Thermodynamics of ternary mixtures of random copolymers

A most general formalism based on the Lattice-Fluid theory of polymer solutions is presented for multicomponent mixtures of random copolymers which may consist of any number of different types of monomers. Particular emphasis is given to the phase stability in these mixtures. Equations for the spinodals and the critical points are presented. The formalism is subsequently applied to a number of interesting cases of ternary (co)polymer mixtures such as: mixtures of three random copolymers with the same monomers A and B but in different proportions (A B + A B + A B) mixtures of homopolymers A_m and B_n with the random copolymer A_i B_j, and mixtures of the random copolymers (A B + A B + A C). The effect of temperature on the phase behavior of these systems is discussed. The agreement of theoretical predictions with available experimental information is satisfactory. Because of its simplicity, the model may be used as a tool for studying multicomponent mixtures exhibiting lower or upper critical solution temperature behavior.     

Gas permeation through two side-chain liquid-crystalline polyacrylate-based membranes containing 4-methoxyphenyl 4-hexyloxybenzoate or 4-cyanophenyl 4-hexyloxybenzoate mesogenic side groups

Two kinds of side-chain liquid-crystalline (LC) polymers with different side-chain mesogenic end groups were synthesized. The laminated membrane was prepared by sandwiching the side-chain LC polymer between two porous polypropene (Celgard) films. Permeation properties for O₂, N₂, CO₂ and CH₄ through the laminated side-chain LC polymer-based membranes were measured using a gas-chromatographic method at several temperatures corresponding to the stability range of the different phases of the side-chain LC polymers. The gas permeation behaviour depends strongly on the state of the side-chain LC polymer. The activation energy for permeation depends on the state, too. The plot of separation factor P/P versus P exhibits an unusual behaviour. P/P increases with P when the temperature rises and the phase of the side-chain LC Polymer changes from the glassy state to the liquid-crystalline state. The magnitude of gas permeability coefficients for the laminated membranes is rather low compared to those of some common polymers. The low gas permeability seems to originate from the low gas solubility rather than from the low gas diffusivity in the laminated side-chain LC polymer membrane.     

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.     

Anomalous diffusion of dextran in DMF-water mixed solvent system: A case of preferential solvation of the dextran molecule?

Anomalous diffusional behaviour — not evident for the carbohydrate oligomers glucose, sucrose, and raffinose — was observed for dextran in the DMF-H₂O mixed solvent system at 25°C. The plot of interdiffusion coefficients (D₀) for the dextran against the mole fraction of water (X) in the DMF-H₂O mixtures shows a discontinuity with a maximum in D₀ at X = 0,85. Plots of intrinsic viscosities [η], for two higher molecular weight dextrans, against X also show transitions at X = 0,85. The anomalous behaviour of the dextrans at this solvent composition is discussed in terms of a solvent induced conformational transition of the dextran molecule.     

Effect of molecular weight distribution of the original polymer on separation characteristics in successive solutional fractionation

An attempt has been made to clarify the effect of molecular weight distribution (MWD) in the original polymer on the separation characteristics in successive solutional fractionation (SSF) and comparisons were made with successive precipitational fractionation (SPF). Polymers with Schulz-Zimm distribution and Wesslau distribution of the degree of polymerization (ratio of the weight- to number-average degree of polymerization, X?/X? = 2 to 5) were brought into solution, and cooled to cause precipitation according to the modified simulative procedure of Kamide and Sugamiya, based on the Flory-Huggins's theory of dilute solutions of polymers. No double-peak distributions were observed in the fractions obtained by SSF under the conditions which give double-peak distributions in the case of SPF. The minimum value of X?_w in the fractions obtained in a given run is almost the same for SSF and SPF, the minimum increasing with decreasing X?/X? (the suffix zero denoting the original polymer). The ratio X?_w/X?_n in the fractions is not greatly influenced by X?/X? except for the first few fractions. The standard deviation σ′ of the MWD in the fractions decreases with increasing X?/X? in an initial stage, while this situation is reversed in the later stages. In general SSF furnishes sharp fractions regardless of X?/X?.     

Copolymerization of styrene with Zn(II), Co(II), Ni(II) and Cu(II) acrylates

The radical copolymerization of styrene with Zn(II), Co(II), Ni(II) and Cu(II) acrylates in methanol at 60°C was studied and that of styrene with Cu(II) acrylate also in acetonitrile at 80°C. In a given period of time an increase of conversion was observed with increasing concentration of the first three metal acrylates in mixtures with styrene. With Cu(II) acrylate, however, a decrease of conversion was found. The monomer reactivity ratios were determined as follows: r_St = 1,10, r = 0,90; r_St = 1,74, r = 0,56; r_St = 1,83, r = 0,53; r_St = 5,94, r = 0,12 (in acetonitrile). The products of the reactivity ratios, almost equal to one, reflect an “ideal” copolymerization and therefore a very little alternating tendency in propagation reactions. The Alfrey-Price Q-e parameters for the metal acrylates were calculated and discussed.     

