We developed a synthetic route, based on radical polymerization, to a fluorescent monolithic hierarchically porous polymer composed of extended π-conjugated triphenylene motifs. A hexa-vinyl cross-linker containing the triphenylene core was synthesized and copolymerized with styrene in the presence of a polylactide macro-chain transfer agent to produce a cross-linked block copolymer monolith. Polymerization-induced microphase separation occurred during polymerization in situ, resulting in a disordered bicontinuous morphology of polylactide and cross-linked polystyrenic domains at a nanometer scale. Removal of polylactide generated percolating mesopores with controllable pore size and exposed micropores within the polystyrenic network. A strong bluish fluorescence was observed from the resulting porous monolith, originating from the embedded triphenylene. Fluorescence was quenched upon exposure to a solution of nitroaromatic compounds. Much stronger and faster quenching compared to the nonporous analog was attributed to the improvement in access to the triphenylene group via enhanced diffusion of the analyte through the interconnected mesopores.

Synthesizing nanoporous polymer from the block polymer template by selective removal of the sacrificial domain offers straightforward pore size control as a function of the degree of polymerization (N). Downscaling pore size into the microporous regime (<2 nm) has been thermodynamically challenging, because the low N drives the system to disorder and the small-sized pore is prone to collapse. Herein, we report that maximizing cross-linking density of a block polymer precursor with an increased interaction parameter (χ) can help successfully stabilize the structure bearing pore sizes of 1.1 nm. We adopt polymerization-induced microphase separation (PIMS) combined with hyper-cross-linking as a strategy for the preparation of the bicontinuous block polymer precursors with a densely cross-linked framework by copolymerization of vinylbenzyl chloride with divinylbenzene and also Friedel–Crafts alkylation. Incorporating 4-vinylbiphenyl as a higher-χ comonomer to the sacrificial polylactide (PLA) block and optimizing the segregation strength versus cross-linking density allow for further downscaling. Control of pore size by N of PLA is demonstrated in the range of 9.9–1.1 nm. Accessible surface area to fluorescein-tagged dextrans is regulated by the relative size of the pore to the guest, and pore size is controlled. These findings will be useful for designing microporous polymers with tailored pore size for advanced catalytic and separation applications.

A hierarchically porous polymer (HPP) consisting of micropores (∼1 nm) within a 3D continuous mesoporous wall (∼15 nm) was used to support well-defined Pt nanoparticles (2 nm in diameter) as a heterogeneous catalyst for the Suzuki–Miyaura cross-coupling reaction in the liquid phase. The ligand-capped nanoparticles were loaded into the polymer and treated with plasma to expose the active surface. The dual porosity was essential: the block polymer-templated mesopores provided the reactants facile access to the nanoparticle center, which was firmly immobilized by the microporous surface. Compared to inorganic mesoporous silica supports, which are intrinsically susceptible to basic hydrolysis, the Pt-HPP featured higher activity for all halide leaving groups, even in green solvents, as well as excellent recyclability. Only 5% decrease in activity was observed after 10 cycles. Pt-HPP was one of the most active heterogeneous catalysts for aryl chloride substrates compared to literature Pt or Pd examples.

We report a new methodology that allows for forming micropores in hierarchically porous polymers by employing the reversible addition–fragmentation chain transfer (RAFT) copolymerization of conjugated multi-vinyl cross-linkers with styrene. Using divinylbenzene, 4,4′-divinylbiphenyl, 1,3,5-tris(4-vinylphenyl)benzene and tetrakis(4-vinylbiphenyl)methane as cross-linkers, the RAFT copolymerization was carried out in the presence of polylactide macro-chain transfer agents. During the polymerization, microphase separation occurred spontaneously to produce cross-linked block polymer precursors with a bicontinuous morphology composed of polylactide and cross-linked polystyrene microdomains. Hierarchically porous polymers with strong fluorescence were successfully derived by polylactide etching. We demonstrate that the rigid conjugated structure of the cross-linkers with a high cross-linking density is critical for creating the micropores and for stabilizing the mesopores that are templated by the polylactide domain.

We report the preparation of hierarchically porous polymers containing fully interconnected and controlled micro-, meso-, and macropores, where a hyper-cross-linked microporous polymer skeleton forms a reticulating mesoporous wall that supports a highly porous macropore framework. These materials provide high specific surface area and >90% porosity, useful for rapid sorption of organic molecules.

This image from the research of Soobin Kim and Myungeun Seo on page 900 shows a scanning electron micrograph of a hierarchically porous polymer synthesized by combination of hyper‐crosslinking with polymerization‐induced microphase separation (PIMS). Three‐dimensionally continuous mesopores with size of ca. 10 nm are evident. The PIMS process allows them to readily produce a crosslinked block polymer precursor with a disordered bicontinuous morphology composed of polylactide (PLA) and polystyrenic microdomains. A hyper‐crosslinking reaction degrades the PLA to generate the mesoporous space, and it simultaneously creates micropores smaller than 2 nm (not visible) within the polystyrenic microdomain to yield the hierarchical pore structure. This provides improved stability and accelerated diffusion to microporous surface. (DOI: 10.1002/pola.28966)

We report on the phase separation behaviors of polymerization mixtures containing a polylactide macro-chain transfer agent (PLA-CTA), styrene, divinylbenzene, hydroxyl-terminated PLA (PLA-OH), and a molecular chain transfer agent which enable the ability to tune the pore size of a cross-linked polymer monolith in a facile manner. Cross-linked monoliths were produced from the mixtures via reversible addition-fragmentation chain transfer (RAFT) polymerization and converted into cross-linked porous polymers by selective removal of PLA while retaining the parent morphology. We demonstrate that pore sizes are tunable over a wide range of length scales from the meso- to macroporous regimes by adjusting the ratio of PLA-CTA to PLA-OH in the reaction mixture which causes the phase separation mechanism to change from polymerization-induced microphase separation to polymerization-induced phase separation. The possibility of increasing porosity and inducing simultaneous micro- and macrophase separation was also realized by adjustments in the molar mass of PLA which enabled the synthesis of hierarchically meso- and macroporous polymers.

We report synthesis of hierarchically porous polymers (HPPs) consisting of micropores and well-defined 3D continuous mesopores by combination of hyper-cross-linking and block polymer self-assembly. Copolymerization of 4-vinylbenzyl chloride (VBzCl) with divinylbenzene (DVB) in the presence of polylactide (PLA) macro-chain-transfer agent produced a cross-linked block polymer precursor PLA-b-P(VBzCl-co-DVB) via reversible addition–fragmentation chain transfer polymerization. A nanoscopic bicontinuous morphology containing PLA and P(VBzCl-co-DVB) microdomains was obtained as a result of polymerization-induced microphase separation. While a basic treatment of the precursor selectively removed PLA to yield a reticulated mesoporous polymer, hyper-cross-linking of the precursor by FeCl3 generated micropores in the P(VBzCl-co-DVB) microdomain via Friedel–Crafts alkylation and simultaneously degraded PLA to produce the HPP containing micropores in the mesoporous framework. The mesopore size of the HPP could be precisely controlled from 6 to 15 nm by controlling the molar mass of PLA. We demonstrate acceleration in adsorption rate in the HPP compared to a hyper-cross-linked microporous polymer.