Clean Block Copolymer Microparticles from Supercritical CO₂: Universal Templates for the Facile and Scalable Fabrication of Hierarchical Mesostructured Metal Oxides

Abstract

Metal oxide microparticles with well-defined internal mesostructures are promising materials for a variety of different applications, but practical routes to such materials that allow the constituent structural length scales to be precisely tuned have thus far been difficult to realize. Herein, we describe a novel platform methodology that utilizes self-assembled block copolymer (BCP) microparticles synthesized by dispersion polymerization in supercritical CO2 (scCO2) as universal structure directing agents for both hydrolytic and non-hydrolytic sol-gel routes to metal oxides. Spherically structured poly(methyl methacrylate-block-4-vinyl pyridine) (PMMA-b-P4VP) BCP microparticles are translated into a series of the corresponding organic/inorganic composites and pure inorganic derivatives with a high degree of fidelity for the metal oxides TiO2 and LiFePO4. The final products are comprised of particles close to 1 μm in size with a highly ordered internal morphology of interconnected spheres between 20 -40 nm in size. Furthermore, our approach is readily scalable, enabling grams of pure or carbon coated TiO2 and LiFePO4, respectively, to be fabricated in a facile two step route involving ambient temperature mixing and drying stages. Given that both length scales within these BCP microparticles can be controlled independently by minor variations in the reagent quantities used, the present general strategy could represent a milestone in the design and synthesis of hierarchical metal oxides with completely tunable dimensions.

Influence of structure and solubility of chain transfer agents on the RAFT control of dispersion polymerisation in scCO2

“…This is evidenced by the observation of efficient chain extension and formation of block copolymers. 13,19,36,52 Additionally, the swelling and sorption of PMMA lms with MMA has been studied extensively in scCO 2 . [53][54][55] As PMMA particles have a higher surface area than lms, they are even more likely to swell, with a K j estimated at 0.4 for MMA and 0.25 for CO 2 .…”

Synthesis of two-phase polymer particles in supercritical carbon dioxide

“…The second low T g monomer was subsequently added using methodologies that have previously been reported in the literature. 27,32,42,44,45 The initial focus of this research was the synthesis of particles containing a PBzA phase (Table 3), as a model system. The conversion of BzA was calculated from the 1 H NMR spectrum by comparing the integral of the unreacted vinyl peak in the monomer (Fig.…”

Porous hollow TiO2microparticles for photocatalysis: exploiting novel ABC triblock terpolymer templates synthesised in supercritical CO2

“…9,[17][18][19] We have recently shown that diblock copolymers of poly (methyl methacrylate) (PMMA) and P4VP can be used as templates to fabricate hierarchically structured metal oxides, in both a versatile and scalable manner. 20 Reversible additionfragmentation chain transfer (RAFT) controlled dispersion polymerisation in supercritical carbon dioxide (scCO 2 ) was used to synthesise nanostructured block copolymer microparticles. 21 The method yielded block copolymers with high blocking efficiencies and minimal block tapering, due to almost complete conversion of monomers at each stage of the polymerisation.…”

“…23 The resulting PMMA-b-P4VP microparticles were then used as sacrificial templates in the inorganic sol-gel synthesis of TiO 2 and LiFePO 4 with structural features on both the micro and nano-length scales. 20 However, our studies thus far have only focused on the use of simple AB-type diblock copolymers for application in structure directing. While it is well-established that AB copolymers predominantly form four distinct morphologies in the bulk (spheres, cylinders, bicontinuous gyroid and lamellar), addition of a third unique block has the potential to produce a wealth of additional nanostructures.…”