SYNTHESIS OF ELASTOMERIC POLY(PROPYLENE) USING UNSYMMETRICAL ZIRCONOCENE CATALYSTS - MARKED REACTIVITY DIFFERENCES OF RAC-LIKE AND MESO-LIKE DIASTEREOMERS

Synthesis of ''meso''- and ''racemic''-like diastereomers of Me2Si(3-M eInd)(Ind)ZrCl2 (5 and 6, respectively) was achieved through either me tathetical reactions between the dianion of Me-2(3-MeIndH)(IndH) (4) w ith ZrCl4 or via amine elimination reactions, followed by fractional c rystallization. Propylene polymerizations using meso-5 in the presence of methyl aluminoxane under a variety of conditions leads to the form ation of low molecular weight, semicrystalline, low tacticity, poly(pr opylene)(PP). The dominant chain transfer mechanism in this case is sh own to involve B-H transfer to monomer. In contrast, rac-6 provides hi gher molecular weight, semicrystalline, elastomeric poly(propylene) (e lPP) under a variety of conditions; chain transfer in this case involv es, predominantly, beta-H transfer to Zr. The properties of elPP produ ced using catalyst 6 show a gradual change from a lightly, cross-linke d elastomer to a poorly crystalline thermoplastic, depending on both p olymer molecular weight and crystallinity as revealed by differential scanning calorimetry and tensile testing. In particular, more crystall ine material exhibits a higher initial modulus, yielding behavior and lower strain to break than less crystalline material of equivalent mol ecular weight. These findings further define polymer properties for th e synthesis of flexible elastomers using this class of catalysts.