Multimerisation: Assoziation und aggregation. III. Einfluß der offenen assoziation auf die ungestörten dimensionen von polyäthylenglykolen

Intrinsic viscosities [η] of poly(ethylene glycols) of mol. wts. 62–38,000 were measured at 25°C. in water, methanol, dimethylformamide, acetonitrile, dioxane, carbon tetrachloride, methyl acetate, and benzyl alcohol, and at 10 and 37°C. in benzene. The function [η]/M = f(M) passes a minimum with increasing viscosity average of mole. wt. M_v, and increases first more than less steeply. The extrapolation of the asymptotes at high mol. M → 0 gave a independent of the degree of association of the polymers in the different solvents. A conventional evaluation for the mol. wt. ranges between the minimum in the function and the highest mol. wts. investigated leads to values of K_Θ, which decrease with increasing equilibrium constant of association. The intrinsic viscosities approach a limiting value [η]₀ at low mol. wts., which is [η]₀ = 2.5 ml/g for non-associating solvents. [η]₀ decreases with increasing association constant. The structure of the associates is interpreted as due to hydrogen bonding between hydroxyl end groups and ether groups in the chain.     

Kinetics of the anionic polymerization of ϵ-caprolactone with K+ · (dibenzo-18-crown-6 ether) counterion. Propagation via macroions and macroion pairs

Following our earlier work on the polymerization of lactones involving crowned cations, kinetics of the anionic polymerization of ?-caprolactone (?CL) with K⁺ · (dibenzo-18-crown-6 ether) (K⁺DB18C6) counterion was studied calorimetrically in THF solution in the temperature range from 0 to 20°C. Dissociation constants of CH₃(CH₂)₅O^?K⁺DB18C6, modelling the active centers, were determined conductometrically: K_D (20°C) = 7,7 · 10^?5 mol · dm^?3, ΔH = 9,3 ± 0,2 kJ · mol^?1, ΔS = ?47 ± 2J · mol^?1 · K^?1. From kinetic measurements and from measurements of the dissociation constant of CH₃(CH₂)₅O^? K⁺DB18C6, rate constants of propagation via macroions and via macroion pairs were determined. Activation parameters for propagation via these species are equal to: ΔH = 39,2 ± 0,2 kJ · mol^?1, ΔS = ?63 ± 1 J · mol^?1 · K^?1, ΔH = 13,7 ± 0,1 kJ · mol^?1, ΔS = ?185 ± 2 J · mol^?1 · K^?1. At 20°C, k = 3,50 · 10² dm³ · mol^?1 · s^?1 and k = 5,2 dm³ · mol^?1 · s^?1. Due to the large difference of ΔH^≠ for propagation via macroions and macroion pairs (vide supra), the isokinetic point (k = k) would appear at ?65°C.     

Coenzyme models, 6. Addition reaction of sulfite ion to monomeric and polymeric nicotinamides. Correlation between equilibria and reaction rates

Rate and association constants (k and K) for the addition of sulfite ions to five nicotinamides substituted at the ring nitrogen, ( 2a–e ), and to poly(1-(4-vinylbenzyl)nicotinamide chloride) (poly{1-[4-(3-aminocarbonylpyridiniomethyl)phenyl]ethylene chloride}) (poly( 1 )) were determined at 30°C in aqueous systems. It was found that the reaction parameters for the addition of SO to poly( 1 ) are markedly enhanced (20500-fold in the k term and 510-fold in the K term) compared with the addition to the corresponding monomeric compound, 3-aminocarbonyl-1-benzylpyridinium chloride ( 2d ), and the enhancements are suppressed with increased ionic strengths. These enhanced reaction parameters for poly( 1 ) are deviated to the upper area by two logarithmic units from a linear log K vs. logk relationship which holds for monomeric nicotinamides. This means that the rate constant is enhanced more effectively that the association constant in the polymeric system. Plots of log K_CN^? vs. log K and of log k_{f, CN}- vs. log k- gave good linear relationships. The plot for poly( 1 ), greatly deviated again to the upper area. The SO ion interacts with poly( 1 ), a cationic polyelectrolyte, more strongly than the CN^? ion.     

