Grafting reactions to polymers with double bonds

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. 

When unsaturatcd polymers have hydrogen or halogen atoms in a-position to the double bonds, they are especially sensitive to chain transfer by a free radical attack. Therefore in these cases, the graft copolymerization may involve a combination of two initiation processes which occur simultaneously and compete with each other, one by chain transfer, the other by addition copolymerization. The relative importance of both processes is again dependent on the nature of the polymerizing monomer and of the backbone polymer involved in the reaction. 

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. 

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