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Showing 1 to 20 of 45 for “"isotactic"”.
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A study of the crystallization kinetics of isotactic polystyrene
… rate data for a molecular weight series of isotactic polystyrene are analyzed in context of the Lauritzen-Hoffman kinetic theory of polymer crystallization. The primary objectives of the study are to critically test the Lauritzen-Hoffinan theory under conditions not rigorously investigated …
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Polymer Crystallization: Micro- and Nano- Filler Effects on Isotactic Polypropylene
Isotactic polypropylene (iPP) is one of the commodities used in the largest quantity today. Its good mechanical properties and relatively low price result in continuous growth of pro-duction and expansion of its market. The continuously increasing application accelerates research on all related …
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Relationships between micromorphology and impact properties of injection moulded isotactic polypropylene
… examination of the micromorphology of a range of isotactic polypropylene injection mouldings, paying particular attention to the outer layers which are difficult to characterise and to then relate the micromorphology revealed to the impact properties. Models which relate the mechanism of impact …
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An investigation into thermally induced structural modifications in isotactic polypropylene and its blends with amorphous terpolymers
Isotactic polypropylene undergoes rearrangement of its ternary structure when rapidly quenched from the molten state. This is an important area since cooling from the molten state is a fundamental aspect of a typical industrial extrusion process.<br/><br/>Studies were carried out on a range of …
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Production And Structure/Properties Of Nylon-6 Core / Isotactic Polypropylene Sheath Bicomponent Fibers Suitable For Use In Carpeting Applications
Bicomponent fibers consisting of nylon-6 and isotactic polypropylene were produced. In-situ, reactive compatibilization was achieved using a maleic anhydride functionalized polypropylene between the materials at the interface. The overall goal of the research was to produce a bicomponent fiber of …
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A study of miscibility, morphology, crystallization and melting behavior of isotactic poly(propylene) in blends of poly(propylene) and poly(1-butene)
… mechanical analysis on the melt blends of isotactic polypropylene and poly(1-butene) (it-PP/it-PB1), made of commercial high molecular weight materials, indicates a single but broad, composition dependent glass transition temperature. Crystallization studies of the a phase of it-PP in these …
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Examination of Dynamic Processes in Living Ziegler-Natta Polymerization and New Polypropylene Architectures through Bimolecular Control
… = nPr, iPr, iBu, and 2-Et-Bu, as well as living isotactic poly(1-butene) and living isotactic poly(1-sup13C-decene) revealed significant differences with respect to isomerization and decomposition. Studies carried out with various isotopically labeled iso-butyl derivatives revealed isomerization …
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Toughening mechanisms in polypropylene filled with rigid particles
… The mechanisms of deformation and fracture of isotactic polypropylene filled with CaCO3 particles were studied. In slow tension, addition of fillers increased the modulus and decreased the yield stress independent of filler type. An optimum size of particles was found to improve Izod impact …
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Z-selective olefin metathesis processes and Cis/syndioselective ROMP with high oxidation state molybdenum alkylidenes
… leads to the production of 92% trans-isotactic polyDCMNBE. The structure of trans-isotactic polyDCMNBD is proved through hydrogenation and comparison of its 3C NMR spectrum with that of known cis-isotactic polyDCMNBE. Both cis/syndiotactic/alternating poly-rac-DCMNBE and …
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Dipole moments and Kerr effect of poly(n-vinylcarbazole) and its complexes with trinitrofluorenone
… Modeller was used to examine the 3/1 helical isotactic and 2/1 helical syndiotactic forms of poly(N-vinylcarbazole). These models were used to calculate the pitch distances of helices and the results were interpreted in terms of van der Waal's radii on TNF. This study indicated that the pitch …
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The synthesis of novel biodegradable polyesters and copolyesters from anhydrosulfites
… (0.5 to 6)x104. Highly crystalline and purely isotactic poly(lactic acid) was synthesised from L-lactic acid anhydrosulfite (L-LAAS) whereas DL-LAAS led to an amorphous polymer with randomly distributed D-and L-lactic units. This indicated that this polymerisation was not stereoselective. …
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Equilibrium Melting Temperature Determination of Semicrystalline Polymers through Nonlinear Hoffman-Weeks Extrapolation and Secondary Crystallization of Ethylene/Styrene Copolymers
… analysis is successfully applied to the cases of isotactic polypropylene and poly(ethylene oxide). The predicted initial lamellar thickness as a function of the crystallization temperature matches well with experimental results and/or literature values. Results based on the nonlinear HW analysis …
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Single wall carbon nanotubes as viscosity modifiers in polypropylene matrix nanocomposites
… ranging from 2.5wt% to 10wt% of F-SWNTs in isotactic polypropylene, with Mw = 250,000 g/mol (iPP250,000), were shown to have lower complex viscosity profiles than the neat iPP250,000 sample at low shear rates. These fibers demonstrated decreases in the complex viscosities, in the low …
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Crystallization behavior and morphological features of two LARC polyimides and local orientation studies of two semicrystalline model composites
… superstructure in poly(glycolide co-lactide) and isotactic polypropylene. An increase in orientation on an absolute basis as a function of position was successfully measured. Orientation function values were higher on an absolute basis for the transcrystalline superstructure. However, the sign of …
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Molecular weight modulation in polyhydroxybutyrate fermentations
… It has material properties similar to isotactic polypropylene; it can be produced from renewable resources; it is biodegradable. Unfortunately, it is very brittle when compared to polypropylene. The physical property that most significantly affects elastic behavior is molecular weight. …
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Study of the miscibility, crystallization and morphology in poly(propylene) based blends and copolymers
… Miscibility behavior of high molecular weight isotactic poly(propylene) (it-PP) and isotactic poly(1-butene) (it-P1B) blend is investigated by a combination of optical microscopy and scanning electron microscopy, differential scanning calorimetry and dynamic mechanical analysis. These studies …
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Computational modelling of interfacial failure behaviours in polymer–metal joints
… focuses on polymer–metal joints consisting of isotactic polypropylene (iPP), iPP grafted with maleic anhydride (iPPgMA), or iPP grafted with amine groups (iPPgNH₂) and hydroxylated γ-Al₂O₃, which is a model for an oxidised aluminium surface, and investigates the contributions of the stiffnesses …
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Infrared Frequency Shifting in Thermally- and Mechanically-Stressed Polymers (Anharmonicity, Nonequilibrium, Ftir, Fourier, Transform, Spectrometer)
… shifting in samples of highly oriented, isotactic polypropylene. Each chain is modelled as a one-dimensional anharmonic system, whose wavefunctions and energies are obtained in the quasiharmonic approximation in order to obtain the stress-induced frequency shifting coefficient …
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