Georgina L. Gregory

Synthesis of 6-membered cyclic carbonates from 1,3-diols and low CO2 pressure: a novel mild strategy to replace phosgene reagents

Low pressure carbon dioxide is used as the carbonation agent in a simple, safe and efficient procedure for the synthesis of 6-membered cyclic carbonates from 1,3-diols. Using readily available reagents and proceeding at room temperature, this route offers a novel mild alternative to phosgene derivatives.

Polymers from sugars and CO2: ring-opening polymerisation and copolymerisation of cyclic carbonates derived from 2-deoxy-D-ribose

Bio-based aliphatic polycarbonates (APCs) are attractive synthetic materials for biomedical applications because of their biodegradabilty and biocompatability properties. A high yielding 3-step process that utilises CO2 as a C1 synthon is presented for converting raw sugar, 2-deoxy-D-ribose into a novel 6-membered cyclic carbonate for ring-opening polymerisation (ROP) into carbohydrate-based APCs. The α- and β-anomers of the monomer could be isolated and revealed very different polymerisability, as rationalised by DFT calculations. Whereas the β-anomer could not be polymerised under the conditions tested, organocatalytic homopolymerisation of the α-anomer, in solution at room temperature (rt) or under melt conditions, yielded highly insoluble polycarbonates, composed of both cyclic and linear topologies, and exhibiting a glass transition temperature (Tg) of ∼58 °C. Random copolymers with controllable incorporation of this new sugar monomer were prepared with trimethylene carbonate (TMC) at rt in the bulk or in solution with Mn up to 64000 g mol−1. With increasing sugar content, the Tg values of the copolymers increased and their thermal degradability was enhanced, giving access to a new class of APCs with tailored properties.

CO2-Driven stereochemical inversion of sugars to create thymidine-based polycarbonates by ring-opening polymerisation

The development of biodegradable polymers from renewable resources is vital in addressing the dependence of plastics on petroleum-based feedstocks and growing ocean and landfill waste. Herein, both CO2 and natural sugar diols are utilised as abundant, safe and renewable building blocks for the synthesis of degradable and biocompatible aliphatic polycarbonates. Despite a strong potential for advanced polymer properties, inspired by Natures supramolecular base-pairing, polycarbonates from the sugar components of DNA, 2′-deoxyribonucleosides have been limited by the inability of phosgene derivatives to form the cyclic carbonate monomers that would allow for controlled ring-opening polymerisation. CO2 insertion at 1 atm pressure into methylated thymidine 2′-deoxyribonucleoside, facilitated by organic base 1,8-diazabicyclo-[5.4.0]-undec-7-ene, affected an intramolecular SN2-like displacement of a tosyl leaving group to yield the cyclic carbonate by stereochemical inversion. Organocatalytic ring-opening polymerisation proceeded rapidly in solution resulting in high monomer conversions of 93% and number-average molecular weights, substantially greater and more controlled than via polycondensation routes. The thermodynamic parameters of the polymerisation (ΔHp = −12.3 ± 0.4 kJ mol−1 and ΔSp = −29 ± 1.1 J mol−1 K−1) were determined from the equilibrium monomer conversions over a temperature range of 0 to 80 °C and pseudo-first order kinetics demonstrated. The amorphous thymidine-based polycarbonates exhibited high glass transition temperatures of 156 °C and were found to be highly degradable to the constituent diol under basic aqueous conditions. Static water contact angle measurements and cell studies with MG-63 cell line indicated slightly hydrophilic and biocompatible materials, promising for tissue-engineering applications. The novel, CO2-driven approach to cyclic carbonate synthesis represents a means of expanding the scope of sugar-based monomers for tailored material properties derived from natural products.

Polymers from sugars and CS2: synthesis and ring-opening polymerisation of sulfur-containing monomers derived from 2-deoxy-D-ribose and D-xylose

Thionocarbonate (–O–CS–O–) and xanthate (–S–CS–O–) cyclic monomers were synthesised by cyclothiocarbonation of 2-deoxy-D-ribose- and D-xylose-derived diols with carbon disulfide, then polymerised using organocatalytic ring-opening methods. Regular polymer linkages were obtained, with the sugar backbone influencing the regioselectivity of monomer opening. Thermal analysis revealed lower glass transition temperatures compared to carbonate analogues and a low onset of thermal degradation.

DFT Modelling of Ring-opening Thermodynamics of mannose-based cyclic carbonate

DFT study of the thermodynamics of the reaction between dimethyl carbonate and 1-O-methyl-2,3-O-isopropylidene-4,6-O-carbonate-α-ᴅ-mannopyranose 1) Isodesmic reaction modelling Data deposited in figshare repository: DOI: 10.6084/m9.figshare.3469283 2) Transesterification ring-opening modelling Data deposited in figshare repository: DOI: 10.6084/m9.figshare.3469373

DFT Modelling of the Initiation Step in the ROP of a mannose-based cyclic carbonate

DFT study of the reaction between TBD, 4-methyl benzylalcohol initiator, and one molecule of 1-O-methyl-2,3-O-isopropylidene-4,6-O-carbonate-α-ᴅ-mannopyranose (ring-opening polymerization initiation step). Data deposited in figshare repository: DOI: 10.6084/m9.figshare.3469466