Stereokontrolle. VI. Zum mechanismus der radikalischen polymerisation von methylmethacrylat

Methylmethacrylate has been polymerized by free radicals in bulk and in 14 different solvents at temperatures between ?5 and +120°C. The tacticity of the polymethylmethacrylates depends on temperature, solvent and initial monomer concentration. The stereocontrol follows at least a MARKOFF first order statistics. A general compensation effect exists between the difference (ΔH ? ΔH) of two activation enthalpies and the corresponding differences (ΔS ? ΔS) of activation entropies, independent of monomer concentration and solvent (a, b = i/i, i/s, s/i, s/s). The compensation temperature T₀ is independent of the mode of dyad formation. The compensation enthalpy ΔΔH is the highest for the difference between the formation of an isotactic and a syndiotactic dyad at a given syndiotactic dyad (s/i vs. s/s). The compensation enthalpy equals practically zero for the process i/i vs. i/s. At the compensation temperature, isotactic dyads are preferentially formed at isotactic dyads and syndiotactic at syndiotactic dyads. The tendency to form heterotactic triads does not increase in all solvents with increasing temperature.     

Influence des traitements thermiques à l'état fondu sur les cinétiques de cristallisation du poly(oxyméthylène)

The influence of the temperature of the melt T₁ on the kinetics and the morphology of a semicrystalline polymer (poly(oxymethylene)) was investigated using thermal analysis and optical microscopy. The thermodynamic melting point T and the enthalpy of melting at thermodynamical equilibrium ΔH were determined by extrapolation of the graphs T_f = f(T_c) and ΔH_f = f(T_c); (T = 198°C, ΔH = 251 J/g). For different temperatures of the melt (T₁ = 185°C, 195°C, 205°C), isothermal and non-isothermal crystallizations were analysed using the Avrami and Ozawa equations. Nucleation and spherulitic growth in this polymer were studied by using optical microscopy at elevated temperatures. Using different analyses, we observed initial nucleation followed by spherulite growth with the following influence of the temperature of the melt on the distribution and the number of spherulites: T₁ < T produces many small spherulites; T₁ > T gives rise to few large spherulites.     

Stereokontrolle. IV. Konstitutionseinflüsse bei radikalischen Polymerisationen

A compensation effect exists between the quantities (ΔH ? ΔH) and (ΔS ? ΔS) in the free radical polymerization of a monomer in different solvents ΔH, ΔH, ΔS, and ΔS are the activation enthalpies and entropies, resp. for the formation of isotactic and syndiotactic dyads. The quantities ΔΔH and T₀ are by definition independent of the temperature of polymerization and other polymerization conditions and thus a pair of constants characteristic for each monomer. A linear relationship between ΔΔH and T₀ has been found for acrylic and vinyl monomers each. Both true activation and conformational effects seem to be responsible for the stereocontrol in free radical polymerizations.     

Anionic Ring‐Opening Polymerization of Propylene Oxide in the Presence of Phosphonium Catalysts at Various Temperatures

Anionic ring‐opening polymerization of propylene oxide in the presence of a potassium alkoxide initiator was accelerated by the addition of the bulky phosphonium salts tetrakis[cyclohexyl(methyl)amino]phosphonium‐, tetrakis[propyl(methyl)amino]phosphonium‐, and tetrakis[octyl(methyl)amino]phosphonium‐tetrafluoroborate. Dipropylene glycol (DPG) was partially deprotonated (5%) and used as initiator. The delocalization of the positive charge over five atoms promoted the formation of a separated ion‐pair, thus enhancing nucleophilicity and reactivity. The polymerization behavior of the counterions at varied temperatures was studied. Characterization of poly(propylene oxide)s by means of ¹H NMR spectroscopy, size exclusion chromatography (SEC), and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry (MALDI‐TOF‐MS) showed low polydispersities and the absence of by‐products and impurities. The degree of polymerization (DP _n) for the polymers was in the range of 8–60 (M _n = 630–3 620 g · mol^?1) and M _w/M _n obtained was 1.03–1.35 and 1.11–1.32 for MALDI‐TOF‐MS and SEC, respectively. Values calculated from the titration of hydroxyl groups (OHV) showed good agreement. Determination of the total degree of unsaturation in the range 13–60 mmol · kg^?1 indicated larger amounts with decreasing polymerization rates and increasing polymerization temperatures.

