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Functionalization of Graphite and Graphene
Published in Titash Mondal, Anil K. Bhowmick, Graphene-Rubber Nanocomposites, 2023
Akash Ghosh, Simran Sharma, Anil K. Bhowmick, Titash Mondal
In this technique, surface graphitic material is modified with the initiator moiety and associated with the monomer. These initiators are attached with hydroxyl and carboxyl groups of graphene oxide or covalently modified with a small organic moiety to generate the desired functionality for initiator attachment. Initiator molecule gets anchored onto the basal plane and edges of graphene and initiates the polymerization reaction. The growth of the polymer chain initiates from the graphene surface without any steric hindrance. These make polymer growth more feasible and controllable. Generally, controlled radical polymerization (CRP) has been dominantly used for the synthesis of polymer with narrow molecular weight distribution. Other factors like grafting density, grafting site, functionality, and polymer thickness can easily be controlled using CRP. ATRP and reversible addition fragment transfer (RAFT) are highly considered CRP for preparing polymer brushes on graphene in situ. However, ATRP technique is mainly preferred over RAFT as a narrow polydispersed system can be grown within a controlled manner. Different block copolymers can be synthesized using the technique on the surface of graphitic material.
Recent Advances and Future Perspectives in Heterophase Polymerization
Published in Hugo Hernandez, Klaus Tauer, Heterophase Polymerization, 2021
Controlled radical polymerization has become very important for heterophase polymerization, not only because it allows the synthesis of a wide variety of novel surfactants and stabilizers, but also because it allows a precise control of the architecture and molecular mass of the final polymer. From all types of controlled polymerizations, the reversible addition-fragmentation chain transfer (RAFT) process is perhaps the most promising for being used in heterophase polymerization [58]. The mechanism of RAFT polymerization is similar to a conventional radical polymerization, but additional equilibrium reactions (depicted in Fig. 4.5) are present. Pn represents a growing polymer with chain length n, and X, Z, A, and R represent certain particular molecular groups (e.g., methylene or sulfur for both X and A). A radical is represented by a dot, and k denotes the rate coefficient of reaction.
Synthesis and Functionalization of Magnetic Particles
Published in Jeffrey N. Anker, O. Thompson Mefford, Biomedical Applications of Magnetic Particles, 2020
Erika C. Vreeland, Dale L. Huber
There is another approach to radical polymerization termed “controlled radical polymerization,” or more formally “reversible-deactivation radical polymerization” (Jenkins, Jones, and Moad 2010), which refers to a collection of methods that modifies the kinetics of a radical polymerization to yield a more controlled product. These reactions include the well-known techniques of atom-transfer radical polymerization (ATRP) and reversible-addition-fragmentation chain-transfer polymerization (RAFT), as well as a number of related techniques. These reactions are often referred to as “living radical polymerizations” in the literature, although that term is no longer preferred (Jenkins, Jones, and Moad 2010). These methods share a common approach to controlling the polymerization reaction, and all have a reversible reaction that deactivates the free radical. The precise details of the various approaches are described elsewhere (Matyjaszewski and Spanswick 2005) but can be envisioned simplistically as a free radical reacting with some capping species to form a metastable dormant species that periodically dissociates reforming the active radical. In a well-controlled reaction, the vast majority of the radicals are in the dormant, deactivated state at any given time, while a small proportion of the radicals are in an active state and are adding monomer (if it is available). Individual radicals freely convert between the dormant and active state, while maintaining a low, equilibrium concentration of the active state throughout the reaction.
Mechanical characterization of additively manufactured photopolymerized polymers
Published in Mechanics of Advanced Materials and Structures, 2023
Roberto Brighenti, Liviu Marsavina, Mihai P. Marghitas, Mattia P. Cosma, Matteo Montanari
The light radiation going inside the material is absorbed by photo-initiators, photo-absorbers, and by other light reactive species present in the matrix, leading to a liquid (monomers) solid (polymer chains) transformation. Such a solidification process takes place thanks to the following phenomena: the light radiation induces the photo-initiators molecules whose concentration in the liquid monomer bath is to be converted into free radicals () whose concentration is Then, free radicals react with monomer molecules () inducing the appearance of functional groups (), which constitute growing chains whose evolution in space (chain growth: ) is interrupted either when the polymer chain encounters a free radical (in symbols: ) or when it joints to another chain encountered along its growing path [22]. In the above relations and are reaction rate parameters, depending on the environmental conditions, such as the temperature, characterizing the chemical process. For the sake of simplicity, in the following all the involved chemical processes are assumed to be isothermal so the above rates are constant. The above-described photopolymerization kinetics is representative of a conventional radical polymerization, which is the polymerization mechanism considered in the present study. It is worth mentioning that, in contrast to conventional radical polymerization, the so-called reversible deactivation radical polymerization (RDRP) exists. This latter chemical-physical transformation, whose kinetic mechanism is governed by the same laws of the conventional radical polymerization, allows obtaining a polymer characterized by a “living” or “controlled” radical polymerization. RDRP typically exploits the ability of some chemical species inserted in the resin being printed, of reversibly controlling the propagation of radical species (and thus of polymer chains), allowing for a precise tuning of the polymer chains architecture. This makes possible to obtain intriguing post-synthesis transformations level such as self-healing, network alterations, etc., taking place at the molecular level [29, 30].