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Synthesis and characterization of iPP-sPP stereoblock produced by a binary metallocene system

: Descour, C.; Macko, T.; Cavallo, D.; Parkinson, M.; Hubner, G.; Spoelstra, A.; Villani, M.; Duchateau, R.


Journal of polymer science. A, polymer chemistry 52 (2014), Nr.10, S.1422-1434
ISSN: 0360-6376
ISSN: 0887-624X
ISSN: 1099-0518
ISSN: 1096-990X
Fraunhofer LBF ()

Stereoblock polypropylenes comprising of iPP and sPP segments are synthesized by polymerization of the following binary system of metallocenes: the C-s-symmetric [2,7-t-Bu-2(Flu)(2)Ph2C(Cp)ZrCl2] and the C-2-symmetric rac-Me2Si(2-Me-4-Ph-Ind)(2)ZrCl2. Blends of samples made either by each catalyst individually (solution blend) with materials obtained with the mixed catalyst system (reactor blend) are compared. The simultaneous presence of MAO and DEZ, enhancing fast and reversible transfer of the growing chains between the two active centers, leads to the formation of a stereoblock microstructure. In this case, low molecular weight polymers are obtained. The junction between the blocks is qualitatively observed in C-13 NMR. When made in toluene, the stereoblock material consists of a majority of syndiotactic sequences, whereas the ratio is more equilibrated when the polymerization was conducted in the more polar chlorobenzene. This is confirmed by the results obtained with C-13 NMR, CRYSTAF, HT HPLC, DSC, SSA, WAXD, and optical microscopy.