Hancock Stuart L, Mahon Mary F, Jones Matthew D
Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, UK.
Chem Cent J. 2013 Aug 6;7(1):135. doi: 10.1186/1752-153X-7-135.
The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics. Lewis acidic metal centres are currently one of the most popular choices for the initiator for the polymerisation. Thus, in this paper we report the synthesis and characterisation of a series of monometallic homopiperazine Ti(IV) complexes where we have systematically varied the sterics of the phenol moieties.
When the ortho substituent of the ligand is either a Me, tBu or amyl then the β-cis isomer is isolated exclusively in the solid-state. Nevertheless, in solution multiple isomers are clearly observed from analysis of the NMR spectra. However, when the ortho substituent is an H-atom then the trans-isomer is formed in the solid-state and solely in solution. The complexes have been screened for the polymerisation of rac-lactide in solution and under the industrially preferred melt conditions. Narrow molecular weight material (PDI 1.07 - 1.23) is formed under melt conditions with controlled molecular weights.
Six new Ti(IV) complexes are presented which are highly active for the polymerisation. In all cases atactic polymer is prepared with predictable molecular weight control. This shows the potential applicability of Ti(IV) to initiate the polymerisations.
由于其积极的环境特性，可生物降解/可持续聚合物领域在21世纪变得越来越重要。路易斯酸性金属中心目前是聚合反应引发剂最受欢迎的选择之一。因此，在本文中，我们报告了一系列单金属高哌嗪钛（IV）配合物的合成与表征，其中我们系统地改变了酚部分的空间位阻。
当配体的邻位取代基为甲基、叔丁基或戊基时，β-顺式异构体仅在固态中分离得到。然而，在溶液中，通过核磁共振谱分析可以清楚地观察到多种异构体。然而，当邻位取代基为氢原子时，反式异构体在固态和溶液中均单独形成。已对这些配合物在溶液中和工业上优选的熔融条件下对消旋丙交酯的聚合反应进行了筛选。在熔融条件下形成了窄分子量材料（PDI 1.07 - 1.23），分子量可控。
本文展示了六种新型钛（IV）配合物，它们对聚合反应具有高活性。在所有情况下，均制备出了具有可预测分子量控制的无规聚合物。这表明钛（IV）引发聚合反应具有潜在的适用性。
