Rayleigh Scattering From Polystyrene SolutionsBY N. C. FORD, JR., * F. E. KARASZ t AND J. E. M. OWENDepartment of Physics and Astronomy and polymerscience and Engineeringprogram, University of Massachusetts, Amherst,...
Rayleigh Scattering From Polystyrene SolutionsBY N. C. FORD, JR., * F. E. KARASZ t AND J. E. M. OWENDepartment of Physics and Astronomy and polymerscience and Engineeringprogram, University of Massachusetts, Amherst, Massachusetts, 01002, *** 8th January, 1970A laser homodyne spectrometer has been used to study the power spectrum of light scattered fromdilute polystyrene+2-butanone solutions. From the measurements the translational diffusionconstants for the macromolecules were determined as a function of molecular weight and soluteconcentration. The analysis of the data included an estimation of the unperturbed dimensions of *** recent years laser homodyne spectroscopy has been applied to studies of thespectral distribution in Rayleigh light scattering from polymers in dilute ~olution.l-~The principal quantity that can be obtained from such investigations is the transla-tional diffusion constant, though in special cases the rotational diffusion constant ofanisometric polymers may be determined also.2* Compared to conventionaltechniques, the measurement of diffusion constants from light scattering studies offerscertain inherent advantages : a relatively high precision, rapid measurement times,minimal data analysis and small sample ***, because thesystem is in macroscopic equilibrium, the differential binary diffusion constant D(c)for the system (as distinct from an integral diffusion constant) is obtained *** significance of translational diffusion constants, in common with parametersobtained from other hydrodynamic measurements of macromolecules in dilutesolution, lies in their application to the characterization of such molecules in terms ofmolecular weight or size, and of *** spectroscopy studies have beenlargely confined to studies of the latter parameter, particularly with respect to thechanges in shape concomitant with conformational transitions in biological *** present study, in contrast,
A study has been made of the relaxation phenomena in three series of polyurethanes in the neighborhood of their glass transition temperatures and above. The technique of dynamic mechanical relaxation was used in the i...
Enthalpies and entropies of fusion have been determined for two series of semicrystalline polyurethanes. The H series is based on 1,6-hexamethylene diisocyanate and various α, ω-diols containin...
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Enthalpies and entropies of fusion have been determined for two series of semicrystalline polyurethanes. The H series is based on 1,6-hexamethylene diisocyanate and various α, ω-diols containing from 2 to 10 methylene units. The DP series is based on 4,4′-methylene diphenyl diisocyanate and various α, ω-diols containing from 2 to 10 methylene units. Differential Scanning Calorimetry (DSC) was used in conjunction with X-ray analysis (X-ray method) and low molecular-weight diluents (diluent method) to determine the enthalpies of fusion. Agreement between the X-ray method and the diluent method was *** between the enthalpies and entropies of fusion of the H and DP series could be largely attributed to differences in intermolecular hydrogen bonding in the melts of the two series. On the other hand, differences in the entropies of fusion between the H series and corresponding polyamides arise largely from differences in backbone-chain stiffness between the two series.
A dynamic mechanical study has been made of two series of partially hydrolyzed ethylene-vinyl acetate copolymers. Series A contains 75 mole % ethylene and series B contains 59 mole % ethylene. The frequencies employed...
A dynamic mechanical study has been made of two series of partially hydrolyzed ethylene-vinyl acetate copolymers. Series A contains 75 mole % ethylene and series B contains 59 mole % ethylene. The frequencies employed were 3.5, 11, and 110 Hz, and the temperature range was from −180° to +120°C. Three relaxation regions are discernable in this range and these are labeled α, β, and γ in order of decreasing temperature. The α relaxation is associated with the glass transition of the copolymers. The β relaxation is absent in the unhydrolyzed copolymers and is dependent on hydroxyl content. It is assigned to local motions of hydrogen bonded groups. The γ relaxation is insensitive to hydroxyl content and is assigned to local motions of methylene sequences. The above assignments are supported by the effect of water added to the polymers. Added water decreases the temperatures of the α and β relaxations but does not affect the γ relaxation significantly. The magnitude of the β relaxation is considerably enhanced by water.
