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The ability to control the outcome of polymerisations using an external stimulus remains a formidable challenge. Herein, we report a series of photoactive Schiff base ligands bearing azobenzene moieties, as well as seven Al(III) and Zn(II) complexes. Trans–cis isomerisation of the ligands and complexes occurred by exposure to UV light. Photoisomerisation was investigated using spectroscopic techniques and real-time reaction monitoring was conducted using FlowNMR. The activity of the complexes was tested in ring-opening polymerisation (ROP) of ε-caprolactone and rac-lactide under ambient and UV light conditions, with the isomers of the Al(III) complexes displaying marked differences in activity in the ROP of ε-caprolactone.

Bioplastics such as poly(lactic acid) (PLA), which are derived from renewable sources, promoted as biodegradable and implemented for numerous functions, offer a promising alternative to the enduring synthetic plastics abundant in society. However, the degradation of PLA is slow under natural environmental conditions. A chemical recycling route is thus required to couple mitigation of plastic persistence repercussions with circular economy adherence. In the present work, the production of ethyl lactate by the catalysed transesterification of post-consumer PLA was investigated. The catalyst employed was a propylendiamine Zn(II) complex. The PLA samples investigated consisted of a phone case, an infant’s toy, a film, a cup and 3D printing material. Degradation reactions were studied at 50 °C and 90 °C and the concentrations measured at two different time intervals, 1 h and 3 h. The results revealed that greater activity of the catalyst was observed at 50 °C for two PLA samples (cup, 3D print). PLA film achieved the greatest lactate yield (71%) of all samples after 3 h at 50 °C. It is concluded that the propylenediamine Zn(II) catalyst can be used to produce green solvent ethyl lactate at mild temperatures from post-consumer PLA, even in the presence of unknown additives.

A series of well-defined mono- and dimeric Zn(II)-complexes were prepared and fully characterised by X-ray crystallography and NMR spectroscopy. Their application to the ROP of rac-LA to produce biocompatible atactic PLA was demonstrated in both solution and under industrially preferred melt conditions at 180 °C with a [rac-LA] : [Init] : [BnOH] of 3000 : 1 : 10. Exceptional activity was observed in all instances, albeit with generally poor molecular weight control (Mn) and broad dispersities (Đ), with dimers outperforming their monomeric counterparts. The propensity of all Zn(II)-complexes to facilitate PLA degradation into methyl lactate (Me-LA) under mild conditions is also demonstrated. Zn(2–3)2 were identified as the outstanding candidates, achieving full conversion to Me-LA within 8 h at 80 °C in THF. Further degradation kinetic analysis revealed Zn(2–3)2 to have kapp values of 0.63 ± 0.051 and 0.44 ± 0.029 h−1 for the rate of consumption of PLA respectively.

A stereoselective, solvent-free ring-opening polymerisation (ROP) of lactide (LA) in supercritical carbon dioxide (scCO2) is reported for the first time. The key aim is to exploit scCO2 to lower the temperature of traditional melt polymerisations, lowering the energy requirement and leading to cleaner polymeric materials. We have utilised a zirconium amine-trisphenolate initiator-stereoselective catalyst [(iPrO)Zr(OPh(tBu)2-CH2)3N] to yield highly heterotactic poly(lactide) (PLA) homopolymer (Pr = 0.74–0.84) from rac-LA, demonstrating control of the PLA microstructure in scCO2. In addition, high monomer conversion (86–93%) was achieved in short reaction time (1 h), affording poly(lactide) with a very low degree of transesterification and narrow molecular weight distribution. Most importantly, all the reactions were performed at only 80 °C, almost 100 °C lower than the conventional melt process (typically performed at 130–180 °C), representing a very significant potential energy saving.

