Novel Non-Metallocene Catalysts For Styrene Syndiotactic Polymerization

Polystyrenes are classified into three types according to the steric configuration of macromolecular chain: namely, syndiotactic polymers, isotactic polymers, and atactic polymers. Of them, syndiotactic polymers are most useful as heat-resistant materials owing to their higher melting points and lower crystallization rates in comparison with other types of polymers.At present, syndiotactic polystyrenes are prepared by metallocene catalysts. We have been interested in non-metallocene catalysts for a long time and in this thesis a series of new type non-metallocene catalysts based upon titanium complex were reported and applied to catalyze styrene syndioatactic polymerization efficiently.The ligands of the complexes were conveniently synthesized by three steps reactions. Treatment of these ligands with titanium compound such as TiCl₄ and Ti(NMe₂)₄ produced desired titanium complexes. Structure of catalyst 9 is charactered by single crystal X-ray.It is showed from the results, highly syndiotactic polystyrene were produced with these catalysts in the presence of MMAO(modified methylaluminoxane). Reaction temperature, ratio of Al/Ti and solvent havegreat influence on the steroregularity and structure of the polymer such as Mw and DPI. Better result was obtained in toluene with the effect of MMAO. With alkylalunium compounds as co-catalyst, only atactic polystyrene were given, no matter which titanium complex was used in the polymerization reaction.Styrene bulk polymerization catalyzed by these titanium complexes were also investigated in detail. As expected, the activity of the catalyst were improved notably and up to 105 g/molTi?h in the presence of MMAO. Highly syndiotactic polystyrenes were led even at 90 "C showing excellent thermal stability of the catalysts.In summary, a series of titanium complexes were synthesized and which have been showed highly selectively in catalyzing styrene syndiotactic polymerization in the presence of MMAO. Co-catalyst and structure of catalyst as well as polymerization conditions all have important impact on the Mw and sydiotacticity of polymer.Molecular weight of the polymers are somewhat lower and which are hoped to be improved in our later work.YANG Yaoyu (Applied Chemistry) Supervised by Associate Professor QIN WeiminProfessor TANG Yong...