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In situ SAXS studies during RAFT aqueous emulsion polymerization

DOI: 10.1021/jacs.9b06788 DOI Help

Authors: Emma E Brotherton (University of Sheffield) , Fiona L. Hatton (University of Sheffield) , Amy A. Cockram (University of Sheffield) , Matthew J. Derry (University of Sheffield) , Adam Czajka (University of Sheffield) , Erik J. Cornel (University of Sheffield) , Paul D. Topham (Aston University) , Oleksandr O. Mykhaylyk (The University of Sheffield) , Steven P Armes (University of Sheffield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Journal Of The American Chemical Society

State: Published (Approved)
Published: July 2019
Diamond Proposal Number(s): 19852

Abstract: Polymerization-induced self-assembly (PISA) is a powerful platform technology for the rational and efficient synthesis of a wide range of block copolymer nano-objects (e.g. spheres, worms or vesicles) in various media. In situ small-angle X-ray scattering (SAXS) studies of RAFT dispersion polymerizations have previously provided detailed structural information during self-assembly (see M. J. Derry et al., Chem. Sci., 2016, 7, 5078-5090). However, conducting the analogous in situ SAXS studies during RAFT aqueous emulsion polymerizations poses a formidable technical challenge because the inherent-ly heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer drop-lets. In the present study, the RAFT aqueous emulsion polymerization of 2-methoxyethyl methacrylate (MOEMA) has been explored for the first time. Chain extension of a relatively short non-ionic poly(glycerol monomethacrylate) (PGMA) precur-sor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the pre-cise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproduc-ibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved with-in 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ small angle X-ray scattering (SAXS) studies using a stirrable SAXS reaction cell. This bespoke cell enables efficient stirring and hence allows in situ monitoring during RAFT emulsion polymerization for the first time. For example, the onset of micellar nucleation and subsequent evolution in particle size can be studied when preparing PGMA29-PMOEMA30 spheres at 10% w/w solids. When targeting PGMA29-PMOEMA70 vesicles under the same conditions, both the nucleation event and the subsequent evolution in the diblock co-polymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our under-standing of the PISA mechanism during RAFT aqueous emulsion polymerization.

Subject Areas: Chemistry

Instruments: I22-Small angle scattering & Diffraction

Other Facilities: ESRF

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