Growing environmental concerns associated with the accumulation of plastic waste in the natural environment has incentivised considerable research into renewable alternatives, and more recently, alternative waste management strategies. This review aims to introduce poly (lactic acid) (PLA), a bioplastic, and recent research within the field. Attention will then shift to research surrounding plastic waste management. Various end-of-life (EOL) options available to plastics will be discussed more broadly, before presenting existing technologies, challenges and future opportunities exclusively for PLA. Herein, all waste management strategies presented for PLA are discussed within the context of industrial feasibility.

A series of monopyrrolidine metal complexes have been prepared with the aim of elucidating structure-to-activity relationships for the ROP of lactide. Complexes of Li(I), Mg(II), Zn(II) and Zr(IV) were synthesised and fully characterised. Structural comparisons are made to the bipyrrolidine analogues. These monopyrrolidine complexes were found to be active towards the ROP of lactide under both solution and melt conditions. The zirconium complexes were found to have reduced and opposing stereocontrol compared to the bipyrrolidine analogues. The zinc and magnesium complexes demonstrated good activity and control under immortal polymerisation conditions.

Eight new zinc complexes of bisguanidine ligands have been structurally characterised and tested for the polymerisation of lactide. Initially this necessitated the preparation of the new six bisguanidine ligands (TMG2thf, DMEG2thf, trans-TMG2(1,2)ch, trans-DMEG2(1,2)ch, R,R-TMG2(1,2)ch, R,R-DMEG2(1,2)ch). With these ligands in-hand zinc chlorido complexes could be obtained, which were characterized by X-ray crystallography and NMR spectroscopy. Furthermore, two new zinc chlorido complexes are reported, based on previous bisguanidine ligands ((1,3)TMG2ch, (1,3)DMEG2ch). All complexes show a distorted tetrahedral coordination geometry. These eight complexes are utilised as catalysts in melt polymerization of unsublimed, technical rac-lactide at 150°C. The most promising complexes were tested with different purities of lactide (technical and recrystallized) and with or without the addition of a co-initiator. The conversion was determined via 1H-NMR or FT-IR spectroscopy. Kinetic measurements show first-order behaviour with respect to lactide. The end group of the polymer was determined by MALDI-ToF measurements. Moreover, the impact of chiral complexes was examined with regard to the tacticity of the polymer. Complexes containing a thf-backbone show the highest polymerisation activity with recrystallized rac-lactide and benzyl alcohol as co-initiator.

Two series of ligands based on diaminocyclohexane (DACH) have been prepared and successfully complexed to Al(III) and Zn(II) metal centres. Solution and solid-state studies reveal a tendency to form mono- or bis-ligated forms depending on the steric bulk of the ligand. These complexes have been tested for their ability to ring open rac-lactide. Al(III) based complexes generally gave atactic PLA after a polymerization time of 1-2 days. The Zn(II) complexes, were found to be more active and furnished PLA with a slight heterotactic bias.

In this paper a series of 7 salalen ligands based on an aminopyrrolidine backbone have been prepared and characterised. Several systems have been reduced to the salan ONNO type-ligand. All ligands have been complexed to Al III with Al(1–7)Me, Al(2a)(OiPr) and Al(7a)Me being characterised by single-crystal X-ray diffraction. In general the Al III centres are best described as being in a trigonal bipyramidal geometry. The solution and solid-state structures are discussed. All complexes have all been trialled for the production of PLA from rac-lactide, the salalen complexes had a preference for heterotactic PLA (P r = 0.71), whereas the salan had a more isotactic bias (P m = 0.72). In all cases PLA with low dispersities and predictable molecular weights were prepared. The activity of the two classes of ligands is compared with the salan complexes appearing to be significantly more active than the salalen systems.

