[活性自由基聚合,TEMPO.ppt

2,2,4,4-四甲基派啶氮氧稳定自由基(2,2,4,4-tetramethyl-1-piperidinyloxy, TEMPO) Typically these propagating carbon centered radicals are transient species , tend to disappear by self-termination, which is typically a diffusion controlled process. This raises the question, why do we only see minor amounts of irreversible termination in NMP? 2.4 副反应 苯乙烯中的热引发： 说明双基终止的存在? 热引发对苯乙烯的聚合十分有利！ 双基终止的程度：严重影响速率，对分子量和分布影响很小！ 因自由基浓度:约为10-8M，大分子浓度为10-2M! Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 2.4 副反应 烷氧胺的分解或提氢副反应： Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 2.4 副反应 烷氧胺的分解或提氢副反应： These results help to explain the differences in the polymerization of styrenics and methacrylates under the same NMP conditions. Due to the extra β hydrogens on the methacrylates, there is a much greater amount of H transfer and therefore lack of control. This has been observed experimentally with significant amounts of “ene” terminated polymer chains detected by MALDI-MS and NMR and UV-vis studies. Acrylates : much greater amount of H transfer Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. 3. NMP聚合速率的提高 TEMPO体系的聚合速率慢,主要是由于聚合体系中链增长自由基浓度太低。 平衡常数Keq=[P.][T.]/[PT],其中P.为链增长自由基,T·为TEMPO, PT为形成的休眠种。 Keq仅为10-11mol.L-1,而实验发现体系中的TEMPO的浓度约为初始浓度的0.1%(约为10-3mol.L-1).因此体系中P·为10-8mol.L-1，因此提高链增长自由基的浓度有利于聚合速率的提高。 He等在TEMPO的存在下,连续加入少量的自由基引发剂(AIBN)进行苯乙烯的活性聚合, 发现连续加入引发剂体系的聚合速率比一次性加入自由基引发剂分体系的聚合速率快了近3倍。 Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Copyright 2004-2011 Aspose Pty Ltd. Greszta等发现加入半衰期较长的自由基引发剂,如二枯基过氧化物(DCP),可以提高聚合速率，聚合速率和DCP的加入量成正比，分子量随转化率线性变化,多分散系数与不使用DCP的相差不大 .Journal of Polymer Sciene, PART A, 1997,35(9),1857一1861 引发剂的添加：提高活泼自由基浓度，提高聚合速率，对分子量和分布影响很小！因自由基浓度:约为10-8M，大分子浓度为10-2M! Evaluation only. Created with Aspose.Slides for .NET 3.5 Client Profile 5.2.0.0. Co