polymerization of methyl acrylate from uio-66-ddmat for the synthesis of self-assembled metal-organic framework monolayers

Self-Assembly of Polymer-Grafted Metal Organic Framework Monolayers

Metal-organic frameworks (MOFs) are crystalline, porous materials that offer large surface areas while being readily tunable through modifications of the organic ligands or metal nodes1,2. MOFs are constructed from two components: an organic ligand and metal ions (or metal ion clusters referred to as secondary building units, SBUs). MOFs have been investigated for chemical (e.g., gas) storage, separations, catalysis, sensing, and drug delivery. Generally, MOFs are synthesized in the form of crystalline powders; however, for ease of handling in many applications, formulation into other form factors is desirable if not necessary3,4. For example, mixed matrix membranes (MMMs) of MOFs with polymers have been reported as one particularly useful composite of MOFs and polymers5. However, in some cases, MMMs may have limitations due to the incompatibility/immiscibility between MOF and polymer components5,6. Therefore, strategies have been explored to incorporate polymer grafting directly onto MOF particles to form polymer-grafted MOFs.
Inorganic and metallic nanoparticles exhibit unique behavior in terms of optical, magnetic, catalytic, and mechanical properties7,8. However, they tend to aggregate easily after synthesis, which can hinder their processability. To enhance their processability, polymer chains can be grafted onto the particle surface9. Nanoparticles with high grafting density offer excellent dispersion and stability due to favorable enthalpic interactions between surface polymers and the solvent and entropic repulsion interactions between the particles10. Grafting of polymers onto particle surfaces can be achieved through a variety of strategies11. The most straightforward approach is the &#39;grafting to&#39; particle strategy, where functional groups, such as thiols or carboxylic acids, are introduced at the ends of polymer chains to directly bind to the nanoparticle. When complementary chemical groups, such as hydroxyls or epoxides, are present on the particle surface, polymer chains can be grafted onto these groups via covalent chemical approaches12,13. The &#39;grafting from&#39; particle or surface-initiated polymerization method involves anchoring initiators or chain transfer agents (CTAs) to the surface of nanoparticles and then growing polymer chains on the particle surface through surface-initiated polymerization. This method often achieves higher grafting density than the &#39;grafting to&#39; approach. Furthermore, grafting from enables the synthesis of block copolymers, thereby expanding the diversity of polymer structures that can be immobilized on a particle surface.
Examples of polymer grafting onto MOF particles have begun to emerge, largely focused on installing polymerization sites on the organic ligands of the MOF. In a recent study published by Shojaei and coworkers, vinyl groups were covalently attached to the ligands of Zr(IV)-based MOF UiO-66-NH2 (UiO = Universitetet i Oslo, where the terephthalic acid ligand contains an amino substituent), followed by methyl methacrylate (MMA) polymerization to create polymer-grafted MOFs with a high grafting density (Figure 1A)14. Similarly, Matzger and coworkers functionalized the amine groups on a core-shell MOF-5 (a.k.a., IRMOF-3@MOF-5) particles with 2-bromo-iso-butyl groups. Using polymerization initiated by the 2-bromo-iso-butyl groups, they created poly(methyl methacrylate) (PMMA)-grafted PMMA@IRMOF-3@MOF-515.
In addition to functionalizing the ligand of the MOF for grafting from polymerization, new methods that create sites for polymer grafting via coordination to the metal centers (a.k.a., SBUs) of the MOF have also been explored. For example, a ligand that can bind to the MOF metal centers, such as catechol (Figure 1B), can be used to coordinate to exposed metal sites on the MOF surface. Using a catechol-functionalized chain-transfer agent (cat-CTA, Figure 1B) the MOF surface can be functionalized and made suitable for a grafting from polymerization.
Recently, the aforementioned strategy for synthesizing MOFs-polymer composites has also been used for the creation of free-standing MOF monolayers16,17,18. MOFs such as UiO-66 and MIL-88B-NH2 (MIL = Materials of Institute Lavoisier) were surface-functionalized with pMMA using a ligand-CTA strategy (Figure 1B). The polymer-grafted MOF particles were self-assembled at an air-water interface to form self-supporting, self-assembled metal-organic framework monolayers (SAMMs) with a thickness of ~250 nm. The polymer content in these composites was ~20 wt%, indicating that SAMMs contained ~80 wt% MOF loading. Followup studies showed that different vinyl polymers could be grafted onto UiO-66 to produce SAMMs with different characteristics19. Analytical techniques such as thermogravimetric analysis (TGA), dynamic light scattering (DLS), and gel permeation chromatography (GPC) were used to calculate polymer brush height and grafting density of the surface-grafted MOF-polymer composites.
Herein, the preparation of SAMMs from UiO-66-pMA (pMA = poly(methyl acrylate)) is presented. For the polymerization of methyl acrylate (MA), 2-(dodecylthiocarbonothioylthio)-2-methylpropionic acid (DDMAT, Figure 1B) is used as the CTA19. The functionalization of the UiO-66 particles with cat-DDMAT is essential for the grafting of pMA. Cat-DDMAT can be synthesized through a two-step acylation procedure from a commercially available CTA&#160;and dopamine hydrochloride19. It is also crucial to use UiO-66 particles of uniform size for the successful formation of SAMMs19; therefore, the UiO-66 used in this study was prepared using the continuous addition method20. The polymerization method employed for forming the polymer-grafted MOF particles is photoinduced reversible addition-fragmentation chain transfer (RAFT) conducted under blue LED light (using an in-house-built photoreactor, Figure 2) with a tris(2-phenylpyridine)iridium (Ir(ppy)3) photocatalyst. RAFT polymerization gives exceptionally narrow polymer dispersity that can be finely controlled. Free CTA is included during the polymerization reaction because the ratio of transfer agent to monomer allows for control over the molecular weight during polymerization. The amount of cat-DDMAT transfer agent on the surface of the MOF particles is small; therefore, excess free CTA is added and the amount of monomer to be used is calculated based off of the amount of free CTA present21. After polymerization, the free polymer produced from the free CTA is removed by washing, leaving only the polymer-grafted UiO-66-pMA. Subsequently, this composite is dispersed in toluene at a high concentration and used to form SAMMs at an air-water interface.

