| As a new type of functional material with large specific surface area and rich pore structure,porous polymer microspheres have many application prospects in the fields of medicine,biology,electronics,and chemical engineering.The foam-transfer method is a new method of preparing polymer microspheres,which was invented by the author’s research group on the basis of the traditional solvent volatilization method.The method utilized the volatilization of solvent to assist the generation of foam,and foam entrained oil phase droplet to realize the transfer of oil droplets from the reactor to the receiving container and form microspheres.The new method has been proved to have the characteristics of high efficiency and continuous production,which fully meets the development needs of polymer microsphere materials.The driving force of the new method is the volatilization of organic solvents.Therefore,the organic solvent in oil droplets is very important for the preparation of polymer microspheres.It not only affects the foaming process,but may also have a significant impact on the properties of polymer microspheres.Therefore,this thesis systematically studies the influence of the organic solvent system in oil phase on the preparation of polymer microspheres by foam-transfer,based on the early research work of the laboratory,including single solvent and mixed solvent systems.The main research conclusions are as follows:(1)The preparation of polymer microspheres via foam-transfer method was roughly divided into 5 stages: foam generation stage,rapid foaming stage,initial stage of foam transmission,middle stage of foam transmission and end of foaming stage.Compared with a single solvent system,a binary solvent system does not affect the foaming process,but will cause changes in the foaming temperature at the corresponding stage.In addition,the foamtransfer method to prepare polymer microspheres was universal,and it is suitable for commonly used organic solvents(dichloromethane,chloroform,carbon tetrachloride,ethyl acetate,etc.)and nonlinear polymers(polystyrene,Polymethyl methacrylate,etc.).(2)Using a single solvent system(polymer(PS)/good solvent(DCM)),polymer microspheres with tiny pore structure can be prepared.It found that fast volatilized rate of the organic solvent in the oil phase droplets and short curing time of the microspheres were easier to form pores structure on the surface of the polymer microspheres.The concentration of polymer and the stirring rate in the reactor mainly affect the particle size of the microspheres,but have little effect on the pore structure of the polymer microspheres.The preparation polymer microspheres are basically solid microspheres.(3)On the basis of a single solvent system(polymer(PS)/good solvent(DCM)),introducing porogen(HT)realized adjustment of pore structure of polymer microspheres in a wide range.The study found that with increasing carbon chain of porogen,the number of pores of polymer microspheres increased and the pore size decreased;with increasing the concentration of porogen,pore structure of the polymer microspheres changed from porous to hollow.This is mainly because the solubility parameter of porogen increased with the increasing the number of carbon atoms of porogen,meanwhile,compatibility of the porogen with the polymer is also enhanced.In the process of preparation,the degree of phase separates between the polymer and the porogen is reduced,and the pore size of microspheres was reduced,and the number of pores was increased.Increasing the amount of porogen leads the concentration of porogen increased,porogen molecules are more likely to contact and coalesce,finally polymer microspheres with a hollow structure.(4)On the basis of a single solvent system(polymer(PS)/good solvent(DCM)),three organic solvents with high boiling points of ethanol,acetone and ethyl acetate were introduced into the oil phase to form binary solvent system to prepare PS microspheres.The study found that when ethanol and acetone were introduced,as the concentration of ethanol/acetone in the mixed solvent increased,the surface of microspheres gradually changed from porous to smooth,and internal pore structure of the microspheres changed from solid to hollow;The pore structure has almost no effect,when introduced ethyl acetate.This is because the ethanol,acetone,and ethyl acetate added in the dispersed phase will migrate to the continuous phase at varying degrees(the ability to migrate to the continuous phase:ethanol>acetone>ethyl acetate),therefore at the oil-water phase interface will form a liquid film layer of mixed solvent molecules.The mixed solvent liquid film layer changes the way of methylene chloride removing,and finally results in hollow structure of polymer microspheres.As the concentration of ethanol/acetone in mixed solvent increases,molecular liquid film of mixed solvent at oil-water interface becomes thicker,the reblocking effect of solvent on surface of microspheres increases,and the surface of microspheres becomes smoother.Because the amount of migration of ethyl acetate introduced in the dispersed phase to the water phase is very small,the thickness of the liquid film layer of the mixed solvent molecules at the oil-water phase interface hardly changes,so the structure of the microspheres hardly changes.(5)On the basis of the binary solvent system(polymer(PS)/good solvent(DCM)/high boiling point solvent(ET/AC/EA)),porogen was introduced to prepare polymer microspheres.The research results were similar to single binary solvent system.With increasing the concentration of ethanol and acetone in dispersed phase,the surface of polymer microspheres changes from porous to smooth,and inside structure of microspheres changed from porous to hollow;introducing ethyl acetate in the dispersed phase hardly changed the internal and external pores structure of PS microspheres.The change reason of the microsphere structure were comprehensive action of the mixed solvent molecular layer.The binary solvent system realizes the adjustment of the pore structure of the polymer microspheres in a wider range. |
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