Polymerization of Water-Soluble Monomers by ATRP

Control of the polymerization of water-soluble monomers by ATRP is of particular interest, as free-radical polymerization today is the only viable route for the synthesis of industrially relevant water-soluble polymers. 

Numerous water-soluble monomers have been polymerized via ATRP (Fig. 7.3). Polymerization of acrylic and methacrylic monomers can be problematic as these monomers often contain trace impurities of acryhc or methacrylic acid (MAA). The presence of these carboxylic containing monomers can be detrimental for example, Matyjaszewski et al. have observed that (non-aqueous) polymerization of acrylic acid cannot be controlled with ](bpy)2CuCl] (bpy=2,2 -bipyridine), as the monomer (and the polymer) is likely to coordinate to the metal center, to form a species that is unable to control the polymerization [198]. 

The very first example of aqueous controlled radical polymerization was reported by Matyjaszewski et al. with the polymerization of 34 (HEA), catalyzed by CuBr/bpy in water at 90°C [199]. Contrary to polymerizations carried out in or- 

Armes et al. have intensively studied the aqueous ATRP of various monomers. Using CuBr/bpy as a catalyst, methacrylic acid polymerization has been shown to be possible in aqueous media at pH values between 6 and 9 [200]. The polymerization occurs very slowly (80% conversion after 21 h at 90 °C, [monomer] [initiator] [catalyst] = 28 1 1) yielding polymers with low molecular weight (M = 2.9xl0 g mol ) and a polydispersity of Mw/Mn = 1.3. This is probably due to a loss of catalytic species occurring from the competitive coordination of carboxylic acids to the copper centers, as mentioned for the case of acrylic acid. The choice of pH is important at pH 6, protonation of the bipyridyl ligand occurs, resulting in loss of control. The choice of initiator is equally important the polymerization is only controlled when the methoxy-capped macroinitiator 46 is used. 

3 Controlled Free-Radical Polymerization in Aqueous Systems with Metal Complexes 

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