Preparation And Properties Of A Variety Of Polymers And Complex Nanoparticles

Now with the research development in field of catalysis chemistry, bioengineering and functional coating, people are exploring polymer and organic/inorganic nanoparticles with various morphology, structures and sizes which can serve as intelligent tools and efficient agent for catalyst support, drug delivery, functional coating and paper-making, etc. Based on the research background and the development trend of nanoparticles, the research interest of this work focused on the preparation and primary application of nanoparticles with diverse size, morphology and composition, which involves in five parts, i.e. the preparation and size control of polymer nanoparticles, preparation of silica/polymer nanoparticles with diverse morphology, preparation of the core-shell inorganic/polymer nanoparticles with a general phase-reversion method, the formation of regular microphase structure inside the inorganic/polymer nanoparticles, and primary application of polymer nanoparticles as the water-proof agent. We also investigated the thermal stability of the inorganic/polymer hybrids by a two-dimensional infrared correlation spectroscopy method. The results of each part are listed as follows:(1) Polymer nanoparticles were prepared by copolymerization of methyl methacrylate, methyl acrylate, butyl methacrylate, and butyl acrylate in turn. A modified microemulsion polymerization process, which was continuous addition of monomer to a preemulsified system, was performed during the preparation. It was found that the particle size of the copolymer microlatex did not change distinctly with the monomer composition. The estimation of emulsifier coverage on the microlatex particles indicated that the process switched from traditional microemulsion to normal seeded emulsion polymerization successionally just after the monomer dropping. Therefore, a longer dropping time is needed to produce microlatexes with narrow dispersed particle size. Besides, in the modified microemulsion polymerization, less emulsifier is needed to produce stable microlatexes. This behavior is related to the mechanism of normal seeded emulsion polymerization during monomer dropping.And we also restricted the size of particles in the range of 10-30nm by applying super-high stirring speed. The stirring speed, which resulted in the formation of smaller or bigger particles in the pre-emulsion period, had a big influence on the growth of polymer latexes. Because the separation energy was large enough to maintain the smaller size latexes in microemulsion than normal emulsion anddecreased the aggradations of the partiles during the polymerization of the monomer mini-droplets. The emulsifier coverage of the particles was as low as 10%. A model was proposed to illustrate the coadjustment of the emulsifier coverage and separation energy on the particles size, by which the diameter of the particles would be adjusted in the range of 10-100nm.(2) By microemulsion polymerization, the silica/PMMA hybrid nanoparticles, based on the charge attraction between silanol particles and cation initiators, were synthesized in both acidic and alkaline conditions by using coupling agents. In general, at low pH such as pH=2. the surface of silanol precursor has few charges and as a result, each hybrid particle has only one silica core, while at high pH such as pH=9, the large negative surface charge causes auto-condensation between silanols, which leads to the formation of cellular structures in the hybrids.The structure of the hybrid was also affected by the amount of silanol and the coupling agent in the system. Increasing either silanol or the coupling agent caused the change of hybrid structures - from regular core-shell to cellular structure. The former was more stable than the latter. By the modified method of microemulsion polymerization, i.e. an additional monomer-adding process, we successfully prepared the stable nanoscale polymer/inorganic hybrids microemulsion with high solid contents. It probably has some potential application in the hybrid coatings.(3)The silica/polymer nanoparticles are well-established materials. But appropriate general routs for such composite with transition metal oxides core are still rare. Now, the TiO₂/Polymer nanoparticles with various morphology were prepared by adjusting the micro-phase structures of the hybrids in THF solution.With the nanocomposite solution as the precursor, the TiO₂ core-polymer shell microspheres were synthesized with a micro-phase inversion mechanism. The polymer phase with the incompatibility of water was the key factor for the formation of microspheres, and the polycondensation of the inorganic moiety induced to form the core-shell morphology in our experiment. The average particle size was in the range of 70-200nm and the inorganic contents were up to 70% by varying the TiO₂/SiO₂ mol radio of the inorganic moiety and the cross-linking monomer content. .Nevertheless, when the nanocomposite solutions were separated via an emulsion system, the hybrid nanoparticles formed with a parallel layer structure inside and leaves-like shape. By calcining the nanoparticles with different heating process, the pure titania hollow nanoshuttles and nanorodes could be formed respectively with the decomposition of the polymer moiety.(4) The polymer nanoparticles with the size in the range of 10-100nm had strong penetrability, and good film-forming ability. Here, the polymer nanoparticles separated in microemulsion system provided paper with strong water resistance when used as a paper surface treatment agent. The polymer's glass transition temperature highly affected both the film formation process on the fiber surface and the fiber's water resistance. To achieve better water resistance the coated paper should be dried at a temperature of 40-50℃, which was higher than the Tg of the polymer. In addition, the water resistance of the treated paper was closely related to the particle size of microemulsion. Small particle size was beneficial to film formation and therefore enhanced water resistance. As to microemulsions prepared with canionic emulsifier, the water resistance of coated paper was usually satisfied due to the good compatibility between paper fiber and the latex particles.(5) Compared with pure PMMA, PMMA/silica and PMMA/silica/titania nanoparticles exhibit high thermal stability and thermo-oxidative stability even at very low inorganic content because of the special electronic configuration of silica and titania. In order to have a thorough understanding of the thermal properties of the hybrid, 2D IR correlation approach was employed to analyze the degradation behavior of the hybrid. The decomposition of PMMA-co-HEA/SiO2 was investigated as the sample. The study found that the condensation of hydroxyl occurred at about 100-200°C, and resulted in the formation of covalent bonds between the polymer and the inorganic moiety (Si-O-C). Though the covalent bonds are not stable in sol-gel process they do exist during the heating process. The process of degradation of the polymer framework took place at about 300℃. The polymer chains, interweaving with silica networks, were partly grafted on the inorganic phase. Therefore their decomposition rates were lower than other side chain groups such as carbonyl and the grafted part did not fully decompose even at temperature up to 700℃. This also provided a deeper understanding for the TGA and Solid-state ²⁹Si MAS NMR spectra results. The similar phenomena were also investigated during the thermal degradation of PHMA/TiO₂ nanocomposites.The present contribution has demonstrated the usefulness of 2D IR analysis as an advanced interpretative tool for time-resolved FTIR data, in studies on high-temperature, thermal degradation of hybrids.