Investigation Of Efficient Preparation For Functional Particles Via Thiol Click Chemistry

Polymer particles have been widely employed in the field of biomedical science,separation,energy environment management,colloid assembly due to their high surface area,high adsorption capacity,controllable size and ease of functionalization.Such demands have provided great impetus for the development of preparation methods in the last decades,and many preparation methods for particles with size ranging from tens of nanometers to several millimeters have been built up,such as dispersion polymerization,precipitation polymerization,surfactant-free polymerization,microfluidic,membrane emulsification,etc.However,the reactions for particle preparation are quite limited,and more than 90%of particles used in industry are fabricated by radical-mediated chain-growth polymerization of acrylic and styrenic monomers.It is well-known that radical chain-growth polymerization is easily inhibited by oxygen and moisture,resulting in low reaction rate,low conversion and deteriorated performance of final products.As a result,inert gas atmosphere,prolonged reaction time and high initiator concentration are necessary in the preparation process,leading to a huge waste of energy,time and ingredients.Under the background of“Green chemistry”and“Atom economy”,these technologies do not meet the requirement of modern industry any more.Although,a few stepwise polymerizations have been developed for particle preparation,but scale-up preparations are restricted by the need of special catalysts and monomers.Based on above background,this dissertation focuses on the efficient preparation and functionalization of polymer particles.Because click chemistry is energy-saving,highly efficient,high conversions,temporal control and insensitive to oxygen/water,it was introduced into traditional methods for particle preparations to overcome the disadvantages of radical-mediated chain growth polymerization.Besides,the polymerization mechanism of click reactions in different systems were investigated.As an attempt to prepare particles via thiol-click reaction,this work offered new choices for particle preparation,and paved the way for extending application of thiol-X click chemistry and further understanding of step-growth polymerization in heterogeneous system.The main contents of this work are listed as following:Both of UV-catalyzed thiol-ene radical addition and thiol-acrylate Michael additions were adopted to prepare polythioether particles in suspension polymerization.Polymer particles could be prepared within 15 min by UV-catalyzed thiol-ene radical polymerization,which offered high yields?⁸0%?and high monomer conversions,and significantly reduced preparation time and energy input.Macroporous particles with low specific surface area could be obtained when linear polymer was used as porogen.As for thiol-acrylate Michael reaction,photobase and base amplifier were designed and fabricated to make thiol-acrylate Michael reaction UV-curable.However,UV-catalyzed thiol-acrylate Michael reactions were not suitable for particle preparation in suspension polymerization due to undesirable catalysis efficiency of photobase and base amplifier.Even if the base was directly added to the monomer droplets with base amplifier,only collapsed particles were obtained because solidification mainly occurred on the surface.Base-catalyzed thiol-isocyanate click reactions were also used to prepare polythiourethane particles.Firstly,monomer droplets were created by traditional suspension polymerization,Pickering emulsion template,membrane emulsification and microfluidics.Then,the base catalyst was added,and the monomer droplets could be quickly solidified to polymer particles.The preparation was quite easy and energy-efficient.It was demonstrated that particles could be easily fabricated in large scale in conventional and Pickering template suspension polymerizations,while the particle size was polydisperse.The polydispersity of particle size could be improved by membrane emulsification,but the membrane was easy to be blocked by highly efficient thiol-isocyanate reactions.Microfluidics could produce monodisperse particles with the size ranging from 50?m to 1000?m.However,the droplets creation method led to a low preparation efficiency.Uniform,functional and highly cross-linked particles were prepared via one-step dispersion polymerization based on catalyst-free thiol-isocyanate reactions.Compared to traditional dispersion polymerizations,this method not only allowed for one-step preparation of highly cross-linked particles with high solid content,but also provided an energy-efficient,catalyst-free method with high monomer conversion and no side reactions.After analyzing the process of polymerization and model experiments,the nature of catalyst-free thiol-isocyanate reaction was roposed and demonstrated,that is,PVP served as both stabilizer and catalyst at the same time.The FTIR and NMR analysis showed that this polymerization proceeded very efficient,and the conversion of isocyanate monomer could reach 75%and 94%after 10 min and 120 min,respectively.The thiol-isocyanate step-growth mechanism endowed particles with uniform networks,and their width at half height of glass transition region was less than 20 ^oC.Meanwhile,hydrogen bonds in polythioureathanes made for high glass transition temperature?T_g?,and these advantages would make them be applied in the field of chromatographic packing materials.The robust base-catalyzed thiol-epoxy reactions were exploited in one-step dispersion polymerizations for particle preparation.Monodispersed and cross-linked particles with tunable size,T_g and network structure were prepared efficiently without UV,heat and any other energy input,even stirring,and the conversion could reach 90%within 60 min.These polyhydrothioether particles exhibited the potential of oxidization and reinforcement via oxidation by commercial oxidizing agent,such as H₂O₂ and 3-Chloroperbenzoic acid?mCPBA?,and the T_gs were improved significantly after oxidization.In addition,the polyhydrothioether network could become dynamic and reversible when proper catalysts were incorporated,which endowed particles with reprocessability and recyclability.In order to overcome the limited shelf life and volatile odour of thiol monomers,thiolactone?a protected thiol monomer?was adopted to replace thiol monomers,and amine-thiolactone-acrylate multicomponent reactions were used to prepare particles in interfacial suspension polymerizations.Acrylamide thiolactone?AmTLa?and styrene sulfonamide thiolactone?StTla?were fabricated from bio-mass DL-homocysteinethiolactone hydrochloride,and these monomers were further polymerized with dimethylacrylamide?DMA?and Styrene?St?to prepare water-soluble and oil-soluble polythiolactone,reapectively,i.e.Poly?DMA-co-AmTLa?and Poly?St-co-StTLa?.It was demonstrated that pyrrolidine acted as a highly efficient ring-opening reagent for thiolactone,and could efficiently catalyzed thiol-Michael addition.After investigating the possobilities of thiolactone multicomponent reactions in interficaial polymerizations,it was found that the droplets of Poly?DMA-co-AmTLa?were prone to be destroyed once amine was added,despite of their good solubility and fast curing.Fortunately,particles could be successfully prepared when Poly?St-co-StTLa?served as disperse phase with trimethylolpropane triacrylate.