Christer Bergstrom

Investigation of the microstructure of metallocene-catalyzed norbornene-ethylene copolymers using NMR spectroscopy

Norbornene-ethylene copolymers were prepared using the metallocene catalyst ethylene bis (indenyl ) zirconium dichloride with MAO, and their microstructure was characterized with 1 H-NMR and 13 C-NMR methods. From a Cosy 1 H-NMR spectrum it was found that all norbornene units are enchained in the exo-configuration. The sequence distribution of norbornene units was investigated using 13 C- 1 H correlations, hmqc for one-bond correlations, and hmbc for two- or three-bond correlations. It was shown that norbornene diads were formed at a high norbornene content (45 mol %). When further increasing the norbornene incorporation (66 mol %) a number of new signals were obtained. A Cosy 1 H-NMR spectrum revealed a new crosspeak which, according to the corresponding 13 C-NMR shifts (hmqc), correlated well with a terminal unit of a trimer of norbornene. This means that at very high norbornene contents, norbornene triads can be formed. Because the formation of isotactic norbornene triads is very difficult to understand from a sterical point of view, an epimerization process causing stereoirregularities in the norbornene triad is proposed.

Effects of polymerization conditions when making norbornene-ethylene copolymers using the metallocene catalyst ethylene bis(indenyl) zirconium dichloride and MAO to obtain high glass transition temperatures

Using 70 mol % norbornene in the monomer mixture before polymerization, the influences of different polymerization conditions were studied. It was found that by increasing the temperature from 10 to 70°C, the yield increased and the molecular weight decreased; and when increasing the ethylene pressure from 2 to 6 atm, yield and molecular weight increased. The highest glass transition temperatures, however, were achieved at 30°C and 4 atm. Further improvements could be obtained by increasing the amount of catalyst or Al/Zr ratio. Using the conditions of 30°C, 4 atm, 4 mg catalyst, 3000 Al/Zr, 250 mL toluene solution, and 30 min, the amount of norbornene was increased from 31.1 to 90 g, resulting in an increase in the glass transition temperature from 98 to 155°C.

Influence of polymerization conditions on microstructure of norbornene-ethylene copolymers made using metallocene catalysts and MAO

When characterized with 13C-NMR, it was found that norbornene-ethylene copolymers had a more complicated microstructure when dimethylsilyl bis(indenyl) zirconium dichloride was used as the catalyst compared to ethylene bis(indenyl) zirconium dichloride. One could see more block sequences but less alternating sequences. For both catalysts the highest amounts of block sequences were obtained for high norbornene concentrations, medium to high Al/Zr ratios, and low polymerization temperatures. There were also more alternating sequences for high norbornene concentrations and high polymerization temperatures. The isolated norbornene units (separated by more than one ethylene unit) were all exoconfiguration. No unsaturation was seen.

Influence of the polymerization conditions on the rigidity of phenylnorbornene-ethylene copolymers made using ethylene bis (indenyl) zirconium dichloride and MAO

When characterized with DMA it was found that Phenylnorbornene-ethyl-ene copolymers with equivalent comonomer concentrations had very different storage moduli in the glassy state as well as glass transition temperatures. NMR analysis of the copolymers revealed that they had different ratios of Exo- and Endo-diastereomers even if the same comonomer composition had been used. The Exo/Endo-ratio in the polymer was surprisingly higher than in the monomer and increased with higher incorporations of the comonomer. Copolymers with higher Exo/Endo-ratios also had a tendency for lower storage moduli in the glassy state and higher tan δ peaks. These properties are valuable because more flexible and impact-resistant copolymers are obtained.

Influence of the polymerization conditions on the impact properties of metallocene-catalyzed copolymers of ethylene and aryl-substituted norbornenes with low exo/endo ratios

When testing copolymers of ethylene and aryl-substituted norbornenes with the Charpy impact method it was found that under certain polymerization conditions their impact properties increased with increasing polymerization time. It was also found that this improvement on impact properties was due to increasing exo/endo ratios of the incorporated aryl-substituted norbornene comonomers. This effect is important because impact-resistant copolymers can be made using aryl-substituted norbornene comonomers with low exo/endo ratios, which are more easily synthesized and purified.

A GPC method to determine the amount of comonomer in an ethylene-norbornene-copolymer

Abstract The overall composition of an ethylene-norbornene-copolymer can be determined by measuring the GPC-peak area, normalizing it according to sample weight and using a calibration curve established on the basis of 13C-NMR measurements. The normalized GPC-peak area decreases with increasing norbomene content up to 29–30 mol% when it disappears. At higher norbomene contents the polarity of the signal changes but the correlation with norbornene content is still valid. This phenomenon is due to refractive index changes caused by the comonomer. GPC is therefore a very practical tool for characterizing COC which has recently appeared on the market.

Business Opportunities for a New Type of LCP and its Blends

Liquid Chrystalline Polymers, LCP, have received a lot of attention in the recent years because of their very special properties like good heat resistance, flowability, dimensional stability, modulus and strength etc. Because of high prices and anisotropical behaviour their end-uses are, however, still rather limited. LCP is mostly used in the electrical / electronics field and the predominant processing method is injection moulding.