Glass transition temperatures metallocene polymers

Polymers produced at high catalyst concentrations have low molecular weights, consistent with melting over a broad temperature range (150-350°C). At low catalyst concentrations, crystalline polymers (which do not melt even at temperatures as high as about 400° C) may be produced if the catalyst is a chiral metallocene. Another important property of a polymer is the glass transition temperature, which is the temperature at which the polymer becomes flexible. The glass transition temperature of poly(cyclo-pentene) is about 65°C. 

Polymerization of norbornene using chiral metallocenes results in insoluble polymers exhibiting a glass transition temperature of about 210 °C. Although they have been shown by oligomerization to be tactic, no melting up to 500 °C... 

Single-site metallocene catalysts are also highly reactive vis-a-vis cycloolefins such as cyclobutene, cyclopentene or norbornene. While homopolymers of these cycloolefins have melting temperatures (>380°C), much too high for technical processability, ethylene-cycloolefin copolymers (COC s) - e.g. ethylene-norbornene copolymers - are amorphous materials with glass transition temperatures, above which they become soft and processable [W. Kaminsky, J. Polym. Sci. A, Polym. Chem., 2004, 42, 3911]. 

Metallocenes and methylalumoxanes can further be used to synthesize isotactic polypropylene [70, 71], syndiotactic polypropylene [38], other propylene polymers or oligomers [72], ethylene/cycloolefin copolymers [10-13], syndiotactic polystyrene [14, 61], and ethylene/styrene copolymers [64]. Cycloolefin copolymers are amorphous, with high glass transition temperatures [10-13]. The syndiotactic polystyrenes are semicrystalline polymers with a glass transition temperature around 100 °C and a melting point of 270 °C [14]. 

Several examples of ethylene/cyclopentene co-polymers prepared with metallocene catalysts have been reported.596,603,604 As is the case of many other co-polymers, for ethylene/cyclopentene co-polymers, the glass transition temperature increases linearly with the cyclopentene content,605 in the range 25-50 mol% of cyclopentane units. 

Most metallocenes produce copolymers with a statistical stmcture, and a few produce polymers with an alternating stmcture. Statistical copolymers are amorphous if more than 10-15 mol% of cycloolefins are incorporated into the polymer chain. The glass transition temperature can be varied over a wide range by selection of norbomene as cycloolefin and variation of the amount of norbomene incorporated into the polymer chain [104]. 

Thus, it was not until 1990 that the group of Kaminsky and Arndt-Rosenau took a more detailed look at the homopolymerization of norbornene and the structures of the resulting polymers. Driven by the growing interest in copolymers with high norbornene contents and high glass transition (Tg) temperatures, as well as the unusual properties of PNBs, Arndt-Rosenau et al. used the hydrooligomerization technique to produce saturated model norbornene dimers and trimers with metallocene catalysts known to produce atactic, isotactic, and syndiotactic poly(a-olefins) (1-3, Table 16.1). 

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