Novel Living Cationic Polymerizations via・pi-Ligand Systems

这项为期两年的研究项目包括两个主要目标：(A)基于“通过pi-配体体系稳定碳正离子”的新概念，开发用于活性阳离子聚合的新的引发体系；(B)用NMR分析这些活性聚合中不断增长的物种。1.研究pi-配体体系和新的引发体系。对pi-配体体系的广泛搜索发现，以下三类化合物适合于苯乙烯和乙烯基醚的活性阳离子聚合：(1)反阴离子中的pi-配体体系：四苯基硼酸盐和相关阴离子；(2)添加剂中的pi-配体体系：咪唑和相关的氮亲核试剂；(3)活化剂中的PI-配体体系：含苯氧基配体的卤化钛。2.活性阳离子聚合的直接原位核磁共振分析。初步的研究表明，该方法在检测和分析生长碳离子方面是非常有效的，在该领域尚属首次。分析表明，在生命过程中，配基体系显著降低了阳离子浓度，这是由于它们与激活剂之间(1类和2类)或分子内(3类)有很强的相互作用，从而调节了它们的Lewis酸性。这种效应反过来稳定了不断增长的碳正离子，从而抑制了链转移和其他副反应。因此，本研究确立了通过pi-配体体系稳定碳正离子的概念，这是实现活性阳离子聚合的一般原理。

This 2-year research project consisted of two major objectives :(a) To develop novel initiating systems for living cationic polymerizations based on the new concept, "carbocation stabilization via pi-ligand systems" ;(b) To analyze the growing species in these living polymerizations by NMR.1.Search of pi-Ligand Systems and New Initiating SystemsAn extensive search of pi-ligand systems revealed the following three classes of compounds to be suitable for living cationic polymerization of stirene and vinyl ethers :(1) pi-Ligand systems in counteranions : tetraphenylborate and related anions ;(2) pi-Ligand systems in additives : imidazole and related nitrogen-nucleophiles ;(3) pi-Ligand systems in activators : titanium halides with phenoxy ligands.2.Direct In-Situ NMR Analysis on Living Cationic PolymerizationModel reactions of these living processes were analyzed, directly and in-situ, by multinuclear NMR spectroscopy. The initial phase established that this method is highly effective to detect and analyze he growing carbocations, for the first time in this field. The following analysis revealed that in the living processes, the cation concentration is remarkably reduced by thepi-ligand systems, which is due to their strong interaction with the activators, either inter- (class 1 and 2) or intramolecularly (class 3) so as to modulate their Lewis acidity. This effect in turn stabilizes the growing carbocations and thereby suppresses chain transfer and other side-reactions.Thus, this research has established the concept "carbocation stabilization via pi-ligand systems" is a general principle to achieve living cationic polymerizations.