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Time-resolved small-angle X-ray scattering studies during aqueous emulsion polymerization

DOI: 10.1021/jacs.0c11183 DOI Help

Authors: Adam Czajka (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: January 2021
Diamond Proposal Number(s): 21776

Open Access Open Access

Abstract: The persulfate-initiated aqueous emulsion polymerization of 2,2,2-trifluoroethyl methacrylate (TFEMA) is studied by time-resolved small-angle X-ray scattering (SAXS) at 60 °C using a stirrable reaction cell. TFEMA was preferred to styrene because it offers much greater X-ray scattering contrast relative to water, which is essential for sufficient temporal resolution. The evolution in particle size is monitored by both in situ SAXS and ex situ DLS in the absence or presence of an anionic surfactant (sodium dodecyl sulfate, SDS). Post-mortem SAXS studies confirmed the formation of well-defined spherical latexes, with volume-average diameters of 353 ± 9 nm and 68 ± 4 nm being obtained for the surfactant-free and SDS formulations, respectively. 1H NMR spectroscopy studies of the equivalent laboratory-scale formulations indicated TFEMA conversions of 99% within 80 min and 93% within 60 min for the surfactant-free and SDS formulations, respectively. Comparable polymerization kinetics are observed for the in situ SAXS experiments and the laboratory-scale syntheses, with nucleation occurring after approximately 6 min in each case. After nucleation, scattering patterns are fitted using a hard sphere scattering model to determine the evolution in particle growth for both formulations. Moreover, in situ SAXS enables identification of the three main intervals (I, II, and III) that are observed during aqueous emulsion polymerization in the presence of surfactant. These intervals are consistent with those indicated by solution conductivity and optical microscopy studies. Significant differences between the surfactant-free and SDS formulations are observed, providing useful insights into the mechanism of emulsion polymerization.

Journal Keywords: Polymer particles; Monomers; X-ray scattering; Radical polymerization; Surfactants

Subject Areas: Chemistry, Materials

Instruments: I22-Small angle scattering & Diffraction

Added On: 18/01/2021 08:59

Discipline Tags:

Organic Chemistry Materials Science Polymer Science Physics Soft condensed matter physics Chemistry

Technical Tags:

Scattering Small Angle X-ray Scattering (SAXS)