The glycerol acetal of methyl azelaaldehydate is an ω-hydroxy ester that exists as a mixture of dioxolanyl and dioxanyl isomers, each having two geometric isomers. Each of the four isomers was isolated by chromatogra...
The glycerol acetal of methyl azelaaldehydate is an ω-hydroxy ester that exists as a mixture of dioxolanyl and dioxanyl isomers, each having two geometric isomers. Each of the four isomers was isolated by chromatographic (gas–liquid and column) and fractionating (crystallization and distillation) methods. Structural assignments were made on the basis of nuclear magnetic resonance and infrared spectral data. Linear poly(ester-acetals) were prepared from each of the cis and trans forms of the dioxanyl isomers and from a mixture of the dioxolanyl geometric isomers. Physical properties of these polymers were correlated with their structures. When prepared with basic condensation catalysts, the polymers retained the geometric configuration and structural identity of the monomer. When prepared with lead acetate, structural rearrangement as well as polycondensation occurred, resulting in an enrichment of the dioxolanyl isomer and simultaneous increase in polymer crystallinity. The enrichment took place at elevated temperatures and also, unexpectedly, at room temperature upon long standing of the polymer. Isomer redistribution at room temperature appears to be antithermodynamic in the reaction sense, yielding a polymer of unusually high dioxolanyl unit content. The driving force for this isomerization may be crystallization of these units by a phenomenon termed a “crystallization-induced reaction.”
Diester and hydroxy ester monomers containing internal five-, six-, and seven-member acetal rings were prepared and converted into linear polyesters, copolyesters, and copolyamides. The polymers so obtained were chara...
The techniques of differential thermal analysis and photomicroscopy have been combined to eludicate the complex phase relationships and crystallography of cholesteryl myristate. Also, the amount of polarized light rot...
The techniques of differential thermal analysis and photomicroscopy have been combined to eludicate the complex phase relationships and crystallography of cholesteryl myristate. Also, the amount of polarized light rotated by the samples as a function of temperature has been measured at a fixed sample thickness. Cholesteryl myristate exhibits a complex liquid crystal mesophase system on heating. In addition to the phase transformations obtainable on heating, photomicrographs were obtained of the phases which result on subjecting the smectic and cholesteric mesophases to a very low shear. Excellent correlation was obtained between the present work and earlier studies of the myristate ester. The combined instrumental and microscopic method appears to be a valuable tool in the study of subtle phase changes in complex systems.
A quantitative explanation is given for the apparent viscosity increase with increasing capillary shear rate for polystyrene at temperatures approaching the glass transition, T g . Possible shifts in T g as a function...
A quantitative explanation is given for the apparent viscosity increase with increasing capillary shear rate for polystyrene at temperatures approaching the glass transition, T g . Possible shifts in T g as a function of the parameters shear rate, frequency, and pressure are interrelated to viscosity changes. Experimentally, the Instron capillary rheometer and the Weissenberg rheogoniometer provided a means for uncoupling the variables for individual consideration. Calculated and experimental data for the apparent viscosity as a function of the given parameters are presented and discussed. The explanation of the apparent viscosity increase in capillary flow can be quantitatively explained through the pressure dependence of T g . Brief mention is made of the pressure effects on the Bagley and Rabinowitsch corrections normally made in capillary measurements.
The dielectric relaxation of amorphous bulk poly(2, 6‐dimethyl phenylene oxide) (PPO) has been measured between ?160° and 260°C over a frequency range extending from 0.1 to 10 kHz. Two broad loss peaks of c...
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The dielectric relaxation of amorphous bulk poly(2, 6‐dimethyl phenylene oxide) (PPO) has been measured between ?160° and 260°C over a frequency range extending from 0.1 to 10 kHz. Two broad loss peaks of comparable intensities are observed‐a high‐temperature α relaxation identified with the glass transition and a low‐temperature γ relaxation of uncertain origin. The intensity of the α relaxation can be well accounted for in terms of a loss of orientational dipolar correlation in a calculation based on a consideration of a rotational isomeric model and of the geometry of the PPO chain.
A study has been made of the relaxation phenomena in three series of glassy polyurethans in the temperature range from -190 to -100° and at various frequencies up to 110 Hz using dynamic mechanical and dielectric...
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