Search results for "plastic"
showing 10 items of 7296 documents
Sacrificial Synthesis of Hydroxy-Telechelic Metathesis Polymers via Multiblock-Copolymers
2009
The synthesis of well-defined telechelic ring-opening metathesis polymers has been achieved by Sacrificial Synthesis. With the formation of cleavable triblock-copolymers, precise control over the molecular weight and the degree of functionalization was achieved. Introducing cleavable monomers that can be addressed separately, sequential deprotection was accomplished which opened the path to more sophisticated polymeric materials bearing different substituents at their respective chain ends. Sacrificial penta- and heptablock-copolymers are also presented which allow the synthesis of well-defined telechelic polymers in good yields and significantly improved initiator efficiency.
Shear and nonisothermal elongational characterization of a liquid crystalline polymer
1989
A commercial liquid crystalline polymer (LCP) sample was characterized both in shear and in nonisothermal elongational flow over a wide range of temperatures (240–350°C). The LCP sample employed was a copolyesteramide of 2,6 hydroxynaphthoic acid, terephthalic acid, and aminophenol manufactured by Celanese and commercially known as Vectra B950. The viscosity decreases dramatically at temperatures above the crystal-nematic transition of the polymer. At lower temperatures, the extrusion of the sample is mainly due to plastic flow. Die-swell values are very small and contraction of the extrudate is also revealed, but the sample shows high elasticity. The polymer is not spinnable at very low te…
On The Incompatibility of Dextran and Pullulan in Aqueous Solutions and Its Modeling
2012
Joint aqueous solutions of branched dextran and linear pullulan are investigated with respect to their phase separation. The experiments demonstrate that the polymers are – depending on the molar mass of dextran – incompatible in aqueous solutions despite their chemical similarity. This finding can be modeled on the basis of an approach accounting for chain connectivity and conformational relaxation of the components. According to these calculations, the polymers exhibit a miscibility gap in joint solutions despite the favorable interactions between them. Using information on the subsystems H2O/dextran and H2O/pullulan, the assumption of complete miscibility of the polysaccharides is requir…
Interfacial tension of demixed polymer solutions: augmentation by polymer additives
1997
The interfacial tension between phase separated polymer solutions increases pronouncedly upon the addition of asmall amounts of incompatible polymers. This feature is demonstrated by means of measurements with solutions of polystyrene in cyclohexane and the folloowing additives: poly(styrene-block-dimethylsiloxane), polyisobutylene and polydimethylsiloxane. Theoretical considerations based on a correlation between the lenth of the tie lines and the corresponding interfacial tension corroborates this finding
Viscometric study on the compatibility of polymer–polymer mixtures in solution
1999
Abstract The viscosity behaviour of mixtures formed by two uncharged polymers in dilute solution has been studied at 25°C. The ternary systems assayed, and denoted solvent (1)/ polymer (2)/ polymer (3), have in common the poly(ether sulphone) (PES) as polymer 2, and poly(vinylidene fluoride) (PVDF), poly(methyl methacrylate) (PMMA) or poly(styrene) (PS) as polymer 3. The intrinsic viscosity and the viscometric interaction parameters have been experimentally measured for the binary (solvent/polymer) as well as for the ternary systems, and also theoretically evaluated for the latter. The estimation of the compatibility degree of the above polymer pairs have been done by means of three criteri…
Viscometric behaviour of polymer blends based on poly (vinylidene fluoride)
1994
The viscosity behaviour of dilute dimethylformamide solutions of poly(vinylidene fluoride)-poly (methyl methacrylate) and poly(vinylidene fluoride)-polystyrene has been studied at 25°C. The polymer concentration ranges are such that neither phase separation nor microgel formation occurs, although we are very close to theta conditions. The intrinsic viscosity and viscosity interaction parameter of the ternary mixtures have been calculated. The estimation of the compatibility of the above polymer pairs has been studied based on: a) specific viscosities; b) viscosity interaction parameters, according to Krigbaum and Wall formalism, and c) viscosity interaction parameters of a system formed by …
Branched versus linear polyisoprene: Fractionation and phase behavior
2007
Abstract Branched polyisoprene (PI) was prepared from PI-macromonomers. Linear byproducts of the synthesized polymer were removed by means of inverse spin fractionation, using the solvent cyclohexane (CH) and the precipitant acetone (AC). A well-defined fraction (Mw = 17.5 kg/mol, Mw/Mn = 1.8) of the branched polyisoprene obtained in this manner was used to determine different phase diagrams with branched and/or linear PI in the mixed solvent CH/AC at 25 °C. For comparable molar masses of the polymers the two-phase area is smallest for the branched PI and slightly larger for the linear PI; in the case of the unfractionated original sample of the branched polymer one observes a pronounced pe…
Ternary Polymer Solutions with Hydrogen Bonds, 1
2007
The Flory Huggins methodology coupled to AET has been extended to ternary polymer systems, in particular to solvent (A)/polymer 1 (B)/polymer 2 (C) systems, with the two polymers displaying H-bonding interactions. Because the H-bonding can perturb the randomness of polymeric conformations, the change in Gibbs free energy of mixing, AG, should arise from changes in combinatorial entropy as well as in interaction energy. The combinatorial part of AG is evaluated through AET as a function of the association constant η between B and C components, the autoassociation constant a between B components, and the independent number m of interaction sites of acceptor C. The enthalpic contribution is ev…
Correlation between transport and equilibrium properties through the ternary interaction parameter for cosolvent and cononsolvent polymeric systems
1992
A study of the ternary polymer systems dimethyl formamide-ethyl acetate-polystyrene, chloroform-1,4 dioxane-polystyrene and tetrahydrofuran-chloroform-polystyrene was carried out by viscosity and light scattering at 298 K. A good correlation has been found between the excess intrinsic viscosity, unperturbed polymer dimensions, second virial coefficient and the excess Gibbs free energy by using a ternary interaction parameter, dependent on molecular weight. This modification enables the conversion between transport and equilibrium properties.
Interfacial tension between coexisting polymer solutions in mixed solvents and its correlation with bulk thermodynamics: phase equilibria (liquid/gas…
2002
Abstract Vapor pressures, phase equilibria and interfacial tensions σ were measured for solutions of poly(dimethylsiloxane) (PDMS, M w [equals]75 kg/mol and M n [equals]50 kg/mol) in mixed solvents of toluene (TL) and ethanol (EtOH) at 30, 40, 50 and 60 °C. The experimental ternary phase diagrams can be modeled quantitatively from the determined concentration and temperature dependent binary interaction parameters χ ij if the experimentally inaccessible composition dependence of χ EtOH/PDMS is adjusted. The relations between σ and the equation of state of the system differ from that applying to single solvents. The exponents as well as the amplitude prefactors of the corresponding scaling l…