Optically active vinyl polymers, 22. Relationship between intrinsic viscosity and molecular weight for poly-(S)-4-methyl-1-hexene and related polymers

Isotactic poly-(S)-4-methyl-1-hexene (PS4MH), poly-(R,S)-4-methyl-1-hexene (PRS4MH) and poly-4-methyl-1-pentene (P4MP) were fractionated according to stereoregularity and molecular weight. The fractions obtained were characterized and the constants a_η and K of the Mark-Houwink equation calculated for thermodynamically good solvents at low temperatures and for theta solvents at high temperatures.     

Dilute solution properties of methyl methacrylate/acrylonitrile random copolymers, 1. Mark-Houwink relation

Studies on the dilute solution properties of methyl methacrylate/acrylonitrile random copolymers of 0,566 mole fraction (m. f.) of acrylonitrile (AN), designated as MA3 and of 0,657 m. f. of AN, designated as MA4 reveal that the Mark-Houwink exponent values a for MA3 lie in the range 0,6 to 0,8 and for MA4 in the range 0,8 to 1,1 in the solvents studied, viz. acetonitrile (MeCN), 2-butanone (MEK), N,N-dimethylformamide (DMF) and γ-butyrolactone (γ-BL) at the temperatures 30°C, 45°C and 60°C. Such large values of a suggest that these copolymer chains are highly extended in these solvents. The decrease of [η] with an increase in temperature also supports the above conclusion that these are very good solvents.     

The characteristic ratio of poly(methacrylic acid) in organic solvents

Parameters of the Mark-Houwink equation for poly(methacrylic acid) (PMAA) in methanol at 25°C, [η] = 0,0224 · M^0,679, were determined and found to differ markedly from those reported earlier for 26°C. The value of the exponent along with the high value of the second virial coefficient confirms that near to 25°C methanol is not a theta-solvent for PMAA. By employing extrapolation according to Tanaka, the characteristic ratios C of PMAA in methanol (C = 12,0) and in 2-ethoxyethanol (C = 9,7) were determined from viscosity data at 25°C. The unperturbed dimensions of PMAA depend on the solvent used. They are larger in organic solvents than in water, but the difference is not so high as assumed before. By using the Stockmayer-Fixman extrapolation, the characteristic ratio for PMAA in 2-ethoxyethanol was determined at 70°C, i.e. at a temperature not too far from theta-conditions (Θ = 65°C, C = 8,2). A comparison with the value for 25°C shows that the unperturbed dimensions of PMAA decrease with increasing temperature.     

Temperature dependence of the viscosity of dilute poly(N-vinylcarbazole) solutions in 1,4-dioxane

The dependence of the viscosity of dilute solutions of poly(N-vinylcarbazole) in 1,4-dioxane on the temperature is studied by Moore's treatment. The numerical values of the constants from this treatment K_e, K_β, and β indicate that this polymer in 1,4-dioxane assumes the characteristic behaviour of flexible polymers. The numerical values of the parameters K_Θ and B from the Stockmayer-Fixman plot and the Mark-Houwink constants K and a are determined and the temperature coefficient of the unperturbed dimensions is evaluated for this system.     

Solution properties and flexibility of poly(2-biphenylyl methacrylate)

Dilute solution properties of poly(2-biphenylyl methacrylate), (poly[1-(2-biphenylyloxycarbonyl)-1-methylethylene], POB) were studied by viscosity, sedimentation, light scattering and osmotic pressure in different solvents. The solvent dependence of intrinsic viscosity, [η], Huggins constant, K_H, Mark-Houwink exponent, a, and expansion factor, α_η, is very weak, although the chemical nature of the solvents is quite different (CHCl₃, tetrahydrofuran, benzene, 1,4-dioxane). For poly(4-biphenylyl methacrylate) (poly[1-(4-biphenylyloxycarbonyl)-1-methylethylene], PPB) and other aromatic polymethacrylates the changes of [η], K_H, a and a_η are very high. The unperturbed dimensions calculated from viscometric and light scattering data by different methods, are in excellent agreement with one another and good agreement with those obtained from sedimentation data. POB has a higher flexibility factor (σ = 2,8) than PPB (σ = 2,7). In our opinion this is due to the fact that the 2-biphenylyl group is closer to the main chain than the 4-biphenylyl group. The very high value of σ explains the weak solvent dependence of [η], K_H, a and α_η in the case of poly(2-biphenylyl methacrylate).     