The phosphonium salts Cy₄PBF, Pr₄PBF, and Oc₄PBF.     

Polymerization of 2-diethylamino-1,3,2-dioxaphosphorinane, 2. Kinetics

Kinetic studies of the anionic polymerization of 2-diethylamino-1,3,2-dioxaphosphorinane were performed in THF solution with (CH₃)₃SiO^?K⁺ as initiator at temperatures close to r.t. Initiation involves nucleophilic attack of the anion on P atom in the monomer molecule. Breaking of the P? O bond leads to an alcoholate anion as the growing species. Polymerization was shown to proceed via macroion-pairs and to be nearly living; e.g. at r.t. for every 250 propagations there is one termination. Rate constant of propagation k = 3,4 ± 0,31·mol^?1·s^?1 at 25°C, ΔH = 13,3 kcal·mol^?1 and ΔS = ?32,2 cal·mol^?1·K^?1. The ratio k/k was determined by solving a kinetic scheme involving propagation and termination. It was shown that termination consists in the alcoholate anion attack on P in either polymer or monomer molecule with expulsion of (C₂H₅)₂N^? anion and formation of a P? O bond. The dialkylamide anions cannot reinitiate polymerization. In solving the kinetic scheme it was assumed that termination involving both polymer and monomer proceeds with rate constants equal to each other.     

Synthesis of Novel Polycations Using the Chemistry of Ionic Liquids

Summary: In this work, we report the synthesis of a great variety of polycations with varying counter‐anions. These new polymers were obtained by a simple anion exchange reaction facilitated by the phase separation of the resulting products. This strategy has been successfully applied to three different polycations, poly(1‐vinyl‐3‐ethylimidazolium bromide) poly(ViEtIm⁺Br^?), poly(1‐ethyl‐4‐vinylpyridinium bromide) poly(ViEtPy⁺Br^?), and poly(methacryloyloxyethyltrimethylammonium chloride) poly(EMTMA⁺Cl^?), with seven counter‐anions such as PF, CF₃SO, (CF₃SO₂)₂N^?, (CF₃CF₂SO₂)₂N^?, dodecylbenzenesulfonate, toluene‐4‐sulfonate, and bis(2‐ethylhexyl) hydrogen phosphate. The solubility range of the new polymeric ionic liquids becomes very broad, including apolar organic solvents and ionic liquids, depending on the nature of the counter‐anion. Thermogravimmetric experiments showed that the thermal stability of the PILs also depends on the nature of the counter‐anion improving in the order CF₃SO > (CF₃CF₂SO₂)₂N^? > C₁₂H₂₅C₆H₄SO > PF > Br^? > C₁₆H₃₄PO.

A simple anion exchange procedure similar to the reaction used in ionic liquids chemistry is used to the synthesis of new polymeric ionic liquids (PILs).     

Swelling,Elasticity and Spatial Inhomogeneity of Poly(N,N‐dimethylacrylamide) Hydrogels Formed at Various Polymer Concentrations