A range of ligands based upon 2-(aminomethyl)piperidine have been successfully complexed to Mg(ii), Zn(ii) and group IV metal centres. These complexes have been characterised both in solution and solid state with different coordination geometries realised dependant on the nature of the ligand. For the Mg(ii) and Zn(ii) complexes, M(1-2)2, were isolated and analysed by DOSY NMR spectroscopy. These ligands also furnished diastereomeric group IV complexes, M(1-2)2(OiPr)2. Group IV salalen and salan complexes, M(4-5)(OR)2 were also found to be diastereomeric in nature, with either β-cis or α-cis geometriesrespectively. The tridentate ligand, 6H2, yielded five coordinate complexes with both Ti(iv) and Zr(iv). All complexes were screened for the ring opening polymerisation of rac-lactide under both solvent and melt conditions. For the Mg(ii) and Zn(ii) complexes, good activity was observed with Zn(1-2)2 demonstrating immortal polymerisation characteristics.

Following the reduction in the scope of legal aid as a consequence of the Legal Aid, Sentencing and Punishment of Offenders Act 2012, the courts in England and Wales have seen a rise in the number of litigants in person. This article explores whether there is a role for Higher Education institutions in addressing the problem.

In this paper we have prepared a series of Ti(IV), Hf(IV) and Al(III) complexes based on bipyrrolidine salan pro-ligands. The Hf(IV) complexes have all been characterised in the solid-state, the chiral ligands coordinate to Hf(IV) in an α-cis manner whereas the meso ligand coordinates in a β-cis geometry. The Hf(IV) complexes are all active for the ROP of rac-lactide in the melt, with the fluxional meso complex affording a strong isotactic bias Pm = 0.84. As expected Hf(3)(OiPr)2 polymerised L-LA faster than rac-LA (kapp = 5.9 x 10-3 mins-1 vs 3.8 x 10-3 mins-1). For Ti(IV) complexes atactic PLA was formed. The salan pro-ligands have also been complexed to Al(III), with the complexes being characterised in the solid and solution state generating a series of novel Al-Me and Al-OiPr species. Al(1)(OiPr) was fluxional on the NMR timescale, whereas Al(3)(OiPr) was locked in solution with no exchange. Interestingly, the Al(III) complexes of 3H2 produce PLA with a very strong heterotactic bias Pr upto 0.87, whereas atactic PLA is produced with 1H2. For Al(3)(OiPr) a linear relationship is observed with Mn and conversion. Experiments with the addition of an equivalent of rac-LA to the selective initiators have also been performed and are discussed.

Typically, metal–organic frameworks (MOFs) exhibit ordered micropores (

Online quizzes are widely used as formative learning exercises. An important innovation is that online activity log data allow direct measurement of student activity in quizzes, such as time taken and number of attempts. It has previously been shown that participation in quizzes increases dramatically when grades are awarded as incentives. Data from six semesters in an introductory economics course show a significant positive correlation between total quiz activity and final exam marks for a given first test mark. This has implications for the prediction of exam aegrotats. While the results don't necessarily imply a causal link between quiz activity and exam marks, they do provide some evidence to indicate such a link.

The removal of a deposition mass of 8.55 ± 0.43 mg cm −2 of lard from plain-weave cotton fabrics under controlled flow conditions has been investigated using water and a solution containing a non-ionic surfactant. Three distinct flow regimes of cross-flow, through-flow and a 2:1 combination of cross- and through-flow respectively have been studied at three cleaning agent temperatures of 10 °C, 25 °C and 40 °C. The lard removal efficiency has been quantified using weighing and image analysis methods to determine the mass per unit area of lard in the treated region. The hydrodynamic resistance changes of the fouled samples have been monitored during the washing process. A time-dependent colour analysis has been shown to be an effective quantitative method of both showing the kinetics of mass removal and investigating mass re-distribution during cleaning. Computational fluid dynamic simulations have been used to investigate the shear rate distribution on the yarn surface during the flow conditions selected. Results demonstrate that effective removal of lard from fabrics at low temperatures requires a combination of chemical, physical and hydraulic factors as hydrodynamic flow alone is insufficient to ensure complete removal. Trends in hydraulic resistance changes due to fabric swelling during cleaning are also reported.