Synthesis of Elastomeric Poly(propylene) Using Unsymmetrical Zirconocene Catalysts:  Marked Reactivity Differences of “Rac”- and “Meso”-like Diastereomers

Abstract

Synthesis of "meso"-and "racemic"-like diastereomers of Me2Si(3-MeInd)(Ind)ZrCl2 (5 and 6, respectively) was achieved through either metathetical reactions between the dianion of Me2(3-MeIndH)-(IndH) (4) with ZrCl4 or via amine elimination reactions, followed by fractional crystallization. Propylene polymerizations using meso-5 in the presence of methyl aluminoxane under a variety of conditions leads to the formation of low molecular weight, semicrystalline, low tacticity, poly(propylene) (PP). The dominant chain transfer mechanism in this case is shown to involve -H transfer to monomer. In contrast, rac-6 provides higher molecular weight, semicrystalline, elastomeric poly(propylene) (elPP) under a variety of conditions; chain transfer in this case involves, predominantly, -H transfer to Zr. The properties of elPP produced using catalyst 6 show a gradual change from a lightly, cross-linked elastomer to a poorly crystalline thermoplastic, depending on both polymer molecular weight and crystallinity as revealed by differential scanning calorimetry and tensile testing. In particular, more crystalline material exhibits a higher initial modulus, yielding behavior and lower strain to break than less crystalline material of equivalent molecular weight. These findings further define polymer properties for the synthesis of flexible elastomers using this class of catalysts.

Synthesis and properties of elastomeric poly(propylene)

“…Therefore, and considering the values of n iso mentioned above, it seems that this parameter has to reach a value of at least 7 to obtain crystalline domains. This limiting value is approximately the same as that reported recently for elastomeric poly(propylene)s synthesized with unsymmetrical zirconocene catalysts 6) . The samples showed a glass transition temperature, T g , between 0 and 5 8C.…”

“…Subsequently improved catalysts have been made for tailoring this material, which contains blocks of crystallizable stereoregular sequences and stereorandom amorphous ones 3) . The use of metallocene catalysts in the stereoselective propylene polymerization 4) led to further developments for the preparation of elastomeric poly(propylene) 5,6) . Recently, Waymouth et al 7,8) found that unbridged "oscillating" metallocenes such as bis(2-phenylindenyl) 2 ZrCl 2 (1 in Fig.…”

Morphological analysis of highly filled propylene/ethylene copolymers

“…Discoveries in the area of polymer synthesis [1][2][3][4][5][6][7] have resulted in the possibility of designing and synthesizing a wide variety of polymers with unusual properties. Recently, Dow Chemical Co. developed a new technology that allows the copolymerization of propylene with various a-olefin comonomers over a broad range of compositions in an isotactic fashion and with a high molecular weight.…”

Methylbenz[e]indenyl asymmetric ansa-metallocene and silylamido zirconium complexes

“…C 2 symmetric ansa -metallocenes produce highly isotactic polypropylene [4 Á/6], whereas C 1 analogues give thermoplastic elastic polypropylenes in homogeneous processes both at low and ambient temperature [7,8]. The monocyclopentadienylamido so called 'constrained geometry' catalysts have been shown to be very efficient catalysts for copolymerization of ethylene and other larger olefins [9 Á/11].…”