Summary: The equilibrium swelling degree, modulus of elasticity and the spatial inhomogeneity of poly(N,N‐dimethylacrylamide) (PDMAAm) hydrogels were investigated over the entire range of the initial monomer concentration. The degree of dilution of the networks after their preparation was denoted by ν, the volume fraction of crosslinked polymer after the gel preparation. The linear swelling ratio of the gels increased linearly with increasing ν. Depending on the value of ν, three different gel regimes were observed: (1) For ν < 0.3, increasing ν decreases the extent of cyclization during crosslinking so that the effective crosslink density of gels increases with rising ν. (2) For 0.3 < ν < 0.7, increasing ν reduces the accessibility of the pendant vinyl groups during crosslinking due to steric hindrance at high polymer concentrations. As a result, the effective crosslink density of gels decreases with increasing ν. (3) For ν > 0.7, the modulus of elasticity increases sharply with increasing ν due to the increasing extent of chain entanglements in this high concentration regime. Static light scattering measurements on the gels show that the degree of spatial gel inhomogeneity in PDMAAm gels attains a maximum value at ν = 0.06. The appearance of a maximum as well as the ν‐dependence of scattered light intensities from gels was successfully reproduced by the theory proposed by Panyukov and Rabin.

Effective crosslink density ν_e of the hydrogels shown as a function of ν.     

Iodine-poly(vinyl alcohol) interactions, 2. Anomalous slow quenching of the chromophore after extraction of free iodine with carbon tetrachloride

An equilibrium blue colored solution containing poly(vinyl alcohol) (PVA)-iodine-boric acid was prepared at 5°C. With increasing PVA concentration, at the same concentration of iodine, the absorption band of the chromophore I (λ_max = 650 nm, band D) linearly increased and the intensities of the bands for both I^? (λ_max = 226 nm, band A) and I (λ_max = 290 nm, band B) decreased. The band due to another iodide species (λ_max = 355 nm, band C), tentatively assigned to I · I₂, remained unchanged. Three solutions with different PVA concentration were then extracted with the same volume of carbon tetrachloride to remove I₂ present in the system. It was found that the chomophore due to I gradually decays with repeated extractions. After one extraction the change of the absorbance of I with time was measured at 5°C. In the system with a high PVA concentration the chromophore recovers the equilibrium within three days without losing much intensity, while in the systems with lower PVA concentration recovering of equilibrium takes more than four days with a considerable loss of chromophore. In the latter case, free I₂ extracted is supplied by the decomposition of polyiodide ions to I^?. Analysis of the rate of re-equilibration of iodine species revealed two reaction processes: one is a reaction involving free iodine species in an aqueous environment and the other is a slow reaction involving the polyiodide ions bound in a PVA cage.     

Iodine-poly(vinyl alcohol) interactions, 4. Stoichiometry of iodine/iodide in the polyiodide ion bound in the cage of poly(vinyl alcohol)

Aqueous poly(vinyl alcohol) (PVA)-iodine-boric acid solution was treated with anion exchange resin and the system involving only the cage complex was isolated. The system was then extracted with carbon tetrachloride, and I₂ and I^?, which were released from the complex, were separated and pooled in the carbon tetrachloride and the aqueous layers, respectively. From the absorption spectra of the layers the amounts of I₂ and I^? were determined. The ratio I₂/I^? was found to be approximately 2,0, which corresponds to the I₂/I^? stoichiometry in the complex. This result suggested that the major species bound in the PVA cage are pentaiodide ions, i.e., I with linear configuration and/or I₂· I with distorted chain structure. Judging from the resonance Raman spectrum of the PVA-iodine solution that had been revealed before, it was concluded that the two absorption bands of the complex at λ_max = 650 and 355 nm are ascribed to the I and I₂ · I ions, respectively.     

α,ω-dichloropoly(2-methylpropene) as an inifer: A modification to the Kennedy-Smith mechanism