Cationic polymerization of cyclic sulfides

The mechanism of the cationic polymerization of cyclic sulfides, initiated with triethyloxonium salts is reported. Differences due to changing the counter-ion from BF to SbCl are discussed. Initiation consists of the alkylation of monomer forming a cyclic sulfonium ion which is the active species in the propagating step. A generally occurring termination reaction is the formation of non-strained (linear or cyclic) sulfonium ions. In the case of epithiopropane (propylene sulfide) these can slowly re-initiate the polymerization by an intramolecular reaction forming the 3-membered cyclic sulfonium salt. This re-initiation is not possible with the thietanes because of the greater difficulty to form 4-membered cyclic sulfonium salts. When SbCl is the counter-ion, an additional, more drastic termination can occur most probably by reaction of the growing chain with the counter-ion, thereby forming an alkyl chloride and SbCl₅. After the polymerization of propylene sulfide with BF as the counter-ion, the polymer degrades to low molecular weight oligomers, predominantly the cyclic tetramer. This degradation is a back-biting reaction occuring via sulfonium salts. With SbCl as the anion, the sulfonium salts are destroyed by the termination reaction and degradation does not occur. It was possible to follow the concentration of the growing species (4-membered cyclic sulfonium salt) during the polymerization of 3,3-dimethylthietane by means of 300 MHz NMR spectroscopy. By measuring the rate constants of propagation for different initiator concentrations or in the presence of different amounts of an indifferent electrolyte, it was possible to calculate separate rate constants for propagation via free ions (k) and via ion-pairs (k). The ratio k/k was about 60 when BF was the anion and 35 when it was SbCl.     

The thermodynamics of polymerisation of aldehydes and cyclic ethers, 4.1,3-dioxocane and 1,3,6-trioxocane

The equilibrium between gaseous monomer (g) and amorphous polymer (c) has been studied for 1,3-dioxocane and 1,3,6-trioxocane between 100 and 137°C. From the equilibrium pressures of monomer, the ΔH and ΔS values have been calculated. Thermodynamic data for the vaporisation of each monomer have also been measured so that values of ΔH and ΔS for the polymerisations could be calculated (l: liquid phase). For 1,3-dioxocane: For 1,3,6-trioxocane:      

A comment on the estimation of random branching from viscosity measurements

The hydrodynamic behaviour of polydisperse branched copolymers of methyl methacrylate with a small amount of ethylene dimethacrylate was investigated in several solvents possessing different “solvent power”. It was found that with increasing degree of branching the viscometric expansion coeficient α of these copolymers decreases compared with the expansion of the linear analogs α (before the gel point α/α ≈ 0,5). This phenomenon is demonstrated to be useful in the application of viscometry as a method of estimation or determination of branching.     

Study on the possibility of reverse-order fractionation in successive precipitational fractionation

An attempt has been made to account for the occurrence of reverse-order fractionation (ROF) phenomena in successive precipitational fractionation (SPF) in terms of the newly established rigorous fractionation theory, assuming complete thermodynamic equilibrium conditions between a polymer-rich phase and a polymer-lean phase and to throw light on operating conditions under which ROF occurs. For this purpose, the simulation technique was employed. ROF occurs not only between 1st and 2nd fractionation steps but also between two successive higher order steps even under thermodynamic equilibrium state. The molecular weight distribution of the original polymer contributes very sensitively to ROF: For the Schulz-Zimm type polymer ROF is highly observed at a large amount of fraction Q in a narrow range of initial concentration v whereas for the Wesslau type polymer large ROF occurs at small Q over a relatively wide v range. In general, there exist appropriate ranges of the weight-average degree of polymerization of the initial polymer X? the solvent nature expressed by the concentration dependence of the polymer/solvent interaction parameter p, and the initial polymer concentration v for ROF. A broad original polymer gives rise to large ROF. The theoretical predictions obtained here can explain very clearly the experimental results by Fujisaki and Kobayashi concerning the effect of X?, p, and v on ROF in SPF of polyacrylonitrile.     

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.     

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.     

Study by 19F nuclear magnetic resonance spectroscopy of the cationic polymerization of tetrahydrofuran initiated by PF5

By means of ¹⁹F-NMR spectroscopy it was possible to detect and estimate the hexafluorophosphate ion (PF) in the THF polymerization, initiated by PF₅ in methylene dichloride at 25°C. The observed variations with time of [PFPF], [PF₅·THF], and [PPF] were analysed kinetically, and by means of the resulting equations, the rate constants for initiation, propagation and termination were evaluated. Comparison of our k_p value with those of others indicates that our method is sound, and we conclude that it should be applicable to other similar systems.     

