Preparation Of Functional Polymer Microspheres By Foam Transfer Method

Polymer microsphere is a new kind of functional polymer materials.It has the advantages of small size,large specific surface area and better surface modifiable properties.It has been widely used in drug delivery,catalyst carrier,ion adsorption,chromatographic separation,etc.field.There are some representative methods for preparing polymer microspheres,such as suspension polymerization,emulsion polymerization,spray drying,solvent evaporation,and microfluidic technology,etc.In order to prepare polymer microspheres simply and efficiently,our research group invented a new method for preparing polymer microspheres through foam-transfer.This method is a technical improvement on the traditional solvent evaporation method.Using the synergistic effect of the evaporation of the low boiling point good solvent and the stabilizer in the water phase to form a large amount of foam,oil phase droplets in the reactor are entrained by the foam and transported into the receiving vessel to solidify to obtain polymer microspheres.Based on the preparation of polymer microspheres by using this method,this thesis first systematically studied the process of foam entrainment and transportation of oil droplets,followed by the process of oil droplets forming into microspheres,and then explored the influence of different preparation conditions on foam-transfer;Secondly this method was used to prepare biodegradable PLA-azoxystrobin microspheres.Finally,the effect of the introduction of organic solvents into the water phase on the porous polymer microspheres was explored.Research indicates:（1）The foam-transfer method to prepare polymer microspheres was essentially a technical improvement on the traditional solvent evaporation method.The transfer effect of the foam changed the solidification location of the microspheres.A large number of oil droplets were entrained by the foam and transported into the receiving vessel for solidification,which greatly improved the preparation efficiency of polymer microspheres.The generation rate and stability of foam directly affected the ability of foam to transport oil droplets.With the increase of oil-water ratio,rotation speed,and PVA1788 concentration in the water phase,the transfer ability of the foam increased,however the introduction of ethanol in the water phase will reduced the transfer ability of the foam.The composition of water phase had a greater impact on the morphology and particle size of the microspheres.Whenω_PVA1788≤0.3wt%andω_{Et OH}≥20wt%,the polymer microspheres had poor spherical shape and were easy to stick.The average particle size of the microspheres decreased with the increase ofω_PVA1788 andω_{Et OH}.（2）Biodegradable PLA-azoxystrobin microspheres were successfully prepared by the foam-transfer method,and the encapsulation efficiency of azoxystrobin was as high as 86.54%.It was found that the rotation speed,polymer concentration,PVA1788 concentration,heating rate,and porogen content had a great impact on the particle size and the encapsulation efficiency of microspheres.As the rotation speed increased and the polymer concentration decreased,the average particle size and the encapsulation efficiency of microspheres decreased;As the concentration of PVA1788 in the water phase increased,the average particle size of the microspheres gradually decreased,and the encapsulation efficiency of the microspheres first decreased and then increased;As the heating rate slowed down,the average particle size of the microspheres became smaller,and fast or slow heating rate reduced the encapsulation efficiency of microspheres.Although the introduction of n-heptane can successfully prepare drug-loaded microspheres with porous structure,the encapsulation efficiency of microspheres decreased with the increase of the porogen content in oil phase.（3）The introduction of hydrophilic solvents ethanol and acetone into the water phase can achieve effective control of the particle size and pore structure of the polymer microspheres.As the concentration of ethanol in the water phase increased,the pore structure of the microspheres gradually evolved from the porous to the hollow,and the particle size of the microspheres gradually decreased,when the concentration of ethanol in the water phase reached 25wt%,the internal pore structure of the microspheres collapsed and no longer formed microspheres.The result of introducing acetone into the water phase was similar to that of ethanol,as the concentration of acetone in the water phase increased,the microspheres gradually evolved from the porous to the hollow,and the average particle size of the microspheres gradually decreased.Since most of acetone migrated to oil phase after oil phase was dispersed into water phase,a large amount of acetone（≥30wt%）needed to achieve a similar effect to that of ethanol（20wt%）.The main reason for the introduction of ethanol and acetone to control the particle size and structure of polymer microspheres was that the introduction of these two organic solvents changed the surface tension of the system,which caused the particle size of the microspheres to decrease;and the synergistic effect of the introduced organic solvent and DCM in oil droplets changed the evaporation process of DCM,resulting in a change on the structure of polymer microspheres.The introduction of lipophilic organic solvent ethyl acetate into water phase nearly made no significant changes on the pore structure and particle size of the microspheres.Since almost all ethyl acetate migrated into oil phase and formed a co-solvent with DCM after two phases were mixed,it did not play an effective role in controlling the pore structure and particle size of the microspheres.