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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

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.     

Cationic polymerization of cyclic sulfides. IV. Determination of the structure and concentration of the propagating species during the polymerization of 3,3-dimethylthietane by 300 mhz nmr spectroscopy

For atactic as well as for isotactic copolymers of propylene with 1-pentene, styrene, or vinyl chloride the unperturbed dimensions, 〈r〉/nl², have been evaluated using the rotational isomeric state model of FLORY. The chemical composition has been varied over the whole range. 〈r〉/nl² turns out to be lower than an average of the corresponding homopolymer values for all copolymers, if the mol fractions of the components are weighted. The sequence lenth distribution–being characterized by the product r_A · r_B of the copolymerization parameters–has only little influence on 〈r〉/nl², especially for r_A · r_B < 1.     

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.     

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?.     

Synthesis of nonlinear optical polymers functionalized with 4-amino-4′-cyanostilbene and -azobenzene dyes. Second harmonic generation in corona-poled thin films

The synthesis and susceptibilities χ and χ to two series of polymethacrylates functionalized with 4-dialkylamino-4′-cyanoazobenzene and 4-dialkylamino-4′-cyanostilbene dyes are reported. The monomeric dyes were homo- and copolymerized with methyl methacrylate in various ratios, to produce polymers useful for nonlinear optical (NLO) applications. The second-order nonlinear optical properties of corona-poled aligned polymers were evaluated by second harmonic generation measurements. The χ results for the azo-dye polymers are in the range of 25–324 · 10^?9 esu, and for the stilbene-dye polymers in the range of 42–57 · 10^?9 esu, depending on the functionalisation degree of the copolymers. The poled films do not show a significant decay in the second harmonic signal after four months.     

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.     

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.     

Hydride ion transfer processes and cationic polymerization of cyclic acetals

Four topics related to the cationic polymerization of cyclic acetals and mainly based on the author's results are reviewed.

• (1) The kinetics of the H^? transfer from linear and cyclic acetals and ethers to the triphenylmethyl cation were examined. A linear correlation between the ¹H-NMR shift of the H-atom to be transferred as H^? anion and the enthalpy of activation (ΔH) was observed for H^? donors which are linear and cyclic-planar or deviate slightly from planarity. Puckered rings, like 1,3,5-trioxane were found to be very poor H^? donors. A linear relationship between ΔH and ΔS was observed for all studied compounds.
• (2) The equilibria carbenium ion ? oxonium ion involving the unpaired triphenylmethyl cation and different linear and cyclic acetals and ethers were studied. A linear relationship between the basicity of the involved nucleophile (expressed as pK_a or pK_b) and the enthalpy of equilibrium (ΔH) was found.
• (3) The chemistry of the elementary reactions leading eventually to the formation of the active species in the polymerization of 1,3-dioxolane was investigated. The latter was used as a model monomer and initiated with triphenylmethyl salts with various stable anions like AsF and SbF or with the unstable SbCl. The importance of the ambident reactivity of 1,3-dioxolan-2-ylium cations was pointed out and the kinetics of cationation via ring opening of these salts was described. 1,3-Dioxolan-2-ylium salts were shown to be sufficiently stable to be slowly transformed into the linear cations (k?_cat ≈ 10^?3 to 10^?4 mol^?1 dm³ s^?1 at 25°C). This slow reaction was partially responsible for the induction periods observed in the polymerization of 1,3-dioxolane.
• (4) The kinetics and mechanism of the chain propagation of 1,3-dioxolane were described and a structure ( 20 ) was proposed for the growing centres. It was indicated that the growing species, being the tertiary oxonium ions use the polymer segments as ligands and in contrast to the oxycarbenium ions do not abstract hydride anions (H^?).

     

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 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:      

Cationic polymerization of methyl substituted 1,3-dioxepanes

The polymerization of 4-methyl-1,3-dioxepane ( 1a ), 2,4-dimethyl-1,3-dioxepane ( 1b ), and 4,4-dimethyl-1,3-dioxepane ( 1c ) was investigated in 1,2-dichloroethane at different temperatures ranging from ?60 to 0°C by using boron trifluoride etherate as initiator. The polymerization of 1a involves an equilibrium between monomer and polymer, and gives a viscous polymer along with some cyclic oligomers of different sizes. ¹H NMR and ¹³C NMR analysis of the polymer revealed that the bond cleavage of the unsymmetrical 1,3-dioxepane ring in the polymerization occurred nearly randomly at the two acetal C? O bonds. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentrations: ΔH=?9,3±1,3 kJ · mol^?1 and ΔS=?38,8±7,8J · mol^?1 · K^?1. Dimethyl substituted 1,3-dioxepanes were found to be very reluctant to polymerize: Only a liquid oligomer was formed in very low yield from 1b , and even oligomer was not obtained from 1c . The effect of methyl substituents on the cationic polymerizability of 1,3-dioxepanes is discussed from the thermodynamic point of view.     

Enthalpy of polymerisation of 7-oxabicyclo[2.2.1]heptane,and exo- and endo-2-methyl-7-oxabicyclo[2.2.1]heptane

The enthalpies of combustion of poly(oxy-1,4-cyclohexylene) formed from 7-oxabicyclo[2.2.1]heptane ( 1 ) and of its derivatives formed from exo- and endo-3-methyl-7-oxabicyclo[2.2.1]heptane ( 2a and 2b ) have been measured. From literature values for the enthalpies of combustion of the liquid monomers, the enthalpies of polymerisation have been derived: ?ΔH(1→c)=44,3±1,9, 49,7±2,6, and 45.4±3,1 kJ mol^?1, respectively. The results indicate a minimum strain energy in these polymers of ca. 15 kJ mol^?1. The estimated entropies of polymerisation yield ceiling temperatures of 320, 240, 200°C respectively for the three bicyclic ethers.—The reasons for the discrepancy between our present ?ΔH(1→c) for the endo compound and that previously reported², are explained.