Dispersion Polymerization Of Methyl Methacrylate In Supercritical Carbon Dioxide Using Hypercrosslinked Polymer As Stabilizer

Supercritical carbon dioxide（scCO₂）is regarded as a potential green solvent for its wide source,non-flammability,non-toxicity,relatively mild supercritical conditions and easy separation.Polymerization using scCO₂ fluid as the reaction medium has been extensively studied and dispersion polymerization is one of the important research fields.The use of appropriate stabilizers is the key to the successful implementation of dispersion polymerization in scCO₂.Therefore,the design and synthesis of efficient stabilizers has always been the core of this field.Due to the scarcity of CO₂-philic substances,in the past studies,the complex synthetic route and excessive cost of stabilizers are unavoidable problems need to be solved.In this thesis,hypercrosslinked polymers,which are without CO₂-philic structure,were used as stabilizers in scCO₂ dispersion polymerization system.The dispersion polymerization of methyl methacrylate（MMA）in scCO₂ was successfully carried out and the dry polymer powder was obtained.This method breaks the limitation of previous stabilizer designs depending on CO₂-philic groups or structural units and may provide new ideas for the design of stabilizers in scCO₂ dispersion polymerization and the preparation of polymer/porous material composites.The main contents are list as follows:（1）Hypercrosslinked polymer nanoparticles with different pore structures were prepared by two steps of emulsion polymerization and post-crosslinking based on Friedel Crafts reaction.（2）The possibility of dispersion polymerization of MMA in scCO₂ using hypercrosslinked polymer nanoparticles as stabilizers was explored.The results show that the hypercrosslinked polymer stabilizer has good stabilizing effect on the polymerization system.Poly（methyl methacrylate）（PMMA）flowing powders with high conversion（>85%）and molecular weight（up to 3.0×10⁵）have been prepared.（3）The polymerization system was optimized by adjusting the pore structure of the stabilizer,the content of the stabilizer,the monomer concentration,the type of the initiator,the stirring rate and the CO₂ pressure.The results confirmed that the porous structure of the stabilizer had a significant positive effect on the dispersion polymerization system.