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?.     

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.     

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.     

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.     

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:      

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).     

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.     

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.     

Luminescent characteristics of tris(2,2′-bipyridine)-ruthenium(II) adsorbed in a silk fibroin membrane

The emission characteristics of the excited state of tris(2,2′-bipyridine)ruthenium(II), Ru(bpy), adsorbed on a silk fibroin membrane is studied. The life time of the excited state of the adsorbed Ru(bpy) is unusually longer (1 000 ns) than that of Ru(bpy) in aqueous solution (598 ns). The excited state of the adsorbed Ru(bpy)₃²⁺ is quenched by oxygen when dipped in methanol, but not in water. The quenching by oxygen in methanol follows the Stern-Volmer equation. The luminescent characteristics of the adsorbed Ru complex is discussed in terms of binding in hydrophobic domains composed of tyrosine residues of the protein.     

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.     

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.     

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.     

13C cross polarization/magic-angle spinning NMR and infrared spectroscopic study of poly(ε-caprolactam) and of poly(ε-caprolactam)/polystyrene blends

Infrared and ¹³C cross polarization/magic-angle spinning nuclear magnetic resonance (¹³C CP/MAS NMR) spectra and T relaxation times of differently treated poly(ε-caprolactam) 1

1 Systematic IUPAC name: poly[imino(1-oxohexamethylene)].

(PCL) and of poly(ε-caprolactam)/polystyrene blends were measured and the fractions of the α- and α-crystalline and mesomorphous PCL forms were determined. The amounts of the α-form obtained from the infrared and ¹³C CP/MAS NMR spectra are in agreement. In the blends, the fraction of the PCL α-crystalline form is higher as compared with extruded pure PCL. The existence of a single T parameter for PCL in each of the samples indicates small dimensions of the crystalline regions; the obtained T values correspond to the PCL phase composition.     

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.     

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.     

Enthalpy of polymerisation of 7-oxabicyclo[4.1.0]heptane

The enthalpies of combustion in oxygen at 298, 15 K of 7-oxabicyclo[4.1.0]heptane, ΔH(1) = ?3 624,9 ± 0,6 kJ·mol^?1, and of poly(oxy-1,2-cyclohexylene), ΔH(am) = ?3528,2 ± 1,4 kJ · mol^?1 were measured by high-precision bomb calorimetry. The enthalpy of polymerisation was derived, ΔH(1→am) = ?96,7 ± 1,5 kJ·mol^?1. Polymer samples from three separate preparations were found to be indistinguishable in their enthalpies of combustion and in their ¹³C NMR spectra.     

Thermodynamics of 2,2-dimethyltrimethylene carbonate,of its bulk polymerization process and of poly(2,2-dimethyltrimethylene carbonate) from 0 to 470 K at standard pressure

In the present work the thermodynamic properties of 2,2-dimethyltrimethylene carbonate (DTC) and poly-2,2-dimethyltrimethylene carbonate (PDTC) were studied by precise calorimetry. In adiabatic and dynamic vacuum calorimeters the temperature dependence of the heat capacity of DTC and PDTC was studied between 5 and 470 K. Temperature and enthalpies of physical transitions were determined, and in an isothermal calorimeter energies of combustion of the above compounds were measured. From the results the thermodynamic functions C(T), H°(T)–H°(0), S°(T), G°(T)–H°(0) were calculated for various physical states of the monomer and the polymer from 0 to 470 K. The standard enthalpies of combustion and thermochemical parameters of formation ΔH, ΔS, ΔG of the objects studied were estimated at T =298,15 K and p = 101,325 kPa. The zero entropy S(0) and configurational entropy S of PDTC in the glassy state and the difference in zero enthalpies of the polymer in the glassy and crystalline states H(0)–H(0) were estimated. The results were used to calculate the thermodynamic parameters of the bulk polymerization of DTC (ΔH, ΔS, ΔG) in the range of 0 to 420 K. It was established that for the process DTC → PDTC, ΔG < 0 if the polymer is crystalline and ΔG > 0 in the case of amorphous PDTC (glassy or liquid). The ceiling temperature is T = 500 K.     

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.     

Thermodynamics of depolymerization of biotechnological poly[(R)-3-hydroxybutyrate] with formation of (R,R,R)-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,10-trione and of its polymerization with ring-opening to highly isotactic poly[(R)-3-hydroxybutyrate] from 0 to 500 K at standard pressure

In adiabatic vacuum and dynamic calorimeters the temperature dependence of the heat capacity C of (R,R,R-4,8,12-trimethyl-1,5,9-trioxadodeca-2,6,10-trione a twelve-membered cyclic trilactone), biotechnological poly[(R)-3-hydroxybutyrate] and highly isotactic poly[(R)-3-hydroxybutyrate] was studied between 5 K and 500 K; temperatures and enthalpies of melting of the above mentioned substances were measured. In a calorimeter with a static bomb and an isothermal shield the energy of combustion of the same substances was measured. From the results the thermodynamic functions C (T), H⁰(T) ? H⁰ (0), S⁰ (T), G⁰ (T) ? H⁰ (0) were calculated in the range of 0 K to 500 K and thermochemical parameters ΔH, ΔH, ΔS, ΔG were estimated at T = 298,15 K and standard pressure. The thermodynamic parameters of depolymerization of the biotechnological polymer to the 12-membered trilactone ΔH, ΔS ΔG and of the polymerization of the monomer formed in the highly isotactic poly[(R)-3-hydroxybutyrate] ΔH, ΔS, ΔG were calculated for 0 K to 500 K.