Synthesis of star-shaped polydimethylsiloxanes containing SiO2 core units

Star-shaped polysiloxanes consisting of SiO₂ cores and polydimethylsiloxane (PDMS) branches were successfully prepared by three methods using functionalized solvent-soluble silicates as a starting material. The first method involved the lithiation of a Si? OH functional silicate with butyllithium, followed by reaction with hexamethylcyclotrisiloxane (D₃) and termination with a chlorosilane to afford a star polymer. In this case, the chain ends were substituted with vinyl or Si? OH functional groups. In the second method, a Si? Cl functional silicate was used as the source of the SiO₂ core. A PDMS chain with a lithium silanolate terminal group was reacted with the Si? Cl functional silicate to provide a star polymer. In the third method, a PDMS chain with a diethylamino group at one chain end was reacted with the Si? OH functional silicate to form a star polymer. The Mark-Houwink constant a of the star polymer was 0,74, which is very close to that of a linear PDMS.     

Coil expansion and dimensions of poly(dimethylsiloxane) in alkane/2-butanone mixtures

The intrinsic viscosities, [η], for the ternary systems alkane (1)/2-butanone (2)/poly(dimethylsiloxane) (PDMS)(3), with the alkanes decane, dodecane and hexadecane, are determined at 20,0°C. The constants a of the Mark-Houwink equation and the constant of the unperturbed dimensions, K_Θ, of the polymer are evaluated over the whole composition range of the binary solvent mixture. [η] shows a pronounced maximum at intermediate compositions as found in cosolvent mixtures. In these cosolvent mixtures, the numerical values of K_Θ are higher than in the single-component solvents, because the cosolvent mixtures correspond to a mixed solvent with an excess free energy, G^E ≥ 0, the increase in K_Θ being only moderate though. A new procedure taking into account ternary interactions, to evaluate the intrinsic viscosity in ternary systems from G^E values is proposed. The influence of ternary interactions through a constant (1–2a_χ) is also investigated. From these new expressions the constant of the apparent polymer unperturbed dimensions, K, and (1–2a_χ) are calculated and compared with those directly evaluated from second virial coefficients.     

Evaluation of the viscometric constants for chitosan

Viscosity-average relative molecular masses have been determined for a series of chitosans having the same relative molecular mass and relative molecular mass distribution but differing extents of N-acetylation. The results obtained show that the same viscometric constants in the Mark-Houwink equation [η] = K_m ·M^a are applicable to chitosans over the range between 0 and 40% N-acetylation Comparison of literature values for number- and weight-avepge rela-tive molecular masses M _n, and M _w, with the viscosity-average relative molecular mass M, values calculated using the related viscosity data and each of the three sets of viscometric constants that have been proposed for chitosan, confirms that the most accurate values currently available are k_m = 1,81 · cm^?3 · 10^?1 and a = 0,93, using 0,l M acetic acid/0,2M NaCl as solvent.     

Darstellung und [η]-M̄-Beziehung von Mikrogelen aus polyvinylalkohol

Microgels were prepared by crosslinking of poly(vinylalcohol)s with different molecular weights (saponification degree: 88 mole-%) with glutaraldehyde in aqueous solutions. The degree of crosslinking was varied between 0 and 10% (i.e. 10 crosslinks per 100 structural units). Viscosity measurements showed that the viscosity number [η] of the microgels decreases considerably with increasing degree of crosslinking — as to be expected with increasing mean density of the random coils: The mean coil volume in aqueous solution shrinks by introducing 10 crosslinks per 100 structural units to 1/10 of the primary volume. A comparison of the logarithmic [η]-M?-plots of our microgels showed a linear decrease of the exponent a, from a = 0,73 (uncrosslinked) to a = 0,16, with increasing degree of crosslinking. By extrapolation, with a degree of crosslinking of 13% (i.e. 13 cross-links per 100 structural units of polymer chain), it was found that [η] becomes independent of the molecular weight of the primary PVAl-samples.     

4-(α,α-dimethylbenzyl)phenyl methacrylate, 2. Polymerization in N,N-dimethylformamide

The polymerization rate of 4-(α,α-dimethylbenzyl)phenyl methacrylate in DMF at 70°C is of the order 1,6 in [monomer] and first order in [AIBN], which deviates from classical kinetics. This could be reconciled by a reaction scheme in which dimeric monomer associates and a spontaneous termination are postulated. The scheme is supported by the dependence of the kinetic chain length, v, on the 1,6-th power in [monomer] and zeroth power in [AIBN]. The degree of polymerization is smaller than v, which indicates some chain transfer. A remarkable feature is the constancy of the dispersion degree, M?_w/M?_n, of the polymers of about 1,4 up to high degrees of conversion. The overall activation energy of the polymerization, E_a, is 60,1 kJ · mol^?1, and the preexponential factor ln A ≈ 15,5 (A in (mol · dm^?3)^?1,5 · s^?1). The polymer chains seem to have a rod-like character in THF as deduced from the Mark-Houwink exponent of 1,46. In toluene the polymer tends to form associates.     

