Pressure dependence of viscometric relaxation times measured with a new apparatus. Williams-Landel-Ferry behaviour of moderately concentrated solutions of poly(butyl methacrylate)s in 2-propanol

A new rotational viscometer is presented which can be operated up to 2 000 bar and a maximum shear stress of 420 Pa. It allows, for the first time, to investigate the non-Newtonian flow behaviour of moderately concentrated polymer solutions. Results of measurements with two representatives of the system 2-propanol/poly(butyl methacrylate) with weight-average molecular weights M?_w = 520 000 and M?_w = 2 050 000, and ratios of weight- to number-average molecular weights M?_w/M?_n = 1,08 and M?_w/M?_w = 1,23, resp. in the region of moderate polymer concentrations are reported. For a ca. 7 wt.-% solution of the higher-molecular-weight polymer one obtains viscometric relaxation times τ₀ varying from 1 to 100 ms in the region from 1 to 2 000 bar and from 40 to 75°C; at the lower temperature the application of p can raise τ₀ by one order of magnitude. The steady-state shear compliance (proportional to τ₀/η₀, where η₀ is the zero-shear viscosity), is independent of pressure of varies only slightly. For the present system, which gels thermoreversibly upon cooling, η₀ and τ₀ as a function of temperature and pressure can be well represented by the Williams-Landel-Ferry equation.     

Segmental motions of spin-labelled poly(ethylene oxide) in dilute solution

The rotational correlation times (τ) of spin-labelled poly(ethylene oxide), (M_w=20 000) were measured in benzene, pyridine and water. It was found that τ is independent of polymer concentration (c) when c<0,15 g/(ml solvent). In dilute solutions τ values of 49 ps, 43 ps and 100 ps in benzene, pyridine and water at 293 K were obtained. A comparison with results of dielectric relaxation and nuclear magnetic resonance measurements indicated that τ_diel. < τ¹³_CNMR < τ_{spin-labelling} < τ¹_{H NMR}. Values 17.7±2,2 kJ/mol and 17,3kJ/mol for the potential barrier of local conformational changes of PEO in pyridine and water solutions were obtained. The apparent hydrodynamic radii (0,35–0,46 nm) indicated the loosely arranged random coil state of the polymer molecules in solution at 293 K.     

Dielectric properties of poly[bis(trifluoroethoxy)phosphazene] and poly[bis(m-methylphenoxy)phosphazene]

Dielectric properties of poly[bis(trifluoroethoxy)phosphazene] (PFEP) and poly[bis(m-methylphenoxy)phosphazene] (PmMPP) were studied in a temperature range from ?195 to 120°C and at several frequencies between 0,1 and 100 kHz. In PFEP, two relaxations, an α relaxation above the glass transition temperature (T_g) and a β relaxation below T_g, which are related to a glass-rubber transition and a local molecular motion of short segments, respectively, were observed. However, PmMPP shows no β relaxation. From the above dielectric results, it was concluded that side groups play an important role in molecular motion of the polyphosphazenes. In PmMPP a γ′ relaxation was found below T_g by immersing the polymers into water. The γ′ relaxation is related to the molecular motin of absorbed water.     

Unperturbed dimensions of polymers in binary and ternary systems

The unperturbed dimensions parameter K_Θ is one of the most important characteristics of a polymer chain. For binary systems (polymer/solvent) and mostly for ternary systems (polymer/solvent(1)/solvent(2)) the K_Θ values show large discrepancies with respect to those under thetaconditions in a single solvent. These discrepancies can be explained by considering that the interaction parameter χ (and consequently the coil dimensions or the number of intramolecular contacts between polymer segments) changes with molecular weight M. Assuming this dependency, a modified Stockmayer-Fixman equation is proposed from which a unique value of K_Θ for a given polymer, independent of M, is obtained. The use for ternary polymer systems of an interaction parameter between polymer and the solvent mixture (χ_3M) which depends on M, allows to calculate a single K_Θ value for a polymer in different mixtures of solvents and justifies the proportionality found between K_Θ deviations and the excess Gibbs free energy between both solvents of the solvent mixture.     

