Zur molekularen Dynamik der Lösungsprozesse von Polystyrol in verdünnten Lösungen

Relaxation times for the dissolution processes of polystyrene are determined by light scattering investigations. Characteristic frequency numbers of rotation diffusion and torsion oscillations of the solvent molecules are determined from the Rayleigh-wings. A correlation is found between the relaxation times τ_t,k0 of the 3rd stage of the dissolution process of polystyrene in different solvents and the frequency numbers δ₂ of the torsion oscillations of the solvent molecules. Hence, amongst the two kinds of molecular motion of the solvent molecules, torsion oscillations are effective in the dissolution process of the solute and their frequencies have to be considered as dynamically effective. Evaluation of solvents based on these considerations does not correspond to the hitherto used rules which solvents are thermodynamically good ones and which solvents are poor ones. As an example chloroform exhibits for polystyrene the shortest relaxation time of dissolution and therefore is considered to be amongst the best solvents whereas benzene with its long relaxation time would be considered to be a poor solvent for polystyrene.     

Kalorimetrische Untersuchungen zur Adsorption von Makromolekülen aus verdünnten Lösungen

By means of a highly sensitive calorimeter the enthalpies of adsorption of polyethyleneglycols from benzene-, water-and methanol-solutions on fine-grained silica (SiO₂) are measured within the total range of coverages. For collating the values obtained at varying weighed samples of polymer the adsorption isotherms are ascertained supplementarily. The monotonous falling of the differential adsorption enthalpies with increasing adsorbed amount yields a decrease of the number of adhered segments with coverage. From the comparison of the enthalpy-values in the range of the rise and the saturation of the isotherms with the enthalpy-contribution of the hydrogen bond as well as from the comparison of the adsorbed number of monomers with the OH-group-density on the adsorbent surface results, that the macromolecules adsorbs at low coverages in a flat lying form and coils up with increasing coverage, corresponding to a falling number of adhered segment. Due to the interaction between solvent and adsorbent, which is competitive to that one between polymer and adsorbent, the amount of the heat of wetting is decisive for the value of the adsorption enthalpy.     

Polymere Elektron-Donator-Akzeptor-Komplexe. II. Über die Reaktion von Poly-4-vinylpyridin mit Tetracyanäthylen in verdünnter Lösung

The viscosity of poly(4-vinylpyridine) in solution is strongly influenced by added tetracyanoethylene. The viscosities measured show time dependence. At low polymer concentrations or at low concentrations of monomeric electron acceptor they tend toward constant values whereas at higher concentrations viscosity maxima are observed after which the polymeric electron donor acceptor complex separates. The viscosity curves are compared with the UV spectra.     

Über eine beziehung zwischen verdünnungsentropie und verdünnungsenthalpie in lösungen von polystyrol und polymethylmethacrylat

The second osmotic virial coefficient A₂ and its entropic and enthalpic parts of athermal and exothermal solutions of polystyrene (PS) and polymethylmethacrylate (PMMA) were determined by light scattering measurements at 25°C and normal pressure. The intrinsic viscosity dependence on temperature was used to find athermal and exothermal solvents for these polymers. The investigated thermodynamical quantities A₂, A_2,S and A_2,H yield together with earlier measurements a correlation which is nearly independent of the special system.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 1. Kinetik,Molekulargewichtsabhängigkeit und Frage des Bruchmechanismus

The mechanical shear degradation of poly(decyl methacrylate) with weight average molecular weights 1,0·10⁶ ≤ M?_w ≤ 1,7·10⁶, and molecular polydispersity ratio M?_w/M?_n = 5 in dilute solutions is studied in turbulent flow as a function of molecular weight using a special apparatus consisting of two vessels connected by a capillary. Shear stress and shear rate remained constant during degradation. The rate of degradation was followed up by molecular weight distribution curves using gel permeation chromatography and described by ?dc_i/dt = k_i·cⁿ, i being a high molecular weight species of the distribution. The reaction was found to be of the first order (n = 1) independent of solvent and of capillary length. Rate constants k_i in the molecular weight range from 3,2·10⁶ to 13,5·10⁶ proved to be proportional to the hydrodynamic volume of the polymer molecules expressed in terms of the product of intrinsic viscosity and molecular weight [η]_i·M_i. This corresponds to a linear relationship between k_i and M_i^1,75. Additional experiments show that this type of dependence on molecular weight holds only for turbulent flow; in laminar flow the result of the literature could be confirmed that there is a linear relation between k_i and M_i¹. Both results are independent of capillary length. As to the mechanism of breakage in turbulent flow it seems that in one step each macromolecule is broken simultaneously into several smaller parts.     

