M. Bohdanecký

A viscometric study of dilute aqueous solutions of poly(vinylalcohol)-polyacrylamide mixtures

Abstract The viscosity interaction coefficient, k AB , for the system poly(vinylalcohol)-polyacrylamide-water was determined at 25° by two methods: (a) estimation of the Huggins slope coefficients for mixtures of polymers in different proportions; (b) determination of the intrinsic viscosity of polymer (A) in aqueous solutions of polymer (B). The result, k AB = 0.3, indicates a low degree of overlapping of unlike polymer molecules.

Dilute solution properties of aliphatic polyamides

The development of and new trends in the determination of molecular weights and molecular weight distribution of aliphatic unsubstituted linear polyamides (nylons) are reviewed here. Critically discussed are intrinsic viscosity — molecular weight relationships and the conformational regidity of nylon chains. Attention is also given to some peculiarities in the behavior of nylons in multicomponent solvents.

Effect of urea on the behaviour of poly(2-hydroxyethyl methacrylate)-water mixtures

Abstract The effect of urea solutions on the equilibrium swelling of lightly crosslinked poly(2-hydroxyethyl methacrylate) (PHEMA) gels and on the viscometric behaviour of PHEMA, for various concentrations of urea and temperatures, has been studied. Urea raises the degree of swelling of gels and the intrinsic viscosity of PHEMA; the temperature coefficient of both quantities is negative. A thermodynamic analysis of the swelling data shows that a change in entropy is the driving force for the increase in swelling at low temperatures, while at higher temperatures (50–80°) a negative change in enthalpy prevails, both corresponding to the transport of PHEMA from the aqueous medium into urea solutions. The entropy and enthalpy of dilution parameters derived from viscometric measurements have negative values, and their absolute values decrease with increasing urea concentration. It has also been found that the PHEMA molecules in urea solutions under the θ-conditions are much more coiled than in an organic θ-solvent. The results are interpreted in terms of the existence of inter- and intramolecular hydrophobic bonds and by the destruction of hydrophobic clusters caused by urea.

Dilute solution properties of polylaurolactam

Abstract For a number of fractions and unfractionated samples of polylaurolactam, molecular weights ( M w = 1 × 10 4 −12·5 × 10 4 ) were measured by the light-scattering method in a mixed solvent of m-cresol with 60 vol. % 2,2,3,3-tetrafluoropropanol; intrinsic viscosities were determined in m-cresol and 96% H2SO4, and the constants of the Mark-Houwink equation were calculated. The calculated values of the characteristic ratio of unperturbed dimensions (virtually identical for m-cresol and 96% H2SO4) were compared with the respective values for polypyrrolidone and polycaprolactam. It was found that the higher frequency of the CONH-groups reduces the rigidity of the polyamide chain.

Concentration dependence of the sedimentation coefficients of polystyrene in the vicinity of the φ-temperature

Abstract Measurements have been made of the concentration dependence of the sedimentation coefficients of two polystyrene fractions (M = 51 and 1500 × 103) in cyclohexane at several temperatures in the vicinity of the α-temperature. The coefficients of this dependence, km have been correlated with the expansion coefficients αq3. The dependence kη/[η] − αη3 has been compared with the theoretical dependences, and a correlation relationship kη[η] = (kη)0η/[η]-αη/[η]0 + 4 ·5(αα-2-αη-4has been suggested (with (ka)0/[η]0 ≈0·55) which also satisfies the literature data for ks in the range of αη3 from 0·86 to 4.

Estimation of the characteristic ratio of poly[2-(triphenylmethoxy)ethyl methacrylate] from hydrodynamic properties of its dilute solutions

Abstract Properties of poly[2-(triphenylmethoxy)ethyl methacrylate] (PTEMA) molecules in solutions (under O-conditions and in “good” solvents) were investigated by the light scattering, sedimentation, viscometric and by phase equilibria methods. The O-temperature (47°) was determined for the system mesitylene-PTEMA. Unusual correlations of hydrodynamic data with molecular weight are discussed and slight branching of polymer chains is accepted as a probable explanation. Data for mesitylene solutions under O-conditions are used to estimate the characteristic ratio of PTEMA molecules ( R 0 2 /nl 2 = 19 ).

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.

Dilute solutions of nylon 12—II. Relationship between intrinsic viscosity and molecular weight☆

Abstract Samples of poly(12-dodecanelactam) (polylaurolactam, nylon 12) with M n 1 × 103−33 × 103 were prepared. Polymerizations initiated with water or with lauric acid proceeded under conditions for minimum changes in end-group concentration. Values of M n were calculated from the end-group content and M n from light scattering in the mixture m-cresol/60 vol% of 2.2,3,3-tetrafluoropropanol. From measurements of intrinsic viscosity in m-cresol, the relationship [n] − M n was established in the given range of M n. The relationship [n] − M w for M w from 3.3 × 103 to 125 × 103 has been established.

Electrophoretic and viscometric studies of the interactions of polymethacrylamide and polyacrylamide with electrolytes in aqueous solutions

Abstract Free electrophoresis and viscometry were used to study the effects of salts (perchlorates, thiocyanates, chlorides and sulphates of uni- and bivalent metals) on the properties of polyacrylamide and polymethacrylamide in aqueous solutions. In salt solutions, in the electric field both polymers behave as polyanions. It may be inferred from electrophoretic measurements that both anions and cations are bound on the polymer chain; the degree of binding depends on the nature of the ions. The viscometric data show that there is a pronounced salting-in effect of cations (increasing with increasing surface charge density); the effect of anions is either secondary (for polyacrylamide) or rather unfavourable to dissolution (for polymethacrylamide).

The antithixotropy of dilute solutions of copolymers of methyl methacrylate and methacrylic acid

Abstract Dilute solutions of methyl methacrylate-methacrylic acid copolymers (with low content of methacrylic acid) in ethylene dichloride exhibit the effect of antithixotropy which manifests itself in the time dependence on the shear stress (in rotatory viscometers) and in the upturn on the shear stress dependence of viscosity (in capillary viscometers). The upturn vanishes at infinite dilution. Conditions for the appearance of the effect (polymer concentration, temperature, addition of dimethylformamide) were investigated. The explanation of the effect is based on the assumption of strong intermolecular interaction brought about by hydrogen bonds.