Supercritical carbon dioxide for green polymer chemistry

This thesis details novel research on the design of new approaches that might lead to a more sustainable polymer industry by combining the use of supercritical carbon dioxide, a commercially available immobilised enzyme and renewable monomers. First, the key themes explored in this thesis are outlined. Green polymer chemistry, biodegradable and renewable polymers, biocatalysts for polymerisations (i.e. enzymes) and supercritical carbon dioxide as a reaction medium for polymer synthesis and processing are introduced (Chapter 1). Then, the high-pressure equipment and characterisation techniques are detailed. The reaction vessel used extensively in this research work is meticulously described. The high-pressure fixed-volume view cell and the high-pressure rheometer are also detailed (Chapter 2). This chapter includes also the standard operating procedure (SOP) for each piece of equipment. In the first research chapter, the carbon dioxide-induced melting point depression of poly(e-caprolactone) is investigated; thorough rheometric studies are used to provide a rheological viewpoint to this phenomenon (Chapter 3). Shear-viscosity studies were performed in order to assess the advantages that high-pressure carbon dioxide could deliver for semi-crystalline polymer processing. Visual observations of the polymer plasticisation and comparisons with high-temperature studies are also shown. In the subsequent chapter, the development of a novel enzymatic low-temperature approach for the preparation of functional low molecular weight polyesters is detailed (Chapter 4). By exploiting the unique properties of supercritical carbon dioxide and an enzyme catalyst, polymerisations ordinarily conducted using metal catalysts in excess of 200 °C were successfully conducted at milder conditions. Functional molecules could be used to end-cap the chains, thus producing green telechelics. Then, this innovative synthetic approach was extended to the preparation of bio- based amphiphilic polymers, which could be useful for drugs encapsulation and as surfactants in detergent formulations (Chapter 5). Specifically, the self-assembly of these novel polymers and the stability of the aggregated structures in water were investigated in detail. Additionally, encapsulation of a highly lipophilic molecule (Coumarin-6) and surface tension studies provided a clear demonstration of the usefulness of these polymers for a wide range of applications. The final part of the thesis sums up the overall conclusions obtained from this research work and outlines possible opportunities for future research in this area (Chapter 6)

Supercritical carbon dioxide for green polymer chemistry

This thesis details novel research on the design of new approaches that might lead to a more sustainable polymer industry by combining the use of supercritical carbon dioxide, a commercially available immobilised enzyme and renewable monomers. First, the key themes explored in this thesis are outlined. Green polymer chemistry, biodegradable and renewable polymers, biocatalysts for polymerisations (i.e. enzymes) and supercritical carbon dioxide as a reaction medium for polymer synthesis and processing are introduced (Chapter 1). Then, the high-pressure equipment and characterisation techniques are detailed. The reaction vessel used extensively in this research work is meticulously described. The high-pressure fixed-volume view cell and the high-pressure rheometer are also detailed (Chapter 2). This chapter includes also the standard operating procedure (SOP) for each piece of equipment. In the first research chapter, the carbon dioxide-induced melting point depression of poly(e-caprolactone) is investigated; thorough rheometric studies are used to provide a rheological viewpoint to this phenomenon (Chapter 3). Shear-viscosity studies were performed in order to assess the advantages that high-pressure carbon dioxide could deliver for semi-crystalline polymer processing. Visual observations of the polymer plasticisation and comparisons with high-temperature studies are also shown. In the subsequent chapter, the development of a novel enzymatic low-temperature approach for the preparation of functional low molecular weight polyesters is detailed (Chapter 4). By exploiting the unique properties of supercritical carbon dioxide and an enzyme catalyst, polymerisations ordinarily conducted using metal catalysts in excess of 200 °C were successfully conducted at milder conditions. Functional molecules could be used to end-cap the chains, thus producing green telechelics. Then, this innovative synthetic approach was extended to the preparation of bio- based amphiphilic polymers, which could be useful for drugs encapsulation and as surfactants in detergent formulations (Chapter 5). Specifically, the self-assembly of these novel polymers and the stability of the aggregated structures in water were investigated in detail. Additionally, encapsulation of a highly lipophilic molecule (Coumarin-6) and surface tension studies provided a clear demonstration of the usefulness of these polymers for a wide range of applications. The final part of the thesis sums up the overall conclusions obtained from this research work and outlines possible opportunities for future research in this area (Chapter 6)

Polyester derivatives of unsaturated fatty acids and process for their production

The present invention relates to a polyester consisting of hydroxyacid monomer units wherein the hydroxyacid monomer unit is 10-hydroxy stearic acid (10-HSA) having a hydroxyl group in position C-10 involved in the ester bond, wherein said hydroxyacid monomer units are present in a number ranging from 10 to 100 and/or the polyester has a number average molecular weight ranging from 2,800 to 28,000 Da, said number average molecular weight being determined by means of the SEC method. The invention also comprises the process for the preparation and use of said polyester

Poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate) Amphiphilic Copolymers for Long-Acting Injectables: Synthesis, Non-Acylating Performance and In Vivo Degradation

This article presents the evaluation of diblock and triblock poly(ethylene glycol)-b-poly(1,3-trimethylene carbonate) amphiphilic copolymers (PEG-PTMCs) as excipients for the formulation of long-acting injectables (LAIs). Copolymers were successfully synthesised through bulk ring-opening polymerisation. The concomitant formation of PTMC homopolymer could not be avoided irrespective of the catalyst amount, but the by-product could easily be removed by gel chromatography. Pure PEG-PTMCs undergo faster erosion in vivo than their corresponding homopolymer. Furthermore, these copolymers show outstanding stability compared to their polyester analogues when formulated with amine-containing reactive drugs, which makes them particularly suitable as LAIs for the sustained release of drugs susceptible to acylation

Modification of Linear Polyethylenimine with Supercritical CO2: From Fluorescent Materials to Covalent Cross-Links

Along with their DNA binding ability, the secondary amines in linear polyethylenimine (L-PEI) units can also act as a reaction platform to introduce new functionalities. This renders the possibility to make a plethora of copolymers without the burden of new monomer synthesis. In this work the modification of the secondary amines of L-PEI, in either a pure L-PEI polymer or in a PEtOx-PEI copolymer, with supercritical CO2 is reported. This reaction between a secondary amine and CO2 results in formation of a carbamate, a fluorescent zwitterionic group. This gives a facile route to fluorescent carbamate-functionalzied L-PEI and PEtOx, thereby expanding the chemical toolbox of both polymers. In depth analysis of the obtained polymers by 2D nuclear magnetic resonance spectroscopy revealed that, besides the expected carbamate groups, there were also some side reactions leading to the irreversible introduction of (cyclic) urea groups and partial cross-linking of the L-PEI. Altogether, this work introduces a new simple tool for the preparation of fluorescent L-PEI and PEtOx, while also shedding light on the occurrence of side reactions in PEI-based materials for CO2 sorption

Towards Sustainable High‐Performance Thermoplastics: Synthesis, Characterization, and Enzymatic Hydrolysis of Bisguaiacol‐Based Polyesters

The utilization of wood-derived building blocks (xylochemicals) to replace fossil-based precursors is an attractive research subject of modern polymer science. Here, we demonstrate that bisguaiacol (BG), a lignin-derived bisphenol analogue, can be used to prepare biobased polyesters with remarkable thermal properties. BG was treated with different activated diacids to investigate the effect of co-monomer structures on the physical properties of the products. Namely, derivatives of adipic acid, succinic acid, and 2,5-furandicarboxylic acid were used. Moreover, a terephthalic acid derivative was used for comparison purposes. The products were characterized by (HNMR)-H-1 spectroscopy, attenuated total reflectance FTIR spectroscopy, gel-permeation chromatography, thermogravimetric analysis, and differential scanning calorimetry to assess their structural and thermal properties in detail. The polymers showed glass-transition temperatures ranging up to 160 degrees C and thermal stabilities in excess of 300 degrees C. Furthermore, the susceptibility of the polyester to enzymatic hydrolysis was investigated to assess the potential for further surface functionalization and/or recycling and biodegradation. Indeed, hydrolysis with two different enzymes from the bacteria Thermobifida cellulosilytica led to the release of monomers, as quantified by HPLC. The results of this study indicate that our new polyesters represent promising renewable and biodegradable alternatives to petroleum-based polyesters currently employed in the plastics industry, specifically for applications in which high-temperature stability is essential to ensure overall system integrity

Regio- and stereoselective biocatalytic hydration of fatty acids from waste cooking oils en route to hydroxy fatty acids and bio-based polyesters

The development of biorefinery approaches is of great relevance for the sustainable production of valuable compounds. In accordance with circular economy principles, waste cooking oils (WCOs) are renewable resources and biorefinery feedstocks, which contribute to a reduced impact on the environment. Frequently, this waste is wrongly disposed of into municipal sewage systems, thereby creating problems for the environment and increasing treatment costs in wastewater treatment plants. In this study, regenerated WCOs, which were intended for the production of biofuels, were transformed through a chemo-enzymatic approach to produce hydroxy fatty acids, which were further used in polycondensation reaction for polyester production. Escherichia coli whole cell biocatalyst containing the recombinantly produced Elizabethkingia meningoseptica Oleate hydratase (Em_OhyA) was used for the biocatalytic hydration of crude WCOs-derived unsaturated free fatty acids for the production of hydroxy fatty acids. Further hydrogenation reaction and methylation of the crude mixture allowed the production of (R)− 10-hydroxystearic acid methyl ester that was further purified with a high purity (> 90%), at gram scale. The purified (R)− 10-hydroxystearic acid methyl ester was polymerized through a polycondensation reaction to produce the corresponding polyester. This work highlights the potential of waste products to obtain bio-based hydroxy fatty acids and polyesters through a biorefinery approach