Molmassenverteilung und lösungszustand von linearen polyethylenen, 2. Vergleich von berechneten mit experimentell bestimmten streufunktionen

Scattering functions for linear polyethylenes were calculated, using different assumptions, and compared with experimentally determined scattering functions of the system polyethylene/decane. It is pointed out, that the polyethylene macromolecules in a good solvent can be treated as statistical coils with a non-uniform expansion and a constant average expansion exponent ε and not as statistical coils with uniform expansion. Comparison of the experimentally determined and the calculated scattering functions yields a molar mass distribution of polyethylene which is in agreement with the results from GPC-measurements within the limits of experimental error.     

Untersuchungen über den lösungszustand von mäßig konzentrierten polyisobutylen-lösungen

Measurements with a rotational viscometer with polyisobutylen solutions show, that the log η vs. log M plots exhibit breaks. From these the critical molecular weight for entanglement (infinite network according to BUECHE) can be determined. The breaks depend on concentration, and allow an estimation of the degree of coiling.     

Langfristige konformationsänderung von makromolekülen in lösung, 1. Polyacrylamide

The viscosity of aqueous polyacrylamide solutions does not remain constant. During a period of many weeks it decreases by as much as 30%. Simultaneously a loss of flocculation activity occurs. This unusual behaviour — also called ageing or solution instability — is examined. Viscosity and light scattering investigations were made. The viscosity was also determined by addition of substances which influence hydrogen bonds. It could be demonstrated, that in high molecular weight polyacrylamide hydrogen bonds are effective. Light scattering measurements result in curved angular dependence of scattered light, which must be regarded as real and specific for the high molecular weight polyacrylamides in water. The Zimm plot for polyacrylamide in ethylene glycol was undistorted. The refractive index increment decreases with time during the investigations. From the Zimm plots it follows, that the radius of gyration decreases with time. The molecular weight however remains constant. Based on the experimental results a mechanism is assumed with a long-term conformational change of the macromolecules. The orientated segments — stabilized by hydrogen bonds — are slowly destroyed by occupation of “active sites” by water molecules. Chain degradation as well as disentanglement could be excluded. A molecular interpretation is given.     

Bestimmung der langkettenverzweigung von hochdruckpolyäthylen durch streulicht- und viskositätsmessungen

Linear and branched polyethylene were fractionated by solvent gradient chromatography. The fractions were characterized by light scattering and viscosity measurements. The relationship between the molecular weight and the limiting viscosity number and that between the molecular weight and the radius of gyration in α-chloronaphthaline at 127°C were determined. The exponent of the equation between the ratio 〈g_η〉Θ of the limiting viscosity numbers of branched and linear fractions of the same molecular weight M_w and the corresponding ratio 〈g_η〉_Θ,w of the radii of gyration for Θ-conditions was By this equation, the long chain branching of high pressure polyethylene can be determined from 〈g_η〉, the ratio of the limiting viscosity numbers in thermodynamically good solvents, which is within the experimental limits of error identical to 〈g_η〉_Θ in a Θ-solvent. Almost independent of the molecular weight, for the branched polyethylene fractions 1,4 long chain branching points per 1000 C-atoms were obtained.     

Konstitution und lösungseigenschaften von makromolekülen. VIII. Ungestörte dimensionen von polytetrahydrofuran

The numerical value of K₀ = [η]₀/M of a sample of poly(tetrahydrofuran), which is proporational to the unperturbed dimensions, was determined in different solvents by three methods at 25°C. The resulting value of K₀ = 0.202 ml./g. was compared with the corresponding data for polyethylene, poly(ethylene oxide) and polyoxymethylene.     

Herstellung,charakterisierung und lösungseigenschaften von einheitlichen styrol-α-methylstyrol block-copolymeren

An improved anionic polymerization technique for the preparation of highly uniform styrene/α-methylstyrene linear two-block copolymers is described. Three sets of samples with molecular weights M were prepared under equal experimental conditions, namely polystyrenes (2 · 10⁵ < M < 3 · 10⁶), poly(α-methylstyrene)s (7 · 10⁴ < M < 4 · 10⁶), and block copolymers (2 · 10⁵ < M < 2,5 · 10⁶). Ultracentrifugation in a density-gradient does not show any chemical heterogeneities in the block copolymers. The molecular polydispersity U = M_w/M_n–1 is U = 0,03 or less as estimated from GPC-measurements. The high molecular and chemical homogeneity of the block copolymers and the optical similarity of the two segment types yield light scattering measurements which give molecular weights M_w, radii of gyration 〈r²〉^1/2 and second virial coefficients A₂ with almost the same accuracy as in the case of homopolymers. The radii of gyration and the intrinsic viscosities of the block copolymers give no evidence for any “intramolecular phase separation” in the good solvent toluene. The coil conformation corresponds closely to that of the homopolymers.     