Characterization of non-homogeneous polymers with size-exclusion chromatography by implementing an on-line viscometer

The viscosity distribution of a polymer sample can be obtained by using an on-line viscometer as a detector in size-exclusion chromatography. This newly defined viscosity distribution is closely related to the molecular weight distribution and expresses weight fraction times intrinsic viscosity of species i as a function of the corresponding molecular weight times intrinsic viscosity (w_i[η_i] vs. M_i[η_i]). The intrinsic viscosity ([η]) and number-average molecular weight (M?_n) can be obtained directly from a viscosity distribution. If the Mark-Houwink exponent a is known (or approximately known) for non-homogeneous polymer the M?_w/M?_n can be estimated from the viscosity distribution when the molecular weight distribution is approximated with a known distribution function. These estimates are independent of any other detector and are valid even for non-homogeneous polymer samples. The relation between the moments of the viscosity distribution and the M?_w/M?_n is presented for two widely used distribution functions, the Log-Normal and the Generalized Exponential Distributions. Polymer characterization based on the viscosity distribution is shown to be a robust technique. It is particularly attractive in characterizing non-homogeneous polymers since it is solely obtained from on-line viscometer.     

The behaviour of poly(2,3-epoxypropyl methacrylate) in dilute solution

Homopolymers of 2,3-epoxypropyl methacrylate with various molecular masses were prepared by solution polymerization with 2,2′-azoisobutyronitrile as initiator. The effect of polymerization conditions on the molecular parameters (weight- and number-average molecular masses M_W and M_n intrinsic viscosity [η]) and the tacticity of the resulting poly (2,3-epoxypropyl methacrylate)s was investigated. For unfractionated polymers, the constants of the Mark-Houwink equation for 1,4-dioxane and tetrahydrofuran were determined. Gel permeation chromatography was tested as a tool for the determination of the M_w and M_n values.     

Allowance for polymolecularity in polymer structure-property relationships

Relations between molar mass M and molar mass dependent properties E of polymers are mostly strictly valid only for monomolecular samples i: For polymolecular polymer samples the corresponding averages M_av and E_av must be applied: Provided the kind of average (number-, weight- or any general average) of e.g. M_av is known, the corresponding average E_av is given by. Eqs. (1a, b). This is demonstrated for the relationships of van't Hoff and Mark-Houwink, frequently used for the determination of molar masses of polymers. It is also shown that the four different relations for the expansion factor α by Flory-Stockmayer, Fixman, Ptitsyn, and by Yamakawa-Tanaka can be applied to polymolecular polymer samples (i.e. without fractionation), provided the corresponding averages[η]_av and M_av from the Mark-Houwink relationship are taken for the evaluation of the parameters K_Θ and B′.     

Solution properties of poly(N-1,1-dimethyl-3-oxobutylacrylamide), 1. unperturbed chain dimensions

The Mark-Houwink relationship for poly(N-1,1-dimethyl-3-oxobutylacrylamide), (poly[1-(1,1-dimethyl-3-oxo-butylaminocarbonyl)ethylene]), in 2-butanone at 25°C and the unperturbed chain dimensions have been obtained following standard procedures. The characteristic ratio and the steric factor are quite large, indicating that the lateral substituents are effective in expanding the unperturbed dimensions owing either to their bulkiness or to the possibility of being involved in intramolecular hydrogen bonds.     

Mapping of arterial transit time by intravascular signal selection

The arterial transit time (δ_a) is a potentially important physiological parameter which may provide valuable information for the characterization of cerebrovascular diseases. The present study shows that δ_a can be measured by arterial spin labeling (ASL) applied quasi‐continuously in an amplitude‐modulated fashion at the human neck. Imaging was performed using short repetition times and excitation flip angles of 90°, which resulted in the selection of an ASL signal of mostly intravascular origin. Model‐independent estimates of δ_a were obtained directly from the temporal shift of the ASL time series. An extended two‐compartment perfusion model was developed in order to simulate the basic features of the proposed method and to validate the evaluation procedure. Vascular structures found in human δ_a maps, such as the circle of Willis or cerebral border zones, hint at the sensitivity of the method to most sizes of arterial vessels. Group‐averaged values of δ_a measured from the carotid bifurcation to the tissue of interest in selected regions of the human brain ranged from 925 ms in the insular cortex to 2000 ms in the thalamic region. Copyright © 2014 John Wiley & Sons, Ltd.     

Effect of cold stress on gallbladder contractility in humans

Summary The purpose of this study was to determine the validity and practicality of exponential vs linear backward extrapolation of the O₂ recovery curve for prediction of exercise oxygen consumption (VO₂). Eight men and women, age 20.1, 0.9 years, body mass 66.0, 2.5 kg (mean, SEM), completed seven bouts of cycle ergometer exercise at submaximal power outputs ranging from 50 to 175 W. Respiratory gases were collected from each subject during exercise and recovery. The monoexponential extrapolation of five recovery samples (r ²=0.85) and linear extrapolation of one recovery sample taken during the first 20-s of recovery (r ²=0.83) accounted for similar amounts of variance in predicting exercise VO₂. The linear regression equation was the most practical predictor, as only one recovery gas sample was necessary and it did not require the complicated mathematical techniques used in exponential regression.     

