On the Rigidity and Tacticity of Polynorbornenes
Date Issued
2006
Date
2006
Author(s)
Lin, Wei-Yu
DOI
zh-TW
Abstract
The design, synthesis, photophysics and determinate of the tacticity of the polynorbornenes by ring opening metathesis of norbornene derivatives is described. The spacing of each monomeric unit in the polynorbornene backbone was 5-6 Å as revealed by the X-ray crystal structure of the relative ring opening cross metathesis product. It is envisaged that the introduction of another norbornene moiety at the end of this pendant group may furnish a useful entry for double-stranded polymers. Dimers were synthesized by cross metathesis reaction. The two stereoisomers were separated and their photophysical properties were measured. The absorption maxima for the dimers and the corresponding monomer are similar. However, the extinction coefficients for dimer are slightly smaller than that of the monomer. Presumably, weak interaction between the pendant chromophores may take place. It is interesting to note that the values obtained by EFISH method in both dimer were significantly enhanced. These results indicate that the pendant groups in dimer may align essentially toward to a similar direction or adopt syn-conformation. The extinction coefficients of thepolynorbornene showed linearly decrease with increasing degree of polymerization. A plot of the per cent decrease of the relative extinction coefficient of the polymer εd, where εd = [1-(εp/εm)] x 100, and εp and εm are extinction coefficients for PNBS and the corresponding monomer , respectively, against degree of polymerization showed a good linear relationship (R2>0.98). It is interesting to note that the slopes for the plots of the polymers with electron withdrawing substituents in general are larger than those with electron donating substituents. Presumably, the interactions between the chromophores in the pending groups are substituent dependent. Interestingly, a good linear relationship was obtained for εd’s of polymers having electron withdrawing substituents, whereas those with electron donating substituents are off the line. This observation suggested that there might be interactions between pending chromophores in these polymers and the nature of such interactions may depend on substituents. The pyrrolidine moiety is a strong electron donating group. The presence of an electron withdrawing group at the para position may lead to a dipolar character in the pending group. On the other hand, when the substituent is an electron donating group, the aromatic rings would be highly electron rich. As such, the mode of interactions between such electron-rich chromophores might be different from those between dipolar aromatic chromophores. Such difference may lead to discrepancy in εd values due to the nature of substituents.
Subjects
開環複分解聚合反應
降冰片烯
立構規正度
聚合物
ROMP
norbornene
tacticity
polymer
Type
thesis
File(s)![Thumbnail Image]()
Loading...
Name
ntu-95-D90223012-1.pdf
Size
23.31 KB
Format
Adobe PDF
Checksum
(MD5):c673e7192f3f8a8579d56603c207dd55