Control of structure of polymers is an important issue in polymer synthesis because it affects properties such as solubility, crystallinity, and thermal properties. The polymers having stereogenic centers on a main chain can be synthesized by vinyl polymerization of olefinic monomers or ring-opening polymerization of cyclic monomers. Control of trans-cis selectivity is also important for the polymers containing C C double bonds in the main chain. The progress of homogeneous metal complex catalysts for coordination and ring-opening polymerization enables tailor-made control of the stereoregularity of the polymers. In this article, general aspects of stereoregular polymers, especially the polymer of monosubstituted vinyl monomers, are described. Recent progress in stereospecific polymerization of propylene, α-olefins, and styrenes is also summarized.
Propylene Polymerization.Isospecific Polymerization of Propylene by Ziegler-Natta Catalysts. In 1954, Natta found that TiCl 3 /Et 2 AlCl catalyst is effective for the synthesis of isotactic polypropylene (4,5). Ti(III) is the active species of the polymerization, whereas other Ti species are also included in the catalyst. Moreover, the stereospecific Ti(III) site as well as nonstereospecific Ti(III) site exists in the catalyst.