Synthesis and Characterization of Anionic Amphiphilic Model Conetworks Based on Methacrylic Acid and Methyl Methacrylate: Effects of Composition and Architecture Gergely Kali, †,‡ Theoni K. Georgiou, † Be ´ la Iva ´ n, ‡ Costas S. Patrickios,* ,† Elena Loizou ⊥,§ Yi Thomann, # and Joerg C. Tiller # Department of Chemistry, UniVersity of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus; Department of Polymer Chemistry and Material Science, Institute of Materials and EnVironmental Chemistry, Chemical Research Center, Hungarian Academy of Sciences, P. O. Box 17, H-1525 Budapest, Pusztaszeri u ´ t 59-67, Hungary; Department of Chemistry, Louisiana State UniVersity, Baton Rouge, Louisiana 70803; Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899; and Freiburg Materials Research Center and Institute for Macromolecular Chemistry, Department of Chemistry, UniVersity of Freiburg, Stefan-Meier-Str. 21, D-79104 Freiburg, Germany ReceiVed October 18, 2006; ReVised Manuscript ReceiVed January 4, 2007 ABSTRACT: A series of amphiphilic conetworks of methacrylic acid (MAA) and methyl methacrylate (MMA) were synthesized using group transfer polymerization (GTP). The MAA units were introduced via the polymerization of tetrahydropyranyl methacrylate (THPMA), followed by the removal of the protecting tetrahydropyranyl group by acid hydrolysis after network formation. 1,4-Bis(methoxytrimethylsiloxymethylene)- cyclohexane (MTSCH) was used as a bifunctional GTP initiator, while ethylene glycol dimethacrylate (EGDMA) served as the cross-linker. Nine of the conetworks were model conetworks, comprising copolymer chains between the cross-links of precise molecular weight and composition. Eight of the model conetworks were based on ABA triblock copolymers, while the ninth was based on a statistical copolymer. The tenth conetwork was not model but randomly cross-linked. The molecular weight and the composition of the linear conetwork precursors were analyzed by gel permeation chromatography and 1 H NMR, respectively, and were found to bear values close to the theoretically expected. FTIR spectroscopic analyses indicated complete polymerization of the EGDMA cross- linker vinyl units and complete hydrolysis of the THPMA units. The degrees of swelling (DS) of all the conetworks were measured in water and in THF as a function of the degree of ionization (DI) of the MAA units. The DSs in water increased with the DI of the MAA units (and the pH), while the DSs in THF presented the opposite trend. Finally, small-angle neutron scattering and atomic force microscopy confirmed nanophase separation in a triblock copolymer-based model conetwork and lack of it in its statistical copolymer counterpart. Introduction Amphiphilic polymer conetworks (APCN) 1-28 have attracted significant attention in recent years due to their unique structure, properties, and wide range of potential applications (see refs 1 and 2 for recent reviews). These include supports for enzymes with significantly improved catalytic activity, 3 templates for the preparation of inorganic nanoparticles, 4 matrices for controlled drug delivery, 5-8 scaffolds for tissue engineering 9-11 and im- plants, 12 materials for soft contact lenses, 13 where softness, mec- hanical strength, 14 and oxygen permeability 14,15 need to be com- bined, antifouling surfaces 16 and promoted release hosts, 17 and pervaporation membranes. 18 Because of their constitution of hydrophilic and hydrophobic polymer chains, APCNs are able to swell in and interact with both aqueous and organic media and can adsorb both polar and nonpolar solutes. Moreover, the immiscibility of their hydrophilic and hydrophobic components leads to phase separation at the nanoscale in APCNs. 3,4,19-22 Another type of conetworks is that of model conetworks, 29 containing polymer chains of well-defined molecular weight and composition. Most of the APCNs reported in the literature so far cannot be considered as model conetworks because they comprise chains, between cross-linking points, with broad length distributions. 1 The synthesis of model APCNs can be ac- complished by the use of “living” polymerization techniques, 30 such as “living” anionic, cationic, radical, and group transfer polymerizations (GTP). One of our research teams has devel- oped a strategy for the synthesis of quasi-model (almost perfect; some defects are present) APCNs, 23-28 involving sequential addition of monomers and cross-linker under “living” polym- erization conditions. In particular, we used GTP, 31-35 a rapid and facile “living” polymerization technique, to prepare quasi- model conetworks based on end-linked ABA triblock copoly- mers at room temperature. 24-27 This procedure was completed within only three polymerization/addition steps in a one-pot preparation. Most of our syntheses involved the use of a bifunctional GTP initiator and the sequential polymerization of two monomers: one hydrophilic and one hydrophobic. 24,25 These two monomers were commercially available and were the hydrophobic methyl methacrylate (MMA) and the hydro- philic positively ionizable 2-(N,N-dimethylamino)ethyl meth- acrylate (DMAEMA). 24,25 The swelling characterization of these APCNs led to the derivation of accurate structure-property relationships since all the conetworks possessed chains of well- defined structures. * To whom correspondence should be addressed. E-mail: costasp@ ucy.ac.cy. † University of Cyprus. ‡ Hungarian Academy of Sciences § Louisiana State University. ⊥ National Institute of Standards and Technology. # University of Freiburg. 2192 Macromolecules 2007, 40, 2192-2200 10.1021/ma062400y CCC: $37.00 © 2007 American Chemical Society Published on Web 02/21/2007