On-line polymerisation monitoring in scCO2: a reliable and inexpensive sampling method in high pressure applications

A versatile and reliable on-line sampling system for polymerisation reactions in supercritical fluids was developed. By withdrawing a small volume of a high-pressure reaction mixture and expanding it in a controlled volume, reliable kinetic data were obtained for a range of reactions in scCO2, avoiding the need for costly equipment or setup modifications. All experiments were carried out in a stainless-steel high-pressure autoclave with mechanical stirring and a volume of 60 ml. With the polymerisation of methyl methacrylate (MMA) in scCO2 being widely adopted for research in the past, the free-radical and RAFT controlled dispersion polymerisations of MMA were analysed in detail using the sampling system as a proof-of-concept. Additionally, initial implementation of the sampling system to a range of different reactions showed the facile applicability of the monitoring method

Greener extraction-chemical modification-polymerization pipeline of vernolic acid from Ethiopian ironweed plant

Epoxidized oils are commonly used in the plastics industry as additives in the formulation of polyvinyl chloride (PVC) and as monomers in the coating industry. They are produced from petrochemical feedstocks or by chemical epoxidation of natural oils. Currently, the synthesis processes of these materials are expensive, utilize volatile organic solvents and hazardous oxidants, which are unfavorable for the environment. There is a need to find natural epoxidized oils. Vernonia galamensis (ironweed) is a plant found in abundance in Ethiopia with no commercial value, but its seeds contain 40 wt% epoxide rich triglycerides. V. galamensis oil contains up to 80 wt% of vernolic acid (VA), a mono-unsaturated fatty acid with an additional epoxide functionality. The presence of alkene and epoxide(oxirane) groups offers excellent opportunities to synthesize new building blocks for polymerisations. Here, we report a green and efficient extraction methodology (up to 80% of extraction-efficiency) of the triglyceride vernonia oil from V. galamensis using supercritical carbon dioxide (scCO2). We then report the synthesis of a series of polymerisable monomers (conversion in monomers 64%–99%) based on the VA obtained from the saponification process. Finally, the novel monomers are polymerized into different polymers through polycondensation using a mixture of metal-based and enzyme catalysts

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2

Reversible addition-fragmentation chain transfer (RAFT) dispersion polymerisation of methyl methacrylate (MMA) is performed in supercritical carbon dioxide (scCO2) with 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT) present as chain transfer agent (CTA) and surprisingly shows good control over PMMA molecular weight. Kinetic studies of the polymerisation in scCO2also confirm these data. By contrast, only poor control of MMA polymerisation is obtained in toluene solution, as would be expected for this CTA which is better suited for acrylates. In this regard, we select a range of CTAs and use them to determine the parameters that must be considered for good control in dispersion polymerisation in scCO2. A thorough investigation of the nucleation stage during the dispersion polymerisation reveals an unexpected “in situtwo-stage” mechanism that strongly determines how the CTA works. Finally, using a novel computational solvation model, we identify a correlation between polymerisation control and degree of solubility of the CTAs. All of this ultimately gives rise to a simple, elegant and counterintuitive guideline to select the best CTA for RAFT dispersion polymerisation in scCO

2‐Methyltetrahydrofuran (2‐MeTHF) as a versatile green solvent for the synthesis of amphiphilic copolymers via ROP, FRP, and RAFT tandem polymerizations

2‐methyltetrahydrofuran (2‐MeTHF) is a readily available, inexpensive, neoteric, bio‐based solvent. It has been adopted across a wide range of chemical processes including the batch manufacture of fine chemicals, enzymatic polycondensations and ring opening polymerizations. To reduce the environmental burden related to the synthesis of pharmaceutical‐grade polymers based on lactide and caprolactone, we envisaged the use of 2‐MeTHF. For the first time, we combined a series of metal‐free and enzymatic ROPs with free radical and controlled RAFT polymerizations (carried out separately and in tandem) in 2‐MeTHF, in order to easily tune the chemistry and the architecture of the final polymers. After a simple purification, the amphiphilic polymers were formulated into nanoparticles and tested for their cytocompatibility in three model cell lines, to assess their application as potential polymeric excipients for nanomedicines

Antimicrobial ‘inks’ for 3D printing: block copolymer-silver nanoparticle composites synthesised using supercritical CO2

