Copolymerization of a cationic surfmer with HEMA in three-component lyotropic mesophase: A route to nanostructured polymer gels

摘要

The ternary lyotropic mesophase system formed by the surfactant monomer (2-methacry-loyloxyethyl)dodecyldimethylammo-nium bromide (1), 2-hydroxyethyl methacrylate (HEMA), and water is studied on structure, phase behaviour and polymerisation properties. Lyotropic mesophases are only formed at low HEMA content, the 1/HEMA molar ratio being at least 5:1, and the total monomer concentration exceeding 56 wt%. Hexagonal (H_a), cubic (Q_a) and lamellar phases (L_a) occur. The lyotropic phases can be polymerised upon γ-irradiation. However, with increasing HEMA content, the reactivity is progressively diminished. At low radiation dose, a HEMA-rich copolymer is formed, whereas at high dose, a surfactant-rich copolymer is obtained. Homopolymers are not detected. Small angle X-ray scattering and polarizing microscopy indicate that the hexagonal and cubic phases are preserved upon polymerisation whereas the lamellar phase disappears. In non-mesogenic samples with high HEMA content (e.g. a 1/HEMA molar ratio of 3:1), a lyotropic phase behaviour is induced upon polymerisation. In all cases, nanostructured gels with hydrophilic and hydrophobic compartments are formed. A structure model for the copolymerization process in the hexagonal phase is presented.