Experimental details are given of attempts to enumerate the binary ionogenic equilibria (B.I.E.) of 1-chloro-1-methylethylbenzene ( 1 )/BCl₃, 1,4-bis(1-chloro-1-methylethyl)benzene ( 2 )/BCl₃ and 1,3,5-tris(1-chloro-1-methylethyl)benzene ( 3 )/BCl₃ in CH₂Cl₂. Due to chemical reaction (dimerisation or polymerisation) no experimental values for the B.I.E. constants could be obtained. A Born-Haber cycle is constructed to estimate the relative sequence of the overall B.I.E. constants. A similar treatment for 2-chloro-2methylpropane as a thermodynamic model for α,ω-dichloropoly(2-methylpropene) ( 4 ) suggests that the overall B.I.E. constant for these polymers is somewhat smaller than those for 1 and 2 but greater than that for 3 . Using 2 /BCl₃ as initiator for the polymerisation of 2-methylpropene (IB) it is shown, that the degree of polymerisation of 4 can be controlled within the limits 10 < DP < 100. It is shown that 4 can also act as an initiator for the polymerisation of IB, that these polymerisations involve only free ion propagation and, from a kinetic analysis of these polymerisations, that: (k)²/k = 12 1 · mol^?1 · s^?1, k = 1,2 · 10^?3 l · mol^?1 · s^?1, k [P] = 1,7 · 10^?3 s^?1, and k/(k K) = 102. The same analysis demonstrates that the self-ionisation of BCl₃ can be neglected in terms of any influence on the molar mass of the products. Experiments are also described which show that 2-chloro-2-methylpropane is not suitable as a substitute initiator for IB, but that 2-chloro-2,4,4-trimethylpentane is a useful model for 4 as an initiator for the polymerisation of IB.     

Berechnung der ungestörten dimensionen von vinylpolymeren mit unterschiedlichen seitenketten. Poly(propyläthylen), poly(äthyläthylen), polystyrol

The unperturbed dimensions 〈r〉/nl² and their temperature coefficients have been evaluated for poly(propylethylene) (poly-n-pentene-1), poly(ethylethylene) (poly-n-butene-1), and polystyrene with the rotational isomeric state model of FLORY. The calculated values of 〈r〉/nl² for atactic and isotactic chains are in good agreement with the experimental data reported in the literature. The values of the model parameters asked for good agreement change in a meaningfull way with the length of the side chain. The measured temperature coefficients, however, are described satisfactorally by the FLORY model for atactic polypentene and polybutene only.     

Immobilisierte tris(2,2′-bipyridin)ruthenium(II)-komplexe als photosensibilisatoren für die wasserphotolyse

Crosslinked polymers containing pendant tris(bipyridyl)ruthenium(II) complexes [Ru(bipy)] were synthesized and examined as sensitizers for the light-induced formation of hydrogen in the heterogeneous system H₂O/immobilized Ru(bipy)/ethylenediamine-tetraacetic acid/platinum. Hydrogen generation rates of 0,037 ml/h were obtained with Ru(bipy) -complexes immobilized with spacer groups onto hydrophilic carriers based on sucrose-methacrylates as well as hydrophobic carriers based on crosslinked poly(4-aminostyrene), whereas carrier bound complexes without spacer gave lower efficiencies in hydrogen production. The hydrogen generation rates were linear for more than 8 days.     

Effect of cooling rate on the structural relaxation of poly(oxy-2,6-dimethoxy-1,4-phenylene) and poly(oxy-2,6-dimethyl-1,4-phenylene)

The activation enthalpies for the structural relaxation of poly(oxy-2,6-dimethoxy-1,4-phenylene) and poly(oxy-2,6-dimethyl-1,4-phenylene) were determined by studying the dependence of the limiting fictive temperature on the cooling rate, using a differential scanning calorimeter (DSC) interfaced to a computer. The molar mass dependence of the activation enthalpies complied with the empirical equation, ΔH^˙ = ΔH ? A/M, where ΔH is the activation enthalpy of an infinite chain length polymer, M_v is the viscosity-average molar mass, a = 0,64, and A is a constant that depends on the free volume of the chain ends of the polymers. The values of ΔH are 433 kJ/mol for poly(oxy-2,6-dimethoxy-1,4-phenylene) and 449 kJ/mol for poly(oxy-2,6-dimethyl-1,4-phenylene).     

