Polymerizations of butadiene, isoprene, and 2,3-dimethylbutadiene by Gd(OCOCCl3)3–(i-Bu)3Al–Et2AlCl and the cis polymerization mechanism for dienes
✍ Scribed by Eiichi Kobayashi; Shojiro Kaita; Sadahito Aoshima; Junji Furukawa
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 165 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
Homopolymerizations of butadiene (BD), isoprene (IP), and 2,3-dimethylbutadiene (DMBD) were carried out by a Gd(OCOCCl 3 ) 3 -based catalyst, to investigate the effects of the energy levels of the monomers or the sterical factor of the methyl substituents on the polymerizability and the cis-selectivity of the monomers. The order of the polymerizability at 50°C was as follows: BD (4.5 kg of polymer/(mol of Gd h)) ϳ IP (4.8) Ͼ DMBD (0.6). On the other hand, the cis-selectivity of the polymers was as follows: BD (98%) Ͼ IP (94%) ӷ DMBD (35%). These results suggest that the terminal BD and IP units are controlled by the cis configuration by the coordination between the penultimate cis-vinylene unit and the catalyst metal, whereas the penultimate DMBD unit unfavorably controls the terminal DMBD unit to the cis-1,4 configuration through the back-biting coordination with difficulty by two methyl substituents compared with the penultimate BD and IP units. The validity of the back-biting coordination was examined by MO calculation with -allylnickel complexes. According to the formation energy with respect to the BD-BD diad, the cis-cis form is somewhat preferable to the trans-cis form through the coordination of the penultimate BD unit by ⌬E ϭ 0.028 au (ca. 17.6 kcal/mol).