Block polymers comprising covalently joined polymeric segments represent a class of nanostructured, multicomponent polymeric materials. Polymerization-induced microphase separation (PIMS) is an intriguing subset that allows for simultaneous nanostructuring during block polymer synthesis. In contrast to polymerization-induced self-assembly (PISA), useful for the spontaneous formation of block polymer micelles, PIMS is well suited to fabricating monolithic block polymer materials by turning a whole polymerization mixture into a nanostructured solid. With the in situ cross-linking feature, PIMS offers a facile route to nanostructured block polymer thermosets in combination with various polymerization techniques, from emulsion polymerization to 3D printing. This review aims to provide a comprehensive overview and practical guide on PIMS by covering its historical background and mechanistic aspects and also highlighting representative material classes and applicable polymerization techniques.
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.
The present invention relates to a method of preparing a hierarchically porous polymer and a hierarchically porous polymer prepared thereby. The method comprises the steps of: (a) polymerizing an external oil phase of a high internal phase emulsion (HIPE) consisting aqueous droplets to produce a cross-linked block copolymer; (b) obtaining a macroporous polymer with interconnected macropores by removing the aqueous droplets; and (c) treating the obtained porous polymer with a base, thereby obtaining a hierarchically porous polymer having three-dimensional mesopores formed in the macroporous walls. According to the method, the macropore size and mesopore size of the hierarchically porous polymer can all be controlled. The hierarchically porous polymer prepared by the method can easily separate polymers having different sizes, and thus is highly useful in the polymer separation field.
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 that an alternating semifluorinated copolymer of chlorotrifluoroethylene (CTFE) and vinyl ether (VE) is an attractive platform for the synthesis of heterograft copolymers consisting of two distinct side chains. The radical terpolymerization of CTFE with PLA-tethered vinyl ether (PLAVE) synthesized by ring-opening polymerization and isobutyl vinyl ether (IBVE) as a spacer produced PLA-grafted fluorinated copolymer via a “grafting-through” manner. Two PLAVEs with different molar masses (2 and 10 kg mol–1) were successfully incorporated, and the grafting density could be controlled by varying the [PLAVE]/[IBVE] initial molar ratio. From the chlorine atoms in the CTFE repeating units, atom transfer radical polymerization (ATRP) of styrene was further employed to grow PS side chains following a “grafting-from” mechanism per each (CTFE-alt-VE) repeating unit dyad. First-order kinetics was observed for the styrene polymerization and supported controlled growth of PS. The resulting heterograft copolymers possessed regularly spaced PS chains and statistically distributed PLA chains on the backbone, generating a nanoscopic disordered morphology via microphase separation driven by incompatibility between PLA and PS. By copolymerization of styrene and divinylbenzene (DVB) in neat ATRP condition, a cross-linked polymer monolith with the disordered bicontinuous morphology could be also prepared via polymerization-induced microphase separation. The cross-linked precursor was converted into a mesoporous polymer with pore size of 3.7–10.4 nm by removal of PLA. The mesopore size was tunable by adjusting the PLA molar mass and styrene/DVB molar ratio.
We report a route to synthesize polylactide-b-poly(ether sulfone)-b-polylactide (PLA-b-PES-b-PLA) containing PES and PLA, which provide a mechanically robust framework and a sacrificial template for pore formation, respectively. High-molar mass PES terminated with fluorine groups was synthesized by the step-growth nucleophilic aromatic substitution (SNAr) reaction, and the chain ends were transformed into benzylic hydroxyl groups by chain end modification. Growth of the PLA using the hydroxyl groups as initiating sites via chain-growth ring opening transesterification polymerization (ROTEP) produced the target triblock copolymer. Although the step-growth polymerization produced a PES middle block with high dispersity, small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) analyses indicated the formation of an ordered lamellar morphology. We further demonstrated that a nanoporous PES with slit-like pores could be obtained by selective removal of the PLA.
We report the synthesis of microporous hyper-cross-linked polymers (HCPs) with increased specific surface area and porosity by the in situ removal of trimethylsilyl (TMS) groups during hyper-cross-linking. We synthesized poly(4-trimethylsilylstyrene-co-vinylbenzyl chloride-co-divinylbenzene)s (P(TMSS-co-VBzCl-co-DVB)s) with different compositions by reversible addition–fragmentation chain transfer copolymerization and converted them into HCPs by reacting with FeCl3 in 1,2-dichloroethane. The nearly quantitative removal of the TMS groups was observed during the reaction following the electrophilic aromatic substitution mechanism, where the TMS group shows higher reactivity than an aromatic hydrogen. Substantial enhancement in pore characteristics including surface area, microporosity, and mesoporosity was noticed up to a certain level of TMSS incorporation, compared with HCP derived from P(VBzCl-co-DVB). We suggest the porogenic TMS group increases porosity mainly by in situ removal via facilitated substitution reaction, which creates permanent voids in the hyper-cross-linked network. The use of TMSS provides a feasible and complementary route to tuning the pore characteristics of HCPs by varying DVB content, and is applicable to the synthesis of hierarchically porous polymers containing micropores within a mesoporous framework from block polymer precursors.
