Comparison of activities of homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) for synthesis of syndiotactic polystyrene by UV/visible spectroscopic study
✍ Scribed by Jungahn Kim; Keon Hyeong Kim; Jae Cheol Cho; Soonjong Kwak; Kwang Ung Kim; Won Ho Jo; Hye Sung Yoon; Dong Soo Lim
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 246 KB
- Volume
- 36
- Category
- Article
- ISSN
- 0887-624X
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✦ Synopsis
The catalytic activities in syndiospecific polymerization of styrene in hydrocarbon using homogeneous Ti-based catalysts in the presence of methylaluminoxane (MAO) were investigated through UV/visible spectroscopic analysis. A strong UV absorption band of CpTiCl 3 , itself, incipiently appeared at l max Å 400 nm in toluene, followed by a bathochromic shift with its remarkable decrease by the addition of MAO. The absorption band intensity at l max Å 400 nm arising from delocalization of p-electrons on the cyclopentadienyl ring decreased by methylation in the presence of MAO with regard to the mechanism for production of an active center (''cation-like''), for example, the change of the ionic nature. The intensity decrease at l max Å 400 nm was suppressed over 2000 of the [Al]/[Ti] ratio. In the case of Ti(OC 4 H 9 ) 4 having a sligand, new and broad UV absorption bands were developed at l max Å 340 nm and 410 nm in the presence of MAO in contrast with the CpTiCl 3 /MAO system. Comparison between the relative absorption intensities at l max Å 340 nm and 410 nm led to the determination of a maximum catalytic activity of Ti(OC 4 H 9 ) 4 in the presence of MAO related to the polymerization yield. The maximum polymerization yield was observed with regard to the relative maximum value of the absorption intensity at l max Å 410 nm with the [Al]/[Ti] ratio (500). From observation for polymorphism of the final products via differential scanning calorimetric analysis (DSC), the thermally unstable b-form seemed to be produced by the CpTiCl 3 /MAO system independent of the MAO concentration, the Ti(OC 4 H 9 ) 4 /MAO system produced a thermally stable a-form in the low MAO concentration (up to 100 of the [Al]/[Ti] ratio), and a mixture of aand/or b-forms over 200 of the [Al]/[Ti] ratio under our experimental conditions.