Molar Mass Dependence Research Articles

The monomer content of polymers from bis(hydroxyethyl) terephthalate

AbstractThe monomer content in polymers from bis(hydroxyethyl) terephthalate was previously found by Challa to be up to 63% higher than predicted by the classic equations of Flory. A reexamination shows that the apparent anomaly is caused by the approximative nature of the Flory equations which neglect the molar mass of the leaving molecules. Comparison of the experimental data with the predictions of the rigorous theory lowers the difference between experiment and theory significantly. The remaining differences scatter too much to allow any conclusions about a molar mass dependence of equilibrium or rate constants.

Molar mass dependence of hydrodynamic friction of polystyrene molecules in theta solution in cyclohexane as revealed by photon correlation spectroscopy and sedimentation data

The translational diffusion coefficient of polystyrene molecules in dilute theta solution with cyclohexane Dc was studied as a function of the polymer concentration c and the molar mass M by performing photon correlation (PC) measurements and by analyzing data from the literature. The molar mass dependence of the concentration dependent part of Dc was also calculated from the zero concentration extrapolated values with the corresponding effective hydrodynamic radii. For the calculations the Pyun-Fixman theory was applied which regards the polymer coils as soft, interpenetrable spheres with uniform segment density. A similar study has also been presented using data from several sedimentation measurements.

Gradient elution chromatography of polymers on reversed-phase columns with tetrahydrofuran as an eluent component

The chromatographic separation of poly(styrene-co-acrylonitrile) samples (SAN) with an elution gradient iso-octane/tetrahydrofuran is solubility governed. This has been proven by the correspondence between the volume fraction of precipitant as estimated from elution data and as measured by turbidimetric titration, by the molar mass dependence of retention, and by the temperature effect on retention. In addition to these arguments data are presented which have been obtained on columns with different packing materials ranging from bare silica through CN bonded phase material to hydrocarbonaceous stationary phases. The eluent composition at peak position is nearly independent of the stationary phase used.

Effect of cooling rate on the structural relaxation of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and poly(oxy‐2,6‐dimethyl‐1,4‐phenylene)

AbstractThe activation enthalpies for the structural relaxation of poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and poly(oxy‐2,6‐dimethyl‐1,4‐phenylene) were determined by studying the dependence of the limiting fictive temperature on the cooling rate, using a differential scanning calorimeter (DSC) interfaced to a computer. The molar mass dependence of the activation enthalpies complied with the empirical equation, ΔH˙ = ΔH − A/M, where ΔH is the activation enthalpy of an infinite chain length polymer, Mv is the viscosity‐average molar mass, a = 0,64, and A is a constant that depends on the free volume of the chain ends of the polymers. The values of ΔH are 433 kJ/mol for poly(oxy‐2,6‐dimethoxy‐1,4‐phenylene) and 449 kJ/mol for poly(oxy‐2,6‐dimethyl‐1,4‐phenylene).