Study On Preparation Of P(BA-MMA-AA)/TiO₂ And PS/Na～+-MMT Nanocomposites Through Ultrasonically Initiated In-Situ Emulsion Polymerization

Ultrasound irradiation is an advanced, efficient and clean physical technology and widely used in material field. In this paper, P (BA-MMA-AA)/TiO₂ and PS/Na⁺-MMT nanocomposites were successfully prepared through ultrasonically initiated in-situ emulsion polymerization, which broadens the application of ultrasound irradiation technique in the preparation of polymer/inorganic nanocomposites. 1. Good dispersion and stabilization of inorganic nano particles during polymerization process as well as in the polymer matrix were realized by combining ultrasonically initiated emulsion copolymerization and in-situ encapsulation polymerization. By selection of the co-monomers and adjustment of their ratio, the TiO₂ nano particles were well encapsulated by poly (n-butyl acrylate-co-methyl methacrylate-co-methacrylic acid) [P (BA-MMA-AA)], obtaining P (BA-MMA-AA)/TiO2 nanocomposites with expected structure and performance. TEM confirmed that ultrasonic irradiation exerts much more effect on dispersion, pulverization and activation of nano particles as compared to the conventional stirring. This is advantageous to the encapsulation through ultrasonically initiated in-situ emulsion polymerization. The effects of experimental parameters, such as the type and content of inorganic nano particles, surfactant and monomers concentration, etc. on polymerization rate were systemically investigated. The experimental results showed that the polymerization rate increased with increase of SDS concentration and decrease of monomers as well as TiO2 percentage in the system. DSC, GPC and 1H NMR characterizations indicated that with the introduction of TiO2, the average molecular weight of the obtained copolymer decreased, the molecular weight distribution became wider, and BA ratio in copolymer chain increased, as compared to the neat copolymer, resulting in lower Tg. FTIR, XPS, TEM, SEM and soxhlet extraction revealed that polymer encapsulated on TiO2 surface, and there were strong interactions between the polymer and TiO2. TG and DSC analysis suggested that the thermal properties of the extracted nanocomposites enhanced. This method exhibits many advantages such as no addition of chemical initiator, ambient reaction temperature, easy operation process and adjustable structure of the encapsulated copolymer on the surface of nano particles. 2. Taking the advantages of unique physical and chemical effects of ultrasound irradiation to conduct the in-situ intercalation polymerization, the strongly hydrophobic PS can easily intercalate into the galleries of hydrophilic montmorillonite without pre-organic modification, which can hardly be realized by conventional technology. FTIR, XRD and TEM analysis confirmed that under the low ultrasound power, the hydrophobic St can easily enter the inter-galleries of Na+-MMT to polymerize and form PS/Na+-MMT nanocomposites with intercalation structure. The exfoliated PS/Na+-MMT nanocomposites can be obtained by merely increasing ultrasound power. The experimental results showed that the polymerization rate increased with decrease of monomers and Na+-MMT percentage as well as increase of SDS surfactant concentration. However, too high SDS concentration was not helpful to widen the d-space between clay layers because anion surfactant SDS can not spontaneously enter the inter-galleries of negatively charged Na+-MMT. The monomer-swollen micelles, monomer droplets and/or primary latex particles can be forced to enter the galleries of Na+-MMT by strong mechanical effects generated by acoustic cavitation, followed by in-situ polymerization, resulting in the increase in d-space. Compared with the conventional in-situ emulsion intercalation polymerization,acoustic cavitation can effectively break down the clay agglomerates, realize nano scale dispersion and obtain smaller monomer droplets and latexes, beneficial to their entry into the inter-galleries and promote the exfoliation degree of Na+-MMT. TG and DSC analysis showed that the thermal properties of nanocomposites prepared by ultrasonically initiated in-situ emulsion polymerization were better than those prepared by conventional emulsion polymerization. The advantages of this method are: the silicates can be used without any pre-modification, avoiding the physical and ecological problems. ultrasonic irradiation can initiate polymerization of styrene at ambient temperature with the nano scale dispersion of clay layers, shorten the polymerization time and save the energy. Obviously, ultrasonically initiated in-situ emulsion intercalation polymerization is a novel technology in preparing polymer/layered inorganic nanocomposites.