Liu, Huang, Wu and Dai (Advanced Materials, 2017) introduced a solvent-free self-assembly route to nitrogen-doped ordered mesoporous polymers (N-OMPs): solid polymer precursors are mechanically mixed with a block-copolymer template, cured at 140–180 °C, and the template is removed by calcination, giving materials with excellent CO2 capture selectivity and CO2-to-cyclic-carbonate catalytic activity. The method, however, requires that the precursors and template melt and become mobile at the curing temperature, and less reactive monomers (phenol was said to need unspecified 'minor modifications') must be adapted case by case. The open problem is to generalize this solvent-free route: make it work for precursors that do not melt at the curing temperature, and replace case-by-case reactivity tuning for low-reactivity monomers with a systematic, transferable protocol, while retaining ordered mesoporosity and characterizing how the required modifications affect structure and functionality.

Background

Ordered mesoporous polymers (OMPs) are crosslinked polymer networks permeated by a periodic array of pores roughly 2–50 nm across, which gives them high surface areas and fast mass transport; when nitrogen atoms are incorporated into the framework (N-OMPs), the resulting basic sites bind CO2 selectively and catalyze its cycloaddition to epoxides to form cyclic carbonates. The classical way to make OMPs is soft templating: a phenolic prepolymer ('resol', the low-molecular-weight product of phenol or resorcinol with formaldehyde) is co-assembled with an amphiphilic triblock copolymer surfactant such as Pluronic F127 (poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)), which organizes into micellar arrays that the curing polymer network solidifies around; burning out the template leaves the ordered pore system. Conventionally this co-assembly is done by evaporation-induced self-assembly (EISA) from alcoholic solutions, which uses large amounts of volatile organic solvent and is slow. In 2017 Liu, Huang, Wu and Dai showed that the solvent can be eliminated entirely: solid precursors and the F127 template are simply mixed and cured at 140–180 °C, where the components melt and co-assemble into an ordered mesophase, and template removal by calcination yields N-OMPs (and, after carbonization, N-doped ordered mesoporous carbons) with CO2 capacities of 0.67–0.91 mmol/g at 25 °C and 0.15 bar, CO2/N2 selectivities of 98–205, and >95% conversion of CO2 to cyclic carbonates under mild conditions; the same route was extended to polymer/SiO2 nanocomposites, mesoporous SiO2, crystalline mesoporous TiO2, and titanium phosphate. The route's speed, scalability, and avoidance of solvents and catalysts made it an attractive green-chemistry alternative to EISA. Its generality, however, is bounded by two constraints. First, self-assembly in the absence of solvent is driven by the molecular mobility of a molten phase: any precursor or template that does not melt (or form a eutectic) at the curing temperature cannot rearrange into the ordered mesophase, so high-melting precursors simply fail to give ordered mesopores without additional processing or alternative reactive strategies. Second, the network-forming reaction must be fast enough at the curing temperature to lock in the mesostructure before it collapses: low-reactivity monomers such as phenol (much less reactive toward electrophilic substitution than resorcinol) require 'minor modifications' of the protocol that were not specified, so each new precursor currently demands its own empirical optimization. What is missing is a general understanding and protocol that decouples the method from the requirements of intrinsic precursor melt-mobility within the curing window and of high monomer reactivity—i.e., which physical or chemical measures (melting-point depression, plasticizing additives, alternative crosslinking chemistries, catalytic activation) let precursor classes beyond the reach of the present route form ordered mesoporous polymers without solvent, and how those measures affect the mesostructure, nitrogen functionality, and application performance.

Problem Statement

The 2017 solvent-free self-assembly route of Liu, Huang, Wu and Dai produces nitrogen-doped ordered mesoporous polymers by mechanically mixing polymer precursors with a block-copolymer (Pluronic F127) template, curing the solid mixture at 140–180 °C so that the components melt and co-assemble into an ordered mesophase, and calcining to remove the template. In the form demonstrated, the method requires (a) that the precursors and template melt and become mobile at the curing temperature—precursors that do not melt cannot undergo the required self-assembly and fail to produce ordered mesopores without further modification—and (b) sufficiently reactive monomers, with low-reactivity monomers such as phenol needing unspecified 'minor modifications' optimized case by case. The open problem is to generalize this solvent-free self-assembly synthesis to ordered mesoporous polymers in both directions: develop and demonstrate processing modifications or alternative reactive strategies that yield ordered mesoporous polymers from precursor classes that are immobile (non-melting, non-eutectic) within the original route's 140–180 °C curing window, and establish a systematic, transferable protocol or design principle—replacing case-by-case reactivity tuning—under which low-reactivity monomers such as phenol form ordered mesoporous polymers without solvent. Any such generalization retains the route's defining features (no added solvent, soft-template self-assembly, ordered mesoporosity) and characterizes how the required modifications affect the mesostructure and framework functionality (e.g., nitrogen content).