Orientierungsverhalten von segmentierten polyetherurethanen in abhängigkeit von der dehnung und den verwendeten lösungsmitteln

The solvent influence on two- phase structures resulting from drying films of segmented polyetherurethanes of different hard segment contents and molecular weights was investigated by infrared dichroism measurements of the orientational behaviour of the hard segments. A low density of physical crosslinking and/or minor association in solution leads to a lamellae structure resulting in an inhomogeneous distribution of stress at elongation. The formation of lamellae is impeded, if the solution shows pronounced formation of associates. Destruction of the lamellae can be monitored by studying the orientational behaviour for repeated deformations and by means of orientation-extension-hysteresis experiments. Stress-strain diagrams exhibit no contradictions to the discussed structural transformations by the influence of different solvents.     

Strukturuntersuchungen an adsorptionsschichten makromolekularer stoffe, 1. Haftstellenzahlen von linearen polyestern und polystyrol an aerosiloberflächen

By direct IR-spectroscopic determinations of the fraction of attached segments and of the adsorbed amount of linear saturated aliphatic polyesters, of polystyrene, and of butyl propionate, when adsorbed from dilute solution onto Aerosil silica, the structure of the adsorption layers is described. The polyesters are hydrogen bonded via almost all carbonyl groups to up to 80% of the free hydroxyl groups of the Aerosil surface as far as free adsorption sites are available. They form a layer structure consisting of small loops. Variations of molecular weight and chemical nature of end groups of the polyesters do not affect their adsorptive properties. By contrast, only every third aromatic nucleus of polystyrene interacts with the surface of the Aerosil silica. Like the model monoester, polystyrene is not capable of interacting with more than 50% of the surface hydroxyl groups. The adsorption data obey Langmuir's equation. Furthermore, they are in good agreement with the predictions of a statistical theory of Silberberg for polymer adsorption with strong adsorption interaction. The determined fractions of attached segments are compared with the considerably lower values in the literature and are discussed on the basis of the average distances of surface hydroxyl groups, statistical distribution assumed, and the calculated maximum distances of adsorbable groups in the polymer chains.     

Partielle spezifische refraktionen von polymethylmethacrylat und polystyrol. I. Einfluß verschiedener lösungsmittel

The partial specific refractions according to the formulae of LORENTZ -LORENZ , GLADSTONE -DALE , and EYKMAN , respectively, have been determined for poly-(methyl methacrylate) in the solvents acetone, ethylacetate, butylacetate, tetrahydrofurane, dioxane, chloroform, toluene, and benzene, and also for polystyrene in butanone, dioxane, toluene, and benzene. It is shown that these values, which were obtained from experimental data of the refractive index increment, the refractive index of solution, and the partial specific volume with an accuracy of ± 0.1% are not completely independent of solvent. The largest difference was 1.3% in LORENTZ -LORENZ refractios, whereas the EYKMAN refraction seems to the smallest extend sensible against influences of solvatation. It is discussed, whether these effects bear some systematic feature. With respect to light scattering measurements it should be noticed, that refractive index increments may have an error of up to several percents, if calculated from a specific refraction value in another solvent.     

Polypropylenglykol in lösung,zahlenmittelmolekulargewicht und reibungsverhalten

Molecular weights of poly(propylene glycol) are determined by measurement of the elevation of the condensation temperature and of the boiling temperature. For determination of the condensation temperature elevation, a new apparatus with 8 thermoelements is described. The physically determined M_n-values were somewhat lower than those determined chemically by the hydroxyl number. The solution behaviour of the polymer was tested by diffusion measurements in acectone and benzene. From M_n = 4000 down to very low molecular weights, diffusion coefficients D are observed yielding constant exponents in the relation D = K·M^?b with b = 0.52 for acetone and 0.55 for benzene.     

