Anisotropic Functional Microspheres Prepared By Thiol-Isocyanate Click Dispersion Polymerization And Its Application

Polymer microspheres are characterized by large specific surface area and easy surface functionalization.They are widely used in the fields of solid surfactants,drug carriers,fluorescent probes,catalysis and photoelectric materials.Dispersion polymerization is an effective method for preparing micron-sized monodisperse polymer particles.Usually,thermal decomposition initiator is used in the dispersion system to initiate free radical chain growth polymerization,and cross-linked or other functional microspheres can be easily prepared by using functional monomers.In order to ensure the mono-dispersity of the microspheres and avoid the interference on nucleation by using functional monomer,the two-step or multi-step feeding strategy is often used.Click polymerization has the advantages of fast reaction speed,insensitivity to oxygen,mild reaction conditions,and the like.Using click polymerization,functional polymers with excess functional groups can be easily prepared.In recent years,functional microspheres have been prepared using click polymerization in heterogeneous systems.Among them,thiol-isocyanate click dispersion polymerization is an efficient technique to prepare smooth,cross-linked microspheres at room temperature and without catalyst.Functional microspheres can be easily prepared by adding non-stoichiometric monomers.However,in the reported work,only the thiol-isocyanate two-component monomers are used,and the produced microspheres show smooth surface,without rough surface or anisotropic morphology.When stoichiometric monomers are fed,the influence of monomer diffusion and other factors on the click polymerization,particle morphology and composition has not been studied in detail,and only a few examples show the specific application of the obtained microspheres.For this,the research work of this thesis is proposed:monodisperse functional polymer microspheres with smooth,rough,plicated or multi-bulge surface are fabricated by thiol-isocyanate click dispersion polymerization at room temperature,in a medium of ethanol,and using polyvinylpyrrolidone(PVP)as stabilizer and initiator.In addition,the application of the as-prepared microspheres is investigated.The main work of the thesis is described as follows:1.Preparation of functional microspheres by thiol(3-SH/4-SH)-isocyanate(2-NCO)polymerization:monodisperse functional polymer microspheres with rough or multi-bulge surface are prepared by trimethylolpropane tris(3-mercaptopropionate)(TMPMP)or Pentaerythritol tetra(3-mercapto-propionate)(PETMP)and isophorone diisocyanate(IPDI)dispersion polymerization,and the effects of monomer content on the size,morphology and composition of the microspheres are investigated.2.Formation of rough surface and mechanism of the off-stoichiometric reaction:through SEM and Fluorescence Microscope observation,FTIR analysis and monomer conversion measurement,the particle morphology and composition changes during polymerization are showed to reveal the influence of monomer diffusion on the click reaction in the particle phase.After nucleation,the monomer gradually diffuses into the growing particle phase to react.As the monomer conversion increases,the particle cross-linking degree increases,the monomer diffusion is limited,and the polymerization of the monomer at the particle surface is enhanced,forming multiple bulges.In addition,due to limited diffusion of monomers,non-stoichiometric reaction occur,even when stoichiometric monomer is fed.Due to the higher reactivity of the isocyanate groups,the functional microspheres with excess thiol groups are finally obtained.3.The surface functionalization and application of microspheres:functional microspheres with excess thiol or isocyanate groups on the surface are prepared by stoichiometric and non-stoichiometric monomer feeding,and the application of functional microspheres is shown.Fluorescence microspheres are obtained by reaction of thiol or isocyanate groups on the surface of microspheres with FITC or 7-mercapto-4-methylcoumarin,respectively;Ag+is reduced in situ on the surface of functional microspheres with excess thiol groups,producing polymer core/Ag shell composite microspheres;the thiol group on surface of microsphere is successively coupled with cystamine dihydrochloride and FITC to make a fluorescence probe containing FITC,which can be used to detect the thiol group(taking GSH as an example);phthalimide fluorescent compound(DTPDI)is coupled on the surface of isocyanate functionalized microspheres to obtain a polymer microsphere fluorescent probe,which can be used for detecting Hg2+in the aqueous solution,and the detection limit is up to 0.1 ppb.4.Preparation of functional microspheres in the presence of the third component:thiol(1-SH/2-SH)or isocyanate(2-NCO/3-NCO)is added to thiol(3-SH/4-SH-isocyanate(2-NCO)dispersion system;due to the different reactivity of different thiols and isocyanates,different crosslink density networks are formed in the particles,thereby obtaining click particles with smooth,rough,plicated or multi-bulge surface and adjustable glass transition temperature.The monomer type,functionality,amount of the third component and monomer ratio are changed to adjust the crosslink density and swelling degree of the growing particles,thereby regulating and controlling the morphology,shape and glass transition temperature of the as-prepared particles.5.Application of particles prepared using the third component:the particles with folds or bulges are selected to load Ag nanoparticles,and the polymer core/Ag shell composite microspheres are obtained.The surface folds or bulges of particles are beneficial to load Ag nanoparticles.Doxorubicin is added during polymerization,and doxorubicin-containing particles are obtained.