Using A Reactive Surfactant In Ultrasonically Irradiated Emulsion Polymerization To Prepare Polymer Nanoparticles

It is difficult to prepare polymer nanoparticles with narrow particle size distribution by conventional emulsion polymerization. In this paper, a kind of polymerizable surfactant (M12) and ultrasonic irradiation technology were used in emulsion polymerization in order to prepare functional copolymer nanoparticles with high molecular weight. M12 served as not only a surfactant but also a initiator in the reactions.Up till now, the initiation mechanism of ultrasonically irradiated emulsion polymerization is under controversy. In this paper, the sources of free radicals arising from ultrasonically initiated emulsion polymerization were investigated. The effects of water, different kinds of emulsifiers (nonionic surfactants, cationic surfactants and anionic ones) and monomers(butyl acrylate and styrene) on the initiating process were discussed. Experimental results showed that ionic surfactants played a very important role in obtaining a high polymer yield. While the radicals from the dissociation of monomer, H₂O or nonionic surfactants did not efficiently initiate the polymerization. The study indicated that the length of alkyl chain had little influence on the polymerization and the ionic group of surfactant was the most important factor in ultrasonically irradiated emulsion polymerization. FTIR and a radical trapping experiment confirmed that the free radicals involved in the irradiation process originated from the decomposition of the cationic surfactants DTAC. Under ultrasonic irradiation, ionic surfactants undergoed bond scission between the alkyl and ionic group, where the bond was the weakest along the chain .A kind of ionic reactive surfactant sodium sulfopropyl-laurylmaleate (M12) was synthesized which was used as not only the emulsifier but also the initiator inultrasonically irradiated emulsion polymerization. Two polymerization systems were studied, which were styrene(St)-M12 system and butyl acrylate(BA)-M12 system. Studies on influence factors of the polymerization indicated that the polymerization rate was improved with the increase of Ml2 concentration, ultrasonic power output , temperature and velocity of N? flow , and the decrease of the monomer concentration. The FTIR spectrum of product and gravimetric method results indicated that copolymer P(St-M12) and P(BA-M12) were prepared and the composition of Ml2 elevated with the increase concentration of Ml2 added. The molecular weight, particle morphology and particle size were investigated by GPC and TEM. It was shown that the P(S-M12) with high molecular weight (>106) and the nanoparticles with small diameters (20-45nm) were prepared. With the increase of M12 concentration, the particle size became smaller and the size distribution became wider. Increasing the reaction time, the particle size became bigger and the size distribution became wide at first and then narrow. The P(BA-M12) particles size was also small (<100nm) but the size distribution was wide. Because the PBA particles were soft, after stewing they tended to adhere together. The stability of the copolymer latexes prepared by ultrasonically irradiated emulsion polymerization was better than that of the homopolymer latexes prepared by the same way.