Higher ?-olefin polymerizations catalyzed byrac-Me2Si(1-C5H2-2-CH3-4-tBu)2Zr(NMe2)2/Al(iBu)3/[Ph3C][B(C6F5)4]

Effect of Different Aluminum Alkyls on the Metallocene/Methylaluminoxane Catalyzed Polymerization of Higher α‐Olefins and Styrene

“…However, the number-average molecular weight of poly(1-heptene)s was somewhat higher: M n % 30 000 g Á mol À1 (entries 8, 9, Table 1). The reason of such increase in M n with increasing the chain length of the monomer is unclear for us now, although several authors also observed similar effects, [40,41] while others reported that M n is independent of the chain length of the monomer. [37,42] It should be also noted that molecular weights of higher poly(a-olefin)s synthesized, determined by NMR spectroscopy, were typically higher than M n s calculated from SEC data [43] (M n was calculated based only on the olefinic chain end structures, for detail see Experimental Part and Figure 3).…”

Poly(pent-1-ene) Synthesized with the Syndiospecific Catalyst i-Pr(Cp)(9-Flu)ZrCl2/MAO

“…Besides olefinic end-groups that are generated through b-hydride elimination terminating the chain propagation, saturated end-groups could be formed as the result of a chain transfer to the cocatalyst. [20] If such saturated end-groups are indeed formed, calculating the number-average molar mass only by the readily identifiable unsaturated endgroups will lead to an error (the resolution was not good enough to distinguish the signals of such groups from those attributed to the polymer chain). In such a case, M -n determined by NMR end-group analysis can be expected to be higher than M -n determined by SEC.…”

“…[20,21] At lower temperature chain termination by b-hydride elimination can compete with other modes of chain termination, such as chain transfer to the co-catalyst, which can lead to saturated endgroups. [20] 1 H NMR spectroscopy permits the identification of four different groups of unsaturated end-groups with chemical shifts of 4.70-4.76, 4.90-5.05, 5.15-5.25 and 5.3-5.6 ppm, respectively. According to Chien and Odian these signals can be attributed to vinylidene, vinyl, 1,1,2-trisustituted and 1,2-disubstituted end-groups, respectively.…”

“…[15,19,20] With an increase in the 1-pentene concen- tration the ratio of vinylidene and trisubstituted double bonds tends to rise, as the possibility of chain transfer to the monomer is increased, leading to vinylidene groups. [20] 1,1,2-Trisubstituted double bonds are observed at higher polymerization temperatures. These internal double bonds are obtained after migration of the zirconium along the polymer chain, which might be favored by the heat of the reaction.…”

“…Only a few 2,1-misinsertions occurred, terminating the chain propagation and leading subsequently to 1,2-disubstituted double bonds as end-groups. [15,19,20] In the prochiral active catalyst derived from C s -symmetric 1, one catalytic site favors the insertion of a specific olefin enantioface and the so generated alternative catalytic site preferably inserts the opposite enantioface. [24,25] Therefore, it is a crucial requirement for a syndiotactic polymerization with 1/MAO that each olefin insertion takes place at the coordination site opposite to the previous one.…”