Lösungseigenschaften von äthylcellulose. Vergleichende bestimmungen von molekulargewichten und zweiten virialkoeffizienten mittels osmose,lichtstreuung und sedimentation/diffusion

Osmotic and light scattering measurements on ethylcellulose have been carried out in acetone, ethylacetate, 2-butanol, n-butylchloride, and benzene (osmosis only). In some cases the results were controlled by measurements of sedimentation/diffusion. By comparing the different experimental techniques it was possible to distinguish clearly results unaffected from those affected by the presence of gels. The second virial coefficients from osmotic and hydrodynamic measurements are low as compared to those of vinyl polymers. In contrast to this finding the exponent ε of the radius of gyration versus molecular weight relation is low. Negative values of ε reflect the influence of gels. The dependence of the second virial coefficient on the solvent is not pronounced.     

Lösungseigenschaften von polymethylmethacrylat und polystyrol aus Röntgenkleinwinkelmessungen

Light scattering investigations of solutions of polymethylmethacrylat (PMMA) and polystyrene (PST) are extended to low molecular weights by small-angle X-ray scattering. In a medium range of molecular weights (M = 10³ to 3·10⁴) the radius of gyration is proportional to M^0.5 even in good solvents. For M < 3·10⁴ the radii of gyration of PMMA found in the good solvent acetone are equal to those in the used Θ-solvent within the limits of error. In the case of PST in toluene this is not valid. From the relations α⁵ - α³ ～ z and α³ - 1 ～ z graphical methods were derived for the determination of r²₀/M from measurements in goods solvents by extrapolation to M = 0. For these extrapolation procedures it is necessary to perform measurements in the range between M = 10⁴ and M = 10⁵. The dependence of the second osmotic virial coefficient on the molecular weight in the low molecular range can be interpreted by Monte Carlo calculations on model compounds.     

Modellrechnungen zur Lösungsmittel- und Polymerenabhängigkeit der thermodynamischen Eigenschaften von Polymerlösungen

A great number of measurements on polymer solutions showed that there exists a distinct correlation between chemical potential, entropy and heat of dilution. Calculations were carried out on different models (quasi-chemical approximation, theory of orientation effects, theory of corresponding states, etc.) and these results were compared with experimental values. The theory of corresponding states yields the most extensive applicability, whereas the other theories may be applied to special problems.     

Kalorimetrische Untersuchungen zum Lösungsverhalten von Polyacrylsäure und Poly(natriumacrylat) in Wasser,Formamid und Ethylenglykol

Heats of solution and heats of dilution of poly(acrylic acid) (PAAcH), poly(sodium acrylate) (PAAcNa), and poly(acrylamide-co-sodium acrylate) (1:1) (PAAm/PAAcNa) in water, formamide (FA), and ethylene glycol (EG) as measured at 25°C, are reported. While for PAAcH/H₂O and PAAcH/EG only minor caloric effects are observed, the heats of solution for PAAcNa/H₂O are strongly exothermic as a result of dissociation of the polysalt. Heats of dilution in this system are endothermic because of the hydrolysis reaction. PAAcH/FA shows large negative enthalpies on dissolution as well as on dilution. This is due to the dissoziation of the COOH-groups which is much more pronounced in FA than in the aqueous system because formamide has a greater ionizing capability. Comparison between the behaviour of copolymer PAAm/PAAcNa and physical admixing of the homopolymers confirms the specific neighbouring group interaction of carboxylate and carbonamide groups along the same chain. Comparing the calorimetric results for PAAcH with those for the low-molecular-weight model compound propionic acid, it becomes evident that the differences are mostly due to the different state of order of the pure compounds, namely, due to the chain structure, the COOH-groups in the polymers are not as flexible as in the monomers. Therefore, in the pure polymer less hydrogen bonds are formed than in the pure propionic acid. The calorimetric results are discussed in the light of previous work on viscosimetric dilute solution behaviour of these systems, showing the consistency of the different experimental findings.     

