Metallocenes melting points

Syndiotactic polypropylene has an ultimate melting point of 174°C, and extrapolated heat of fusion of 105 J/g (25.1 cal/g) both lower than those of isotactic polymer. The heat of fusion of the polymer produced using a metallocene catalyst is reported as 79 J/g (19 cal/g) (41). 

LLDPE with narrow molecular weight distribution exhibits a lower, a sharper melting point [3], better hot tack and heat seal properties as well as higher clarity and better impact resistance (Fig. 3), tensile strength (Fig. 4) [11], and lower levels of alkane-soluble components. The most distinguishing characteristic of metallocene-based LLDPEs is that they are not restricted by the current immutable property relationships that are... 

Metallocene isotactic polypropylenes (MET.PP) are accessible with different melting points under the commercial range of melt flow rate (Fig. 11). The variation of melting points in these polymers is linked with the presence of different lengths of isotactic sequences. Mechanical properties of polypropylene... 

Metallocene catalysts produce random copolymers [29-31] with different property profiles (Table 14). These data show that random copolymers have higher stiffness and higher transparency at certain melting point levels. A very low content of extractables in low-melting... 

Figure 19 (a) Peak melting temperature as a function of the branch content in ethylene-octene copolymers (labelled -O, and symbol —B (symbol, ) and -P (symbol, A) are for ethylene-butene and ethylene-propylene copolymers, respectively) and obtained from homogeneous metallocene catalysts show a linear profile, (b) Ziegler-Natta ethylene-octene copolymers do not show a linear relationship between peak melting point and branch content [125]. Reproduced from Kim and Phillips [125]. Reprinted with permission of John Wiley Sons, Inc. 

Future challenges for polymerization model catalysts are to study the structure of polymers below their melting point in what is called the nascent morphology. Such work can be undertaken on silica-supported chromium catalysts as discussed above, or on so-called single-site catalysts, such as metallocenes, applied on flat silica supports. 

Spaleck et al. (154) reported a large number of chiral zirconocenes with different bridges and substitutions on the indenyl ligand (Table VII). Some C2-symmetric metallocenes give polypropylenes with a high melting point (162°C) and tacticities (mmmm pentades) of 97-99%, measured by 13C-NMR spectroscopy (155,156). 

Metallocene catalyst Productivity [kg of PP (mmol ofZr x h)-1] 10 3 x molecular weight (g mol-1) Melting point (°C) Isotacticity (% mmmm)... 

The syndiotactic polypropylene has a melting point up to 133°C (2 74). (Me2C(Flu)(Cp))ZrCl2 and similar metallocenes, in combination with MAO or other perfluorinated borates, can produce chiral metallocenium ions in which chirahty is centered at the transition metal. Because of the flipping of the polymer chain, the metallocene alternates between the two enantiomeric configurations and produces a syndiotactic polymer (272, 175). It had not previously been possible to produce such pure syndiotactic polymer. 

The alternating copolymers are characterized both by a glass transition temperature (130°C for ethylene/norbornene copolymers) and a melting point (295°C for the totally alternating copolymer). The melting point and the crystallinity of these copolymers may be influenced by choice of the metallocene and the conditions of polymerization. Compared with the statistical copolymers, the alternating structures show better resistance to nonpolar... 

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