Mono- and dimeric zinc(ii) complexes for PLA production and degradation into methyl lactate – a chemical recycling method

Abstract

A series of well-defined mono- and dimeric Zn(ii)-complexes were prepared and fully characterised by X-ray crystallography and NMR spectroscopy.

Make or break: Mg(ii)- and Zn(ii)-catalen complexes for PLA production and recycling of commodity polyesters

“…Interestingly, shifting to a more electron withdrawing catalen backbone in [Zn(2-3)] 2 had a detrimental impact on Y Me-LA , achieving 0% conversion to Me-LA under analogous conditions in THF. Whilst contrary to previous work by Payne et al, 110 this was consistent with solution polymerisation results (Table 2). Indeed, previously described solution reactivity trends were retained for PLA degradation.…”

“…91,95 PLA recycling processes include hydrolysis [96][97][98][99][100][101][102][103] and alcoholysis. [104][105][106][107][108][109][110][111][112][113][114][115] Hydrogenation [116][117][118] and hydrosilylation 119 processes exploiting ruthenium and iridium have also been reported. Simple, commercially available metal salts and precursors (e.g.…”

Kinetics of Alkyl Lactate Formation from the Alcoholysis of Poly(Lactic Acid)

“…Significantly, a circular economy system is possible when lactide, the dimer of lactic acid used in the ring opening polymerization (ROP) of PLA, is synthesised from alkyl lactates [38][39][40][41][42]. With a circular economy in mind, Jones and co-workers have also developed a series of Zn-based complex catalysts suitable for both, the ROP of lactide and for the depolymerisation of PLA [33,34,[43][44][45].…”

Valorisation of plastic waste via metal-catalysed depolymerisation

“…However, in the absence of THF solvent, the latter catalysts gave a 98% Me-La yield at 130 °C. The comparable complexes ZnL 1 2 , ZnL 2 2 and ZnL 3 2 shown in Scheme 9c resulted in a lower catalytic efficiency (Me-La yield 41–88%, 50 °C, 8 wt % catalyst loading, 18 h), and thus indicating a significant steric and electronic effect of the ligand [ 267 ]. A reaction mechanism for PLA depolymerisation was proposed, consisting of two consecutive first-order steps, in which Me-La production follows the formation of chain-end groups intermediates [ 265 ].…”

“… Structures of the zinc molecular catalysts used for PLA-methanolysis in various works. a) See [ 265 ], b) see [ 266 ], c) see [ 267 ]. …”