Mechanischer Scherabbau von Polymeren in Lösung mittels turbulenter Strömung, 2. Die Abhängigkeit der Abbaugeschwindigkeit von der Polymergesamtkonzentration in guten Lösungsmitteln

Mechanical shear degradation of poly(decyl methacrylate), (viscosity average molecular weight in tetrahydrofuran M?_η = 1,3·10⁶, M?_w/M?_n = 5) in the thermodynamically good solvent tetrahydrofuran has been studied in turbulent flow through a capillary as a function of polymer concentration in the range from 0,22 to 8,9 g/100 cm³. Due to turbulent flow conditions the shear stress, shear rate and shear energy proved to be the same for all concentrations and remained constant during degradation, giving a general insight into mechanism of degradation. The rate of degradation has been followed using molecular weight distribution curves obtained by gel permeation chromatography. The reaction was found to be of first order. Rate constants determined for molecular weights from 3,2–9,5·10⁶ decreased with increasing concentration following a law of the type k_i = (K + b·c)^?1, K and b being constants for each molecular weight. Hydrodynamic volumes of polymer molecules have been calculated according to models of Rudin as function of molecular weight and concentration. It can be shown that rate constants of degradation and calculated hydrodynamic volumes are proportional for the whole range of molecular weight and concentrations up to 3,6 g/100 cm³. There is also a rather good proportionality between these rate constants and the volumes of polymer coils predicted by de Gennes. This result is an additional confirmation of the concept that hydrodynamic volume governs shear degradation of polymer solutions. Additional experiments show that this type of concentration dependence is also to be found for other polymers in other solvents.     

Molmassenverteilung und lösungszustand von linearen polyethylenen, 1. Lichtstreuungs-, viskositäts- und GPC-messungen

Light scattering, viscosity and GPC measurements were performed on a homologous series of linear polyethylenes with viscosity average molar masses in decahydronaphthalene at 135°C between 1,0 · 10⁵ and 2,7 · 10⁶ g · mol^?1 and relatively broad molar mass distributions. 1,2,4-Trichlorobenzene, α-chloronaphthalene, decahydronaphthalene (decalin) and decane were used as solvents. In the case of linear polyethylene in decahydronaphthalene and decane relationships between intrinsic viscosity and weight average molar mass were established. The values of the weight average molar masses obtained by light scattering are considerably higher than those obtained by viscosity and GPC measurements. These discrepancies are explained by molecular aggregation of the polyethylene macromolecules.     

Über die Druckabhängigkeit der viskoelastischen und physikalisch-chemischen Eigenschaften von Polymeren, 7. Einfluß des Lösungsmittels para-Xylol auf das Schmelzen und Kristallisieren von Polyethylen

Melting and crystallization of polyethylene (PE) with various amounts of xylene is investigated by pressure dependent volume-temperature curves. These can be calculated by a reduction formula described earlier. Flory's formula for lowering of the melting point of polymers by solvents proves to be applicable also for high pressures.     

Die Abhängigkeit der Taktizität von der Polymerisationstemperatur und von Lösungsmitteln bei nach radikalischem Mechanismus hergestelltem Polyvinylacetat

Polyvinyl acetate (PVAc) was polymerized according to a radical reaction mechanism with AIBN as an initiator at temperatures between ?60°C and 200°C. Additionally, polymerizations were effected in nine different solvents. The tacticity of the polymers obtained was determined from the methyl resonances of the NMR spectra. The best spectra were obtained from a 3–5% (wt./vol.) polymer solution in deuterochloroform at 100 Mc/sec. It was found that the tacticity of radically prepared PVAc is independent of the polymerization temperature and that an ideal atactic product is always formed. Moreover, in all solution polymerizations examined no influence of the solvent on the tacticity was found.     

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.     

13C-NMR-Sequenzanalyse, 4. Lösungsmitteleinflüsse auf die Chemische Verschiebung bei Polyamiden und niedermolekularen Carbonsäurederivaten

The ¹³C-chemical shift for the carbonyl carbon in polyamides, ω-aminocarboxylic acids, and N-substituted carboxylic amides is studied at different acid concentrations (D₂SO₄, CF₃COOD, D₂O). It is found, that the spectroscopic behaviour of polyamides resembles more to ω-aminoacids than to monomeric amides. The rule of the observed chemical shift and the resulting consequences for the sequence determination in polyamides are discussed.     