Novel organosilicon-containing polymers for an oxygen permselective membrane

Synthesis and gas permeation measurements of several types of polymers from methylstyrene derivatives containing mono-and bis(trialkylsilyl) group(s) were carried out. Upon radical homo-and co-polymerization of silicon-containing monomers high-molecular-weight polymers were obtained. Results from gas permeation measurements showed that these types of silicon-containing polymers exhibit fairly high oxygen permselectivity (ratio of oxygen and nitrogen permeation coefficients P/P = 3,1 ? 4,6), keeping the oxygen permeation coefficients (P) in the range of between 1,4 · 10^?9 and 4,5·10^?9 cm³ (STP) · cm · cm^?2 · s^?1 · cmHg^?1. From time lag measurements, it was found that permeation coefficients are dependent on the solubility of gases in the membranes rather than on diffusivity. Actually, the oxygen solubility coefficients increase with increasing silicon content in the polymers. Permselectivity of oxygen against nitrogen is governed by polymer constitution rather than by silicon content.     

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.     

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.     

Cationic polymerization of N-vinylcarbazole by tropylium salts at low temperatures

Cationic polymerizations of N-vinylcarbazole (NVC) in methylene dichloride containing approximately 1% nitromethane were studied by adiabatic calorimetry at temperatures between ?40 and ?70°C. Tropylium salts containing AsF, SbF and SbCl counterions were used as initiators. Reaction halflives ranged from 2 to 80 seconds and first-order plots displayed induction periods. Evidence indicated that the majority of the initiator was consumed, permitting estimation of propagation rate constants. For polymerizations involving the SbF counterion, these rate constants were found to be relatively insensitive to the concentration of initiator or excess anion and the conclusion is drawn that paired and unpaired PNVC⁺ SbF ions have similar reactivities at low temperatures. Correlation of the present results with those from previous work at 20 and 0°C yielded an Arrhenius exponential factor for propagation by unpaired ions of 30±9 kJ mol^?1. The degree of polymerization approached the ratio [M]₀/[1]₀ at ?70°C. At higher temperatures, molecular weights appeared to be governed by transfer reactions. The absence of significant chlorine content in polymer samples precluded the possibility of chain transfer to solvent.     

Extent of reaction,monomer conversion,and polymer yield in polycondensations

The extent of reaction of functional groups (p_A), the extent of conversion of monomer molecules (q_M), the true relative polymer yield (y_p), the constitutional repeating unit-based apparent relative polymer yield (y), and the monomer-based apparent relative polymer yield (y) are defined and their interrelationships given. The use of y instead of y_p overestimates the true yield, except in the limit of high degrees of polymerization. Use of y, on the other hand, always underestimates the true yield, especially at infinite degrees of polymerization. The correct expression for the calculation of the mass fraction of i-mers in reactants with a Schulz-Flory “most probable” distribution is given and shown to become identical with the usual approximation in the limit of vanishingly small mass of the leaving molecule.     

Photoconductivities of poly[γ-(β-N-carbazolylethyl)-L-glutamate] and its charge-transfer complex with 2,4,7-trinitrofluorenone

Poly[γ-(β-N-carbazolylethyl)-L -glutamate] (PCLG) was prepared by polymerizing the monomer which was synthesized by adapting the NCA method to a reaction product between L -glutamic acid and N-(β-hydroxyethyl)carbazole. PCLG films were prepared on a quartz Nesa (In₂O₃) plate by casting technique. The charge-transfer complex could be successfully formed only near the surface of the PCLG film by immersing the PCLG film into either a benzene or a methyl ethyl ketone solution of 2,4,7-trinitrofluorenone (TNF), since both benzene and methyl ethyl ketone were poor solvents for PCLG and suitable solvents for TNF. A photocell was formed by depositing a translucent gold electrode with vaccum evaporation onto the immersed film. For a small content of TNF in both the immersed films and the homogeneously mixed films of PCLG with TNF, the photocurrent of PCLG was successfully sensitized by TNF, but the sensitized photocurrents retained the relation I>I in a similar way as the photocurrent of PCLG alone, where I was the photocurrent under illumination onto the positive Au electrode and vice versa. On the other hand, as the TNF content increased, I became remarkably greater than I. The PCLG polymer, therefore, can behave as a p-type photoconductor, while the well-doped PCLG-TNF complex can behave as an n-type photoconductor.     

The partial specific volume of lysozyme chloride in water under pressure

The apparent specific volume ν of lysozyme chloride dissolved in pure water has been measured from 1 to 4000 bar using the Adams-Gibson-Anderson method of trapped mercury. A parametric expression for ν as a function of solute weight fraction X₂ is given for the various pressures at which the experiments have been performed. This parametric expression is valid when the densities of the solutions at atmospheric pressure and their compression at pressure P can be considered to be linear functions of the solute weight fraction X₂. The relation between ν and the partial specific ν ₂ is discussed and it is shown that within the range of concentrations considered and given the precision of the experiments under pressure, the two quantities are indistinguishable.