Controlled ring‐opening polymerization of trimethylene carbonate and access to PTMC‐PLA block copolymers mediated by well‐defined N‐heterocyclic carbene zinc alkoxides

Abstract

a Four novel Zinc-NHC alkyl/alkoxide/chloride complexes (4, 5, 9 and 9′) were readily prepared and fully characterized, including X-ray diffraction crystallography for 5 and 9′. The reaction of N-methyl-N′-butyl imidazolium chloride (3.HCl) with ZnEt 2 (2 equiv.) afforded the corresponding [(C NHC )ZnCl(Et)] complex (4) via a protonolysis reaction, as deduced from NMR data. The alcoholysis of 4 with BnOH led to quantitative formation of the dinuclear Zn(II) alkoxide species [(C NHC )ZnCl(OBn)] 2 (5), as confirmed by X-ray diffraction analysis. The NMR data are in agreement with species 5 retaining its dimeric structure in solution at room temperature. The protonolysis reaction of N-(2,6-diisopropylphenyl)-N′-ethyl methyl ether imidazolium chloride (8.HCl) with ZnEt 2 (2 equiv.) yielded the [(C NHC )ZnCl(Et)] species 9. The latter was found to be reactive with CH 2 Cl 2 in solution and to cleanly convert to the corresponding Zn(II) dichloride [(C NHC )ZnCl 2 ] 2 (9′), whose molecular structure was also elucidated using X-ray diffractometry. Unlike Zn(II)-NHC alkoxide species 1 and 2, which contain a NHC flanked with an additional N-functional group (i.e. thioether and ether, respectively), the Zn(II) alkoxide species 5 incorporates a monodentate NHC ligand. The Zn(II) complexes 1, 2 and 5 were tested in the ring-opening polymerization (ROP) of trimethylene carbonate (TMC). All three species are effective initiators for the controlled ROP of trimethylene carbonate, resulting in the production of narrow disperse PTMC material. Initiator 1 (incorporating a thioether moiety) was found to perform best in the ROP of TMC. Notably, the latter also readily undergoes the sequential ROP of TMC and rac-LA in the presence of a chain-transfer agent, leading to well-defined and high-molecular-weight PTMC/PLA block copolymers.

Crystal structures of three complexes of zinc chloride with tri-tert-butylphosphane

“…Zinc chloride-bulky phosphane compounds tend to form ZnCl 2 -monophosphane complexes. Two closely related compounds include a ZnCl 2 -phosphane dimer (LUZVEI; Liang et al, 2010), and a ZnCl 2 -bulky NHC dimer (XONKUI; Fliedel et al, 2014). In both cases, the molecular geometries are very similar to that of (1 Pattacini et al, 2009).…”

Tailor-made block copolymers of l-, d- and rac-lactides and ε-caprolactone via one-pot sequential ring opening polymerization by pyridylamidozinc(ii) catalysts

“…Although hundreds of catalysts for the ROP of lactide and lactones have been reported in the last two decades, catalysts combining non-toxicity, high activity and well controlled polymerization are rare. 3,4 Examples of catalysts based on biologically benign metals include heteroleptic complexes of Mg(II) and Zn(II) of the type LM-X, with L ¼ bdiiminate, [7][8][9][10][11] trispyrazolylborate, 12 N-heterocyclic carbene 13,14 or phenolate-based [15][16][17][18][19][20][21] ligands, and X ¼ alkyl, alkoxy, dialkylamido.…”

Synthesis of PLA-based thermoplastic elastomer and study on preparation and properties of PLA-based shape memory polymers

“…Thermoplastic elastomers based on PLA, mainly triblock copolymers or multiblock copolymers, can be prepared. The prepolymers reported as flexible segments include polyethylene glycol (PEG) [28][29][30], polycaprolactone (PCL) [31,32], poly (3-hydroxybutyrate) (PHB) [33][34][35], polyethylene oxide (PEO) [36][37][38][39], poly (1,3-trimethylene carbonate) (PTMC) [40], polydimethylsiloxane (PDMS) [41,42] and so on. In lowmolecular weight block copolymers, the addition of chain extender or coupling agent can further improve their molecular weight, resulting in multi-block TPU.…”