Combination of ATRP and CuAAC Reactions

Three different strategies have been employed by various workers to combine ATRP and CuAAC reactions, namely, using (i) azide-telechelic macromonomers, (ii) alkyne-telechelic macromonomers, and (iii) azide or acetylenic moieties within side chains. ATRP has the advantage that the polymers produced by the method contain tu(temiinal)-halogen end groups, which can be substituted to contain azide groups. ATRP is thus an attractive technique for the synthesis of well-de ned end-functionalized polymers. 

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Using a combination of ATRP and CuAAC reactions, suggest an ef cient route for the synthesis of narrow-disperse cyclic poly(iV-isopropylacrylamide) with an average of 80 monomer residues in the polymer ring. 

Scheme 28 Synthesis of cyclic PSTY through the combination of ATRP and CuAAC reactions in DMF...

Scheme 7.25 Synthesis of three-arm PS-PEO star-block copolymer grown from a trifunctional ATRP initiator by combination of ATRP and CuAAC reaction.

Star polymers are the simplest of the branched polymers they represent polymers wherein several linear chains are linked to a single multivalent molecular core 3-arm, 4-arm, and even 12-arm star polymers have been synthesized [43]. Typically, the most efficient process to prepare such polymers is to use a living polymerization, such as anionic polymerization, and terminate the process by a nucleophilic substitution reaction onto a multifunctional core. With the advent of CRPs and the CuAAC reaction, Gao and Matyjaszewski utilized, for the first time, a combination of ATRP and click reaction to prepare star-branched polymers [44] as described earlier, ATRP can be readily used to prepare azide-terminated polystyrene by transforming the terminal bromide, which is typically installed at one chain end during ATRP, to an azide. The PS-azide was then reacted with different core molecules bearing multiple propargyl groups an example is the... 

The combination of ATRP and postpolymerization modi cation by CuAAC click chemistry can be employed to prepare well-de ned tu-(meth)acryloyl macromonomers in an ef cient manner. Thus, polystyrene (PSt) can be prepared by ATRP and subsequently derivatized to contain azide end groups. The azide-terminated polymers can then be reacted with alkyne-containing (meth)acrylate monomers to achieve near-quantitative chain-end functionalization by CuAAC reaction. An ef cient synthesis route is shown in Scheme P12.1.1. 

Various end-functionalized polymers can be synthesized by reacting alkynes with azide-derivatized polymers prepared by ATRR Accordingly, suggest a synthetic strategy to prepare o, tu-dihydroxy-terminated polystyrene by a combination of ATRP and subsequent modi cation via CuAAC reactions. 

Scheme 7.21 Synthesis of rod-coil block copolymers by a combination of ROP, ATRP, and CuAAC reaction.

Among these reactions, the Cu(l)-catalyzed azide-alkyne cycloaddition (CuAAC) is the most widely used. This reaction has been implemented for the preparation of segmented block copolymers from polymerizable monomers by different mechanisms. For example, Opsteen and van Hest [22] successfully prepared poly(ethylene oxide)-b-poly(methyl methacrylate) (PEO-b-PMMA) and PEO-b-PSt by using azide and alkyne end-functionalized homopolymers as the click reaction components (Scheme 11.2). Here, PEO, PSt, and PMMA homopolymers were obtained via living anionic ring-opening polymerization (AROP), atom transfer radical polymerization (ATRP), and postmodification reactions. Several research groups have demonstrated the combination of different polymerization techniques via CuAAC click chemistry, in the synthesis of poly(e-caprolactone)-b-poly(vinyl alcohol) (PCL-b-PVA)... 

Scheme P12.14.1 Synthesis of H02C-PSt-0H by ATRP, followed by azidation and combined TEC and CuAAC reactions. (Adapted from Campos et al., 2008.)...

A similar synthetic protocol was employed for the preparation of BCs containing azopolyesters and PMMA blocks, in this case combining step polymerization, CRP and click chemistry. The azopolyester was first synthesized by transesterification polymerization and subsequently functionalized at the end positions. The PMMA block was then prepared by ATRP using an alkyne-containing initiator and finally the preformed blocks were coupled by CuAAC reaction (Berges et al., 2012b). 

Another approach to synthesize multiarm star block copolymers is based on a combination of CuAAC and the arm-first method (Durmaz et al, 2010). Protected alkyne PS polymers were prepared via ATRP and subsequently crosslinked by a divinyl containing compound. The formed 27-arm star-shaped polymers containing a protected alkyne periphery, was deprotected and subsequently coupled with azide-end-functionalized PEG and PtBuA to form star block or mixed block copolymers. The CuAAC reactions occurred at room temperature for 24 h, surprisingly leading to a full click efficiency. The quantitative character of the latter click reaction at ambient temperatures for such dense polymer structures is in contrast to those obtained by other research groups, as mentioned in previous paragraphs. 

The introduction of the concept of Click chemistry, as a family of organic reactions that fulfil certain criteria drawn by Sharpless and coworkers in 2001 [194], has indeed captured the attention of synthetic chemists in the field of postpolymerization modification towards glycopolymer synthesis [32]. The most widely employed Click reaction is the CuAAC reaction. ATRP has been used extensively in conjunction with CuAAC Click chemistry. This is probably because both techniques are mediated by Cu(I). Moreover, the halogen chain ends of polymers prepared using ATRP can easily be transformed into azides to form what is known as azido-telechelic polymers. Many examples of glycopolymers prepared by the combination of Click chemistry and ATRP have been reported [32, 99]. 

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