1617 Research Article Received: 25 May 2012 Revised: 8 November 2012 Accepted: 19 November 2012 Published online in Wiley Online Library: 19 February 2013 (wileyonlinelibrary.com) DOI 10.1002/pi.4458 Evolution of the water – monomer dynamic interfacial properties during methyl methacrylate radical polymerization in a single monomer droplet: dependence on the chemical structure of the surfactant Sabrina Belbekhouche, a Thierry Hamaide, b Virginie Dulong, a Luc Picton, a Didier Le Cerf a and Jacques Desbri ` eres c* Abstract This paper deals with the monitoring of the methyl methacrylate (MMA) droplet interface during its polymerization in one single monomer droplet by using a drop tensiometer. The droplet is stabilized by various molecular and polymer surfactants, in particular Pluronic  F68 and pullulan-block-Jeffamine  . The polymerization in one single droplet of the tensiometer can be seen as a way to study the interface of polymer nanoparticles during a mini-emulsion polymerization assuming the concept of a perfect nanoreactor. It was found that the experimental results (surface tension and interfacial rheology) can be connected with MMA radical polymerization. These results demonstrate that the drop tensiometer technique enables interface evolution to be followed during polymer polymerization. c  2013 Society of Chemical Industry Keywords: interface; radical polymerization; dynamic surface tension; polymer surfactant; interfacial rheology INTRODUCTION Sustainable development implies new constraints that need to be taken into account in order to reduce waste and protect fragile environments. Environmental regulations favor environmentally friendly waterborne systems, and so polymerization processes in dispersed media are subject to increasing attention due to their great versatility to produce polymer latexes. Approximately 45% of polymer materials from free radical polymerization are produced in the form of latex and are used in a wide range of products. They find interest in numerous industrial applications as binders, colloidal supports in catalysis and in diagnostic tests, drug delivery devices etc. and also for academic research investigations of various colloidal phenomena. Both emulsion and suspension polymerizations are thermody- namically unstable, so their implementation requires surfactants, and their roles are numerous. In addition, the solubilization of hydrophobic monomers determines the mechanism of particle nucleation (nucleation inside the monomer droplets, micellar nucleation) and ensures the stabilization of the subsequent poly- mer colloidal state. 1,2 Future developments require the synthesis of latexes with controlled properties, exhibiting new morphologies, e.g. multiphase polymer particles with core–shell structures, and/or new coatings, particularly new surfactants that ensure controlled particle sizes and colloidal stability over long-term storage. In addition, the development of new surfactants is particularly relevant in order to reduce the residual concentration of emulsifier in the aqueous phase. Although emulsifier-free latexes can be prepared by using an excess of initiator such as potassium persulfate (in that case, the oligomers bearing ionic groups at their end act as efficient surfactants), some applications require latexes without any ionic coatings. On the other hand, mini-emulsion polymerization offers very interesting perspectives for the development of new polymer materials. 3,4 Each monomer droplet can be seen as a single nanoreactor where homogeneous mass polymerization occurs. In particular, this quite versatile one-step process allows high contents of hydrophobic compounds to be encapsulated in vinyl polymer nanoparticles 5,6 and is the basis for many promising developments in many fields. Therefore, in all cases, polymeric non-ionic surfactants show some obvious advantages with respect to molecular ∗ Correspondence to: Jacques Desbri` eres, Universit´ e de Pau et de Pays de l’Adour, IPREM (UMR CNRS 5254), H´ elioparc Pau Pyr´ en´ ees, 2 Avenue P. Angot, 64053 Pau cedex 09, France. E-mail : jacques.desbrieres@univ-pau.fr a Universit´ edeRouen,LaboratoirePolym` eres,Biopolym` eres, Surfaces, CNRS-UMR 6270 and FR3038, 76821, Mont Saint Aignan, France b Universit´ e Claude Bernard Lyon 1, Ing´ enierie des Mat´ eriaux Polym` eres, UMR CNRS 5223, 69622, Villeurbanne, France c Universit´ e de Pau et de Pays de l’Adour, IPREM (UMR CNRS 5254), H´ elioparc Pau Pyr´ en´ ees, 2 Avenue P. Angot, 64053, Pau cedex 09, France Polym Int 2013; 62: 1617–1623 www.soci.org c  2013 Society of Chemical Industry