Lubomír Šimek

Sorption of water vapour by segmented polyurethanes

Abstract Segmented polyurethanes were prepared by reacting equimolar quantities of 4,4′-diphenyl-methane diisocyanate (MDI) with low-molecular-weight poly(ethylene oxide), poly(propylene oxide) and triblock copolymers of ethylene and propylene oxides. Equilibrium sorption of water vapour at 23° was measured at three to six values of relative vapour pressure ( 0.32 ⩽ p p o ⩽ 1 ). Sorption isotherms were fitted by a semi-empirical two-parameter equation. The effect of structure of the soft segment on sorption was studied. Clustering characteristics of water were estimated by means of the Zimm-Lundberg treatment and compared with those of corresponding polyethers. It was shown that both MDI and propoxamer units increase the clustering tendency of water, the effect of the latter groups being much more significant.

Note on the Relation between the Parameters of the Mark-Houwink-Kuhn-Sakurada Equation

The relation between the parameters K and a of the equation [η] = KM a , which has been empirically established by several authors, is discussed. Equations describing this relation are derived based on the two-parameter theory of the intrinsic viscosity for flexible chain polymers (where a<0.8) and on the worm-like cylinder model for stiff chains (a>0.8). The correspondence of calculated and empirical results is good.

Specific refractive index increments of segmented polyurethanes

Specific refractive index increments v of polyester-based segmented polyurethanes in N,N-dimethyl formamide have been determined, and the quotient dv/df d has been evaluated (where f d is the weight fraction of hard-segment units). The results are in good agreement with the values calculated from group contributions to the molar refraction, using the Vogel or the Gladstone-Dale equations. The values calculated with the Lorenz-Lorentz equation are too low. A potential explanation of this fact is proposed. The same methods have been applied to reported v values for polyether-based polyurethanes. An explanation is proposed for differences in dv/df d for polyesterand polyether-based polyurethanes.

Estimation of conformational characteristics of bisphenol-A based poly(hydroxyethers)

Two samples of bisphenol-A based epoxy resins (poly(hydroxy ethers)) were fractionated by precipitation. The fractions were characterized by the weight-average molecular weight (1.3<Mw×10−3<40) and the intrinsic viscosity in tetrahydrofuran and chloroform. Theories based on the worm-like touched-bead model were used to treat the molecular-weight dependence of the intrinsic viscosity and to estimate the conformational characteristics (Kuhn statistical segment length lK, Flory characteristic ratio C∞, and steric factor σ). Low values of these characteristics indicating rather high flexibility of the chain are discussed.

Solubility in water of triblock (PEP) copolymers of ethylene and propylene oxides

Abstract Aqueous solutions of hydroxyl-terminated triblock copolymers of ethylene and propylene oxides display turbidity, both on heating and cooling. The lower critical solution temperatures increase with increase in the content of ethylene oxide units. Phase diagrams obtained with acetyl-terminated copolymers are more involved and give evidence of an important effect of end groups.

On the Precision of Particle Size Analysis by Micro‐Thermal Field‐Flow Fractionation

Abstract Micro‐Thermal Field‐Flow Fractionation of polymer colloidal particles was performed in two different laboratories. Short term repeatability of the experimental retentions obtained in a single laboratory has been found to be very high. The short term precision (expressed as percent standard deviation) of the determination of average particle diameter can reach the values greater than 1%, relative. Average repeatability of the retentions in both laboratories was better than 3%, relative when using identical experimental protocol. No other method of particle size analysis can provide the results of a comparable precision. Average repeatability of the width of the raw fractograms, which contains the information on particle size distribution, is of the order of 5%, relative. However, this value cannot be considered as the ultimate limit because the experiments were not carried at the low flow rate of the carrier liquid permitted to reach much higher resolution. The effect of the stability of the most important operational variables, such as the temperature drop between the cold and hot walls, the temperature of the cold wall, and the flow rate of the carrier liquid, on the precision of the analytical results is discussed. This article is dedicated to the memory of J. C. Giddings (1930–1996)

A Study of the Interaction between Chitosan and Poly(Ethylene Glycol) by Viscosity Method

Abstract The viscometric coefficient, kAB, characterizing the interaction of chemically dissimilar polymer segments was estimated from changes of the intrinsic viscosity of chitosan in “pseudosolvents,” i.e., dilute solutions of poly(ethylene glycol) (PEG) in a solution of 0.1 M acetic acid/0.2 M sodium acetate (1:1). The blends were studied at 25°, 35°, and 45°C. The miscibility between chitosan and PEG was found to increase with the temperature of the measured systems and to decrease with increasing molar mass of PEG. In the cases where favorable compatibility was exhibited between chitosan and PEG, H-bonding interaction between the two polymers should be strong enough to overcome the intra- and intermolecular H-bonding among chitosan chains.

Melting points of symmetric oligomeric triblock copolymers (type PEP) of ethylene and propylene oxides

Abstract Melting points of oligomeric triblock copolymers of ethylene oxide and propylene oxide (type P x /2 E y P x /2 with 8 ⩽ y ⩽ 31 and 7 ⩽ x ⩽ 23) were determined. They are lower by 10–20 K than those of poly(ethylene oxide) at the same number of ethoxamer units. The effect of the copolymer composition is discussed in terms of the theory of fusion of crystalline block copolymer. The end interfacial free energy is found to be higher than with ethylene oxide oligomers and to increase with increasing length of propoxamer blocks.

Free-rotation dimensions of some polyurethane chains

Abstract The ratio of the unperturbed mean-square end-to-end distance to the molecular weight in the random-coil limit, (〈 R 2 〉 0, f / M ) ∝ , in the freerotation approximation was calculated for chains of linear polyurethanes PUR-D k prepared from 4,4′-methylenediphenyl diisocyanates and low-molecular-weight diols HO(CH 2 ) k OH ( k = 2, 3, 4 and 6). It was found that the experimental values of (〈 R 2 〉 0 / M ) ∝ estimated in the previous paper are very close to the values of (〈 R 2 〉 0. f / M ) ∝ calculated under the assumption that the groups of bonds CH 2 C 6 H 5 NH and NHCOOCH 2 can be replaced by rigid virtual bonds.

A Study of Blends of Amphiphilic Polymers in Solution

Abstract The viscometric coefficient, kAB, characterizing the interaction of chemically dissimilar polymer segments was estimated from changes of the intrinsic viscosity of poly(vinyl alcohol) (PVA) measured in “pseudo-solvents,” i.e., dilute solutions of poly(ethylene glycol) (PEG) in water and dimethyl sulfoxide (DMSO). The results provide evidence of the compatibility of these polymers in both solvents. The effects of hydroxyl end groups and the character of solvents has been found. The aggregation of PVA molecules in water is not significantly suppressed by PEG.