Hawker 2 Living Polymerizations

This concept was further developed by Hawker and coworkers [193, 194], who performed dual living polymerizations from a single initiating molecule, without the requirement of an additional reaction. The compatibility of either NMRP or ATRP with the AROP of CL was demonstrated by the synthesis of a variety of well-defined block copolymers. The basic strategy followed for the dual polymerization is shown in Scheme 11.43. 

Harth E, BosmanA, Benoit D, Helms B, Frechet JMJ, Hawker CJ. A practical approach to the living polymerization of functionalized monomers application to block copolymers and 3-dimensional macromolecular architectures. Macromol Symp 2001 174 85-92. 

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 literature on Nitroxide-Mediated Polymerization (NMP) through 2001 was reviewed by Hawker el al. vu 7 More recently the subject has been reviewed by Sluder and Schulte10 and Solomon.109 NMP is also discussed by Fischer110 and Goto and Fukuda" in their reviews of the kinetics of living radical polymerization and is mentioned in most reviews on living radical polymerization. A simplified mechanism of NMP is shown in Scheme 9.17. 

Malmstrom, E.E. and Hawker, C.J. Macromolecular engineering via living free-radical polymerizations, Macromol. Chem. Phys., 199, 923, 1998. 

Hawker, C. J. Bosman, A. W. Harth, E. New polymer synthesis by nitroxide mediated living radical polymerizations. Chem. Rev. 2001,101, 3661-3688. 

Hawker CJ, Barclay GG, Orellana A et al. (1996) Initiating systems for nitroxide-mediated living free radical polymerizations synthesis and evaluation. Macromolecules 29 5245-5254... 

Husseman M, Malmstrom EE, McNamara M, Mate M, Mecerreyes D, Benoit DG, Hedrick JL, Mansky P, Huang E, RusseU TP, Hawker CJ (1999) Controlled synthesis of polymer brushes by Living free radical polymerization techniques. Macromolecules 32 1424-1431... 

C.J. Hawker, A.W. Bosman, E. Harth, C/iem. Rev. 101,3661-3688 (2001) (New Polymer Synthesis by Nitroxide Mediated Living Radical Polymerization)... 

Hawker et al. 2001 Hawker and Wooley 2005). Recent developments in living radical polymerization allow the preparation of structurally well-defined block copolymers with low polydispersity. These polymerization methods include atom transfer free radical polymerization (Coessens et al. 2001), nitroxide-mediated polymerization (Hawker et al. 2001), and reversible addition fragmentation chain transfer polymerization (Chiefari et al. 1998). In addition to their ease of use, these approaches are generally more tolerant of various functionalities than anionic polymerization. However, direct polymerization of functional monomers is still problematic because of changes in the polymerization parameters upon monomer modification. As an alternative, functionalities can be incorporated into well-defined polymer backbones after polymerization by coupling a side chain modifier with tethered reactive sites (Shenhar et al. 2004 Carroll et al. 2005 Malkoch et al. 2005). The modification step requires a clean (i.e., free from side products) and quantitative reaction so that each site has the desired chemical structures. Otherwise it affords poor reproducibility of performance between different batches. 

With the recent development of living radical polymerization, the problem of gel formation during radical polymerization possibly can be controlled. This is because termination by radical chain coupling is virtually eliminated. Thus Hawker reported the preparation of soluble hyperbranched polystyrene using alkoxyamine IV as a living radical polymerization initiator [12]. 

Scheme 1.33. Nitroxide-mediated living radical polymerization of styrene using TEMPO. After Hawker et al. (2001).

Bashir R, Hilt JZ, Elibol O, Gupta A, Peppas NA (2002) Micromechanical cantilever as an ultrasensitive pH microsensor. Appl Phys Lett 81(16) 3091-3093 Benoit D, Chaplinski V, Braslau R, Hawker CJ (1999) Development of a universal alkoxyamine for "living" free radical polymerizations. J Am Chem Soc 121 3904-3920 Caykara T, Kiper S, Demirel G (2006) Thermosensitive poly(N-isopropylacrylamide-co-acryl-amide) hydrogels synthesis, swelling and interaction with ionic surfactants. Eur Polymer J 42 348-355... 

Hawker CJ. Nitroxide-Mediated Living Radical Polymerizations. In Matyjaszewski K, Davis TP, editors. Handbook of Radical Polymerization. Hoboken (NJ) John Wiley and Sons ... 

Hawker, C.J., 1994. Molecular-weight control by a living free-radical polymerization process. J. Am. Chem. Soc. 116 (24), 11185-11186. 

Hawker CJ, Bosman AW, Harth E (2001) New polymer synthesis by nitroxide mediated living radical polymerization. Chem Rev 101 3661-3688 Houben-Weyl (1987) Methoden der organischen Chemie. Makromoleknlare Stoffe, vol E20. Thieme, Stuttgart/New York... 

S. Blomberg, S. Ostberg, E. Harth, A.W. Bosman, B. van Horn, C.J. Hawker, Production of crosslinked, hollow nanoparticles by surface-initiated living free-radical polymerization,/. Polym. Sci., Part A Polym. Chem. 2002, 40,1309-1320. 

Principle of controlled radical polymerization (CRP) exemplified via nitroxide-mediated polymerization (NMP). X, nitroxide R,-, living polymer molecule P,+y, dead polymer molecule R (, dormant polymer molecule /, chain length RqX, NMP initiator activation kj a, deactivation /c2, propagation /ctc, termination by recombination (Fig. 10.5A) (Malmstrom and Hawker, 1998) for simplicity the activation/deactivation rate coefficients of the initiator species are assumed the same as... 

Butadiene and isoprene have to date only been polymerized in a living radical fashion via NMP (81). The group of Hawker has shown that nitroxides with an alpha C—H bond to the nitrogen can successfully be applied in the polymerization of dienes. The result is a linear increase of molar mass with conversion, and a PDI below 1.1. 

Stehling, U. M. Malstrom, E. E. Waymouth, R. M. Hawker, C. J. Synthesis of polyfolefin) graft copolymers by a combination of metallocene and living free radical polymerization techniqnes. 

Figure 11.10 Synthesis of three-arm star-shaped polystyrene by TEMPO-mediated living radical polymerization and hydrolysis to TEMPO-capped linear polystyrene. (Drawn following the synthesis method of Hawker, 1995.)...

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