Abstract
BackgroundThe 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.ResultsWhen 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.ConclusionsSix 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.
Highlights
The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics
As part of our on-going studies into the chemistry of group 4 metals and homo/piperazine derived salan ligands [1,2,3] in this paper we report the synthesis and characterisation of series of monometallic complexes based on the homopiperazine backbone
The complexes were prepared by a 1:1 reaction of the salan with Ti(OiPr)4 at 80°C, this was carried out under a flow of Ar to facilitate the removal of isopropanol to drive the reaction to the formation of the 1:1 complex
Summary
The area of biodegradable/sustainable polymers is one of increasing importance in the 21st Century due to their positive environmental characteristics. As part of our on-going studies into the chemistry of group 4 metals and homo/piperazine derived salan ligands [1,2,3] in this paper we report the synthesis and characterisation of series of monometallic complexes based on the homopiperazine backbone. This ligand family has been applied to Fe(III) [4,5], Cu(II) [6], Ni(II) [6] and Mo(VI) [7] metal centres.
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