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Diblock Copolymer Core–Shell Nanoparticles as Template for Mesoporous Carbons: Independent Tuning of Pore Size and Pore Wall Thickness

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posted on 22.11.2019 by Vitalii Tkachenko, Camélia Matei Ghimbeu, Cyril Vaulot, Ludovic Josien, Loïc Vidal, Julien Poly, Abraham Chemtob
Latex templating using core–shell particles represents a unique opportunity to design mesoporous carbons with a high level of control on textural properties. This new class of organic colloid templates is synthesized by polymerization-induced self-assembly (PISA) in which a solvophilic poly­(hydroxyethyl acrylate) (PHEA) homopolymer is chain extended with a solvophobic polystyrene (PS) via a photomediated reversible-addition–fragmentation-transfer (RAFT) polymerization. The resultant PHEA-b-PS diblock copolymer nanoparticles exhibit a PS core stabilized by a PHEA shell, with two blocks characterized by a low molecular weight dispersity (1.1–1.3) and an adjustable degree of polymerization (DP). The core–shell structured nanoparticles are used as soft template for the formation of mesostructured carbons from phloroglucinol and glyoxylic acid in methanol solution. A micro- and mesostructured cellular foam is obtained having uniform, interconnected, and narrowly distributed mesopores ranging between 15 and 30 nm in diameter, a specific surface area up to 719 m2 g–1, and a total pore volume of (0.4–1.3) cm3 g–1. The mesopore size can be controlled by adjusting the diameter of the PS core (16–29 nm), while the wall thickness can be tailored independently by varying the size of the solvated PHEA shell (5–25 nm). An increase of PHEA block’s DP from 25 to 85 gradually extends the stabilizing shell dimension, thus increasing the wall thickness up to 10 nm, and causing the shift from interconnected to isolated mesopores. By comparison, much thinner walls (2–3 nm) are obtained with conventional latex templates such as polystyrene nanoparticles or colloidal silica. Decreasing PHEA DP to 17 induces the formation of copolymer vesicles that can be used as template to create mesoporous carbons with nonspherical mesopores.