| Polymerization in lyotropic liquid crystalline (LLC) media is a promising method for synthesis of nanostructured organic materials. In this study the photopolymerization kinetics and molecular weight evolution in LLC systems have been investigated. Utilizing a kinetic model, individual contributions of initiation efficiency and monomer segregation to the polymerization behavior and structural development have been elucidated. Polymerization occurs much more rapidly and higher molecular weight polymer results in ordered LLC phases compared to isotropic solution. Segregation of oil soluble monomers in nonpolar domains leads to relatively rapid polymerization and high molecular weight in LLC phases formed with low surfactant concentration. Association of water soluble monomers in polar domains yields the opposite behavior. LLC topology and polarity also impact the initiation process, further influencing polymerization behavior and molecular weight evolution. Bulky, hydrophobic initiators exhibit greater efficiency in more ordered LLC phases at relatively high surfactant concentrations while the efficiency of smaller, hydrophilic initiators is less affected by LLC structure.; In addition to understanding the effect of LLC order on the polymerization rate, the converse effect of rate on final polymer structure has been determined using scanning electron microscopy. Interestingly, the speed of polymerization significantly impacts polymer structure and properties when all other factors are equal. The rapid kinetics of photopolymerization produce robust, anisotropic materials with relatively high surface area. The slower kinetics of thermal polymerization yield more randomly ordered materials with lower surface area. Other factors affecting polymer morphology and properties have been investigated including polymerization temperature, cross-link density, monomer polarity, and LLC structure. Significant control of polymer structure has been demonstrated using different LLC morphologies by variation in surfactant concentration and temperature. Highly periodic polymers, in certain cases nanostructured polymers, were obtained using cross-linking polar monomers. Oriented rod-shaped structures measuring 200 nm in diameter result from polymerization of water soluble methacrylates in the hexagonal phase. Select acrylates yield aligned lamellar structures and monodisperse pores from the same phase. These interesting morphologies do not result from direct LLC templating, but from a nucleation, phase separation, and growth mechanism governed by anisotropic diffusion of monomer and polymer in the LLC system. |
