DESIGN OF POLYMERIC MICROSPHERES USING MACROMONOMERS

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This research project aimed at designed synthesis of polymeric microspheres by taking advantage of amphiphilic macromonomers. Poly (ethylene oxide) (PEO) and poly (methacrylicacid) (PMA) macromonomers carrying stryl or methacrylate end groups, hydrophobically enhanced by alkylene spacers, are reasonably expected and in fact found to work as effective, reactive (copolymerizable) emulsifiers and disperants in emulsion dispersion polymerizations of hydrophobic monomers in water and alcoholic media. Thus the macromonomers copolymerized with the comonomers to produce in situ the graft copolymers, the branches of which cover the particle surfaces to effect steric stabilization while the trunks serve as the anchors into the particles. This project has proposed a basic mechanism and theory of the formation of such sterically-stabilized polymeric particles and has applied the theory to various emulsion and dispersion systems using the PEO and PMA macromonomers to establish a fundamental guideli … More ne to the microspheres, design, with the main conclusions as follows.(1) The PEO macromonomers effectively afforded monodisperse microspheres of submicron to micron size in dispersion polymerization of stirene and butyl methacrylate in methanol-water. A theory of particle size control, based on the steric stabilization by the graft-copolymerized macromonomer chains covered on the surface, reasonably accounted for the experiments ; the size changes according to 1/3rd order of conversion, 2/3rd order of the comonomer concentration, and-1/2nd order of the macromonomer concentration. Change of the grafted PEO chains from a random coil to an extended conformation was also confirmed by NMR measurement.(2) PEO and PMA macromonomers were also effective in emulsion polymerization of stirene. The traditional theory of emulsion polymerization has to be modified to account for the macromonomers to take part in the copolymerization in addition to function as the emulsifiers.(3) Very rapid polymerization of the PEO macromonomers in water was studied kinetically by use of ESR among others, to be ascribed to their micelle formation. The resulting comb polymer in water could be described as a semiflexible wormlike chain just like a bottle brush with a hard, hydrophobic polystirene axle with an uncountable number of soft, soluble PEO hairs which will exert an extensive excluded-volume effect.To summarize, the macromonomer technique for design of polymeric microspheres is relatively simple both in principle and in practice, promising a variety of applications. Less