Block Copolymer Nanoparticles for Agrochemical Applications
Lead Research Organisation:
University of Sheffield
Department Name: Chemistry
Abstract
Background. The Armes group is currently world-leading in the field of polymerisation-induced self-assembly (PISA), with considerable additional expertise of the design and synthesis of controlled-structure water-soluble polymers.1-3 We propose to prepare several series of (meth)acrylic block copolymers that are designed to act as model dispersants for various active ingredients (AI) to be selected by the Company. A typical AI is an organic crystalline small molecule that is used in the form of a concentrated aqueous dispersion of micrometer-sized particles. Such dispersions are prone to sedimentation, aggregation or crystallisation over the required two-year lifetime, which can make deployment by end-users problematic.
Proposal. The following range of diblock copolymers will be prepared using RAFT polymerisation:
1. PGMAx-PHPMAy diblock copolymer chains prepared in water via RAFT aqueous solution polymerisation. For y values of around 50 to 80, the weakly hydrophobic PHPMA chains are too short to induce micellar nucleation.4 Thus such molecularly dissolved amphiphilic copolymers can adsorb onto AI particles in the form of single chains, rather than nanoparticles.
2. PGMAx-PHPMAy diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.4-6 For y values above approximately 90, spherical nanoparticles of tunable size (e.g. 20 to 100 nm diameter as y is systematically increased) are obtained that may act as effective dispersants for the AI particles. Similar results have been recently obtained for carbon black particles in non-polar media using block copolymer micelles.7
3. PGMAx-P(HPMA-stat-GlyMA)y diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.8 Introducing 10-30 mol % epoxy groups into the hydrophobic core-forming block via statistical copolymerisation of GlyMA with HPMA should provide suitable reactive anchoring groups to aid adsorption onto at least some AI particles. Alternatively, these epoxy groups could be derivatised using various amines so as to introduce either cationic and/or other functional groups (hydroxyl, thiol, carboxylic acid, long-chain alkyl groups etc.) that may promote surface anchoring via specific physical interactions (hydrogen bonding, electrostatics, van der Waals forces etc).
4. PEGx-PHPMAy diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.9 PEG (MW = 5,000) offers an alternative and much cheaper option than PGMA as a suitable stabiliser block. However, PEG may lead to greater thermal instability for these AI dispersions compared to PGMA. Another alternative stabiliser block could be PMAA, which would confer electrosteric stabilisation.
5. PGMAx-PBzMAy diblock copolymer nanoparticles prepared in water via RAFT emulsion polymerisation.10 PBzMA is significantly more hydrophobic than PHPMA and may offer stronger binding onto particles comprising aromatic AIs. Again, well-defined PGMA-PBzMA nanoparticles can be readily prepared over a wide range of particle size (25-150 nm diameter). An alternative (somewhat lower Tg) core-forming block in this context could be PBuMA.
Polymer/monomer key for above RAFT formulations: PGMA = poly(glycerol monomethacrylate); PHPMA = poly(2-hydroxypropyl methacrylate); PBzMA = poly(benzyl methacrylate); PEG = poly(ethylene glycol); GlyMA = glycidyl methacrylate. PMAA = poly(methacrylic acid), PBuMA = poly(n-butyl methacrylate).
Characterisation Techniques. Copolymer chains will be characterised by gel permeation chromatography (DMF eluent) and 1H NMR spectroscopy. Copolymer nanoparticles will be sized using dynamic light scattering and transmission electron microscopy (and possibly SAXS). Concentrated aqueous suspensions will be characterised in terms of their particle size distributions using laser diffraction (Malvern Mastersizer), optical microscopy and differential sedimentation (disc centrifuge or LUMiSizer instruments11).
Proposal. The following range of diblock copolymers will be prepared using RAFT polymerisation:
1. PGMAx-PHPMAy diblock copolymer chains prepared in water via RAFT aqueous solution polymerisation. For y values of around 50 to 80, the weakly hydrophobic PHPMA chains are too short to induce micellar nucleation.4 Thus such molecularly dissolved amphiphilic copolymers can adsorb onto AI particles in the form of single chains, rather than nanoparticles.
2. PGMAx-PHPMAy diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.4-6 For y values above approximately 90, spherical nanoparticles of tunable size (e.g. 20 to 100 nm diameter as y is systematically increased) are obtained that may act as effective dispersants for the AI particles. Similar results have been recently obtained for carbon black particles in non-polar media using block copolymer micelles.7
3. PGMAx-P(HPMA-stat-GlyMA)y diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.8 Introducing 10-30 mol % epoxy groups into the hydrophobic core-forming block via statistical copolymerisation of GlyMA with HPMA should provide suitable reactive anchoring groups to aid adsorption onto at least some AI particles. Alternatively, these epoxy groups could be derivatised using various amines so as to introduce either cationic and/or other functional groups (hydroxyl, thiol, carboxylic acid, long-chain alkyl groups etc.) that may promote surface anchoring via specific physical interactions (hydrogen bonding, electrostatics, van der Waals forces etc).
4. PEGx-PHPMAy diblock copolymer nanoparticles prepared in water via RAFT aqueous dispersion polymerisation.9 PEG (MW = 5,000) offers an alternative and much cheaper option than PGMA as a suitable stabiliser block. However, PEG may lead to greater thermal instability for these AI dispersions compared to PGMA. Another alternative stabiliser block could be PMAA, which would confer electrosteric stabilisation.
5. PGMAx-PBzMAy diblock copolymer nanoparticles prepared in water via RAFT emulsion polymerisation.10 PBzMA is significantly more hydrophobic than PHPMA and may offer stronger binding onto particles comprising aromatic AIs. Again, well-defined PGMA-PBzMA nanoparticles can be readily prepared over a wide range of particle size (25-150 nm diameter). An alternative (somewhat lower Tg) core-forming block in this context could be PBuMA.
Polymer/monomer key for above RAFT formulations: PGMA = poly(glycerol monomethacrylate); PHPMA = poly(2-hydroxypropyl methacrylate); PBzMA = poly(benzyl methacrylate); PEG = poly(ethylene glycol); GlyMA = glycidyl methacrylate. PMAA = poly(methacrylic acid), PBuMA = poly(n-butyl methacrylate).
Characterisation Techniques. Copolymer chains will be characterised by gel permeation chromatography (DMF eluent) and 1H NMR spectroscopy. Copolymer nanoparticles will be sized using dynamic light scattering and transmission electron microscopy (and possibly SAXS). Concentrated aqueous suspensions will be characterised in terms of their particle size distributions using laser diffraction (Malvern Mastersizer), optical microscopy and differential sedimentation (disc centrifuge or LUMiSizer instruments11).
Organisations
People |
ORCID iD |
| Steven Armes (Primary Supervisor) | |
| Derek Chan (Student) |
| Description | Synthesis of diblock copolymer nanoparticles which have been used as dispersants for agrochemical formulations. Step one involves milling or reducing the particle diameter of the active ingredient. The nanoparticles have helped with this stage of the formulation. They have also shown positive results when comparing to industrially standard dispersants. |
| Exploitation Route | Further understanding of how these novel dispersants behave in other systems. Very long-term ambitions may be to commercialise the same dispersants. Patents or publishing would be an achievable target. |
| Sectors | Agriculture, Food and Drink,Chemicals |