Coordinative chain transfer polymerization styrene

The syndiotacticity of sPS resnlts from the homogeneons coordinative polymerization process (1,42). Styrene monomer complexes at a vacant coordination site on the transition metal, typically titanium, and inserts into a titanium carbon or hydride bond (Fig. 5). In the case of the growing polsrmer chain, the insertion occurs via cis-addition with secondary insertion so that the titaniiun is attached to the carbon bearing the phenyl substituent (43). Chain transfer occurs typically via -hydride elimination, forming a titanium hydride, or via reaction with an... 

Transition metal complexes functioning as redox catalysts are perhaps the most important components of an ATRP system. (It is, however, possible that some catalytic systems reported for ATRP may lead not only to formation of free radical polymer chains but also to ionic and/or coordination polymerization.) As mentioned previously, the transition metal center of the catalyst should undergo an electron transfer reaction coupled with halogen abstraction and accompanied by expansion of the coordination sphere. In addition, to induce a controlled polymerization process, the oxidized transition metal should rapidly deactivate the propagating polymer chains to form dormant species (Fig. 11.16). The ideal catalyst for ATRP should be highly selective for atom transfer, should not participate in other reactions, and should deactivate extremely fast with diffusion-controlled rate constants. Finther, it should have easily tunable activation rate constants to meet sped c requirements for ATRP monomers. For example, very active catalysts with equilibrium constants K > 10 for styrenes and acrylates are not suitable for methacrylates. 

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