Author Spotlight: Exploring Self-Assembled MOF-Polymer Composites

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-coated Particles(고분자 코팅 입자를 사용한 자체 조립된 금속-유기 프레임워크 단층의 합성 및 특성 분석)

자체 조립된 금속-유기 프레임워크 단층의 합성을 위한 UiO-66-DDMAT의 메틸 아크릴레이트 중합

먼저 DMSO에서 2밀리리터의 UiO-66-DDMAT 입자 분산액을 피펫팅하여 교반 플레이트에 있는 10밀리리터의 둥근 바닥 플라스크에 옮깁니다. 플라스크 내부에 교반 막대를 놓습니다. 분산액을 교반하기 시작합니다.다음으로, 12 마이크로 리터의 이리듐 III 페닐 피리딘 촉매 스톡을 플라스크에 피펫팅합니다. 이제 교반하면서 0.45ml의 DDMAT 원액을 플라스크에 추가합니다. 다음으로, 1.7ml의 메틸 아크릴레이트를 20milL 바이알에 피펫팅합니다.마이크로피펫을 사용하여 바이알에 DMSO 2mL를 추가합니다. 바이알을 흔들어 메틸 아크릴레이트를 녹입니다. 메틸 아크릴레이트 용액을 반응 플라스크에 적하 방향으로 천천히 주입합니다.교반 작업을 중단하십시오. 그런 다음 격막으로 플라스크를 단단히 밀봉합니다. 긴 바늘을 질소 공급 매니폴드에 연결합니다.중격을 통해 바늘을 삽입하여 플라스크의 내부 공기층에 도달합니다. 중격을 통해 짧은 바늘을 삽입하여 배출구를 만듭니다. 질소 밸브를 열어 용액의 가스를 제거합니다.긴 바늘을 플라스크 바닥으로 15분 동안 내립니다. 그런 다음 바늘을 내부 공기층으로 올립니다. 탈기 후 짧은 바늘을 순차적으로 제거한 다음 긴 바늘을 제거합니다.그런 다음 질소 밸브를 닫습니다. 이제 교반판에 맞춤형 청색광 LED 광반응기를 놓습니다. 전원 공급 장치에 연결한 후 청색광 방출을 확인하십시오.빛에 노출된 상태에서 혼합물의 교반을 다시 시작하십시오. 과도한 빛 노출을 방지하기 위해 반응기 상부를 알루미늄 호일로 덮으십시오. 반응 용액의 점도가 더 이상 교반할 수 없는 지점까지 증가하면 LED를 끕니다.입자 자체 조립을 위해 먼저 톨루엔에 있는 입자의 분산을 생성합니다. 약 10마이크로리터의 톨루엔 분산액을 탈이온수로 채워진 60mm 너비의 페트리 접시에 조심스럽게 떨어뜨립니다. 물 표면의 톨루엔이 증발하면 구리선으로 만든 고리를 사용하여 단층의 일부를 조심스럽게 제거합니다.나머지 상호 연관된 물을 증발시킨 후, 독립형 단층을 관찰할 수 있었습니다. 농축된 톨루엔 분산액에서 고분자-그래프 금속-유기 프레임워크를 물에 떨어뜨리면 무지개 빛깔의 단층이 생성되었습니다. 구리 와이어 몰드를 사용하여 단층을 들어 올리면 독립형 SAMMS를 형성할 수 있습니다.

Research

JoVE Journal

Chemistry

Polymerization of Methyl Acrylate from UiO-66-DDMAT for the Synthesis of Self-Assembled Metal-Organic Framework Monolayers

Synthesis and Characterization of Self-Assembled Metal-Organic Framework Monolayers Using Polymer-Coated Particles

Metal-organic frameworks (MOFs) are materials with potential applications in fields such as gas adsorption and separation, catalysis, and biomedicine. ...

연구

화학

Surface Modification of UiO-66 with cat-DDMAT for the Synthesis of Self-Assembled Metal-Organic Framework Monolayers