Diffusion Of Small Molecule Substances In Polymer And Nano-composite Polymer

Study on the interaction parameter of small molecule substance and polymer shows important theoretical and practical significance, with increasingly widespread of the research and application of polymer materials. Diffusion of small molecule substance in polymer is related to many polymer producing and machining producers, like diffusion of monomer and free radical in polymerization, diffusion of volatile in devolatilization of polymer and diffusion of plasticizer, antiager, light stability agent and dye in extrusion molding producer. It is obvious that diffusion of small molecule substance in polymer has great guiding significance of both fundamental theoretical study and technical progress of industrial production devices. So diffusion of small molecule substance in polyolefin becomes as the target of this thesis. The diffusion coefficients of small molecule substances in PE were measured. PE/palygorskite nano-composite was synthesized by in-situ polymerization, and the diffusion coefficients of small molecule substance in the composite were measured. The innovative results can be summarized as following:(1) The polymer particles were used as supplied by the producers to pack the chromatographic column without any pretreatment except for sieving. The infinite dilution diffusion coefficients of CH2Cl2, CHCl3, CCl4 and n-C6H14 in HDPE and LLDPE have been measured. The variance in the diffusion coefficients at infinite dilution of small molecule solvents was analyzed according to the differences in molecular size, temperature and structure of polymer chain. It was discovered that the diffusion coefficient decreases with decrease of the temperature, rising of the size of small molecule substance and the number of polymer branched chain.(2) The diffusion coefficients got from the experiment was compared and demonstrated by literature data, Krevelen model and free-volume theory. The experimental data is larger than the literature data, in which measurement polymer is dissolved in solvent and coated onto the particles. It can be explained that in theproducer of coating, morphology of polymer was changed. The data we got meets well to Krevelen model, which can prove the reliability of the experiment and classical theory of linear and non-equilibrium chromatography process. Finally, the correlations of the experimental with the free-volume theory equation were preformed.(3) Five different kinds of supported catalysts were prepared by varying the method for support pretreatment, and PE/palygorskite nano-composite was synthesized using the direct supported catalyst by in-situ polymerization. The so-called direct supported catalyst gave the highest activity among these supported catalysts, even more than that of homogeneous Cp2TiCl2 catalyst. No significant catalytic activity loss was observed under low Al/Ti molar ratios with the direct supported catalyst, which also showed a slower decay of polymerization rate. It was found that the surface Lewis acid sites of the support played an important role in activating of the metallocene compound and enhancing the catalyst activity.Molecular (?)ghts and melting points of the polymers produced with the supported catalysts were higher than that with the homogenous Cp2TiCl2 catalyst, while crystallinities were lower. Morphological replication of the support was observed with the polymer sample obtained from the direct supported catalyst.(4) The diffusion coefficients of n-hexane in the composite were measured. The result declared that the diffusion coefficient of small molecule substance in the nano-composite was smaller than it in the pure PE by percent of sixty, and the coefficient decreases with the rising of the weight content of the palygorskite clay. As a consequence, the addition of the carrier in the composite can advances its barrier property.