Combination ATRP

In combination ATRP, the catalyst is again present in its more stable oxidized form. A slow decomposing conventional initiator e.g. AIBN) is used together with a normal ATRP initiator. Initiator concentrations and rate of radical generation arc chosen such that most chains arc initiated by the ATRP initiator so dispersities can be very narrow.290 The conventional initiator is responsible for generating the activator in situ and prevents build up of deactivator due to the persistent radical effect. Reverse or combination ATRP are the preferred modes of initiation for ATRP in emulsion or miniemulsion (Section 9.4.3.2).290 291... 

Scheme 3 Synthesis of Y-shaped polymers combining ATRP and enzymatic ROP [41, 42]...

Scheme 13 Synthesis of a chiral block copolymer by combining ATRP and enantioselective enzymatic ROP of 4-MeCL [27]...

Lutz, J.F., Borner, H.G., and Weichenhan, K. "Combining ATRP and click chemistry a promising platform toward functional biocompatible polymers and polymer bioconjugates". Macromolecules 39(19), 6376-6383 (2006). 

Scheme 48. Preparation of pNVP-g-pS by combining ATRP with a conventional radical process [317]...

Miller et al. combined condensation polymerizations with both nitroxide-mediated and ROP (Scheme 61) [363]. The condensation polymerization of 2,7-dibromo-9,9-dihexylfluorenes (DHF) was carried out in the presence of a Ni(COD)2 catalyst using (l-(4 -bromophenyl)l-(2", 2", 6", 6"-tetramethyl-l-piperidinyl-oxy)ethyl) as a capping agent/initiator for the CRP of St. This led to a central block of pDHF and outer blocks of pSt (Mn=36,000,Mw/Mn=l.52). Similarly, a diol functionalized with a bromine moiety was used as the end cap-per/initiator for the simultaneous polymerizations of CL and DHF in the presence of both Ni(COD)2 and Sn(Oct)2 (Mn=17,000-31,600, Mw/Mn=1.65-2.39) [363]. The molecular weight distribution narrowed as the content of the DHF in the feed decreased for the condensation/ROP combination. Combining ATRP... 

Scheme 1. Chemoenzymaticpolymerization combining ATRP and eROP in two consecutive steps (1) and in a one-pot cascade approach (2).

The transformation reaction may be also possible by using an opposite strategy, from a controlled radical polymerization to a living anionic polymerization. The most widely applied controlled radical polymerization for this particular transformation is ATRP, due mainly to the fact that hydroxyl and amino groups, which are potential initiating sites for the AROP of certain monomers, are compatible with the ATRP of vinyl monomers. Examples of such transformations have been summarized recently [62, 63], while the general concept is shown in Scheme 11.15, based on an example of the combination ATRP of vinyl monomers with the AROP of lactides [71]. 

The use of click chemistry has also influenced the construction of more sophisticated star polymers, such as those with block copolymer arms. Maty-jaszewski has eloquently demonstrated the preparation of three-arm star block copolymers by again combining ATRP with CuAAC click couphng [109]. In these studies the ATRP of styrene, starting from a trifunctional initiator, yielded the three-arm star homopolymer bearing bromide end groups that subsequently were transformed by substitution with sodium azide. CuAAC reaction with PEO-alkyne... 

Matyjaszewski and Gao synthesized functional polymers by combining ATRP and the click reactions. They also prepared telechelic polymers, star polymers and brush polymers [282]. Formation of telechelic polymers was illustrated as follows ... 

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. 

Shinoda, H., Miller, P. J., and Matyjaszewski, K. (2001). Improving the structural control of graft copol5miers by combining ATRP with the macromonomer method. Macromolecules, 54(10) 3186-3194. 

Recently, two different water-soluble ABC p-stars composed of PEO, P BMA, and poly(2-(diethylamino)ethyl methacrylate) arms plus PEO, P BMA, and poly(A/-isopropylacrylamide) arms were synthesized by combining ATRP with click chemistry in a manner similar to that... 

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