Metallocene isotactic poly propylenes

Table 1 Comparison of degree of crystallinity for metallocene isotactic poly(propylenes) from wide-angle X-ray scattering analyzed by different methods...

Randall, J. C. Alamo, R. G Agarwal, P. K. Ruff, C. J. Crystallization rates of matched fractions of MgCl2-supported Ziegler-Natta and metallocene isotactic poly(propylene)s. 2. Chain microstructures from a supercritical fluid fractionation of a MgCl2-supported Ziegler-Natta isotactic poly(propylene). 

Simultaneous In-Situ SAXS and WAXS Study of Crystallization and Melting Behavior of Metallocene Isotactic Poly(propylene)... 

Dai, P.S., Cebe, P Capel, M Alamo, R.G., and Mandelkern, L. (2000) Simultaneous in-situ SAXS and WAXS study of crystallization and melting behavior of metallocene isotactic poly(propylene), in Scattering from Polymers. Characterization by X-Rays, Neutrons and Light (eds P. Cebe,... 

Figure 2 X-ray diffractograms recorded at room temperature, (a) Metallocene-synthesized isotactic poly(propylene), mmmm — 0.996 crystallized at 145°C. (b) Atactic poly(propylene). Reproduced with permission from Ref. [43], Copyright John Wiley Sons, Inc., 1999.

Table 8. Isotactic poly(propylene) polymerized by bridged- and unbridged-metallocene catalysts... 

Fischer, D. Miilhaupt, R. The influence of regio- and stereoirregularities on the crystallization behavior of isotactic poly(propylene)s prepared with homogeneous group IVa metallocene/methylaluminoxane Ziegler-Natta catalysts. MacromoZ. Chem. Phys. 1994,195, 1433-1441. 

The metallocene botactic poly(propylene) (m-iPP) used in thb study is an experimental product of Hocchst. Characterization of the material shows that the fractional content of isotactic pentads (mnunm) b low at 0.908 mol-%, the Mw b 335,500 g/mol, and the polydispersity b 2.3 [20]. Defect content was assessed by C-NMR [20] and the stereo and regio defects arc 1.68mol% and 0.67mol%, respectively. The material, received as pellets, was formed into films by compression molding at 200°C, then was quenched to room temperature in cold water. 

Fig. 9.56a Overall birefringence change as a function of crystallization temperature and time for a metallocene catalyzed isotactic poly(propylene), M = 5.75 X 10 with 0.3% chain structural defects. (From Alamo and Chi (209))...

Three stereoisomers are possible in the cholestanylindene-derived zir-conocene complexes illustrated in Scheme 67. Two are racem-like, and the other is meso-like depending on the geometry of the metallocene moiety. The stereochemistry of the reaction is controlled by both the structure of the metallocene skeleton and steroidal substituent. Polymerization of propylene with 0-C activated with MAO gave polypropylene of 240,000, about 40% mmmm approximately 70% is due to enantiomorphic site control and the rest is due to chain-end control. Use of the catalyst derived from a /3-A-B mixture produced a mixture of polymers. The a-A and a-B/MAO catalysts afforded isotactic poly-... 

As discussed earlier, ethylene propylene rubber (EPR or EPM) has been blended with PP and PE to improve the impact strength and to render the materials softer. Recently, metallocene catalysts or postmetallocene catalysts provide new pathways to generate elastic copolymers that can replace EPR. These pathways possess cheaper manufacturing cost and generate new materials with better compatibility to PP or PE. Such new materials included ethylene-propylene random copolymers with dominant ethylene component (33-34) or propylene-dominant component (35 1), propylene-ethylene block copolymer (42), ethylene-octene copolymer (43), poly(propylene-co-ethylene) (44), ethylene-hexene copolymer (45), ethylene-butene copolymer (46), low isotactic PP (47), and stereoblock PP (48). These materials are generally compatible with PP or PE, thus can be used to tailor the toughness (or the softness) of... 

Soga and Shiono used some C -symmetric ansa-metallocenes for their ZnEtj-assisted system. Typical catalyst precursors for isospecific propylene polymerization, such as 44,45 and 46, produced highly isotactic poly(MMA) with catalyst control [141, 142]. Marks showed that the binuclear cationic species [(rac-MejSillndljZrljlp-Me)] with PBB anion gave highly isotactic poly(MMA) ([mnj]=0.93) [135]. 

Stevens et al. (2) observed that the haze content of poly(ethylene-co-[isotactic]-propylene) was directly related to the monomer content and whether the material was prepared using a metallocene catalyst. Low haze values were obtained for polymers prepared using nonmetallocene catalytic agents with polymers having moderately high ethylene levels. 

D-Limonene and ot-pinene have been used as renewable solvents and chain transfer agents in metallocene-methylaluminoxane (MAO) catalysed polymerization of ot-olefins. Chain transfer from the catalyst to the solvent reduces the achieved in limonene compared with toluene and also reduces the overall catalyst activity. This was confirmed, as in the ROMP studies, by performing identical reactions in hydrogenated limonene. However, an increase in stereospecificity was seen when D-limonene was used as the solvent. This is measured as the mole fraction of [mmmm] pentads seen in NMR spectra of the polymer. 100% isotactic polypropylene would give a value of 1.0. On performing the same propylene polymerization reactions in toluene and then in limonene, the mole fraction of [mmmm] pentads increased from 0.86 to 0.94, indicating that using a chiral solvent influences the outcome of stereospecific polymerizations. Unfortunately, when a-pinene was used, some poly(a-pinene) was found to form and this contaminates the main polymer product. 

Czv-Symmetric Catalysts. Syndiotactic polymers have been formed using metallocene catalysts where the polymer chain end controls the syndiospecificity of olefin insertion. Resconi has shown that Cp 2MCl2 (M = Zr. Hf) derived catalysts produce predominantly syndiotactic poly(l-butene) with an approximate 2 kcal/mol preference for syndiotactic versus isotactic dyad formation." At —20 °C. Cp 2HfCl2/MAO produces poly(l-butene) with 77% rr triads. Pellecchia had reported that the diimine-ligated nickel complex 30 forms moderately syndiotactic polypropylene at —78 °C when activated with MAO ([rr] = 0.80)." " Olefin insertion was shown to proceed by a 1.2-addition mechanism." in contrast to the related iron-based systems which insert propylene with 2.1-regiochemistry. ... 

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