Preparation Of Poly(St-alt-MAn) Microspheres By DPE Method

The poly(methyl methacrylate) oligomer containing 1,1-diphenylethene structural units (PMMA-DPE) was prepared by bulk polymerization of methyl methacrylate (MMA) in the presence of 1,1-diphenylethene (DPE) with azodiisobutyronitrile (AIBN) as initiator. Then, narrow disperse poly (styrene-alt-maleic anhydride) [Poly(St-alt-MAn)] microspheres were obtained by meta-stable precipitation polymerization of styrene (St) and maleic anhydride (MAn) initiated by the PMMA-DPE, with isoamyl acetate as solvent.The structure of copolymer was characterized by IR, UV-vis,'H NMR and GPC. The morphology and size of microspheres were observed by SEM. Effects of the mass percent of PMMA-DPE (based on total monomer), monomer concentration, monomer molar ratio of [St]:[MAn],polymerization temperature, the volume fraction of methyl ethyl ketone, and polymerization time on the molecular weight, morphology, particle size and size distribution were investigated.The result showed that, the size of the composite microspheres is between 378 and 776 nm initiated by precursor PMMA-DPE. The morphology and average size of microspheres initiated by precursor PMMA-DPE are much better than that of particles by thermal self-initiation.Meanwhile the coefficient of diameter distribution is lower. When the mass percent of PMMA-DPE (based on total monomer) increased, the conversion increased, and the microspheres and the molecular weights decreased, but the distribution of diameter increased a little. As the monomer concentration increased, the conversion, the microspheres and the molecular weights increased. However, there was almost no change of the distribution of the polymer particle diameter. With the increase of monomer molar ratios of [St]:[MAn], the molecular weights increased, and the distribution of diameter was remained unchaged. In the same time, the conversion and microspheres increased at first and then decreased. As the temperature raised, the conversion and the distribution of diameter increased but the diameters of the microspheres decreased. In the meantime, the molecular weights and the size of microspheres increased at early and then decreased. When the volume fraction of methyl ethyl ketone increased, the conversion decreased but the coefficient variation of the particle size became great. At the same time, the molecular weights and microspheres increased firstly and then decreased. Based on the above observations, a mechanism of the polymer particle formation has been proposed.