In Situ Small-Angle X-ray Scattering Studies During Reversible Addition–Fragmentation Chain Transfer Aqueous Emulsion Polymerization

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 reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization have previously provided detailed structural information during self-assembly (see 30155157 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 inherently heterogeneous nature of such PISA formulations requires efficient stirring to generate sufficiently small monomer droplets. 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) precursor block leads to the formation of sterically-stabilized PGMA-PMOEMA spheres, worms or vesicles, depending on the precise reaction conditions. Construction of a suitable phase diagram enables each of these three morphologies to be reproducibly targeted at copolymer concentrations ranging from 10 to 30% w/w solids. High MOEMA conversions are achieved within 2 h at 70 °C, which makes this new PISA formulation well-suited for in situ SAXS studies using a new 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 micellization and subsequent evolution in particle size can be studied when preparing PGMA 29 -PMOEMA 30 spheres at 10% w/w solids. When targeting PGMA 29 -PMOEMA 70 vesicles under the same conditions, both the micellar nucleation event and the subsequent evolution in the diblock copolymer morphology from spheres to worms to vesicles are observed. These new insights significantly enhance our understanding of the PISA mechanism during RAFT aqueous emulsion polymerization.

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research

“…The polymerization-induced self-assembly is a powerful approach for the synthesis of a range of block copolymer morphologies such as spheres, worms, vesicles, etc. [59]. SAXS has been used to follow the evolution of these morphologies and gain insight into their formation mechanism depending on the reaction conditions [59].…”

“…[59]. SAXS has been used to follow the evolution of these morphologies and gain insight into their formation mechanism depending on the reaction conditions [59]. It is possible to encapsulate large amounts of nanoparticles in these large block copolymer vesicles during the synthesis and trigger their release over slower time scales by temperature or pH change [60].…”

RAFT‐vermittelte polymerisationsinduzierte Selbstorganisation (PISA)

“…Aber die Anzahl der Beispiele bleibt im Vergleich zur boomenden Entwicklung von Morphologien höherer Ordnung durch Dispersions‐ und Fällungspolymerisationen gering. Für den Einsatz als hydrophobes Monomer wurde hauptsächlich Styrol untersucht, aber es wurde gezeigt, dass auch tert ‐Butylacrylat und Monomere mit etwas höherer Löslichkeit in Wasser wie MMA, 2‐Hydroxybutylmethacrylat (HBMA), GlyMA und 2‐Methoxyethylmethacrylat (MOEMA) nicht‐sphärische Morphologien liefern können. Es ist in diesem Zusammenhang zu erwähnen, dass – mit Ausnahme der letzten beiden Monomere – für alle anderen Beispiele Pfropfcopolymere, die PEG(M)A‐Makromonomere enthielten, als Stabilisatoren verwendet wurden (Copolymere von PEG(M)A mit entweder (M)AA, NAM oder Hydroxyethylacrylamid (HEAAm)) .…”

Core–Shell Nanoparticle Interface and Wetting Properties

“…One of the recent developments to further improve latexes and to utilize block copolymers in the latex production is polymerization‐induced self‐assembly (PISA) 14,22. In such an approach, a hydrophilic polymer (commonly a macro reversible addition‐fragmentation chain‐transfer (RAFT) agent23,24) is chain extended in situ with hydrophobic monomers.…”

“…Different spray‐coating devices have been applied in both industry and academia for a long time depositing conventional colloids, however more recently focused on more advanced colloidal systems and NPs including gold,41 silica,42 Cu 2 FeSnS 4 ,43 polymeric,44 and titianium dioxide 45. Previous studies investigated how both drying and annealing of thin films of NPs can be analysed in situ and result in various functional high‐end applications40,46 as well as following the PISA process itself22 using both transmission small‐angle X‐ray scattering techniques (SAXS) and surface sensitive grazing incidence SAXS (GISAXS). 47…”