Preparation Of Hollow Microspheres Based On Hyperbranched Poly (Aryl Ether Ketone)

In rencent years, colloidal particles with a void in the center can be applied toencapsulation, a process that has found widespread use in many aspects, likecontrolled release of drugs, contrast agents, cosmetics, inks, pigments, or chemicalreagents, protection of biologically active species and removal of wastes. Severalapproaches have been developed to fabricate hollow polymer microspheres, such asemulsion polymerization, acid/alkali swelling method, solvent swelling method,template method, solvent evaporation, phase separation, self-assembly, and so forth.Among them, the formation process of microspheres using solventextraction/evaporation method appears to be relatively simple without theinvolvement of complicated chemical reactions. However, there are many imperfectdetails on the explaination of the whole process. Hence, the study on its mechanism isalso one of the current research focus.Using solvent extraction/evaporation method to prepare hollow microsphereshave received considerable attention recently. However, we have noticed that thepolymers used in this method were mostly linear polymers with the flexible chain.Combined with the work of our group, hyperbranched poly (aryl ether ketone) is ahyperbranched polymer with rigid chainand has very good thermal properties whichcan be applied to many special areas. Thus, we hope to prepare hollow micelles basedon hyperbranched poly (ether ether ketone) using the solvent evaporation method.Onthe one hand, we hope to get a kind of hollow micelles which can meet certain conditions of application; on the other hand, we also want to study the performancesof the hyperbranched polymer with rigid chain in the solvent evaporation system.First, a novel hyperbranched rigid polymer (OH-HPEEK) was prepared using A2+BB’2reaction, and characterized using NMR and FTIR. We prepared successfullyhollow porous micelles using a combination of self-assembly and solvent evaporationmethod, and discussed the influence of the dropping sequence, the systemtemperature， solution concentration of PVA, solution concentration of HPEEK andpolymer branching structure on the assembly process. We prepared a linear poly (arylether ketone) with a similar structure, discussed its differences in the assembleprocedure comparing with the hyperbranched polymers. On the basis of a series ofexperimental results, we obtained a simple speculation on the assembly mechanismand understood the influence of various factors on the assembly process: Preparationof hollow micelle must be carried out under the conditions of a low PVAconcentration, otherwise only solid micelle could be obtained; the temperature of thesystem affected the evaporation rate of THF, followed by the difference in the micelleshape; HPEEK concentration should be higher than the critical concentration so thatporous hollow structure could be obtained, otherwise only solid micelles could beobtained at the low concentration; polymer structure also plays a very important role,and the interaction between the polymer and tetrahydrofuran was also a veryimportant factor for preparation of hollow porous micelles.Furthermore, two novel kinds of hyperbranched polymers (pyridyl-terminatedand amine-terminated) were synthesized successfully. Using the combination ofself-assemble and solvent evaporation method, hyperbranched rigid polymer achievedthe preparation of polymer microspheres with hollow core/porous shell structure inthe presence of PVA at first. However the presence of PVA makes the microspherescould not stand the high temperature and limit the potential application of themicrospheres. Hence, we attempt to make polymer crosslinked in order to fix thestructure. After the removal of PVA, we finally got the polymeric microspheres withhollow core/porous shell structure of hyperbranched poly(ether ether ketone)s successfully. And we are believed that the high Tg of HPEEK will allow the materialmeet the need of some potential applications such as the high-temperatureenvironment.