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Uniform Composition (uniform + composition)

Distribution by Scientific Domains
Polymers and Materials Science50%

Selected Abstracts

Model development for semicontinuous production of ethylene and norbornene copolymers having uniform composition

AICHE JOURNAL, Issue 3 2009
Shaojie Liu
Abstract Terminal and penultimate models for controlling copolymer composition distribution (CCD) in ethylene and norbornene (NB) copolymerization were developed by taking into account the variation of active site concentration with the initial comonomer ratio. The models were validated by batch polymerization experimental data. The terminal model gave better correlation with the composition data whereas the penultimate model had a better fit to the rate data. The terminal model was then used to design NB feeding policies in semicontinuous processes for targeted CCD profiles. Based on the model results, a series of ethylene-NB copolymers with various NB contents were prepared. With the same NB content, the semicontinuous process produced a uniform composition, whereas the batch process yielded broad CCD. The batch samples had lower Tg values and broader transition ranges, even yielded crystalline materials. In contrast, the semicontinuous samples overcame the disadvantages. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source]

Microstructure, Phase and Thermoelastic Properties of Laminated Liquid-Phase-Sintered Silicon Carbide,Titanium Carbide Ceramic Composites

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 7 2007
John H. Liversage
Hot-pressed silicon carbide,titanium carbide (SiC,TiC) composites sintered with liquid-phase forming Al2O3 and Y2O3 mixtures have been studied. Samples were fabricated by successively stacking tape-cast sheets of a single composition, resulting in a laminated body of uniform composition. This approach required the development of a technology easily transferable into the production of functionally graded SiC,TiC materials. The effects of this processing route on the resultant microstructures and phases were explored in detail. Additionally, because of the consequences for graded materials, the effects of TiC proportion on the thermal expansion coefficients, Young's modulus, and Poisson's ratios for several SiC,TiC composites were also determined. [source]

Multi-Component Kinetic Modeling for Controlling Local Compositions in Thermosensitive Polymers

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 8 2006
Todd Hoare
Abstract Summary: An explicit terminal copolymerization kinetic model accounting for the copolymerization of up to four different comonomers is developed and applied to model the conversion profiles and local compositional gradients in functionalized PNIPAM-based polymer and hydrogel systems. The kinetics of the functional comonomer(s) have a large influence on both the mole fraction and chain distribution of functional groups in polymers. Strategies are developed to synthesize polymers with uniform compositions by applying semi-batch techniques or via copolymerization of multiple monomers with the same target functionality but with divergent reactivities relative to NIPAM. Synthetic protocols are also designed to maximize the compositional uniformity and randomness of ampholytic polymers. Instantaneous mole fractions of monomers in polymers as a function of the overall monomer conversion for the copolymerizations of NIPAM, MBA, and two functional monomers: MMA and acrylamide. [source]