降冰片烯聚合物之結構探討

Abstract

本論文圍繞在降冰片烯聚合物的設計、合成、物理性質、以致於結構的鑑定。依以下的三大部分作深入的探討。 首先決定在降冰片烯聚合物中，每一個單體所佔有的空間。以釕金屬卡賓觸媒，催化降冰片烯衍生物之開環交互複分解反應，經由X-光單晶繞射可知每個單體所佔有的空間由相對應的單體的單結構可知約為5-6 Å， 此空間上的距離將提供使我們在降冰片烯聯結基團設計一個重要的準則。第二部分的工作包括利用複分解反應合成二聚物，並決定其立體構型。立體構型鑑定主要依照以下的三種方法，藉由可見光光譜中二聚物的消光係數值小於單體的消光係數， 說明了二聚物上的兩個發色團彼此之間是有相互作用的現象，因此這兩個發色團可能是朝著同一個方向。再者，二聚物的發色團含有偶極矩，因此以EFISH的方法，發現兩個二聚物的μβ0 均大於單體，且由其增益值以計算出，兩個發色團在二聚物中的夾角約為60度。最後經由核磁共振光譜以及對稱性的觀念解析出了兩個合成出的二聚物分別屬於全同異構物以及間同異構物。 第三部分則是利用二聚物的資訊，合成以及探討各種不同的降冰片烯聚合物的立體化學及構型。在合成聚合物方面，以降冰片烯為主，合成一系列具有張力烯，可進行開環複分解的單體。這包括了合成向內以及向外的懸掛基團中乃至於更具剛性的槳翼烷單體，探討聚合基團之剛性結構對於整體聚合物的影響。經由催化複分解聚合所得到聚合物之立體構型鑑定則依照以下的幾種方法，藉由可見光光譜中聚合物的消光係數值小於單體的消光係數， 也說明了聚合物上的發色團彼此之間是有相互作用的現象，因此這些發色團可能是朝著同一個方向。經由重複單元和聚合物中消光係數的衰減εd 做圖比較，含有偶極矩的發色團彼此間的作用力會大於含二推電子基團的芳香環，再者由EFISH 的方法，發現聚合物μβ0 均大於單體，而且由其增益值比較可以知道在這些骨架下的發色團均朝同一個方向。越具剛性的聚合物其增益值越大。這些發色團排列整齊的一個重要因數來自於聚合物骨架上的雙鍵。經由雙鍵還原後的降冰片烷聚合物，發色團的增益值已大為減小，表示發色團的排列程度小於含有雙鍵骨架的聚合物。於核磁共振光譜，紅外線吸收光譜以及對稱性的觀念解析出了，這類聚合物骨架是以反式雙鍵所連結，而且13C NMR 顯現出降冰片烯聚合物立體結構的單一性。基於以上種種和對稱性的觀念解析出此降冰片烯聚合物可能是屬於全同立體排列。

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.