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

पॉलिमर-लेपित कणों का उपयोग करके स्व-इकट्ठे धातु-कार्बनिक फ्रेमवर्क मोनोलेयर्स का संश्लेषण और लक्षण वर्णन

स्व-इकट्ठे धातु-कार्बनिक फ्रेमवर्क मोनोलेयर्स के संश्लेषण के लिए UiO-66-DDMAT से मिथाइल एक्रिलेट का पोलीमराइजेशन

शुरू करने के लिए, डीएमएसओ में यूआईओ -66-डीडीएमएटी कण फैलाव के दो मिलीलीटर को विंदुक करें और इसे सरगर्मी प्लेट पर स्थित 10-मिलीलीटर गोल नीचे फ्लास्क में स्थानांतरित करें। फ्लास्क के अंदर एक हलचल पट्टी रखें। फैलाव की सरगर्मी शुरू करें।अगला, फ्लास्क में इरिडियम III फेनिलपाइरीडिन उत्प्रेरक स्टॉक के पिपेट 12 माइक्रोलीटर। अब, हिलाते हुए फ्लास्क में 0.45 मिलीलीटर DDMAT स्टॉक घोल डालें। अगला, एक 20 मिलीलीटर शीशी में मिथाइल acrylate के विंदुक 1.7 मिलीलीटर.एक माइक्रोपिपेट के साथ, शीशी में डीएमएसओ के दो मिलीलीटर जोड़ें। मिथाइल एक्रिलेट को भंग करने के लिए शीशी को हिलाएं। धीरे-धीरे प्रतिक्रिया फ्लास्क में मिथाइल एक्रिलेट समाधान ड्रॉप-वार पेश करें।सरगर्मी कार्रवाई बंद करो। फिर, फ्लास्क को सेप्टम से सुरक्षित रूप से सील कर दें। एक नाइट्रोजन आपूर्ति कई गुना करने के लिए एक लंबी सुई कनेक्ट करें.फ्लास्क की आंतरिक वायु परत तक पहुंचने के लिए सेप्टम के माध्यम से सुई डालें। एक आउटलेट बनाने के लिए पट के माध्यम से एक छोटी सुई डालें. समाधान degas नाइट्रोजन वाल्व खोलें.15 मिनट के लिए फ्लास्क के नीचे करने के लिए लंबी सुई कम करें. फिर, सुई को आंतरिक वायु परत तक बढ़ाएं। degassing के बाद, क्रमिक रूप से छोटी सुई को हटा दें, उसके बाद लंबी सुई।फिर, नाइट्रोजन वाल्व बंद करें। अब, सरगर्मी प्लेट पर एक अनुकूलित नीली बत्ती एलईडी फोटोरिएक्टर रखें। इसे बिजली की आपूर्ति से जोड़ने के बाद, नीली बत्ती उत्सर्जन को सत्यापित करें।प्रकाश जोखिम के तहत मिश्रण की सरगर्मी को फिर से शुरू करें। अत्यधिक प्रकाश जोखिम को रोकने के लिए रिएक्टर के ऊपरी हिस्से को एल्यूमीनियम पन्नी के साथ कवर करें। एलईडी को बंद कर दें जब प्रतिक्रिया समाधान की चिपचिपाहट उस बिंदु तक बढ़ जाती है जहां इसे अब हिलाया नहीं जा सकता है।कण स्व-विधानसभा के लिए, पहले, टोल्यूनि में कणों का फैलाव बनाएं। ध्यान से विआयनीकृत पानी से भरा एक 60 मिलीमीटर चौड़ा पेट्री डिश पर टोल्यूनि फैलाव के लगभग 10 माइक्रोलीटर ड्रॉप. जब पानी की सतह पर टोल्यूनि वाष्पित हो गया है, तो मोनोलेयर के हिस्से को सावधानीपूर्वक हटाने के लिए तांबे के तार से बने लूप का उपयोग करें।शेष सहसंबद्ध पानी को वाष्पित करने के बाद, एक फ्रीस्टैंडिंग मोनोलेयर देखा जा सकता है। एक केंद्रित टोल्यूनि फैलाव से पानी पर बहुलक-ग्राफ्टर धातु-कार्बनिक ढांचे को छोड़ने के परिणामस्वरूप एक इंद्रधनुषी मोनोलेयर हुआ। मोनोलेयर को उठाने के लिए तांबे के तार के सांचे के उपयोग ने फ्रीस्टैंडिंग एसएएमएमएस के गठन की अनुमति दी।

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. ...

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