An unexpected chiral spiro tetramer offers mechanistic insight into an improved sodium cyanide initiated polymerization of n-hexyl isocyanate in toluene
An unexpected chiral spiro tetramer offers mechanistic insight into an improved sodium cyanide initiated polymerization of n-hexyl isocyanate in toluene
复制标题
意想不到的手性螺四聚体为改进氰化钠引发的甲苯中异氰酸正己酯聚合提供了机理见解
DOI：
10.1021/ma00046a066
复制
发表时间：
1992
期刊：
影响因子：
5.5
通讯作者：
Mark M. Green
中科院分区：
文献类型：
--
作者：
Y. Okamoto;Yoshikazu Nagamura;K. Hatada;C. Khatri;Mark M. Green
聚异氰酸烷基酯是典型的蠕虫状大分子，是稀溶液和溶致液晶理论研究的理想实验模型。2 - 4它们的动态外消旋刚性螺旋骨架结构5· 6也刺激了对它们的光学活性性质的研究，这揭示了螺旋正义比对微小手性扰动的极端敏感性。7Aharoni 8最初在氰化钠引发的异氰酸酯聚合反应中使用不同的DMF和甲苯混合物，以克服各种脂肪族单体在DMF中的溶解度问题。我们报告说，使用甲苯作为压倒性的溶剂也给出了显着的优点，在聚合过程的性质与高产率的分子量的一些控制，甚至在以前难以获得低分子量。1此外，我们还发现了一种强烈的温度依赖性的不寻常的链转移产生的四聚体结构，它与长期已知的三聚体副产物1一起作用，扭曲了单体与引发剂的比例和分子量之间的关系。这种易于使用的方法1· 2的改进可以作为最近开发的活性聚合的辅助方法，该活性聚合需要某种专门的干箱技术来制备引发剂。9
Poly (alkyl isocyanates) 1 are archetypical wormlike macromolecules which make them ideal experimental models for both dilute solution and lyotropic liquid crystal theoretical work. 2" 4 Their dynamically racemic stiff helical backbone structure5· 6 has also stimulated studies of their optical activity properties which has revealed on extreme sensitivity of the helix sense ratio to tiny chiral pertur-bations. 7Aharoni8 had originally used varying mixtures of DMF and toluene in the sodium cyanide initiated polymeriza-tion1 of isocyanates to overcome the solubility problems of various aliphatic monomers in DMF. We report that the use of toluene as the overwhelming solvent gives also significant advantages in the nature of the polymerization process with high yields with some control of the molecular weight even at previously difficult to obtain low molecular weights. 1 Moreover we have discovered a strongly temperature-dependent unusual chain transfer produced tetramer structure which in concert with the long known trimer byproduct1 acts to distort the relationship between the monomer to initiator ratio and the molecular weight. This modification of an easy to use method1· 2 may act as an adjunct to a recently developed living polymerization which requires somewhat specialized drybox techniques to prepare the initiator. 9