MICROSPHERE SYNTHESIS BY DISPERSION COPOLYMERIZATION OF METHYL-METHACRYLATE WITH POLY(ACRYLIC ACID) MACROMONOMERS - PH EFFECT ON MICROSPHERE FORMATION

The pH effect on microsphere formation in the dispersion copolymerizat ion of methyl methacrylate with vinylbenzyl-terminated poly(acrylic ac id) (PAA) macromonomers is studied. The diameter of poly(methyl methac rylate) (PMMA) microspheres is minimum around pH = 8. Dynamic light sc attering data indicate that the shell thickness of PAA-grafted chains shows a maximum around this pH. The degree of expansion of PAA chains drastically affects the particle size of PMMA microspheres during the dispersion copolymerization. In previous work(1)), we prepared polymer microspheres by dispersion copolymerization of methyl methacrylate (M MA) with poly(methacrylic acid) (PMR) macromonomers in aqueous ethanol solution. The particle size (submicrometre to micrometre range) and s ize distribution are controlled by selecting the solvent composition a nd the feed amount and molecular weight of the PMA macromonomers. Howe ver, the particle diameter does not depend strongly on the pH of the s olvent medium. More recently, we synthesized polymer microspheres by d ispersion copolymerization of MMA with poly(acrylic acid) (PAA) macrom onomers in aqueous ethanol solution(2)). The particle diameter of the polymer microspheres decreases as the water fraction in the mixed solv ent, macromonomer concentration, and macromonomer molecular weight inc reased. For this dispersion copolymerization system it is expected tha t the pH in an aqueous solution drastically affects the particle size of the microspheres. In this short communication, we studied the pH ef fect in aqueous solution upon microsphere formation in the dispersion copolymerization of MMA with PAA macromonomers.