4 results
Search Results
Now showing 1 - 4 of 4
- ItemDonor-acceptor covalent organic frameworks for visible light induced free radical polymerization(Cambridge : RSC, 2019) Pachfule, Pradip; Acharjya, Amitava; Roeser, Jérôme; Sivasankaran, Ramesh P.; Ye, Meng-Yang; Brückner, Angelika; Schmidt, Johannes; Thomas, ArneCovalent organic frameworks (COFs) are promising materials for applications in photocatalysis, due to their conjugated, porous and chemically stable architectures. Alternating electron donor-acceptor-type structures are known to enhance charge carrier transport mobility and stability in polymers and are therefore also interesting building units for COFs used as photocatalysts but also as photoinitiator. In this work, two donor-acceptor COFs using electron deficient 4,4′,4′′-(1,3,5-triazine-2,4,6-triyl)trianiline and electron rich thiophene-based thieno[3,2-b]thiophene-2,5-dicarbaldehyde or [2,2′-bithiophene]-5,5′-dicarbaldehyde linkers are presented. The resulting crystalline and porous COFs have been applied as photoinitiator for visible light induced free radical polymerization of methyl methacrylate (MMA) to poly-methyl methacrylate (PMMA). These results pave the way to the development of robust and heterogeneous systems for photochemistry that offers the transfer of radicals induced by visible light. © The Royal Society of Chemistry 2019.
- ItemPolymeric monolithic materials: Syntheses, properties, functionalization and applications(Amsterdam : Elsevier, 2007) Buchmeiser, M.R.The synthetic particularities for the synthesis of polymer-based monolithic materials are summarized. In this context, monoliths prepared via thermal-, UV- or electron-beam triggered free radical polymerization, controlled TEMPO-mediated radical polymerization, polyaddition, polycondensation as well as living ring-opening metathesis polymerization (ROMP) will be covered. Particular attention is devoted to the aspects of controlling pore sizes, pore volumes and pore size distributions as well as functionalization of these supports. Finally, selected, recent applications in separation science, (bio-) catalysis and chip technology will be summarized. © 2007 Elsevier Ltd. All rights reserved.
- ItemThermophilic films and fibers from photo cross-linkable UCST-type polymers(Cambridge : RSC Publ., 2015) Liu, Fangyao; Jiang, Shaohua; Ionov, Leonid; Agarwal, SeemaPhoto cross-linkable thermoresponsive polymers of UCST-type based on acrylamide (AAm) and acrylonitrile (AN) useful for preparing thermophilic hydrogel films and fibers are presented. The polymers prepared via free radical and reversible addition fragmentation chain-transfer (RAFT) polymerization methods using N-(4-benzoylphenyl)acrylamide (BPAm) as photo cross-linkable comonomers provided highly stable UCST-type phase transition in water reproducible without hysteresis for many cycles. The cloud point could be manipulated by varying the acrylonitrile amount in the feed. Chemically cross-linked hydrogel films and nanofibers (average diameter 500 nm) were successfully prepared from the ter-copolymers by solution casting and electrospinning followed by UV irradiation. These hydrogels showed a continuous positive volume transition behavior in water with increasing temperature that was utilized for the design of microactuators.
- ItemAmphiphilic block copolymers featuring a reversible hetero Diels-Alder linkage(London [u.a.] : Royal Society of Chemistry, 2014) Langer, M.; Brandt, J.; Lederer, A.; Goldmann, A.S.; Schacher, F.H.; Barner-Kowollik, C.The present article reports the preparation of a novel class of switchable amphiphilic diblock copolymers with a temperature switchable linkage. Reversible addition fragmentation chain transfer (RAFT) polymerization was used to synthesize the individual blocks: for the preparation of the non-polar block, i.e. poly(isoprene-co-styrene) (P(I-co-S)) (9200 g mol-1 ≤ M n ≤ 50000 g mol-1, 1.22 ≤ ≤ 1.36), a chain transfer agent (CTA, 3-((2-bromo-2-methylpropanoyl)oxy)propyl 2-(((dodecylthio)carbonothioyl)thio)-2-methylpropanoate) carrying a bromine group was employed, ready for subsequent cyclopentadienyl (Cp) transformation. For the preparation of the polar block, triethylene glycol methyl ether acrylate (TEGA) was polymerized (6600 g mol-1 ≤ Mn ≤ 35000 g mol-1, 1.12 ≤ ≤ 1.30) using a RAFT agent carrying a phosphoryl Z-group, which is able to undergo hetero Diels-Alder (HDA) ligation with Cp moieties. Both building blocks were conjugated at ambient temperature in the presence of ZnCl2 as catalyst yielding the amphiphilic block copolymer P(I-co-S)-b-PTEGA (16000 g mol-1 ≤ Mn ≤ 68000 g mol-1, 1.15 ≤ ≤ 1.32). To investigate the bonding/debonding capability of the HDA linkage, high temperature nuclear magnetic resonance (HT-NMR) spectroscopy, high temperature dynamic light scattering (HT-DLS) and high temperature size exclusion chromatography (HT-SEC) were carried out, evidencing that efficiently switchable amphiphilic block copolymers were generated (>4 cycles).