China
Africa
Explore chapters and articles related to this topic
Electrochromics: Processing of Conjugated Polymers and Device Fabrication on Semi-Rigid, Flexible, and Stretchable Substrates
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Matthew Baczkowski, Sneh Sinha, Mengfang Li, Gregory Sotzing
While conjugated polymers have been explored both as an EC layer and an ion storage layer, a new class of polymers known as “radical polymers” has recently gained significant attention as an ion storage layer for ECDs. Radical polymers are non-conjugated polymers that are redox active and are defined as macromolecules with a non-conjugated backbone with stable radical groups as pendant groups. The unpaired electrons are stabilized in radical polymers either by bulky substituent groups or through substituent groups that contain a substantial degree of conjugation in the pendant group. The large amounts of unpaired electrons, which are present on nearly every repeating unit of the polymer chain, are capable of undergoing reversible redox reactions. Radical polymers find application in organic electronic devices because of their ability to transport charge in both electrolyte and solid-state devices. For example, the nitroxide functionality is often used in radical polymer systems, which can undergo either oxidation to form the oxoammonium cation species or reduction to form the aminoxyl anion species. Similar to conjugated polymers, the tuning of the pendant groups generates either hole-transporting (p-type) or electron-transporting (n-type) radical polymers.135
Recent Advances and Future Perspectives in Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
Nitroxide-mediated polymerization (NMP) is another type of controlled polymerization mechanism, which has been explored in heterogeneous systems. NMP polymerization uses nitroxide structures, as radical traps due to the relatively stable (persistent) radicals formed by nitroxides (such as those depicted in Fig. 4.6). Their operating principle is similar to RAFT in the sense that an equilibrium reaction (reversible deactivation) controls the polymerization (Fig. 4.7).
Solar Cells Based on Diblock Copolymers: A PPV Donor Block and a Fullerene Derivatized Acceptor Block
Published in Sun Sam-Shajing, Sariciftci Niyazi Serdar, Organic Photovoltaics, 2017
Rachel A. Segalman, Cyril Brochon, Georges Hadziioannou*
The use of a fully conjugated macromolecular initiator (macroinitiatior) will bypass this difficulty. Indeed, it is possible to convert the rod block into a macroinitiatior and then polymerize the second block directly onto it. This route has been used in conjunction with anionic living polymerization by Marszitzky et al. [24] to polymerize ethylene oxide with a polyfluorene macroinitiator as the conjugated rod block. Anionic polymerization, which is a popular route towards block copolymers because it yields nearly monodisperse molecular weight distributions, requires drastic reaction conditions (very high sensitivity to impurities and functional groups) and cannot be used with a wide variety of monomers, particularly those with functional groups. In fact, controlled/‘living’ radical polymerization techniques are more versatile than anionic polymerization. Also, a donor–acceptor rod–coil block copolymer requires the use of functional monomers for the grafting of C60 or other electron-accepting groups. The two main controlled/‘living’ radical polymerization techniques are the nitroxide-mediated radical polymerization (NMRP) [25] and the atom transfer radical polymerization (ATRP) [26]. These are compatible with a wide range of monomers (acrylates, styrene, etc.) including functionalized derivatives and result in narrow polydispersities molecular weight control, which are necessary for controlled self-assembly. Furthermore, (macro) initiators for NMRP or ATRP are very stable and it is possible to purify and characterize these compounds before (re)initiating the radical polymerization. Various rod–coil block copolymers have been synthesized by polymerization of styrene or methacrylate derivatives either by ATRP with polyfluorene as macroinitiatior [27] or by NMRP with PPV [28,29]. The use of conjugated macroinitiators for controlled/‘living’ radical polymerization is actually one of the best routes for the synthesis of the targeted rod–coil diblock copolymer. The general synthesis strategy is displayed in Figure 18.2.
Atom transfer radical polymerization initiated by activator generated by electron transfer in emulsion media: a review of recent advances and challenges from an engineering perspective
Published in Journal of Dispersion Science and Technology, 2023
Mohammed Awad, Ramdhane Dhib, Thomas Duever
The CRP technique can take place according to three different reaction schemes: 1) Atom transfer radical polymerization (ATRP), 2) Nitroxide – mediated radical polymerization (NMRP), and 3) reversible addition-fragmentation chain transfer polymerization (RAFT). Dynamic equilibrium reaction between dormant species and active radicals is the standard of all three CRP techniques, this is to synthesize a wide range of polymers with a low polydispersity index (Ð) under mild conditions. The equilibrium reaction helps reduce the termination reaction by providing a low concentration of radicals and simultaneously allowing a slow growth of polymer chains.[12,21,22] The achievement of reasonable chemical control over the reaction extent is governed by the fast reciprocity between the dormant and active species, as well as the instantaneous and rapid initiation of all chains. Consequently, this may not occur unless the initiator has high efficiency and negligible chain breaking reactions. In fact, the same lifetime of the propagating radicals will result from a similar chain length in all polymer chains, which indicates a Ð close to unity. In other words, during the chain growth the propagation reaction is slowed down by the dynamic equilibrium reaction, which results in a narrow Ð of the polymer chains.[23]
Chiral nitroxide radical with terminal trifluoromethoxy group
Published in Liquid Crystals, 2023
Yoshiaki Uchida, Takuya Akita, Norikazu Nishiyama
Liquid crystalline (LC) compounds incorporating a chiral nitroxide group into their mesogen cores (LC-NRs) show unique magnetic properties [1,2]. The core nitroxide group gives the molecule chirality, large electric dipole moments, and paramagnetic properties. They affect the phase transition behaviour of the compound; large electric dipole moments decide intermolecular attraction and repulsion [3], and chirality in the mesogen core strongly induces twisted structures [4]. There have been LC-NRs showing a variety of LC phases; nematic [5], chiral nematic [5], smectic A [6], chiral smectic A [6], smectic C [6], chiral smectic C [7], twist grain boundary [6] and columnar phases [8].