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Polymer Growth (polymer + growth)
Selected AbstractsPolymerization at the gas/solution interface: Preparation of polymer microstructures with gas bubbles as templatesJOURNAL OF APPLIED POLYMER SCIENCE, Issue 4 2007Maciej Mazur Abstract We report on the chemical polymerization of 2-methoxyaniline at the interface between an aqueous solution and air. The polymer is formed in the interfacial region, whereas the soluble trimer is yielded in the bulk of the polymerization solution. The preferential polymerization of 2-methoxyaniline is discussed in terms of monomer and oligomer accumulation at the interface, which influences the reactivity of these species and allows further polymerization. The phenomenon of polymer growth is employed to selectively deposit polymeric material onto glass slides decorated with gas microbubbles. Because of preferential polymerization at the bubble/solution interface, hemispherical features are produced on the surface of glass. When some polymeric material is mechanically removed, microrings or microholes are obtained. The anomalous polymerization of 2-methoxyaniline is compared to that of 2-methylaniline. This monomer polymerizes uniformly within the entire volume of the reaction mixture; thus, no preferential polymer formation at the gas/solution interface is observed. As a result, deposition on microbubble-decorated glass slides produces polymeric films containing a number of microholes. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007 [source] Long-lived layered silicates-immobilized 2,6-bis(imino)pyridyl iron (II) catalysts for hybrid polyethylene nanocomposites by in situ polymerization: Effect of aryl ligand and silicate modificationJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 2 2009Giuseppe Leone Abstract Heterogeneous-layered silicate-immobilized 2,6-bis(imino)pyridyl iron (II) dichloride/MMAO catalysts, in which the active polymerization species are intercalated within sodium- and organomodified-layered silicate galleries, were prepared for producing hybrid exfoliated polyethylene (PE) nanocomposites by means of in situ polymerization. The inorganic filler was first treated with modified-methylaluminoxane (MMAO) to produce a supported cocatalyst: MMAO reacts with silicates replacing most of the organic surfactant, thus modifying the original crystallographic clay order. MMAO anchored to the nanoclay was able to activate polymerization iron complexes initiating the polymer growth directly from the filler lamellae interlayer. The polymerization mechanism taking place in between the montmorillonite lamellae separates the layers, thus promoting deagglomeration and effective clay dispersion. Transmission electron microscopy revealed that in situ polymerization by catalytically active iron complexes intercalated within the lower organomodified clay led to fine dispersion and high exfoliation extent. The intercalated clay catalysts displayed a longer polymerization life-time and brought about ethylene polymerization more efficiently than analogous homogeneous systems. PEs having higher molecular masses were obtained. These benefits resulted to be dependent more on the filler nature than on the ligand environment around the iron metal center and the experimental synthetic route. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 548,564, 2009 [source] Video Microscopy for the Investigation of Gas Phase CopolymerizationMACROMOLECULAR MATERIALS & ENGINEERING, Issue 11 2005Daniela Ferrari Abstract Summary: Video microscopy as a tool for investigating olefin gas phase copolymerization is presented for the first time in this paper. The central theme of this work is the study of the comonomer effect shown by an unbridged metallocene catalyst supported on silica. By using video microscopy, it is possible to observe the increase in catalytic activity in terms of particle growth as well as monomer consumption. The observation that a more pronounced induction period in the particle growth profile is shown with increasing propylene concentration led us to investigate the copolymers obtained at different polymerization times using 13C NMR analysis and single particle energy dispersive X-ray (EDX mapping). This allowed us to adapt the "polymer growth and particle expansion model" to the copolymerization. Besides physical causes for the comonomer effect, we wanted to determine whether the catalyst structure plays an important role in the comonomer effect. To this end we investigated two metallocenes bearing the same long bridging unit but differing in the ligand bound to the zirconium center. One metallocene bears a cyclopentadienyl ring, while the other bears an indenyl group. From a close analysis of the 13C NMR, it is clear that both catalysts insert ethylene more easily then propylene, probably due to the long bridging unit that results in a narrower aperture angle of the ligand. In addition to this, the indenyl ligand does not allow the formation of propylene blocks even at high propylene concentration. Snapshot of the polymer particles taken after 165 min of ethylene-1-butene copolymerization with catalyst 1. [source] Bridging Experiments and Simulations in Oblique Angle PolymerizationCHEMICAL VAPOR DEPOSITION, Issue 4-6 2009Murat Cetinkaya Abstract In this paper, we report the growth of nanostructured poly(p-xylylene) (PPX) films by oblique angle polymerization at various deposition angles. Additionally, a two-dimensional computational (Monte Carlo) model is implemented to study the nanostructured growth process. The morphology of the nanostructured polymer films are characterized by atomic force microscopy and scanning electron microscopy. Based on the experimental results, a competitive growth model is proposed and quantified in terms of column geometry (i.e., diameter and height), column spacing (i.e., periodicity), and column packing (i.e., number of columns per unit area). We show that the nanostructured polymer growth obeys a universal power-law scaling mechanism at various deposition angles. The computational model predicts similar nanostructured morphologies to the oblique angle polymerization obtained experimentally. Nanostructured polymer films may provide great advances in sensing and biomedical applications. [source] | ||||||||||