Macroradicals generation

The mechanical degradation and production of macroradicals can also be performed by mastication of polymers brought into a rubbery state by admixture with monomer several monomer-polymer systems were examined (10, 11). This technique was for instance studied for the cold mastication of natural rubber or butadiene copolymers in the presence of a vinyl monomer (13, 31, 52). The polymerization of methyl methacrylate or styrene during the mastication of natural rubber has yielded copolymers which remain soluble up to complete polymerization vinyl acetate, which could not produce graft copolymers by the chain transfer technique, failed also in this mastication procedure. Block and graft copolymers were also prepared by cross-addition of the macroradicals generated by the cold milling and mastication of mixtures of various elastomers and polymers, such as natural rubber/polymethyl methacrylate (74), natural rubber/butadiene-styrene rubbers (76) and even phenol-formaldehyde resin/nitrile rubber (125). 

Our investigations suggest that grafted copolymers are obtained probably by the recombination reactions of the macroradicals generated both on the cellulosic support and on the nitrogen and phosphorus containing polymers. 

The improved activity of the above polymeric photoinitiators has been explained [108] assuming that macroradicals generated by photofragmentation... 

Preparation of telechelic polymers by ATRCC was also demonstrated. The concept is based on the activation of the dormant species at the chain ends of polystyrene (PS-Br) prepared by ATRP and also functional ATRP initiator (F-R-Br) in the absence of a monomer. Depending on the number of functionality of the polymer used in the system, ATRCC yields co-polystyrene and a,co-polystyrene telechelics. However, at least in principle, not only the desired functional polymers but also various side products may be formed due to the self coupling reactions of macroradicals generated from PS-Br, and low-molecular weight radicals from F-R-Br. The possible reactions of the model system are depicted in Scheme 3. 

Macromolecular dispersion in HDPE with patch—like transfer is defined by polymer—metal and polymer—polymer adhesive interactions. The major contribution to macromolecular dispersion is from the alternating areas of polymer—polymer and metal-polymer contacts. Macroradicals generated within polymer—polymer contact may recombine on the metallic surface to form chemisorption and coordination complexes with an oxide film. Under the dynamic contact this process may increase the effect of mechanical actions on the macromolecular dispersion of polyolefine. 

The reaction mechanism in this case is shown in Scheme 7.12. It is based on the fact that allyl-type hydrogens are readily abstracted by reactive radicals such as ketyl species. Side-chain macroradicals generated in this way combine to form intermolecular cross-links. 

In the first instance, the SIPNs containing 5 and 10 % CER were characterized by Ea values higher than the calculated ones, aspect attributed to the high mobility of the polyurethane chains in the melt states, thus increasing the probability of recombination reactions occurrence between macroradicals generated during thermal decomposition [18]. 

Reactions of NO with Macroradicals Generated by the Photoiysis and Radioiysis of Poiymers... 

Coupling of macroradicals generated by hydrogen abstraction through reactive radicals for example, triplet nitrene or benzoyl radicals... 

In the direct or simultaneous method, polymer A j is irradiated in the presence of monomer B (Scheme 5.9) free macroradicals generated by the radiolysis of A j then initiate the polymerization of B, thus forming grafts. Simultaneously, monomer B is homopolymerized because, apart from polymer A j, also monomer B is radiolyzed (though this might be an unwanted effect). Notably, this scheme operates in the absence of oxygen. 

---