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.     

The adiabatic compressibility of polyelectrolytes: Binding of Na+ ions on the multivalent site of polymer chains

The adiabatic compressibility of a 1:0,35 acrylic acid/maleic acid copolymer (AA/MA) and of its three “sodium salts” obtained by neutralizing (25%, 50% and 100%) with sodium hydroxide was studied. In 100% neutralized AA/MA copolymer, the dissociation of the counter ions was complete so that the limiting values of the apparent molal compressibility δK and apparent molal volume δV were found to be lowest with values of ?83,0·10^?4 cm³ bar^?1 mol^?1 and 52,9 cm³/mol respectively. This showed a decrease of 89,0·10^?4 cm³ bar^?1 mol^?1 and 20,9 cm³ mol^?1 from that of the unneutralized acid copolymer. The δK and δV values were resolved into the ionic components, δK and δV. The electrostriction caused in the copolymer by an increase of the negative charge from 0 to ?0,425, from ?0,425 to ?0,85 and from ?0,85 to ?1,7 produced a decrease of 3,9.10^?4, 6,9.10^?4, and 5,7.10^?4 cm³ bar^?1 mol^?1 in δK and 3,7,4,5 and 10,2 cm³ mol^?1 in δV. Contrary to the volume change, the compressibility data showed a disproportionate decrease for the neutralized products. The reduced viscosity for the sodium salts was also found to have reduced values. A notable point emerging from this study is that the apparent ion binding on the multivalent site of the polymer chain, as obtained by the two methods—the adiabatic compressibility and density determinations—shows an appreciable variation.     

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?.     

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.     

Ultracentrifuge study of critically branched polycondensates, 4. Hinge point analysis and higher average molecular weights

Model polycondensates of 1,10-decanediol and 1,3,5-benzenetriacetic acid stabilised by means of diazodiphenylmethane and ketene are utilised to extend further our understanding of the critically branched state and to investigate possible contributions of the ultracentrifuge to the study of highly polydisperse macromolecules in non-ideal, dilute solutions. By way of computerised curve fitting, the concentration gradient curve is obtained from its concentration profile in the ultracentrifuge cell. From this the weight average molecular weight M?₁ is calculated by the hinge point method. It is also confirmed that values of the two next higher moments of the molecular weight distribution, viz. M?_2/1 and M?_3/2 (i.e. M_z and M_z+1) can hardly be distinguished from infinity for these samples. Application of the hinge point method to systems of high polydispersity is found both theoretically and experimentally to furnish M?₁ after a dual extrapolation of the measured M? against the generalised speed parameter λ and the initial concentration c⁰. It is found theoretically that for estimation of the higher molecular weight moments, plots of M? M? and M? M? M? (not merely M? and M?) must be extrapolated against the same variables, i.e. λ and c⁰. The quantitative results thus obtained are discussed in the context of previous results on these materials. They are compared with the classical theory for random f-functional polycondensates and statistical cut-off effects on the high molecular weight tail of distribution are assessed.     

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.     

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.     

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.     

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.     

Enthalpy of polymerisation of 2-oxabicyclo[2.2.2]octan-3-one

The enthalpies of combustion of crystalline 2-oxabicyclo[2.2.2]octan-3-one ( 1 ), and five different crystalline poly(oxycarbonyl-1,4-cyclohexylene) samples formed from 1 were measured at 298, 15 K by high-precision bomb calorimetry. For 1 , the enthalpies of combustion and of formation were, ?ΔH(c) = 3717,5 ± 1,3 kJ·mol^?1 and ?ΔH(c) = ? 466,2 ± 1,6 kJ·mol^?1. After correction for the presence of n-butyl- or tert-butoxy-end groups in the polyester samples, a consistent enthalpy of polymerisation of 1 was obtained, ΔH(c → c) = ? 20,9 ± 2,3 kJ·mol^?1. The enthalpy of sublimation of 1 was measured, ΔH (1) = 69,6 ± 2,1 kJ·mol^?1; the value for the polyester unit was derived as 49 kJ·mol^?1.     

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:      

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.     

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.     

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.     

The anionic polymerization of styrene under pressure

The kinetics of the anionic polymerization of styrene were investigated under pressure (1≤p/bar < 1800) with Na⁺ as counter ion in tetrahydropyran (THP) as solvent and with Cs⁺ as counter ion in 1,2-dimethoxyethane (DME) as solvent. The results yielded the activation volume of the contact ion pair ΔV and the sum (ΔV + ΔV_cs) of the activation volume of the solvent separated ion pair ΔV and the volume change upon formation of solvent separated ion pairs from contact ion pairs ΔV_cs. The numerical values are negative. The activation volume of the solvent separated ion pairs could be estimated.     

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.     

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.     

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.     

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.