| Research Abstract |
This research project aimed at design of amphiphilically organized polymers by taking advantage of amphiphilic macromonomers. Poly(ethylene oxide) (PEO) and poly(methacrylic acid) (PMA) macromonomers carrying styry1 or methacrylate end groups, hydrophobically enhanced by alkylene spacers, were prepared. These macromonomers were found to polymerize very rapidly in water to afford regular comb polymers with hydrophobic trunks and hydrophilic branches, and copolymerize with a hydrophobic monomer in water or alcoholic media to give controlled polymeric microsheres of submicron to micron size. This project has thus disclosed a basic mechanism of micellar polymerization of these amphilic macromonomers in water, conformational characterization of regularly and densely branched comb polymers, and a fundamental guideline to the polymeric microspheres' design using amphiphilic macromonomers. The main conclusions follow.
(1) Very rapid polymerization of the PEO macromonomers in water was studied k
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inetically 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 bottlebrush with a hard, hydrophobic polystyrene axle with voluminous number of soft, soluble PEO hairs which will exert an extensive excluded-volume effect.
(2) The PEO macromonomers effectively afforded monodisperse microspheres of submicron to micron size in dispersion polymerization of styrene 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.
(3) PEO and PMA macromonomers were also effective in emulsion polymerization of styrene. 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.
To summarize, the surface-active macromonomers are useful for design of polymeric amphiphiles including regular comb polymers and microspheres, promising a variety of applications. Less
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