Synthesis and characterization of anionic amphiphilic model conetworks based on methacrylic acid and methyl methacrylate: Effects of composition and architecture

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 1H 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. © 2007 American Chemical Society.