Highly isotactic polypropene prepared with rac-dimethylsilyl-bis (2-methyl-4-t-butyl-cyclopentadienyl) zirconiumdichloride: An NMR investigation of the polymer microstructure

Abstract

67Isotactic polypropene was prepared using rac-dimethyl-silylbis(2-methyl-4-t-butyl-cyclopentadienyl)zirconiumdichloride (1) and methyla!umoxane (MAO) at temperatures between 0 and 80°C and with Al/Zr ratios of 300 and 1500. The polymers, prepared at temperatures below 30°C had melting points of 162°C and above. The chain ends were determined by means of distortionless enhancement by polarization transfer (DEPT)-NMR spectroscopy. The pentad intensities were corrected according to the chemical shifts of the end groups. The intensity distributions are shown to arise from enantiomorphic site control of the chiral catalyst species.

Zirconocene Propylene Polymerisation: Controlling Termination Reactions

“…Based on the detected end groups accompanied with the increase in the M w suggest that two termination routes, b-H/b-CH 3 transfer to Zr and chain transfer to aluminium, are operative with 2/MAO. The detected termination routes agree well with the results reported previously by Rieger et al [25] The detected intensities of the end group carbons (A1-A6, B1-B6 and C1-C7) at varying TMA concentrations are illustrated in Figure 6. The amount of n-propyl (A) and vinylidene (B) end groups is expected to be equal because n-propyl (A) is the initiated chain end and vinylidene (B) is the terminated chain end from the same termination reaction.…”

“…From the M w dependency on the monomer and TMA concentrations at 40 8C, we can conclude that b-H/b-CH 3 transfer to Zr is an important operative termination mechanism accompanied with chain transfer to aluminium. For 2/MAO Rieger et al [25] have reported a strong M w dependency on polymerisation temperature, and they determined a M w value of 10.6 kg Á mol À1 at 50 8C and 1.2 kg Á mol À1 at 80 8C for 2/ MAO. Our M w values, detected for 2/MAO, agree well with the values reported by Rieger et al…”

The detailed analysis of the vinylidene structure of metallocene-catalyzed polypropylene

“…And, it is well known that the metallocenecatalyzed polypropylene has vinylidene end group produced by b-hydride elimination [7,8]. Recently, the terminal chain end structures such as vinyl, butenyl and isobutenyl structures have been reported on polypropylene prepared by metallocenes that had different ligand structures [9,10].…”

Study on chain end structures of polypropylenes prepared with different symmetrical metallocene catalysts

“…On the basis of the previous papers described the assignment of NMR spectra [21,22,25,26], 1,2-inserted chain end could lead to vinylidene group (A), n-propyl group (G) and i-propyl group (H) as described in schemes 1-3 in Fig. 3.…”