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Recent Developments in MOF-Polymer Composites
Published in Ram K. Gupta, Tahir Rasheed, Tuan Anh Nguyen, Muhammad Bilal, Metal-Organic Frameworks-Based Hybrid Materials for Environmental Sensing and Monitoring, 2022
A bottom-up approach in which polymer ligands transform into crystalline frameworks after the incorporation of metal ions leads to the formation of fascinating MOF-polymer composites, named ‘PolyMOFs’. In this field, Cohen et al. have done pioneering work. The first polyMOFs were synthesized by using a linear polymer containing 1,4-benzenedicarboxylic acid (H2bdc) units by varying different lengths of methylene spacers. The ligands self-assemble into a MOF-5 [Zn4O(bdc)3]n structure by incorporation of Zn2+ ions. The typical MOF-5 has cubic geometry, however, with the use of polymeric ligands, spherical crystals were obtained [19]. In the following reports, Zr4+-based UiO-66 framework polyMOFs with a unique morphology and hierarchical porosity were synthesized with different spacer lengths in the polymer backbone between bdc units. The polymers with precise end-groups and higher molecular weights were obtained by acyclic diene metathesis (ADMET) polymerization, but with reduced surface area [20]. To address the issue of surface area, the isoreticular polyMOFs with enhanced pore volumes and surface areas were prepared [21].
Poly(siloxane)s, Poly(silazane)s and Poly(carbosiloxane)s
Published in Narendra Pal Singh Chauhan, Functionalized Polymers, 2021
Claire E. Martin, Giovanni Fardella, Ricardo Perez, Joseph W. Krumpfer
The final two polymerization techniques require a transition metal catalyst. Figure 8C shows the polymerization of 1,1,3,3-tetramethyldisiloxane and 1,1,3,3-dimethyl-1,3-divinyldisiloxane catalyzed by a platinum catalyst. Given the high efficiency and exothermic nature of hydrosilylation reactions, such preparations must have very careful temperature control in order to prevent explosions. Acyclic diene metathesis (ADMET) is another route towards creating polycarbosiloxanes, especially those containing unsaturated bonds in the backbone. ADMET requires the use of common ruthenium catalysts, such as Grubb’s II, to prepare polymer (Smith and Wagener 1993). Both hydrosilylation and ADMET can also be used in the preparation of polycarbosilanes through the use of difunctional silanes or monomers that do not contain siloxane bonds. Furthermore, the number of different addition techniques shown here opens up many avenues to orthogonal syntheses, particularly for dendrimer preparations, which are briefly discussed later in this chapter.
Ring-Opening Polymerization and Metathesis Polymerizations
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
A metathesis reaction is defined as a chemical transformation in which atoms from different functional groups interchange with one another, resulting in the redistribution of functionality yielding similar bonding patterns for both molecules.38 The term olefin metathesis was proposed by Calderon in 1967 and since then it has been applied for the synthesis of complex molecules, particularly cyclic systems to prepare active pharmaceutical ingredients as well as polymers. It is a great advancement in polymer synthesis since functionalized polyolefins are made easily accessible using metathesis polymerization. Two types of metathesis polymerization will be discussed in this chapter—(a) ring-opening metathesis polymerization (ROMP),39 a chain-growth polymerization and (b) acyclic diene metathesis polymerization (ADMET), a step-growth polymerization.
Interaction between the end groups and the main chain of conjugated polymers by time-resolved EPR and fluorescence spectroscopy
Published in Molecular Physics, 2019
Motoko S. Asano, Sho Hashimoto, Takuya Shinozuka, Yasutaka Fushimi, Kotohiro Nomura
Acyclic diene metathesis (ADMET) polymerisation is a promising method for synthesis of high molecular weight poly(2,5-dialkylphenylene-1,4-vinylene)s (PPVs), poly(9,9-dialkylfluorene-2,7-vinylene)s (PFVs), poly(N-alkylcarbazole-2,7-vinylene)s [27–35]. This is because the approach not only affords defect-free materials, but also enables exclusive end-functionalisation by combining olefin metathesis with Wittig-type cleavage [36,37]. We have demonstrated the feasibility to introduce the same or different end groups into the conjugated polymer chain-ends by adopting this approach [22].