscose wood pulp, respectively. This can be... 

KMn04 and different parameters affecting the grafting process, e.g., reaction temperature, reaction time, and monomer concentration, were investigated to ascertain the optimum conditions of the grafting process [23]. 

Graft copolymerization of methylmethacrylate onto paper wood pulp using ceric ammonium nitrate as the initiator has been studied. Different experimental conditions have been used, including both water and water-organic solvent systems. The effects of composition of the grafting medium and grafting temperature on the grafting process are examined. 

A mixture of methanol and butanol or isobutanol in water with a ratio of 4 4 22 in the grafting process produces a higher graft yield than a mixture of butanol or isobutanol in water with a ratio of 8 22. 

Since Ce4+ salts are capable of causing the homopolymerization of vinyl monomers starting after a certain induction period, the grafting process is carried out during a time period shorter than the period of induction so as to synthesize graft PAN copolymers without any homopolymer being formed68). 

Grafting from methods involve creation of metalated sites on a polymer backbone, and subsequent use of these sites to initiate the polymerization of a second monomer. Several examples of such grafting processes have been described 135 ,39>. However, no control of the number and length of the grafts is provided, since some sites may be inaccessible to the incoming monomer. As no accurate characterization... 

The first step of the grafting process is probably the physisorption of Bu4Sn on the surface of the support (higher surface area), which then migrates from the support to the metal surface. Then, when the physisorbed complex interacts with the surface Pt atoms covered by hydrogen atoms (Pts-H ), there is... 

A polymeric composition for reducing fluid loss in drilling muds and well cement compositions is obtained by the free radical-initiated polymerization of a water-soluble vinyl monomer in an aqueous suspension of lignin, modified lignins, lignite, brown coal, and modified brown coal [705,1847]. The vinyl monomers can be methacrylic acid, methacrylamide, hydroxyethyl acrylate, hydroxypropyl acrylate, vinylacetate, methyl vinyl ether, ethyl vinyl ether, N-methylmethacrylamide, N,N-dimethylmethacrylamide, vinyl sulfonate, and additional AMPS. In this process a grafting process to the coals by chain transfer may occur. 

Define grafting. How is free radical attack employed during a grafting process ... 

Solid-state NMR studies have provided important information on the grafting process and the mobility of anchored metal complexes in this respect, reference is made to investigations by the groups of Fyfe [76], Bliimel [77], Lindner [78], and others [79]. 

Grafting from method, 7 652-653 Grafting onto method, 7 654 Grafting process, 73 537 Grafting through method, 7 653 Graft polymerization. See also Graft copolymerization ABS, 7 419, 421 acrylic ester monomers, 7 386 of methacrylic ester polymers, 76 289-290... 

In Tables III and IV, the effect of urea on grafting initiated by ionising radiation was reported. Anologous results are obtained with the corresponding UV system (Table XII). The other important observation in Table XII involves the use of two commercial additives in the grafting process. These materials are used in... 

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