NIPAM, living polymerization

As for the other methods mentioned above, NMP and ATRP living polymerizations of NIPAM have also been reported very recently. NMP has been carried out with initiator 6 (Fig. 3), cK-hydrogen alkoxyamine derivatives, instead of the TEMPO-based systems [53-55]. Although the living polymerization behavior has not been reported in detail, the synthesis of homopolymer of NIPAM with a narrow MWD, its block copolymers with polystyrene (PS) [53], and well-controlled star block copolymers having PNIPAM and PS segments was achieved by Hawker and Fr6chet et al. [54]. On the other hand, the successful ATRP of NIPAM has been reported by Masci et al. [56] and StOver et al. [57]. In each case, alkyl 2-chloropropionate (7), copper(I)... 

The anionic polymerization of NIPAM derivatives having an LCST has also been examined in detail [63]. Because these monomers had no acidic amide protons, the living polymerization proceeded easily in comparison with NIPAM, and the influence of tacticity, etc., has been examined. 

Dithiocarbamatc 16 has been used to prepare low dispersity PMAA ( Mw 1 Mn-1.2).52 Photopolymerization of S in the presence of dithiocarbamate 16 also displays some living characteristics (molecular weights that increase with conversion, ability to make block copolymer). However, 17 appears to behave as a conventional initiator in S polymerization.53 The difference in behavior was attributed to the relatively poor leaving group ability of the 2-carboxyprop-2-yI radical. This hypothesis is supported by MO calculations. Dithiocarbamatc 17 was used to control polymerizations of MMA,54 HEMA54 and NIPAM.5... 

The synthesis of a well defined block copolymer, containing a poly(N-vinylimidazole) block (PVim), has been demonstrated by Ge et al. [23]. The polymerization was realized via a RAFT procedure employing xanthates as chain transfer agents. Initially, the polymerization of NIPAM monomer, affording PNIPAM macro-CTA, was realized followed by the polymerization of Vim, Figure 4. The obtained block copolymers had controllable molecular characteristics with a Mw/M value ca. 1.2. The living nature of the Vim polymerization has been confirmed by kinetic experiments, for the first 150 min of the polymerization reaction. It has to be noted that the above procedure was the first example of the synthesis of PVim containing block copolymers. 

Heterobifiinctional block copolymers of PEO and poly (N-isopropylacrylamide) (PNIPAM) were synthesized by RAFT polymerization of N-isopropylacrylamide (NIPAM) using a PEO-based trithiocarbonate macromolecular CTA. The polymerization exhibited all the expected characteristics of living radical polymerization and allowed the synthesis of copolymers with different lengths of the PNIPAM block. 

Living cationic polymerization can be also transformed to RAFT polymerization to synthesize well-defined block copolymers. Very recently, PIB-CTA was prepared by site transformation of hydoxyl-terminated PIB, which was obtained by living cationic polymerization of IB using the TMPCl/TiCU initiation system and subsequent conversion of chlorides into hydroxyl groups. Consequently, RAFT polymerization of MMA or St was mediated by the PIB-CTA resulting in AB block copolymers with narrow polydispersities (Scheme 55). In a very similar report, the PIB-CTA was prepared via click chemistry rather than esterification reaction and used in the polymerization of NIPAM yielding PIB-b-PNIPAM. " ... 

In this paper, the living radical polymerization of N-isopropylacrylamide (NIPAM) and the living cationic polymerization of vinyl ethers having oxyethylene groups are outlined (Fig. 1), as they constitute a new wave of the... 

Development of Living Radical Polymerization and Radical Polymerization of NIPAM... 

Numerous reports describing the successful RAFT polymerization of NIPAM have appeared [35]. For example, in 2000, Rizzardo et al. first reported the RAFT living radical polymerization of NIPAM by AIBN employing benzyl dithiobenzene or cumyl dithiobenzoate RAFT agents 1 (Fig. 2) [39]. Fukuda et al. synthesized block copolymers using these systems [40]. Subsequently,... 

Many studies have been carried out on the anionic polymerization of NIPAM using conventional organometallic catalysts. However, the acidic amide proton of NIPAM inhibited anionic polymerization, instead inducing hydrogen-transfer polymerization imder basic conditions, as shown in Scheme 2. The polymers obtained were insoluble in water and did not show LCST phase separation [14,15]. Recently, the polymerization of monomers in which this active hydrogen was protected by methoxymethyl or trialkylsi-lyl group 9,10 was examined and living anionic polymerization has become possible [60-62]. Ishizone et al. have prepared atactic PNIPAM with a narrow MWD via the anionic polymerization of N-methoxymethyl-NIPAM (9)... 

The establishment of the living radical polymerization of NIPAM encouraged not only many polymer chemists but also polymer physicists to prepare functionalized NIPAM polymers with various controlled sequences and/or shapes, as discussed in this chapter. In the following parts, block, random, or graft copolymers will be simply designated by the acronym A-B for a diblock copolymer, A-B-A for an ABA-type triblock copolymer, A-B-C for an ABC-type triblock copolymer, A-co-B for a random copolymer, A-g-PNIPAM for grafting of NIPAM segments onto the polymer A. For example, PNIPAM-PEO stands for a diblock copolymer of PNIPAM and PEO. 

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