Bestimmung physikalischer konstanten durch die funktion y/x = a + b·x in der lösungsviskosimetrie,ebulliometrie und dampfdruckosmometrie

Calculations of most probable values on the basis of the equations y = a · x + b · x², y/x = a + b · x and x = a^* + b^* · y/x have been carried out with data from solution viscometry, ebulliometry, and vapor pressure osmometry. The calculations carried out with the method of least squares give different coefficients for the equations taken as a basis. However equal coefficients are obtained with the method of Deming in which the measured data are weighted. Furthermore the so calculated slopes of the equations differ from those determined by the method of least squares whereby the differences depend upon the type of equations and upon the deviation of the measured data.     

Effect of UV light on the system styrene/maleic anhydride at −196°C

The effect of UV light (λ > 300 nm) on the system styrene/maleic anhydride/solvent (acetone or chloroform) in the presence and/or absence of the alternating styrene/maleic anhydride copolymer was studied by the ESR method at ?196°C. It was found that the concentration of paramagnetic species increased with the time of irradiation. The intensity of the ESR spectra at ?196°C did not change when the light was cut off. By analysis of the ESR spectra of the systems studied the methyl (a_H = 2,3 mT), dichloromethyl (a_H = 1,66 mT), and acetyl (a_H = 0,52 mT) radicals as well as the radicals A and D (a_H^α = 2,25 mT, a_H^β = 3,19 mT) and (a_H^β = 1,1 mT), respectively, were identified.     

Studies of hyperimmune restricted and partially restricted anti-pneumococcal polysaccharide antibodies from allotype-defined pedigreed rabbits. I. Preparative liquid isoelectric focusing of the antibodies and characterization of the isolated fractions by electrophoretic techniques

Four heterozygous rabbits (a² a², b⁴ b⁵; a¹ a², b⁶ b⁹; a² a², b⁵ b⁹; a³ a³, b⁴ b⁵) and one homozygous rabbit (a² a², b⁶ b⁶) were hyperimmunized with either type 3 or 8 pneumococcal vaccines. Four antisera were partially restricted and one antiserum was highly restricted. The immunoglobulins (Ig) were obtained by salt precipitation, ion-exchange chromatography, and affinity chromatography. The total Ig, obtained by salt precipitation, were fractionated by preparative liquid isoelectric focusing (IEF) at various pH ranges. From each antiserum a number of fractions were obtained with significantly different isoelectric points. Many major fractions had reduced electrophoretic heterogeneity when compared with the Ig isolated before IEF. These fractions were tested for isoelectric purity by analytical IEF in polyacrylamide gels and by preparative refocusing over a narrow pH range. After complete reduction and alkylation, the light and heavy polypeptide chains of the focused antibody fractions were examined both by disc electrophoresis in alkaline urea gels and by IEF in polyacrylamide gels containing urea. From each antiserum, a number of fractions were obtained which yielded single light chains often with different electrophoretic mobilities. This method provided a successful means of preparatively obtaining different antibody fractions from a single antiserum.     

Miscibility and Crystallization Behavior of Poly(ethylene terephthalate)/Poly(vinylidene fluoride) Blends

Poly(ethylene terephthalate) (PET) and poly(vinylidene fluoride) (PVF₂) are miscible in the melt‐state for the whole composition range. The glass transition temperature (T_g) of the solvent cast film decreases with the decrease in W_PET (weight fraction of PET) in the blend, however, the T_g for the repeated melt quenched blends remains invariant with W_PET. The melting point (T_m) and crystallization temperature (T_c) of PET decrease significantly with decrease in W_PET in the blend, but the T_m and T_c of PVF₂ decrease slightly with increase in W_PET. The crystallinity of both PET and PVF₂ decreases with increasing concentration of the other component in the blend, however, the decrease is larger for the former. The equilibrium melting points (T_m⁰'s) of PET in the blends are determined by the extrapolation procedures using (i) T_m–T_c method for 5% crystallinity and (ii) T_m–T_a method, where T_m, T_c and T_a are melting, crystallization and annealing temperatures, respectively. The data of both the methods indicate a large depression of T_m⁰ of PET with increase in PVF₂ concentration. The χ₁₂ values determined from both the data are essentially the same, –0.14. This negative value of χ₁₂ indicates that the two polymers are miscible in the melt‐state, however, they are not miscible in the crystalline state. The onset of degradation of PET increases with increase in PVF₂ concentration in the blend.