Synthesis Of Novel Stabilizers And Their Application In Miniemulsion

Miniemulsion polymerization has many unique advantages compared with classic emulsion polymerization. The one-to-one copy from the monomer droplet to latex particles can be realized by the unique droplet nucleation mechanism in miniemulsion polymerization, which makes the composition and size of the polymer controllable. The stabilization of miniemulsion and the process of polymerization have a closely relationship with the structure of the emulsifier and costabilizer. To further study the stabilization mechanism of miniemulsion system, an nonionic emulsifier, hydroxyethyl acrylate-2, 4-diisocyanatotoluene- polyethylene glycol (HEA-TDI-PEO) were synthesized. The hydrophilicity and solubility in oil or water of HEA-TDI-PEO can be controlled by adjusting the molecular weight of PEO, which makes HEA-TDI-PEO combine the function of emulsifier and costabilizer and be solely used to prepare stable St miniemulsion. Another new nonionic comblike surfactant P[St-HEA-TDI-PEO(1900)] is obtained by the copolymerization of HEA-TDI-PEO and St. The results show that this new surfactant is more effective than HEA-TDI-PEO to stablize St miniemulsion. The major work and results of this thesis are as follows:1. A new kind of polymerizable nonionic emulsifier HEA-TDI-PEO, who combines both the function of emulsifier and costabilizer had been synthesized by polycondensation. The surface activity of HEA-TDI-PEO was studied. The CMC values of HEA-TDI-PEO were obtained by measuring the cu relationship between surface tension and HEA-TDI-PEO concentration. The results show that with the increase of the EO chains, CMC value decrease from 5.12×10^-4 to 4.01×10^-4 g/ml.2. HEA-TDI-PEO was employed as the sole stabilizer in St miniemulsion. The polymerization was induced by 60Coγ-ray radiation. The DLS results show that the size of the droplet is a little larger than that of the latex and the number of monomer droplets and latex are the same, consistent to the characteristic of miniemulsion polymerization and verifying that HEA-TDI-PEO can work as a costabilizer. The presence of peak of O and N in XPS spectrum of latex indicates that the surface of the latex contains O and N elements, implying that this emulsifier can copolymerize with monomers. TEM images of HEA-TDI-PEO latex show that latex particles with a uniform size distribution can be obtained only when the concentration of HEA-TDI-PEO is between 2% and 2.5%. It indicates that HEA-TDI-PEO can work as the emulsifier and the costabilizer simultaneously under a proper distribution of HEA-TDI-PEO in oil and water phase. The study also reveals that the stability of miniemulsion depends on the inhibition to Ostwald ripening effect of highly hydrophobic material. However, there also exist some disadvantages in this system, for example, the rate of polymerization of monomer is relatively low. But the rate of polymerization can be improved by increasing the molecular weight of the emulsifier.3. A comblike surfactant P[St-HEA-TDI-PEO(1900)] is obtained by the copolymerization of HEA-TDI-PEO(1900) and St. The CMC value of this surfactant is 3.86×10^-4 g/ml. It performs better as a solely stabilizer in St miniemulsion than HEA-TDI-PEO. A uniform size distribution of latex particles can be obtained when the concentration of the surfactant is 2.5%. In addition, the surfactant can contribute to the formation of PS porous microhemisphere.