Stereoregularity of Metallopolymeric Chains

Unit variability as a result of the stereoregularity along the metallopolymeric chain, unlike those considered above, is fi equently encountered in traditional polymers. Although the difference between the activation energies of iso- and syndio-addition during radical polymerization is small ( 1 kcalmol ), in the case of MCM there exists prerequisites for the formation of steieoiegular polymers. The prerequisites 

As for conventional monomers, a decrease in the polymerization temperature increases the content of the structurally ordered fraction in metal polyacrylates. For a Co salt, the syndiotactic fraction was 60% (i.e., polymerization of acrylic acid under the same conditions gives only 25-30%). At low-temperatures (5-10°C) the radical polymerization of barium diacrylate gave 74% of the syndiotactic form and 80% for zinc diacrylate. 

The process of polymerization of bifimctional monomers (e.g., diacrylates) can be divided into two steps (scheme 33). The first step yields a linear combshaped polymer with a degree of stereoregularity that depends on the natme of the metal ion. The second step results in a spatial network polymer. In this step, chain growth involves predominantly the C=C sidechains of the macroradicals. Chain growth occurs under conditions of severe steric hindrance and with an increasing level of internal (shrinkage) stresses and results in the formation of an atactic structure. 

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