Electroinitiated cationic polymerization of ethyl and i-butyl vinyl ethers

The electroinitiated cationic polymerization of ethyl and i-butyl vinyl ethers has been studied under various experimental conditions using NaB(C₆H₅)₄ as background electrolyte. Differring from other electrolytes with higher oxidation potentials, the NaB(C₆H₅)₄ allows appreciable current intensities and the polymerizations can occur at moderate rates. The monomer to polymer conversion presents a slightly sigmoidal shape as a function of the quantity of electricity and at a fixed quantity of electricity is independent from the current intensities. The molecular weights of the polymers are substantially controlled by chain transfer to monomers and solvents: the relative chain transfer constants are reported. The reaction temperature affects remarkably the molecular weights while the influence of dielectric constant of the reaction medium is negligible. An interpretation is given of the effect of NaB(C₆H₅)₄ electrolyte on the initiation mechanism and on the resulting conditions of polymerization.     

Changes in renal blood flow measured by radionuclide angiography following exhausting exercise in humans

We measured renal blood flow (RBF) repeatedly in six male volunteers following exhausting cycling exercise using radionuclide angiography (RA) with technetium 99 m phytate (99 ^mTc-phytate), which is a nondiffusible radio-active tracer for kidney imaging and which is taken up quickly by the liver after injection into the circulation. The relationships between changes in RBF and creatinine clearance (C _cr,), urine volume (UV) and plasma hormone involved in the regulation of renal function were also investigated. A bolus of 99 ^mTc-phytate (92.5 MBq·ml^–1) was injected into the brachial vein via a catheter, while each subject was maintained in a supine position with his back to a scinticamera, which was connected to a computer for data processing. The pool transit time (PTT) was calculated from the time-concentration flow curve in the left kidney following injection of the bolus. The PTT normalized by the PTT of the heart (PTTn : kidney PTT/heart PTT), and the change in the reciprocal of PTTn (1/PTTn) were used as indices of the change in RBF. The resting RBF was also measured simultaneously by both RA and the para-aminohippuric acid (PAH) clearance method (C _PAH). Post-exercise RBF was measured only by RA within 60 s of exercise, then again within 30 and 60 min of exercise on different days, since RBF can be measured successively only three times even with the use of ^{99 m}Tc-phytate. The resting value of 1/PTTn was converted to the value of C _PAH corrected for haematocrit, and post-exercise change of l/PTTn (RBF) was represented as a change in the value of C _PAH in order to express a definite numerical change, rather than a percentage change, from resting RBF. The RBF decreased by 53.4% immediately after exercise, and remained decreased by 17.5 % 30 min after and by 21.1 % 60 min after exercise in comparison with the resting value. The RBF was found to be correlated with changes in C _cr(r = 0.773, P < 0.001), UV (r = 0.598, P < 0.001), and the concentrations of plasma angiotensin II (r = – 0.686, P < 0.001) and noradrenaline (r = 0.652, P < 0.001) after exercise. However, there were no significant correlations between the changes in plasma aldosterone ([Ald]) and plasma noradrenaline, or in [Ald]_p1 and plasma angiotensin II concentrations. The change in [Ald]_p1 did not coincide with the variation in reabsorption of Na⁺ in the renal tubules. Results of the present study showed that change in C _cr after exhausting exercise depended mainly on change in RBF and that changes in UV and osmolality after exhausting exercise were induced not only by change in RBF, but also by changes in reabsorption of water and solutes in the renal tubules. It is suggested that changes in reabsorption of water and solutes might be influenced by metabolites induced by exercise and an increased release of hormones, other than aldosterone, involved in the regulation of renal function.     

Subcutaneous Tissue Mechanical Behavior is Linear and Viscoelastic Under Uniaxial Tension

Subcutaneous tissue is part of a bodywide network of “loose” connective tissue including interstitial connective tissues separating muscles and surrounding all nerves and blood vessels. Despite its ubiquitous presence in the body and its potential importance in a variety of therapies utilizing mechanical stretch, as well as normal movement and exercise, very little is known about loose connective tissue's biomechanical behavior. This study aimed to determine elastic and viscoelastic mechanical properties of ex-vivo rat subcutaneous tissue in uniaxial tension with incremental stress relaxation experiments. The elastic response of the tissue was linear, with instantaneous and equilibrium tensile moduli of 4.77 kPa and 2.75 kPa, respectively. Using a 5 parameter Maxwell solid model, material parameters μ₁ = 0.95 ± 0.24 Ns/m and μ₂ = 8.49 ± 2.42 Ns/m defined coefficients of viscosity related to time constants τ_1M = 3.83 ± 0.15 sec and τ_2M = 30.15 ± 3.16 sec, respectively. Using a continuous relaxation function, parameters C = 0.25 ± 0.12, τ_1C = 1.86 ± 0.34 sec, and τ_2C = 110.40 ± 25.59 sec defined the magnitude and frequency limits of the relaxation spectrum. This study provides baseline information for the stress-strain behaviors of subcutaneous connective tissue. Our results underscore the differences in mechanical behaviors between loose and high-load bearing connective tissues and suggest that loose connective tissues may function to transmit mechanical signals to and from the abundant fibroblasts, immune, vascular, and neural cells present within these tissues.     