Silver nanoparticles (AgNP) are widely exploited for their effective antimicrobial activity against a range of pathogens. Their high efficacy in this regard has seen the global demand for AgNP in consumer products steadily increase in recent years, necessitating research into novel low environmental impact synthesis approaches. Here we present a new synthetic methodology to produce polymer-AgNP composite microparticles using supercritical carbon dioxide (scCO2) and avoiding use of any petrochemically derived solvents. Poly(methyl methacrylate)-poly(4-vinylpyridine) (PMMA-b-P4VP) block copolymers were synthesised via RAFT-mediated dispersion polymerisation in scCO2, with in situ thermal degradation of various amounts of a CO2-soluble silver complex. Selective interaction of the silver with the pyridinyl moieties of the block copolymer allowed the formation of AgNP, dispersed within the block copolymer microparticles, leading to homogeneous composites. The by-products of the reaction were also removed by extracting with a flow of CO2 to yield a clean dry product in a single process. The composites were found to be non-cytotoxic and proved to have good antimicrobial activity against two bacterial strains. Though no significant activity was seen for at least the first 24 hours, inhibition of bacterial growth afterwards proved to be extremely persistent, with inhibition observed even after 15 days. Finally, the microparticulate nature of the synthesised composites was exploited and tested for compatibility in the Laser Sintering (LS) 3D printing process. Composite microparticles were fused to produce solid objects, without aggregation of the AgNP. With further optimisation, these composites could prove to be an incredibly versatile ‘ink’ that may be used within additive manufacturing and 3D printing to rapidly produce bespoke medical devices with inherent antimicrobial activity

Synthesis of core–shell polymer particles in supercritical carbon dioxide via iterative monomer addition

A new, robust methodology for the synthesis of polystyrene–poly(methyl methacrylate) (PS–PMMA) core–shell particles using seeded dispersion polymerisation in supercritical carbon dioxide is reported, where the core–shell ratio can be controlled predictably via manipulation of reagent stoichiometry. The key development is the application of an iterative addition of the MMA shell monomer to the pre-prepared PS core. Analysis of the materials with differing core–shell ratios indicates that all are isolated as single particle populations with distinct and controllable core–shell morphologies

A ‘greener’ one-pot synthesis of monoterpene-functionalised lactide oligomers

© 2020 Elsevier Ltd In this work we aimed to achieve a totally sustainable Ring Opening Polymerisation (ROP) process, by harmonising the use of naturally occurring or derivable initiators and the green solvent 2-Methyltetrahydrofuran (2-MeTHF). First, a library of novel monoterpene-alcohols and existing terpenoids was used to provide renewably sourced initiators for a metal-free ROP synthetic step. A number of these initiators are derived from waste materials, further improving their sustainability. Secondly, we selected lactide (LA) as a monomer, because not only is it derived from biomass, but its resultant polymers are biocompatible and biodegradable. Interestingly, these new polymers self-assembled in water producing well defined, biocompatible nanoparticles (NPs) via direct nanoprecipitation without the use of additional stabilisers. We have highlighted a novel and promising (ROP) approach to produce biodegradable, amphiphilic ester-based macromolecules, based on lactide and terpenes (as initiators) in a green solvent, 2-MeTHF thus reducing solvent toxicity in an efficient, simple and sustainable new synthesis. The monoterpenes may provide a highly functionalisable and bio-renewable toolbox for a new generation of ROP initiators

A facile one step route that introduces functionality to polymer powders for laser sintering

Laser Sintering (LS) is a type of Additive Manufacturing (AM) exploiting laser processing of polymeric particles to produce 3D objects. Because of its ease of processability and thermo-physical properties, polyamide-12 (PA-12) represents ~95% of the polymeric materials used in LS. This constrains the functionality of the items produced, including limited available colours. Moreover, PA-12 objects tend to biofoul in wet environments. Therefore, a key challenge is to develop an inexpensive route to introduce desirable functionality to PA-12. We report a facile, clean, and scalable approach to modification of PA-12, exploiting supercritical carbon dioxide (scCO2) and free radical polymerizations to yield functionalised PA-12 materials. These can be easily printed using commercial apparatus. We demonstrate the potential by creating coloured PA-12 materials and show that the same approach can be utilized to create anti-biofouling objects. Our approach to functionalise materials could open significant new applications for AM