Controlled radical polymerization cationic

Other functional core moieties include stable TEMPO-based radicals for controlled radical polymerization,342 crown ethers,343 344 hexacyclenes,170 poly-(quarternary ammonium) cations,345 ethylene thio-lates,346,347 calixarenes,348-352 cyclodextrins,178 inorganic clusters,93-95 340 353,354 dichalcogenides,355 and silses-quioxanes.356... 

Since the discovery of living polymerizations by Swarc in 1956 [1], the area of synthesis and application of well-defined polymer structures has been developed. The livingness of a polymerization is defined as the absence of termination and transfer reactions during the course of the polymerization. If there is also fast initiation and chain-end fidelity, which are prerequisites for the so-called controlled polymerization, well-defined polymers are obtained that have a narrow molar mass distribution as well as defined end groups. Such well-defined polymers can be prepared by various types of living and controlled polymerization techniques, including anionic polymerization [2], controlled radical polymerization [3-5], and cationic polymerization [6, 7]. 

Despite the fast development and versatility of controlled radical polymerization methods for a variety of vinyl monomers, there is still a need for cationic polymerization methods for certain important monomer classes, in... 

Each strategy involves various polymerization techniques, such as conventional and controlled radical polymerizations (CRPs), anionic polymerization, ring-opening metathesis polymerization (ROMP), and cationic polymerization. A judicious combination of a synthetic strategy and a polymerization technique can facilitate the preferential control of certain structural parameters, and this demonstrates distinct advantages with respect to the molecular design, as well as... 

Transformations Involving Cationic and Controlled Radical Polymerization... 

In parallel with the recent advances in controlled radical polymerizations, many transformations of ATRP, NMRP, and RAFT to living cationic polymerization have been reported [62, 63]. A typical example of this transformation is illustrated by the... 

Transformation of free radical polymerization to cationic polymerization is also possible and has been applied to all controlled radical polymerizations, namely, ATRP, NMP, and RAFT (Table 5). The most representative example of this approach is summarized in Scheme 56. A dual initiator containing active sites for both CROP and ATRP is employed first in ATRP generating a macro initiator for the cationic polymer-ization. In this case, PSt macroinitiator was synthesized via ATRP of St initiated by 2-hydroxylethyl 2 -bromobutyrate and consequently utilized in cationic ring polymerization of 1,3-dioxepane (DOP). The AB-type diblock copolymers (PSt-Z -PDOP) that resulted, with narrow polydispersity, indicated that the polymerizations were controlled. 

Table 5 Transformations of controlled radical polymerization to cationic polymerization...

For the synthesis of block copolymers the reader is refered to a previous article in this series (23) and some other works describing the application of various controlled polymerization techniques for their synthesis, such as anionic polymerization (24-26), cationic polsmierization (27,28), controlled radical polymerization (29,30), as well as combinations of various techniques (31-34). Synthetic procedures for star copolymers have been reviewed (35). The first synthesis of a heteroarm star terpolymer with three immiscible blocks has been described in Reference 36. 

Another example of polymerization in self-assembled spherical complexes is related to polymerization of an anionic monomer within the nanocavity of a highly cationic M12L24 coordination sphere with 24 ammonium cations on its interior surface [60]. The highly cationic nanoenvironment of this nanocage was exploited for controlling radical polymerization of anionic sodium p-styrenesulphonates. It was demonstrated that a cationic sphere can have electrostatic interactions with anionic guests and encapsulate them within its cationic interior. 

Various synthetic techniques have been used to obtain homopolymers and copolymers with defined chemical compositions and low polydispersity (1) living anionic or cationic polymerization [26,27], (2) controlled ring-opening polymerization (CROP) [28], and (3) controlled radical polymerization (CRP), which includes (a) atom transfer radical polymerization, (b) reversible addition-fragmentation chain transfer polymerization (RAFT), and (c) nitroxide mediated radical polymerization (NMP) [29-31]. 

Various in situ polymerization methods have been used in the production of well-dispersed silicate layers, including ROP [63-66] and ROMP [67-69] controlled radical polymerization [63, 70-78] such as ATRP, NMP, and RAFT cationic polymerization [79-81] living anionic polymerization [82, 83] and coordination polymerization [56, 60, 84-86]. In addition to the above in situ methods, nanocomposite preparations involving multimode [63] and click chemistry [69] have also been reported. 

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