Chain copolymerization monomer complex participation

In these models, the complex formed by the monomer pair competes with the individual monomer molecules for the propagation reaction with the radicals. There are two variations of this approach in the complex participation model, the pair of monomers form a complex and are added to the chain radical [106-109]. On the other hand, in the complex dissociation model, the complex participates in the propagation process, but dissociates upon reaction and only one of the monomers is added to the chain [101, 103]. Although there is ample experimental evidence for the existence of such complexes in these copolymerizations (such as the bright colors associated with them) [76], it is questionable whether the complexes actually participate in the propagation step [76]. Additionally, for several years, Hall and Padias have accumulated experimental and theoretical evidence that refutes the validity of the models based on complex participation [76, 77]. Both the complex participation and the penultimate models were combined in the so-called comppen model [110]. 

Some characteristics of free-radical terpolymerization of tri-butylstannyl methacrylate, styrene and maleic anhydride governed by the pentacoordination state of the tin atom are reported in Refs. 95),96). It is shown that a coordination-bound monomer has a considerable effect on chain initiation and propagation. Copolymerization mainly involves the participation of complex-bound monomers. 

When chains grow from more than two monomers, we speak of multicomponent copolymerization. In a simple case, the number of active centre types in the medium equals the number of copropagating monomers. Many systems are also known where the number of participating centres exceeds the number of monomers. In other cases, the monomers undergo complex formation so that their complexes take part as individual components in copropagation. Let us first pay attention to some cases generated by complications in nominally two-component systems. 

Different valence states are also a fairly widespread type of unit variability. By analogy with macromolecular complexes (Section II), it may be expected that homopolymerization and copolymerization of metal-containing monomers would prevent or retard redox processes involving participation of metal ions. Experimental data confirm the fact that a polymeric matrix stabilizes complexes of metals in low oxidation states (e.g., Pd" ). Moreover, the stability of the Cu+ state during polymerization (including thermal polymerization) of copper acrylate controls the use of this method for the preparation of coordination compounds of Cu". The polymeric framework plays a stabilizing role, whereas the metal ions that are localized on the surface layer are oxidized to Cu +. However, polymerization of monomers that contain metal ions in high oxidation states is often accompanied by their reduction Fe + ->Fe +, and Mo + ->Mo" (scheme 14). For example, polymerization of Cu " and Fe + acrylates may be accompanied by intramolecular chain termination. This may be attributed to the relatively low standard reduction potentials of these metal ions (7io(Cu + Cu+) = 0.15, o(Fe ->Fe ) = 0.77 V). 

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