One-pot surfactant-free functional latexes by controlled radical polymerization in ab initio emulsion Jeff Tonnar and Patrick Lacroix-Desmazes * Received 31st January 2008, Accepted 12th March 2008 First published as an Advance Article on the web 15th April 2008 DOI: 10.1039/b801752b Acrylic acid is commonly added to industrial formulations in order to enhance the stability and the properties of the final latexes. Herein, we report the first one-pot surfactant-free batch ab initio emulsion polymerization process to obtain acrylic acid functionalized polymer latexes by controlled radical polymerization. Reverse Iodine Transfer Polymerization (RITP) is successfully used to synthesize stable and uncolored latexes with good control over the molecular weights. The in situ synthesis of amphiphilic poly(acrylic acid-co-butyl acrylate) gradient copolymers, which provide an electrosteric stabilization to the latex, enables the polymerization in a surfactant-free process. The living character of this novel functional latex is demonstrated by successful block copolymer synthesis. Introduction Emulsion polymerization is the method of choice to synthesize large quantities of polymer and latex at an industrial scale. 1,2 In industrial applications, latexes are commonly stabilized electro- statically by the addition of an ionic surfactant. Small amounts of carboxylic acid monomers are often employed in latex formula- tions in order to improve the colloidal stability of the polymer particles. Indeed, the carboxylic acid monomers not only enhance the performance of the latex, such as adhesive properties, mechanical properties of the films and compatibility with pigments, but they also allow the incorporation of functional, potentially ionic groups on the particle surface. 3 The carboxylic acid groups at the particle surface contribute to the latex stabili- zation by steric and electrosteric mechanisms. 4 This strategy permits reduction in the amount of surfactants that can cause deleterious side effects on the properties of the final product. 2 In recent years, controlled radical polymerization (CRP) 5 has allowed the synthesis of complex macromolecular architectures like gradient, block and star copolymers. Among CRP methods, the most wide-spread ones are nitroxide-mediated polymeriza- tion (NMP), 6 metal-catalyzed radical polymerization, 7–9 iodine transfer polymerization (ITP), 10 and reversible addition–frag- mentation chain transfer polymerization (RAFT/MADIX). 11 All these methods rely on a reversible activation–deactivation of the growing polymer chains. 12 Although CRP in bulk or solution polymerization was widely studied, the implementation of CRP in dispersed aqueous media and especially in ab initio emulsion polymerization faced some difficulties. 13–15 Controlled radical polymerization has allowed the synthesis of carboxylic functional polymer latexes using multi-step proce- dures. Emulsion polymerization was achieved by using an amphiphatic RAFT agent. This RAFT agent was used in the aqueous phase polymerization of the water soluble acrylic acid to a low degree of polymerization. 16,17 The resulting oligomeric (AA) x –RAFT agent was then used in the polymerization of the hydrophobic butyl acrylate giving micelles (eventually frozen micelles) in which the controlled polymerization of butyl acrylate was continued. No surfactant was necessary because the latex was stabilized by the anchored poly(AA) moieties. 16–18 A similar approach was used in NMP, based on the prior formation of a hydrosoluble poly(sodium acrylate) macroalkoxyamine, followed by emulsion polymerization of a hydrophobic mono- mer. The semi-continuous addition of monomer required at the early stages of RAFT emulsion polymerization to avoid droplet nucleation is not necessary with macroalkoxyamine (batch process). The initiator efficiency of the alkoxyamine was however limited to 35% for styrene and 60% for butyl acrylate polymer- ization. 19,20 RAFT and NMP were performed by a multi-step procedure and neither of these methods have succeeded in preparing functional polymer latexes by a one-pot surfactant- free ab initio emulsion polymerization. Recently a new controlled radical polymerization method, called Reverse Iodine Transfer Polymerization (RITP), based on the use of molecular iodine as a control agent (Scheme 1) was developed by our group 21–23 and patented by Solvay. 24,25 In RITP, iodinated transfer agents are synthesized in situ in the reaction medium. When RITP was implemented in emulsion polymerization, the hydrolysis of one part of the iodine was responsible for an upward deviation of the molecular weights. 26,27 This problem was overcome by regenerating the hydrolyzed iodine by addition of an oxidant 28,29 in miniemulsion polymerization of styrene 30,31 and in ab initio emulsion poly- merization of butyl acrylate. 32 The poorly water soluble and hazardous molecular iodine I 2 was even successfully replaced by the water soluble non hazardous and non toxic sodium iodide NaI in combination with potassium persulfate. 33 Moreover, the living character of the resulting latexes was demonstrated by executing block copolymerizations. Herein, we report the first results on RITP in ab initio emulsion to prepare surfactant-free latexes with acrylic acid as a functional comonomer. Institut Charles Gerhardt - UMR5253 CNRS/UM2/ENSCM/UM1 - Inge´nierie et Architectures Macromole´culaires, Ecole Nationale Supe´rieure de Chimie de Montpellier, 8 rue de l’Ecole Normale, 34296 Montpellier Cedex 5, France. E-mail: patrick.lacroix-desmazes@enscm. fr; Fax: (+33) 4 67 14 72 20 This journal is ª The Royal Society of Chemistry 2008 Soft Matter , 2008, 4, 1255–1260 | 1255 PAPER www.rsc.org/softmatter | Soft Matter