Polymerisation, Encapsulation and Self-Assembly in Deep Eutectic Solvents (DES)

Atom Transfer Radical Polymerisation (ATRP), a form of controlled radical polymerisation (CRP), is a highly useful
technique for preparing functional and bespoke polymeric materials, since it provides control over a number of factors
including polymer molecular weights and low polydispersity indices. However, the technique is still limited by the fact
that it requires complete exclusion of oxygen in order to avoid hindering the polymerisation procedure.
In this project, it is proposed to develop ATRP reaction protocols in Deep Eutectic Solvents (DES), a class of green
solvents related to ionic liquids. DES are characterised not by the ionic interactions of ionic liquids, but instead by
favourable hydrogen-bonding interactions and are formed by mixing a hydrogen-bond donor molecule, such as urea,
with salts, such as choline chloride (1,2). Whilst individual components of a DES may be solid at ambient
temperatures, the melting point is greatly depressed in the mixtures, with a minimum at the eutectic ratio, a property
unique to each system (3). These minima facilitate the formation of many DES that are liquid at (or near) room
temperature. DES share many properties with ionic liquids that are desirable for green solvents, such as low volatility,
non-flammability, and the property of being liquids over a wider temperature range than many conventional solvents.
Advantages of running ATRP and other CRP procedures in DES include the possibility of carrying out the
polymerisation in an ambient atmosphere, since reactions involving other oxygen- (and water-) sensitive reagents
have previously been shown to be successful in DES when performed in air (4,5). Moreover, due to the low volatility
of DES and the large range of temperatures over which they are liquid, it may be possible to heat these reactions
without the use of a reflux condenser, further saving the consummation of resources during polymerisation reactions.
DES solvent structures and their interactions with the reagents will be examined using neutron scattering
techniques, NMR, DSC and spectroscopic probes, with an aim to define the selection of the optimal DES for a given
reaction type. Moreover, it will be examined whether or not solvent-monomer interactions can be manipulated to
control specificity and chirality in polymer products, characterised via NMR, mass spectrometry, and size exclusion
chromatography, among other methods.
Additionally to examining polymerisation techniques in DES, the application of DES in emulsification and
encapsulation for drug delivery systems will also be investigated (6). DES enhance the dissolution of poorly water
soluble drugs, and are of interest for use in sustained release systems. In this project, it is intended to examine the
potential of DES for incorporation into polymer microspheres using ultrasonication techniques, common commercial
surfactants and synthesised polymers, an area which has received little attention to date. The encapsulation and
release properties of these systems will be examined using a range of scattering techniques (SAXS, SANS, DLS),
confocal microscopy and electron microscopy.
References
(1) Hammond, Bowron, Edler, Green Chem. 2016, 18, 2736.
(2) Hammond, Bowron, Edler, Angew. Chem. 2017, 56, 9782.
(3) Abbott, Boothby, Capper, Davies, Rasheed, J. Am. Chem. Soc. 2004, 126, 9142.
(4) Vidal, Garcia-Álvarez, Hernán-Gómez, Kennedy, Hevia, Angew. Chem. Intl Ed. 2014, 53, 5969
(5) Vidal, Garcia-Álvarez, Hernán-Gómez, Kennedy, Hevia, Angew. Chem. 2016, 128, 16379.
(6) Skinner, Price, Chem. Commun. 2012, 48, 9260.