The structure of poly(ethylene oxide)-salt complexes with 13c CPMAS NMR and relaxation studies

¹³C cross polarization and magic-angle spinning (CPMAS) NMR studies were made on poly(ethylene oxide) (PEO) complexed wit LiClO₄, NaClO₄, BaSCN, Bal₂ and Ba(ClO₄)₂. The proton and carbon spin-lattice relaxation times in a rotating frame (T_1ρH, T_1ρC) as well as the rate of cross polarization were measured at room temperature. For Ba(ClO₄)₂ the measurements were made with different polymer molar masses and salt concentrations. The changes in relaxation behaviour indicate changes in polymer chain mobility as well as strong interaction between ions and PEO chains. The T_1ρH and T_1ρC decrease with decreasing salt concentration towards the relaxation times of the pure polymer. Nonexponential relaxation behaviour was found for the samples according to the T_1ρC and T_CH measurements.     

Time resolved light scattering measurements on the disentanglement diffusion following the degradation of poly(phenyl vinyl ketone)

Poly(phenyl vinyl ketone) was irradiated in 1,4-dioxane solutions with 25 ns flashes of 347, 1 nm light at various incident intensities. The rate of fragment separation following the very rapid rupture of chemical bonds in the main chains was measured. For this purpose the decrease of the intensity of light scattered by the polymer solution (LSI) was monitored as a function of time after the flash at various scattering angles. It was found that the lifetime of the LSI change τ(LSI) decreased with increasing scattering angle. This is due to the fact that main chain breaks are statistically distributed over all molecules and along the chains thus causing the generation of small and large fragments. The larger fragments which move at smaller speed contribute stronger to the LSI at low scattering angles than the small ones. It was, furthermore, found that τ(LSI) is independent of Z_s, the average number of scissions per initial macromolecule, if the fragment size exceeds a critical value which was estimated as being of the order of 10³ base units in this case. τ(LSI) decreased with increasing Z_s steadily if the average size of fragments was smaller than the critical value. This was evidenced both by measuring τ(LSI) as a function of the initial molecular weight and of the scattering angle. In conclusion: intramolecular interaction is determining disentanglement motions if the chain length exceeds a critical value. At shorter chain lengths pure translational motions become rate determining.     

Dilute solution properties of poly(m-methyl styrene)

Viscometric and osmometric studies have been carried out with fractions of poly(mmethyl styrene) in solutions of benzene, cyclohexane, and ethyl acetate at 30, 40, and 50°C. The values of K′ and ‘a’ in the KUHN-HOUWINK relation have been reported for the above polymer-solvent systems. The values of unperturbed dimension, (r /M)^1/2, solvent polymer interaction constant (B) and conformational parameter (σ) have been computed applying the theories of FLORY-FOX-SCHAEFGEN, KURATA-STOCKMAYER-ROIG, and STOCK-MAYER-FIXMAN. The applicability of the theories of FLORY, KURATA et al., and PTITSYN has been critically analysed from the dependence of the expansion factor (α) on molecular weight. Values of thermodynamic parameters, Θ, Ψ₁, x₁, and X₁, have also been calculated.     

Small-angle X-ray scattering study on concentration dependence of polymer chain dimension

The concentration dependence of polymer chain dimensions was studied by a new type of “tagged polymer method” in small-angle X-ray scattering. A small fraction of partially iodinated polystyrene, the tagged polymer, was mixed with polystyrene in toluene. From the excess scattering originated from the iodine, the radius of gyration of the polystyrene chain (M_v = 110000) was estimated at various concentrations. It was found that the chain dimension decreases first rapidly and then decreases gradually with increasing polymer concentration, and that, in the bulk, it coincides with the unperturbed chain dimension. The result was compared with theoretical predictions. The theories applicable to low concentrations could predict well the chain dimension upto mass concentrations of ca.0,1 g/cm³, while the theories applicable to higher concentrations could not predict well the chain dimension at high concentrations. The conformation of the polymer chain was also discussed. More compact conformations than a random coil as well as the bundle model were not supported by the results.     

