RAFT reagents

The (a-sulfanylalkyl)phosphonates and their difluorinated derivatives are also, by easy radical cleavage of the C-S bond, useful precursors of phospho-nomethyl or phosphonodifluoromethyl radicals, which can be added to double bonds and so, introduced in a variety of structures. Besides, the use of phospho-nodithioformates as radical trapping agents and their use as RAFT reagent for controlled polymerization open a new interesting field of appHcation for these dithioesters. 

Polymer-linked MWCNT nanocomposites were prepared by reversible addition fragmentation chain transfer (RAFT). The RAFT reagent was successfully grafted on to the surface of MWCNTs and PS chains were grafted from MWCNTs via RAFT polymerization [192], By covalently linking acyl chloride functions of functionalized MWCNTs with living polystyryllithium, Huang et al. succeeded in the preparation of polystyrene-functionalized MWCNTs (Scheme 1.32) [193],... 

A further important application of CD is the preparation of relatively low polydispersity polystyrenes (compared to radical CD polymerization) using the water-soluble RAFT reagent 3-benzylsulfanyl thiocarbonylsulfanylpropionic acid (TTC) complexed in aqueous Me-P-CD solution (Fig. 28) [65], This method also allows the direct synthesis of amphiphilic block copolymers in aqueous solution without compatibility issues. 

Many ATRP initiators, including multifunctional systems, are either commercially available or very simple to make [86, 87]. Alkoxyamines and RAFT reagents are usually prepared from the corresponding alkyl halides. ATRP, however, requires the aforementioned catalysts, although they can be used in much less than equimolar amounts. The terminal halogens produced in ATRP can be easily... 

The stracture - reactivity correlation will also help to identify new enviromnentally friendly and less expensive mediating agents. This will include a range of new ATRP catalysts, to be used at ppm amounts in benign media, new alkyl (pseudo)halide initiators, nitroxides operating at lower temperatures and apphcable to methacrylates, and also more enviromnentally friendly RAFT reagents. 

Trithiocarbonates were reported as effective RAFT agents by Le et a Trithiocarbonates are less active than other RAFT CTAs, but are effective at controlling the polymerization of styrenic and meth(acrylic) monomers. Trithiocarbonates are also more easily synthesized and purified than other RAFT reagents. A wide variety of functionalized trithiocarbonates have been reported in the literature, and some are given in Table a number... 

The AIBN-initiated radical copolymerization of P-pinene and methyl acrylate (MA) [58] with n-butyl acrylate (wBA) [60] produced results similar to those described above for AN [59] and thus the structure of the ensuing macro-molecules were characterized by the presence of MA or nBA blocks alternated with single P-pinene units but the incorporation of p-pinene could again be enhanced by the addition of Et2AlCl [58, 60]. When the authors attempted to turn this system into a controlled process by using RAFT reagents, the results were rather disappointing in the case of MA [58], whereas, when wBA was used [60], the results obtained were similar to those reported for AN [59]. 

Amazingly, CSIRO researchers (261) used the RAFT chemistry to make an S-nBA-S triblock copolymer having an Af of 162,000 and a polydispersity of 1.16. This was accomplished using a difunctional RAFT reagent (thiocarbonate (17)). The chemistry is depicted in Figure 49. 

Very recently, Mn2(CO)io was, however, used as a photo-coinitiator for activated alkyl iodides (IDT) [101-103], or RAFT reagents [104] in controlled radical photo(co)polymerizations of VAc, acrylates, styrene, and alkenes, where Mn(CO)5 irreversibly activated iodine terminated chains [101], but the in situ generated Mn(CO)5-I [83] was not involved in the IDT. 

RAFT is another controlled radical polymerization, which gives access to interesting polymer structures [106], The RAFT process offers some advantages because it tolerates a variety of functional groups. However, the RAFT reagents are dithioesters, which are sensitive towards amino groups as they are present in... 

Due to the sensitivity of the dithioesters to nucleophilic attack, no bifimctional initiators have yet been designed for combination of an NCA and a subsequent RAFT reaction. However, reversal of the polymerization sequence, i.e., RAFT polymerization employing a Boc-protected amino group-containing RAFT reagent and subsequent deprotection and amine-initiated NCA polymerization is possible [110]. 

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