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Star-Shaped Amphiphilic Polymers as Soluble Carriers for Drug Delivery
Published in Vladimir Torchilin, Handbook of Materials for Nanomedicine, 2020
Karolina A. Kosakowska, Scott M. Grayson
By the core-first approach (also called the grafting-from or divergent approach), polymerization is initiated from a multifunctional core. Such cores may be polymeric in nature or, in the case of miktoarm stars, orthogonally functionalized. Just as with linear copolymer synthesis, the polymerization of the contrasting monomers is typically stepwise, such that reagents are added sequentially to achieve distinct copolymer block domains. This route offers the most direct approach (fewest synthetic steps) to obtaining star-shaped copolymers in high yield. Towards that end, any polymerization technique which offers control over the simultaneous growth of multiple arms is well-suited to star polymer synthesis by the core-first approach. These include controlled living radical polymerizations, namely nitroxide-mediated radical polymerization (NMP) [14–16], atom transfer radical polymerization (ATRP) [17, 18] and reversible addition-fragmentation chain-transfer polymerization (RAFT) [19], as well as ring-opening polymerization (ROP) and living anionic/cationic polymerizations. Furthermore, under appropriately controlled polymerization conditions—i.e., faster rate of initiation than propagation and in the absence of competing initiations—the obtained products can be readily purified from residual monomer through simple precipitation. Considering the ultimate commercialization and clinical implementation of polymeric DDSs, the core-first approach is better suited to meet the requirements of good manufacturing practices (GMP) and large-scale production needs.
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]