The solution properties of poly-o-chlorostyrene

The solution properties of poly-o-chlorostyrene in toluene were measured by means of light-scattering and viscosity method, and the results were compared with those obtained from other polystyrene derivatives. The dependence of the intrinsic viscosity, the second virial coefficient and the end-to-end distance of the polymer chain on the molecular weight is follows: These relationships do not differ substantially from those of other polystyrene derivatives. The unperturbed dimension of poly-o-chlorostyrene was calculated. Results showed that the polymer chain of poly-o-chlorostyrene at the theta state, {<L²>o/<L²>_f}^1/2 = 2.42, was more extended than that of poly-p-chlorostyrene, {<L²>o/<L²>_f}^1/2 = 2.15 to 2.30.     

Branching in free radical polymerization due to chain transfer, 2. Theory of the effect of polyfunctional transfer reagents

Polyfunctional chain transfer reagents applied in free radical polymerization have two effects on the polymer molecular weight. As in the case of monofunctional regulators the chain length is reduced; the polyfunctionality of the transfer reagents causes, however, branching and thus an increase in molecular weight. A general theory is developed on the basis of Cascade Theory to describe the polymer structure in dependence on the monomer conversion. The theory takes advantage of the graph theoretical concept of digraphs by which the directed chain reaction can be properly represented. Analytic equations are derived for the weight average molecular weight M_w, z-average mean square radius of gyration 〈S²〉_z and the average particle scattering factor P_z(μ). Furthermore, a simple equation is given for the condition of gelation. Special concern is given to the formation of fractions of branched and linear polymers during the polymerization process. The derived equations are discussed in terms of kinetic constants known for polystyrene. Gelation is shown to be possible for a chain transfer constant of C_tr = 22 if the number of functional groups per transfer molecule exceeds at least a value of 7.     

Hydrodynamic behaviour of 1,4-trans-polyisoprene

The unperturbed dimensions of 1,4-trans-polyisoprene (TPIP) were estimated using various [η] – M _w extrapolation methods. The results of various methods agree very closely, however, the solvent-polymer interaction parameter, B, assumes different values from method to method. The polymer chains are found to assume random coil structure in solvents like benzene, toluene and cyclohexane. A more compact coiled structure is found in hexane. This was further substantiated by estimation of the excluded volume per segment: 7,3 ų in good solvents and 4,0 ų in hexane. On a relative scale, the stiffness parameters for TPIP chains were found to be: σ = 1,26 and C_∞ = 5,99 for the expanded coil configuration, and σ = 1,11 and C_∞ = 4,46 for the compact coil configuration, which is smaller than the literature data. If the latter are corrected for molecular heterogeneity, the agreement with the present data is excellent. The temperature coefficient of the unperturbed dimensions also supports this results.     

Small angle neutron scattering studies of poly(ethylene oxide) in the melt

The neutron scattering from mixtures of deuterated and undeuterated poly(ethylene oxide), (D-PEO, H-PEO), in the small angle and intermediate angle region has been measured in the melt. We found no indications of a molecular segregation. The value of molecular weight evaluated agreed with that obtained by other methods. For a sample with a molar mass of 120000 g/mol the radius of gyration 〈r_w²〉^1/2 was found to be 13,6 nm, which corresponds to a characteristic ratio of C = 6,9. The form factor of a single chain can be described by the Debye equation for a random coil with the same unperturbed dimensions. Our results are compared with rotational isomeric state calculations and measurements in solvents.     

Determination of the elastic modulus of polyamide crystals along the chain axis by x-ray diffraction, 1. The α-form of nylon-6

Studies were carried out to determine the crystalline elastic modulus E₁ along the chain axis for the α-form of nylon-6 [poly(ε-caprolactam)] by X-ray diffraction. To obtain an inherent E₁ value of this polymer the problem was solved that different orders of meridional reflections give different E₁ values. Thus the disagreement was found to be due to the increase of the crystallite size by the applied stress. When corrected for this effect, the values from the 040 and 0.14.0 reflections agreed well with each other. The resulting modulus was 183 GN/m² at 23°C, which was much lower than a theoretically calculated value of 262,8 GN/m² for the fully extended structure model by Manley and Martin. This seems to be due to the slight shortening at the amide group of the molecular chain because it was confirmed from the intensity changes of the 040 and 0.14.0 reflections of this polymer by the applied stress that the amide part is more extensible than the polymethylene section. Judging from similar considerations the previously reported E₁ values for nylon-66 and nylon-6,10 are valid.     