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)
Microcapsules with nanoporous membranes can regulate transmembrane transport in a size-dependent fashion while protecting active materials in the core from the surrounding, and are thereby useful as artificial cell models, carriers for cells and catalysts, and microsensors. In this work, we report a pragmatic microfluidic approach to producing such semipermeable microcapsules with precise control of the cutoff threshold of permeation. Using a homogeneous polymerization mixture for the polymerization-induced microphase separation (PIMS) process as the oil phase of water-in-oil-in-water (W/O/W) double emulsions, a densely cross-linked shell composed of a bicontinuous nanostructure that percolates through the entire thickness is prepared, which serves as a template for a monolithic nanoporous membrane of microcapsules with size-selective permeability. We demonstrate that the nanopores with precisely controlled size by the block polymer self-assembly govern molecular diffusion through the membrane and render manipulation of the cutoff threshold.
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.
본 발명은 블록 공중합체 자기조립을 응용하여 세공 크기가 정밀하게 조절된 다공성 고분자막을 제조할 수 있는 한외여과막용 블록공중합체 및 이의 제조방법에 관한 것이다.
본 발명의 블록공중합체는 블록공중합체를 형성하는 고분자들의 분자량과 함량을 조절하여 세공 크기와 분포를 정밀하게 제어할 수 있으며, 또한, 현재 한외여과막으로 사용되고 있는 폴리이서술폰을 기본 소재로 사용하고 있어 기계적 물성이 우수하다.
본 발명은 현재 한외여과 분리막에 쓰이고 있는 폴리이서술폰을 포함하는 블록 공중합체를 합성하고 이에 기반한 나노다공성 고분자 제조 기술 개발을 통해 차세대 한외여과용 나노다공성 여과막을 구현하였으며, 기존의 상반전법을 통한 폴리이서술폰 한외여과 분리막 제조공정을 적용할 수 있어 평판 분리막 또는 중공사막 분리막으로 쉽게 가공할 수 있으므로 높은 산업적 응용 가치를 가진다.
We report on the use of photoinitiated reversible addition–fragmentation chain transfer (RAFT) polymerization for the facile fabrication of cross-linked nanoporous polymer films with three-dimensionally (3D) continuous pore structure. The photoinitiated polymerization of isobornyl acrylate (IBA) in the presence of 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (CTA) and 2,2-dimethoxy-2-phenylacetophenone as a photoinitiator proceeded in a controlled manner, yet more rapidly compared to thermally initiated polymerization. When polylactide-macroCTA (PLA-CTA) was used, PLA-b-PIBA with high molar mass was obtained after several minutes of irradiation at room temperature. We confirmed that microphase separation occurs in the PLA-b-PIBA and that nanoporous PIBA can be derived from the PLA-b-PIBA precursor by selective PLA etching. To fabricate the cross-linked nanoporous polymer, IBA was copolymerized with ethylene glycol diacrylate (EGDA) in the presence of PLA-CTA to produce a cross-linked block polymer precursor consisting of bicontinuous PLA and P(IBA-co-EGDA) microdomains, via polymerization-induced microphase separation. We demonstrated that nanoporous P(IBA-co-EGDA) monoliths and films with 3D continuous pores can be readily obtained via this approach.
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.
Using a simultaneous block polymerization/in situ cross-linking from a heterofunctional initiator approach, we produced a nanostructured and cross-linked block polymer in a single step from a ternary mixture of monomers and used it as a precursor for a cross-linked nanoporous material. Using 2-(benzylsulfanylthiocarbonylsulfanyl)ethanol as a heterofunctional initiator, simultaneous ring-opening transesterification polymerization of d,l-lactide in the presence of tin 2-ethylhexanoate as a catalyst and reversible addition–fragmentation chain transfer polymerization of styrene at 120 °C produced a polylactide-b-polystyrene (PLA-b-PS) block polymer. Incorporation of divinylbenzene in the polymerization mixture allowed in situ cross-linking during the simultaneous block polymerization to result in the cross-linked block polymer precursor in one step. This material was converted into cross-linked nanoporous polymer by etching PLA in a basic solution.
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