Concentrated Solutions Of Poly Research Articles

Study of structure formation during phase transitions in poly- p-phenyleneterephthalamide solutions

The methods of polarizing and electron microscopy were used to investigate structure formation during phase transitions in concentrated solutions of poly- p-phenyleneterephthalamide in sulphuric acid. The data obtained are explained in terms of various types of phase equilibrium. It is shown that under certain conditions a major role in structure formation is played by crystallization in the form of crystal-solvates of the type of poly- p-phenyleneterephthalamide · pH 2SO 4. All the observed structuro-morphological patterns may be described satisfactorily by using the phase diagram previously proposed for poly- p-benzamide.

Dielectric relaxation in concentrated solutions of poly(methyl methacrylate)

AbstractMeasurements of dielectric relaxation have been made for a series of solutions of poly(methyl methacrylate) in toluene. A range of concentrations between 2% and 20% was used for a number of polymers of differing molecular weights. The dispersion was studied over the frequency range 103‐106 Hz for temperatures between −90°C and +20°C. It has been found that both the distribution of relaxation times and the activation energy increase with increasing concentration. The magnitudes of the effects vary with molecular weight. A significant observation is that the increase in dielectric constant with concentration is not linear.

High shear viscometry of concentrated solutions of poly (alkylmethacrylate) in a petroleum lubricating oil

High shear capillary viscometry at 37.8°C (100°F) of concentrated solutions of a series of polyalkylmethacrylate viscosity index improvers in a petroleum lubricating oil is reported. Viscosity average molecular weights of the four polymers varied from 355 000–1650 000 and solution concentrations varied from 2–20 wt.-%. An approximating function based on the error function was computerfit to the complete flow curves by correlating the distribution of apparent viscosity with the product ( $$\dot \gamma $$ τ), the rate of viscous energy dissipation. This gave an estimate of the secondNewtonian viscosity (η ∞ ) and two parameters of the approximating function. The fourth quantity required to completely define the flow curve is the low shear or firstNewtonian viscosity (η 0 ). Representation of the original data was within 2%, by this technique. The parameters of the flow function — the energy level at the inflection point and the slope of the transformed flow function — were found to vary in a regular manner with both molecular weight of the polymer and polymer concentration, expressed as relative viscosity (η rel). The limiting asymptotes of the approximating function —η 0 andη ∞ — could not be treated according to the conventionalHuggins equation, but they were fit adequately by theMartin equation: log(η sp/C)=log[η]+K[η]C. The intrinsic viscosities thus determined for both low shear ([η M ]0) and high shear ([η M ]0) demonstrate aMark-Houwink relationship, i.e., [η M ]0=5.668×10−5 M 0.660 and [η M ]∞=2.574×10−5 M 0.0669 so that ([η M ]∞≈[η M ]0/2) over the range studied. The relationship of these results to other reports of high shear viscometry of polymer solutions is discussed.

Structurization in the poly (m‐phenylene isophthalamide)–dimethylacetamide system

AbstractThe methods of turbidity spectrum and viscometry have been used to investigate structurization in the concentrated solutions of poly (m‐phenylene isophthalamide) (Pm‐PIPA) in dimethylacetamide (DMA). The kinetics of formation of the supermolecular order (SMO) were studied under isothermal conditions within the temperature and concentration range of 30 to 150°CC and 5 to 25 g/dl, respectively. Two stages of formation of SMO were observed, viz., a comparatively slow stage and after that a very fast increase in the SMO level. In the first stage, the average particle radius, rλ, decreases, which probably is related to the continuous formation of nuclei. In the second stage, rλ and the turbidity, τ, of solution increase steeply. In the same stage, an increase in the viscosity of solution was also observed. A diagram of the properties of the system was constructed, which is analogous to the phase diagram. The temperature limit of the stability, Tbi, fulfills the requirement of Vτ = 0, where Vτ (the rate of increasing turbidity), was determined. Tbi determines the binodal curve depending on the polymer concentration. The temperature limit of absolute instability, Tsp, fulfilling the requirement of Vτ→∞, was determined. Depending on the concentration of solution, Tsp was identified with a spinodal curve. The property diagrams obtained are characteristic of the curves of amorphous separation with the lower critical solution temperature. With increasing molecular weight, Mζ, Tc decreases. Additions of a third component cause a deformation of the binodal curve and shift it to higher (lithium and calcium chlorides) or lower (water) temperatures. The time, ts, of reaching a certain level of SMO during thermostabilization at T = 80°CC was taken as a measure of stability of technological solutions.

Study of the rheological characteristics of moderately concentrated solutions of poly(amido acids)

Study of the rheological characteristics of moderately concentrated solutions of poly(amido acids)

Conformational studies on concentrated solutions of poly(gamma-benzyl L-glutamate).

AbstractWe have studied the effect of polypeptide concentration on the helix–coil transition of poly(γ‐benzyl L‐glutamate) (PBLG) in both dichloroacetic acid (DCA) and DCA–chloroform (CHF) mixtures. In agreement with other reports, we find the van't Hoff transition enthalpy to be strongly dependent on PBLG concentration. Also, an apparent effect of polypeptide concentration was noted on the transition temperature; however, corrections for finite PBLG concentration on the mole fraction of DCA seem to remove this effect. In order to explain our data, as well as some calorimetric data in the literature, we consider the transition free energy and enthalpy as a sum of three partial terms. These represent the thermodynamic parameters associated with: (1) conformational changes of the polypeptide, e.g. formation or disruption of intramolecular hydrogen bonds; (2) binding by the strong acid to the nonhelical segments of the polypeptide; (3) an overall (weak) interaction of the polypeptide with the nonbound solvent giving rise to dilution parameters that are dependent on the polypeptide conformation. The latter effect is generally ignored, since it is assumed that solvent interactions, other than specific binding, are similar for both the helical and the nonhelical conformation. Striking effects of water (small amounts) and solution aging on the formation of PBLG helices was observed. Water, as expected, acts as a helicogenic solvent when combined with DCA. The processes occurring during solution aging are not known, although the net effect is to stabilize the helical conformation. Finally, we present some rather unique thermally induced transitions of concentrated PBLG (about 200 mg/ml) in DCA. At low temperatures the soluble randomly coiled conformation is present. Heating produces first an isotropic gel, followed at higher temperatures by an isotropic solution consisting of about 70% α‐helicity.

Liquid-liquid phase separation in concentrated solutions of non-crystallizable polymers by spinodal decomposition

Two mechanisms of liquid-liquid phase separation in polymer solutions are possible: nucleation and growth of one of the equilibrium phases, and decomposition by a spinodal mechanism. The conditions for and characteristics of both mechanisms are discussed. By combining a number of observations on phase separation in concentrated solutions of poly(2,6-dimethyl-1,4-phenylene ether) and of an ethylene — vinyl acetate copolymer in caprolactam, it becomes clear that a spinodal mechanism is operative at the onset of the separation process. In later stages the flow properties of the concentrated polymer phase determine the final state of the separated mixture.