Photopolymerization In Supercritical Carbon Dioxide

Super-critical fluid refers to such a condition that the temperature and pressure of the material are higher than its critical point. In this condition gas-liquid interface disappears, but the characters of both the liquid and the gas are retained. The density of supercritical fluid is similar to liquid, but its solubility, heat transfer coefficient, viscosity and diffusion coefficients are approximate to those of gas. The physical properties of supercritical fluid can be continuously adjusted by changing temperature or pressure, especially in the vicinity of the critical point. Tiny changes in temperature and pressure can significantly affect its density, viscosity, dielectric constant, diffusion coefficient and solvent-based capabilities. Besides, supercritical carbon dioxide is non-toxic, non-flammable, inexpensive and easy to implement its critical condition (31.06℃,7.39 MPa), which makes it suitable for many organic reactions.Photopolymerization technology, recognized as a "green" technology, is efficient, enabling, economical, energy saving and environmental friendly. This thesis combined photopolymerization with supercritical fluid technology to obtain the advantages of both the two "green" technologies, e.g., milder reaction conditions, faster polymerization, less or even no organic solvent using, without surface active agent, simpler handling process and controllable in its particle size and microstructure, etc.. Main results are as follows:1. The results showed that photopolymerization could be carried out in liquid and in supercritical carbon dioxide. The polymerization of C=C was measured by FTIR. Micro-morphology of the product was studied with an optical microscope. The size of the products was distributed in 0.1-100μm;2. The best photoinitiator used in supercritical carbon dioxide was TPO, the optimum concentration was 3 wt%;3. The particle size reduced with temperature increase, while it increased with pressure increase;4. The solvents affected the particle size distribution of the products photopolymered in supercritical carbon dioxide. The higher the polarity of the solvent, the lower the solubility in supercritical carbon dioxide, the less the reactants dissolved in supercritical carbon dioxide, the wider the productions particle size distributed;5. Larger and wider size distribution of the productions could be achieved by increasing the concentration of the reactive monomer.