Synthesis and Rheological Properties of Poly(5‐n‐hexylnorbornene)

Summary: Poly(5‐n‐hexylnorbornene) (PHNB) was obtained in high molecular weight and high yields by vinyl‐type polymerization of 5‐n‐hexyl‐2‐norbornene (endo/exo = 77/23) with [NiBr(NPMe₃)]₄/B(C₆F₅)₃ as catalyst precursor. The combination of size exclusion chromatography with on‐line light scattering and intrinsic viscosity measurements allowed the Mark‐Houwink expressions to be evaluated in tetrahydrofuran. The unperturbed chain dimensions for poly(5‐n‐hexylnorbornene) were estimated via the extrapolation procedure of Burchard‐Stockmayer‐Fixman. This evaluation of the unperturbed chain dimension in turn permits the calculation of the entanglement molecular weight and the plateau modulus via the packing length model. This allows the determination of rheological properties for these materials where conventional rheology measurements are difficult, or impossible.

[η]‐M data for PHNB in THF at 35 °C.     

Deuteron NMR study of molecular order and motion of the mesogenic side groups in liquid-crystalline polymers

The molecular order and mobility of two liquid-crystalline polyacrylates with phenyl benzoate moieties as mesogenic side groups and (CH₂)_m spacers (m = 2 and m = 6) were investigated by pulsed ²H NMR. The mesogenic side groups were isotopically labelled at the terminal phenylene ring. In the glassy state the orientational distribution function was characterized from the angular dependence of the ²H NMR line shape of samples macroscopically ordered in their nematic phase by the 8,4 T magnetic field of an NMR spectrometer. It was found to be Gaussian with widths of ± 18,5° and ± 10,5° for the m = 2 frozen nematic and m = 6 frozen smectic system, respectively. The phenylene rings undergo 180° jumps about their local C₂-axes in the glassy state. The time-scale of this process, however, was found not to be uniform. Instead, the analysis of ²H NMR line shapes and their intensities as a function of temperature yielded a log-Gaussian distribution with correlation times characteristic of amorphous solids, 2,2 versus 2,5 decades in width and mean activation energy ē_A = 42 versus 47 kJ/mol for the m = 2 and m = 6 system, respectively. The correlation times for the centre of the distribution agree with those obtained by dielectric relaxation measurements of the same systems, suggesting that reorientation of the whole mesogenic group is detected via the phenylene rings.     

Configuration of amylose acetate in dilute solution

Intrinsic viscosities of potato amylose acetate fractions have been investigated as function of temperature, solvent, and molecular weight. Relationship of viscosity with molecular weight has been established and the exponent ν in [η] = K′M^ν has been discussed in the light of heterogeneity of the fractions. From the study of flexibility of the amylose acetate molecule in CH₃NO₂ as calculated from the effective bond length the KUHN-KUHN equivalent chain segment length, and the ratio of the unperturbed dimension to the dimension assuming free rotation of chain units, it has been observed that amylose acetate is not as stiff as cellulose but stiffer than polystyrene. However, the values of \documentclass{article}\pagestyle{empty}\begin{document}$\overline {\cos } $\end{document}Φ indicates that the steric hindrance in the amylose chain is equal to that in the cellulose chain which is much higher than a flexible polymer chain.     

Influence of configuration upon heterogeneity in anisotropic glasses as determined by thermally stimulated current

Thermally stimulated current (TSC) as well as differential scanning calorimetry (DSC) was used to determine the glass transition temperature of anisotropic glasses for semiflexible polyesters with polymethylene spacers. The highly sensitive technique of thermal-windowing polarization or relaxation map analysis (RMA) was used to further study the relaxation behavior of the anisotropic glasses as well as the heterogeneity of the samples. Experimental results indicate that phase separation is dependent upon the length of the polymethylene chain, i.e., the configuration of polymethylene segments and the number (n value) of methylene groups. The longer the polymethylene segment the larger the difference in the two transition temperatures, the higher transition temperature (T_g,H) and lower transition temperature (T_g,L). For a polymer with even value of n, ΔT_g (T_g,H minus T_g,L) of the anisotropic glass is lower than that for the neighboring two polymers with odd n values. In addition, the distortion effect of the polymethylene segment with even number of methylene groups on the polymer chains under polarization was studied by the Vogelian relaxation behavior of the ρ-peak. These results indicated that the maximum fractional volume of the polymethylene segments of the anisotropic glass for a polymer with even n value would be smaller than that for a polymer with odd n value under polarization.