Investigation of poly(arylenevinylene)s, 40. Electrochemical studies on poly(p-phenylenevinylene)s

Differential pulse polarography (DPP) and cyclovoltammetry (CV) were conducted to study the redox behaviour of poly(p-phenylenevinylene) (PPV; E = 0,76 V; E = ?1,74 V) as well as of three insoluble PPV-derivatives and four soluble aryl-substituted PPV's. Oxidation studies of DP-PPV, DMOP-PPV and DPOP-PPV in comparison with two series of the oligomeric model compounds 1a–e and 2a–d lead to the conclusion that for DMOP-PPV (E = 0,98, 1,24,1,31 V) and DPOP-PPV (E = 1,10, 1,29, 1,44 V) three distinct oxidation stages exist, which are reversibly occupied and represent 1/2, 1 and 2 positive charges per repeating unit. In DP-PPV two oxidation stages representing 1/2 and 1 positive charges were found to be reversibly occupied (E = 1,17, 1,69 V), whereas at higher potentials irreversible dehydrocyclization occurred.     

Physicochemical studies of oligodextran. II. Intrinsic viscosity-molecular weight relationship

The viscosity behavior of dextran in two good solvents and four mixtures of a good and a bad solvent was studied over the molecular weight range of 410 < M _n < 32,000 at 25 and 50°C. In the molecular weight region larger than 2,000, the plot of log [η] versus log M _n gave the usual linear relationship for all solvents used. The constants K and a of the equation [η] = KM^a were determined and their dependence on the concentration of the nonsolvent in mixed solvents and on the temperature were discussed. Using the unperturbed dimensions of the dextran molecule estimated from the Stockmayer-Fixman plots, the value of {〈L〉/〈L〉}^1/2 was calculated to be 1.7–1.8. The viscosity behavior for dextran with M _n < 2,000 was qualitatively discussed as a deviation from the randomly coiled model.     

Untersuchungen über Poly(arylenvinylene), 30. Synthese,Photoleitfähigkeit und Redox-Verhalten von Poly(9-methylcarbazol-3,6-diyl-1,2-diphenylvinylen)

Soluble poly(9-methylcarbazole-3,6-diyl-1,2-diphenylvinylene) ( 1 ) M _n = 10000, was prepared by dehalogenating polycondensation of 3,6-bis(α,α-dichlorobenzyl)-9-methylcarbazole with chromium(II) acetate. The monomer was obtained from 3,6-dibenzoyl-9-methylcarbazole by reaction with PCl₅. The chemical structure of 1 was verified by elemental analysis, UV, IR, and NMR spectroscopy, GPC, and VPO. 1 was found to be highly photoconducting, exhibiting a dark conductivity of 10^?14 S/cm, which increases on doping with AsF₅ to 10^?4 S/cm. Its thermal stability under nitrogen is as high as with other phenylsubstituted poly(arylenevinylene)s (dec. temp.: 540°C; residue: 72 weight-%). The spectral distribution of sensitized (TNF, dyes) photoconductivity was studied and the redox behaviour was investigated by cyclovoltammetry. The redox potentials were found to be E = 0,90 V and E = ?2,07 V (vs. Ag/AgCl). The electrochemical oxidation is reversible, associated with the formation of polydications derived from chain segments which consist of two carbazolediylvinylene units. Thus, 1,2-dicarbazole-3-yl-1,2-diphenylethylene as model compound well reflects the redox properties of the polymer. The electrochemical band gap energy was found to be 2,97 eV, which agrees closely with the energy of the optical absorption edge of 3,04 eV.     

Struktur und Eigenschaften segmentierter polyetherester, 3. Synthese definierter Oligomerer des polybutylenterephthalats

The synthesis of some series of oligo(oxytetramethylene oxyterephthaloyl) [oligo(butylene terephthalate)s] with different but well-defined end groups is described. The separation of artificial mixtures of the oligomers by high pressure liquid chromatography was studied under various elution and column conditions, and thus, the purity of the individual oligomers was demonstrated. The equilibrium melting point T = 236 ± 4°C and the corresponding heat of melting ΔH = 28,7 kJ·mol^?1 of poly(butylene terephthalate) was determined from the analysis of the melting behaviour of the oligomers as depending on the degree of polymerization and the structure of the end groups.