Controlled Synthesis And Applications Of Switchable Polymeric Surfactants

The non-uniform particle dispersion and aggregation in various solvent-based and aqueous dispersing systems is a key problem encountered in many chemical industries.In particular,the controlled synthesis and application of novel polymeric surfactants can provide effective solutions to this key chemical industrial problem.Polymeric dispersants can sufficiently overcome the lack of anchoring strength,application versatility and dispersing stability of molecular surfactants for solid particle dispersion in organic media.Similarly,CO₂-switchable polymeric surfactants can effectively coagulate and redisperse latex powder particles back to stable latex solution,thus substantially lowering cost and energy consumption from the handling and transportation of latex water content.Hence,this thesis focuses on developing controlled synthetic strategies via reversible addition-fragmentation chain transfer?RAFT?polymerization to prepare a series of polymeric dispersants and CO₂-switchable polymeric surfactants,which were utilized in solvent-based SiO₂ and aqueous latex dispersing systems respectively.In the SiO₂ dispersing system,polymeric dispersants in three different structural types?AB,ABA and comb?were systematically designed,optimized and compared over SiO₂ particle dispersion and stabilization in organic media,in order to develop“structure-performance”relationships between polymeric dispersants'molecular structure and dispersion performance.Specifically,within the study range,it was found that AB diblock copolymer dispersants were at least as effective as or superior to their ABA triblock equivalents in particle dispersion.Thus,the overall dispersion effectiveness of the three structural types could be ordered as:AB?ABA>comb.Meanwhile,in the latex dispersing system,a dual CO₂-switchable initiator plus polymeric surfactant approach was adopted to achieve solely CO₂/N₂-switchable latex particles.In particular,the latexes were systematically analyzed over repeated coagulation and redispersion cycles via only N₂ and CO₂ treatment respectively,which demonstrated reversible coagulability and effective redispersibility.Moreover,within the study range,it was discovered that increase in the three variables of polymeric surfactant's poly?2-?dimethylamino?ethyl methacrylate??PDMA?degree of polymerization,coagulation temperature and heating time all produced enhancing effects on the latex coagulation performance.Additionally,based on this dual CO₂-switchable approach,a solely gas-switchable“solid emulsion”system with powder redispersibility was further developed,which displayed facile powder redispersion back to stable latex solution from both freshly dried latex powder and those after three months storage under ambient conditions.Furthermore,this latex system exhibited long-term powder storage stability and versatility in emulsion copolymerization monomer selection,where four different monomer types could be copolymerized with styrene?St?to obtain reversibly coagulatable and redispersible latexes with similar powder redispersibility as pure polystyrene?PS?latexes.Therefore,all the results and findings of this thesis can assist to overcome the key chemical industrial problem of particle aggregation through achieving uniform particle dispersion,reversible redispersion and long-term stabilization in various solvent-based and aqueous systems,in order to optimize storage and application performances,providing significant economic and environmental benefits and major contributions to many chemical industries.