(517c) Kinetics and Morphological Development in Syndiotactic Styrene Polymerization over Heterogeneized Metallocene Catalysts

Syndiotactic polystyrene (sPS) is a high heat resistant and chemical resistant engineering thermoplastic that can be synthesized over homogeneous metallocene catalysts. SPS is not soluble in organic solvents and hence submicron size sPS particles precipitate out from the liquid phase during polymerization. As monomer conversion incrases, these particles agglomerate and develop to a global gel that does not have any mobility. Thus, it is not possible to agitate the reaction mixture with conventional mixing devices. The sPS gel is not a crosslinked gel but a physical gel that has complex molecular structure. The gelation can be reduced or avoided by using heterogenized metallocene catalysts for a certain range of polymerization conditions. One of the catalyst heterogenization techniques is to immobilize the catalyst (Cp*Ti(OMe)3/MAO) onto sPS prepolymers by catalyst embedding or supporting. For varying monomer concentrations and catalyst concentrations, we have carried out heterogeneous styrene polymerization and observed that the polymerization kinetics are greatly affected by the presence of solid phase. Also, the nascent morphology of sPS is quite complex and some interesting morphological structures develop at certain reaction conditions. For examples, particle disintegration or fragmentation phenomena that are commonly observed in heterogeneously catalyzed olefin polymerization do not seem to occur in heterogeneous sPS polymerization. The strikingly different polymer morphology observed in nascent sPS is presented and the mechanism of such morphological development is presented.