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Materials and Synthesis of pH-Responsive Membranes
Published in Randeep Singh, Piyal Mondal, Mihir Kumar Purkait, pH-Responsive Membranes, 2021
Randeep Singh, Piyal Mondal, Mihir Kumar Purkait
Atom Transfer Radical Polymerization (ATRP) is a technique for the preparation of polymers by using reversible-deactivation radical polymerization [5]. It was independently discovered by Krzysztof Matyjaszewski and Mitsuo Sawamoto in 1995. The atom transfer, as its name suggests, is important and plays a crucial role in the uniform growth of a polymer chain. There are four components of an ATRP reaction system, namely, monomer, initiator, catalyst, and solvent. In general, it implies a transition metal complex as a catalyst and a halide as an initiator. In this process, the transition metal complexes activate a dormant species for the generation of free radicals. Meanwhile, the transition metal is oxidized to a higher oxidation state. ATRP is a reversible process and attains equilibrium instantly, which is inclined toward the side with low radical concentrations. ATRP results in the formation of polymers with a narrow molecular weight range due to the tendency of each chain to grow with a monomer, because the number of initiators defines the number of chain growths [6]. Figure 4.2 shows schematically the process of surface polymerization and grafting using ATRP.
Controlled Radical Polymerization
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
In ATRP, a transition metal complex or halide (Mn-Y/Ligand, where Y may be a ligand or a counter-ion) is used as a catalyst and a halogen compound (e.g., alkyl or acyl halide) is employed as an initiator. The radicals (active species) are generated through a reversible redox process involving abstraction of a halogen atom from a dormant species. The dormant species is the initiator in the initiation step, whereas it is the propagating chain in the propagation step. The generation of radicals is catalyzed by the metal complex, which concomitantly undergoes a one-electron oxidation. Propagation takes place in a manner similar to FRP by addition of monomers to growing radicals. Growth of polymer chains stops after all the monomer is consumed and the halide at the chain end can be reactivated to prepare block copolymers. Termination reactions and other side reactions also occur in ATRP, however, if the polymerization is well controlled, percentage of the terminated polymer chains is very low (<10%). At the most 5% of the total growing polymer chains terminate during the initial, short, nonstationary stage of the polymerization, which generates persistent radicals (X-Mn+1) that reduce the stationary concentration of growing polymer radicals and thereby minimize the contribution of termination. Thus, ATRP shows the characteristics of a RDRP, which are fast initiation and reversible deactivation (slow propagation) with minimal contribution of transfer or termination reactions resulting in almost uniform growth of all the chains to afford low polydispersity.
Controlled Polymerization
Published in Timothy P. Lodge, Paul C. Hiemenz, Polymer Chemistry, 2020
Timothy P. Lodge, Paul C. Hiemenz
where the copper atom is oxidized from Cu(I)Br to Cu(II)Br2. Reaction (4.Z) suggests that the polymerization could be initiated by the appropriate halide of the monomer in question, such as 1-phenylethyl bromide when styrene is the monomer. Alternatively, a standard free-radical initiator such as AIBN could be employed (recall Section 3.3). A particularly appealing aspect of ATRP is the wide variety of monomers that are amenable to this approach: styrene and substituted styrenes, acrylates and methacrylates, and other vinyl monomers. Dienes and amine- or carboxylic acid–containing monomers are more challenging (see Table 4.3).
A review on surface modification methods of poly(arylsulfone) membranes for biomedical applications
Published in Journal of Biomaterials Science, Polymer Edition, 2021
Vahid Hoseinpour, Laya Noori, Saba Mahmoodpour, Zahra Shariatinia
Atom transfer radical polymerization (ATRP) is one of efficient techniques concerning grafting polymers, which is accomplished in rather gentle conditions and permits a diversity of vinyl monomers to be polymerized with well-defined shapes in a controllable way. Generally, three kinds of grafting techniques are employed using ATRP for the preparation of grafted copolymers, which are (1) grafting-from, (2) grafting-to, and (3) grafting-through. For the surface modification, the ATRP was used to change the functionality of the sample so that the chloromethylation of poly(aryl sulfone) under gentle circumstances afforded surface benzyl chloride groups as the active initiators. By employing surface-initiated ATRP, hydrophilic polymers were grafted onto the poly(aryl sulfone) samples. Other controlled living polymerization techniques such as iodine transfer polymerization, free radical-mediated polymerization (SFRP), and reversible addition-fragmentation chain transfer (RAFT) polymerization may also be employed to modify the poly(aryl sulfone) membranes [29].
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 ATRP reaction has the characteristic of the living radical polymerization, as the concentration of the growing polymer chains is governed by the equilibrium reaction. The ATRP initiation technique is simply described as the growth of a typical chain that consists of a very large number of activation/deactivation steps. All of the chains are assumed having similar chances for activation, grow at comparable rates and end up having similar molecular weights. The reaction continues until the whole monomer is consumed. If a different monomer is added into the reactor, it creates a new copolymer block.