References

  1. F. Liu, K. Huang, Q. Wu, S. Dai, 'Solvent-Free Self-Assembly to the Synthesis of Nitrogen-Doped Ordered Mesoporous Polymers for Highly Selective Capture and Conversion of CO2', Advanced Materials 29 (2017) 1700445. DOI: 10.1002/adma.201700445, https://doi.org/10.1002/adma.201700445
  2. Q. Wu, F. Liu, X. Yi, Y. Zou, L. Jiang, 'A solvent-free, one-step synthesis of sulfonic acid group-functionalized mesoporous organosilica with ultra-high acid concentrations and excellent catalytic activities', Green Chemistry 20 (2018) 1020–1030. DOI: 10.1039/C8GC00002F, https://doi.org/10.1039/C8GC00002F
  3. K. Huang, J.-Y. Zhang, F. Liu, S. Dai, 'Synthesis of Porous Polymeric Catalysts for the Conversion of Carbon Dioxide', ACS Catalysis 8 (2018) 9079–9102. DOI: 10.1021/acscatal.8b02151, https://doi.org/10.1021/acscatal.8b02151
  4. Y.-C. Lou, S.-C. Qi, D.-M. Xue, C. Gu, R. Zhou, X.-Q. Liu, L.-B. Sun, 'Solvent-free synthesis of N-containing polymers with high cross-linking degree to generate N-doped porous carbons for high-efficiency CO2 capture', Chemical Engineering Journal 399 (2020) 125845. DOI: 10.1016/j.cej.2020.125845, https://doi.org/10.1016/j.cej.2020.125845
  5. X. Liu, Y. Zhou, C.-L. Wang, Y. Liu, D.-J. Tao, 'Solvent-free self-assembly synthesis of N-doped ordered mesoporous carbons as effective and bifunctional materials for CO2 capture and oxygen reduction reaction', Chemical Engineering Journal 427 (2022) 130878. DOI: 10.1016/j.cej.2021.130878, https://doi.org/10.1016/j.cej.2021.130878
  6. X. Liu, F.-F. Mao, Z.-M. Li, Z.-H. Xu, X.-J. Shu, J.-P. Mi, Y. Zhou, D.-J. Tao, 'Solidothermal synthesis of nitrogen-decorated, ordered mesoporous carbons with large surface areas for efficient selective capture and separation of SO2', Chemical Engineering Journal 431 (2022) 134142. DOI: 10.1016/j.cej.2021.134142, https://doi.org/10.1016/j.cej.2021.134142
  7. X. Kan, S. Xiao, Y. Zheng, Y. Cao, Y. Xiao, F. Liu, L. Jiang, F.-S. Xiao, 'Sustainable synthesis of ordered mesoporous materials without additional solvents', Journal of Colloid and Interface Science 619 (2022) 116–122. DOI: 10.1016/j.jcis.2022.03.100, https://doi.org/10.1016/j.jcis.2022.03.100
  8. X. Li, H. Yoshikawa, K. Ishihara, K. Miyake, Y. Uchida, N. Nishiyama, 'Solvent-Free Soft-Template Synthesis of Highly Ordered Mesoporous Carbons via Self-Assembly Promoted by Mg(NO3)2', Langmuir 39 (2023) 2036–2042. DOI: 10.1021/acs.langmuir.2c03197, https://doi.org/10.1021/acs.langmuir.2c03197
  9. Y. Zheng, J. Yuan, H. Wu, W. Zhang, X. Kan, S. Li, S. Zhong, Z. Liu, A. Zheng, F. Liu, L. Jiang, 'Solvent-Free Self-Assembly to Ordered Mesoporous Poly(pyridine@Schiff base) Catalysts for Efficient Upcycling of Waste Gaseous Sulfides from Natural Gas', Small 22 (2026) 2510030. DOI: 10.1002/smll.202510030, https://doi.org/10.1002/smll.202510030
  10. X. Li, X. Yang, Z. Amanah, K. Miyake, Y. Uchida, N. Nishiyama, 'Pore size control of ordered mesoporous carbon by amino acid addition in solvent-free soft-template preparation', Microporous and Mesoporous Materials 400 (2026) 113831. DOI: 10.1016/j.micromeso.2025.113831, https://doi.org/10.1016/j.micromeso.2025.113831
  11. S. Wang, J. Yu, Z. Lin, H. Wu, F. Liu, G. Zhang, X. Kan, L. Tong, 'Solidothermal self-assembly to design N-doped ordered mesoporous carbons for efficient capture and conversion of CO2', New Journal of Chemistry 50 (2026) 12817–12826. DOI: 10.1039/d6nj01773h, https://doi.org/10.1039/d6nj01773h