Lösungseigenschaften methyl- und chlorsubstituierter Bisphenol-A-Polycarbonate

Solution properties of dilute polymer solutions are studied for polycarbonates from 3,3′,5,5′-tetramethylbisphenol A, from 3,3′-dimethylbisphenol A, from 3,5-dimethylbisphenol A, and from 3,3′,5,5′-tetrachlorobisphenol A in regard to the influences of the different methyl and chloro substitutions. The Mark-Houwink relationships are established in dichloromethane at 25°C. The unperturbed dimensions, evaluated from viscosity data using the Burchard-Stockmayer-Fixman method, are compared with those for bisphenol A polycarbonate. The unperturbed end-to-end distances are increased by the methyl and chloro substituents. The flexibility factors, calculated on the basis of the unperturbed dimensions and the dimensions of the freely rotating chain, indicate a greater rigidity of the polymer chain of the methyl and chloro substituted polycarbonates.     

Größe und gestalt des fibrinogenmoleküls, 2. Röntgenkleinwinkelstreuung an verdünnten lösungen

Small angle X-ray scattering (SAXS) measurements were carried out in the angular range from s=0,4.10^?2Å^?1 to 0,23Å^?1 (s=(4π/λ)sinθ) with dilute solutions (c=3–17g/l) of highly purified bovine fibrinogen. The pH varied between 6,4 and 9,0. All measurements were carried out at 6°C. With filtered (0,47 μm Millipore) solutions the molecular weight was M=335000±25000, the radius of gyration R=122Å and the cross section radius of gyration of the scattering-equivalent rod R_q=24Å. The dependence of these molecular dimensions from pH was low. Comparison of the data with calculated scattering curves     

Zerlegung von hemicellulosereichem biologischem material mit wasser in einem strömungsreaktor

Biological materials, rich in hemicelluloses (birch and pine wood, wheat straw and rice hulls) were disintegrated batchwise in a flow reactor with pure water at elevated temperatures and pressures. The resulting extractives and residual fibre compounds were characterized. Because of rapid removal of carbohydrate based extractives from the hot reaction zone, the degradation of pentosans and hexosans to furfural and hydroxymethylfurfural could be limited to only a small amount. Contrary to normal prehydrolysis conditions employing a sealed batch reactor, temperatures of 190 to 210°C and residence times of goods of 60 min are the optimum. Thus, hemicelluloses are dissolved and isolated with up to more than 90% yield. At temperatures above 225°C severe destruction of hemicelluloses and solvolysis of cellulose starts. Depending on disintegration temperatures, pentosan average molecular weights (M?_w) vary in case of birch wood between 3800 at 150°C and 900 at 225°C. The content of monomers rises with temperature and reaches a maximum of 45% at 225°C. DP _w of residual cellulose is also temperature dependent and varies in case of birch wood and wheat straw between 1500 and 450. Lignin, which is mostly not dissolved, can be removed almost quantitatively by further treatment of the residue with ethanol/water at 250°C, thus allowing the isolation of relatively pure cellulose.     

Polymerisationen und polymerisationsinitiatoren, 16. Einfluß von Thioxo-Gruppen in barbitursäurederivaten auf die polymerisationsauslösung von methacrylsäure-methylester

In the presence of Cu²⁺ and Cl^? ions as well as atmospheric oxygen 5-alkyl-1,3-dimethylbarbituric acids initiate the radical polymerisation of methyl methacrylate. If a thioxo group is introduced in position 2 of the barbituric acid, initiating capability is slightly increased; thioxo functions in position 4 or 4,6, on the other hand, suppress initiation almost completely. In this case, the radicals formed at C-5 are stabilized by the neighbouring thioxo groups and dimerize at the sulfur atoms, yielding disulfides. Thus, these thiobarbituric acids may act as inhibitors. In the case of Cu(II)-catalyzed initiation, this inhibiting effect is enhanced by formation of almost insoluble Cu(I) thioxobarbiturates.