Grafting reactions to polymers with double

Free-Radical Grafting Reactions to Polymers with Double Bonds... 

Discuss free-radical grafting reactions to polymers with double bonds. Give examples and show reactions. 

Transfer to polymer may occur by addition of the growing radical end to a double bond of the polymer chain, or it may occur by II atom abstraction from an active H atom of the chain. H atoms in the a position to a double bond (C=C or C=0) or an ether linkage are easily abstractable and thus lend themselves to polymer transfer reactions. The transfer reaction to polymer may be intramolecular or it may be intermolecular. Both have been demonstrated. In the case of intermolecular transfer the demonstration has been made of the productioTi of graft polymers. The method is to polymerize a monomer in the presence of inert polymer of a different composition. " The final product will contain the inert polymer with the new polymer grafted onto it. 

The mechanism proposed in Reaction 3—i.e., the generation of a polymeric carbonium ion by the reaction of Et2AlCl with PVC and the addition of the carbonium ion to a double bond in cts-1,4-polybutadiene —would appear to be applicable to the polymer-polymer grafting reaction. The monomer-polymer grafting reaction may involve polymerization of butadiene on the polymeric carbonium ion site or the reaction between polybutadiene generated in situ and the polymeric carbonium ion. 

Graft Copolymers. In graft copolymerization, a preformed polymer with residual double bonds or active hydrogens is either dispersed or dissolved in the monomer in the absence or presence of a solvent. On this backbone, the monomer is grafted in free-radical reaction. Impact polystyrene is made commercially in three steps first, solid polybutadiene rubber is cut and dispersed as small particles in styrene monomer. Secondly, bulk prepolymerization and thirdly, completion of the polymerization in either bulk or aqueous suspension is made. During the prepolymerization step, styrene starts to polymerize by itself forming droplets of polystyrene with phase separation. When equal phase volumes are attained, phase inversion occurs. The droplets of polystyrene become the continuous phase in which the rubber particles are dispersed. R. L. Kruse has determined the solubility parameter for the phase equilibrium. 

This was followed by casting a film, drying, and raising the temperature to induce crosslinking. For example, the urethane polymer was crosslinked thermally by reaction with triols, while the polyacrylate was essentially crosslinked through sulfur and double bonds by a free-radical process. In this manner, grafting reactions between the two polymers were minimized. 

Grafting a second polymer to the NR molecule in the latex stage is one of the many routes to chemically modified NR. An olefinic monomer with unsaturated double bonds such as methyl methacrylate (MMA), styrene and acrylonitrile are important monomers used for such grafting. " For example, MMA monomer is first converted into an emulsion with some suitable emulsifiers and then mixed with NR latex to copolymerize the monomer in a seeded emulsion polymerization process. It is important to ensure the seed latex particles are saturated with the monomer supplied through diffusion from the emulsified monomer droplets. An oil- or water-soluble initiator can be used to start the reaction. With proper control of the system and reaction conditions, the free radical reaction can be made to propagate within the latex particles as far as possible, so that only grafted NR occurs, without the formation of free homopolymer from the monomer. In this way only chemically modified NR... 

ESR can equally be used for detection of radicals in masticated rubber their identification in relation to the chemical structure might be approached with specific techniques such as electron nuclear double resonance (ENDOR). ESR studies also contribute to the understanding of the char forming process of various polymers [815], to the study of mechanical fracture, which produces free radicals, grafting reactions, etc. Pedulli et al. [816,817] have determined the bond dissociation enthalpies of a-tocopherol and other phenolic AOs by means of ESR. The determination of the O—H bond dissociation enthalpies of phenolic molecules is of considerable practical interest since this class of chemical compounds includes most of the synthetic and naturally occurring antioxidants which exert their action via an initial hydrogen transfer reaction whose rate constant depends on the strength of the O—H bond. 

Of all the polymerization methods, the anionic [2] and controlled radical polymerizations [3] give the best control over the chain length and produce polymers with the lowest polydispersities. In addition, polymers prepared through these routes bear a terminal function that can add to one of the double bonds (6-6 bonds) of Cgq respectively, a carbanion, a stabiUzed radical or a bond that can be converted into a radical. Furthermore, it is possible to take advantage of the specific shape and chemical reactivity of Qo to perfectly control the number of polymer chains grafted onto the fullerene using these two types of addition. This is why the mechanism of these two addition reactions will be discussed in more detail. 

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