Die bestimmung der molekulargewichtsverteilung von nichtkristallisierenden polymeren mit dem elektronenmikroskop, 7. Präparation durch verdampfung des lösungsmittels aus lösung

A preparation method is described by means of which it is possible to transfer individual molecules of a high molecular weight polymer on a support, in order to determine their mass and therefrom their molecular weight distribution, using our previously published electron microscopic method. The advantages of the new procedure as compared to the previously described freeze-drying are 1 that the range of solvents, which can be used is much larger, and 2 that the preparation is performed by evaporation from a dilute solution, which means that the molecules are distributed statistically on the support. The risk of formation of associates is avoided by keeping the polymer concentration correspondingly low and the rate of evaporation high. As examples the results for three samples of poly(methyl methacrylate) and one sample of natural rubber are reported and discussed.     

Die radikalausbeute beim thermischen zerfall von azoisobuttersäuredinitril in gegenwart von sauerstoff und in methylmethacrylat als lösungsmittel

The efficiency ε of the thermal radical formation from bisazoisobutyronitrile (AIBN) in oxygen-containing solutions, was determined by two direct analytical methods, which complement one another. The first consists in the gaschromatographic determination of tetramethyl succinodinitrile, which originates from combination of the primarily formed 2-cyanoisopropyl radicals; it yields a value for (1-ε). The second method consists in the jodometric determination of 2-cyanoisopropyl hydroperoxide and p-benzoquinone which originate from those radicals which have escaped from the primary combination reaction and which latterly undergo a seavengering-reaction with hydroquinone; it yields value for ε. For the system methylmethacrylate/AIBN/O₂/hydroquinone and for 90°C both methods correspondingly result ε + 0.810 ± 0.005. Between 70 and 100°C ε increases linearely from 0.785 ± 0.005 to 0.833 ± 0.005. For n-propyl acetate and toluene as the solvents and at 90°C the same ε-value as for methyl methacrylate was found, i.e. 0.813 ± 0.005 and 0.810 ± 0.005, respectively.     

Zur ermittlung der struktur und unverträglichkeit von pfropfcopolymeren durch messungen der lichtstreuung und phasentrennung in lösung

From theoretical considerations it is concluded that molecular weights and radii of gyration of the grafted chains in graft copolymers as well as the incompatibility of the grafted chains with the backbone polymer can be determined by light-scattering measurements in solution if the solvent used for these measurements is isorefractive with respect to the backbone polymer and if the weight fraction of the grafted chains is known. The new method for determining the incompatibility from anomalous Zimm-Diagrams is illustrated for mixtures of polystyrene and a chemically homogeneous ethylene/vinyl acetate random copolymer and is applied to fractions of the corresponding graft copolymers. The results of the light scattering measurements are compared with phase separation data from turbidimetric measurements.     

Untersuchungen zur klärung der sensibiliserten photodegradation von polystyrol in lösungen, 1. Experimentelle befunde zum kettenabbau

Polystyrene (mass average molar mass M? = 609700 g/mol; molecular non-uniformity M?/M? ? 1 = 0,55) solutions in 8 different solvents were irradiated by light of a mercury lamp (wavelength λ ≥ 270 nm). The rate of photodegradation of the polymer (as determiened from ΔM?_w measurements by light scattering) is strongly solvent-dependent and only slightly dependent on the O₂ concentration in the irradiated solutions. An attempt to interpret this ?sensibilized”? photodegradation will be given in the second part of this series.     

Fließverhalten und molekulare struktur von polymeren und ihren lösungen eine systematik quantitativer beziehungen

For viscosities at low and high shear forces τ, critical shear forces τ_w of the structural viscosity, YOUNG moduli in the rubbery region of the relaxation behaviour of entangled polymers, concentrations φ⁺ above which entanglements form a network, and intrinsic viscosities one may formulate quantitative relations to structural parameters (molecularweights M and their distribution, concentration, chemical nature, especially the molar volume V_g of the structural unit) or at least qualitative ones (different types of branching, distribution of chemical composition, sequences of like structural units, heterogeneity as a consequence of phase separation, crystallinity). Several new quantitative relations are presented. These and the known relations are connected to each other much more, than has been formulated up to now. They lead to some laws for the normal behaviour of mixtures and solutions which have not been detected phenomenologically.     

Lichtabbau von polyacenaphthylen in benzolischer lösung

Polyacenaphthylen undergoes degradation in benzene solution under the influence of light. (λ < ca. 546 nm.). The degradation is dependent upon the wavelength of the light used and upon the molecular weight of the polymer.