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.     

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.     

Esterification of benzenecarboxylic acids with ethylene glycol, 11. Kinetics of the initial stage of metal-ion catalyzed polyesterification of isophthalic acid with ethylene glycol

The kinetics of the reaction of isophthalic acid ( 4 ) with excess of ethylene glycol ( 5 ) in the presence of metal compounds as catalysts was determined in an open system and at 171–193°C by using liquid chromatography on silica gel. At an initial mole ratio of 5/4 equal to or higher than 20, the initial stage of metal-ion catalyzed polyesterification is characterized by the absence of oligomers and involves two consecutive and two concurrent reactions, i.e., metal-ion catalyzed and parallel uncatalyzed esterification of 4 to 2-hydroxyethyl hydrogen isophthalate ( 6 ) and metal-ion catalyzed and parallel uncatalyzed esterification of 6 to bis(2-hydroxyethyl) isophthalate ( 7 ). The rate constants for all the individual reaction steps were determined. The metal-ion catalyzed conversion of 4 to 6 (reaction (i)) is first-order in 4 and that of 6 to 7 (reaction (ii)) is half-order in 6 ; both reactions (i)–(ii) catalyzed by tin(II) oxalate are first-order in tin(II) ions. These kinetic relations hold through at least 97% of transformation of 4 into 7 . The activity of metal ions in the catalyzed esterification reactions (i)–(ii) decreases in the order Sn²⁺>Ti⁴⁺ ? Zn²⁺ > Pb²⁺ ≈ Co²⁺≈ Cd²⁺. The activation energies E_i(Sn) and E_ii(Sn) for the tin(II)-ion catalyzed reactions (i)–(ii) are 85,1±4,9 kJ mol^?1 and 83,1±4,2 kJ mol^?1, respectively, and the corresponding activation entropies ΔS and ΔS are ?;134,1±11,0 J K^?1 mol^?1 and ?148,6±9,5 J K^?1 mol^?1, respectively.     

Enthalpy of polymerisation of ethylene oxide and of copolymerisation of ethylene oxide with 7-oxabicyclo[2.2.1]heptane

The enthalpies of combustion of poly(ethylene oxide), ΔH(c)=-1178,7 ± 1,3 kJ . mol^-1, and of a random copolymer of overall molar composition 0,41 (poly(ethylene oxide)) + 0,59 (poly(oxy-1,4-cyclohexylene)), ΔH(c)=-2566,4 ± 1,8 kJ . mol^-1, were measured at 298,15 K by high-precision bomb calorimetry. The enthalpy of polymerisation of ethylene oxide was derived as ΔH (l → c) = -102,4 ± 1,6 kJ . mol^-1. The enthalpy of copolymerisation of ethylene oxide and 7-oxabicyclo[2.2.1]heptane was ΔH (l → c) = -63,0 ± 2,1 kJ . mol^-1, compared with -68,1 ± 1,6 kJ . mol^-1 for producing the two homopolymers in the proportion in which the monomers were present in the copolymer. It is concluded that insertion of an ethylene oxide unit into a poly(oxy-1,4-cyclohexylene) chain does not affect the strain-energy by a significant amount.     

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 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.     

Über die polymerisation von 1-chlor-2,3-epoxypropan

The kinetics and the thermodynamic features of the polymerization of 1-chloro-1,3-epoxypropane with the complex \documentclass{article}\pagestyle{empty}\begin{document}${\rm Cl}_{\rm 5} \mathop {{\rm Sb}}\limits^ \ominus \cdots \mathop {\rm S}\limits^ \oplus {\rm O}_2$\end{document} were studied. It was found that the process proceeds with a negative temperature coefficient, E_a=?51,29 kJ/mol ( ? 12,25 kcal/mol), ΔH_p=?18,8 kJ/mol (?4,5kcal/mol), ΔS_p=?74,5 J mol^?1 K^?1 (?17,8 cal mol^?1 K^?1), and with the ceiling temperature of 52,6°C. The molecular masses of the polymers were determined and a possible mechanism of the polymerization process was suggested.     

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

The enthalpy of combustion of poly(oxy-2-methyl-1,4-cyclohexenylene) prepared from endo-2-methyl-7-oxabicyclo[2.2.1]heptane has been determined by oxygen-bomb combustion calorimetry. The calculated standard enthalpy of formation of the polymer, ΔH (298,15K)= —283,5±3,0 kJ (base-mol)^—1, has been combined with that of the monomer to give the enthalpy of polymerisation of liquid monomer to solid polymer as ΔH = —33,3±3,7 kJ mol^—1.     

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.     

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.     

Anionic polymerization of butyl cyanoacrylate by tetrabutylammonium salts, 2. Propagation rate constants

Anionic polymerizations of butyl cyanoacrylate were initiated in tetrahydrofuran (plus a few experiments in 1,2-dimethoxyethane) by the salts tetrabutylammonium hydroxide, bromide, acetate and three substituted acetates. The hydroxide gives near-ideal ‘living polymerization’ kinetics, with k_p close to 10⁶l·mol^?1. s^?1 at 20°C. The kinetics of the reactions initiated by the acetates and bromide are analysed by the slow-initiation-no-termination theory, using values of the initiation rate constants evaluated in Part 1. The k_p values derived are in the same range as those from the OH-initiated reactions and those of the zwitterionic polymerizations initiated with covalent bases, i.e., tertiary phosphines and amines. A ca. 4-fold variation of k_p with concentration of active species is given a speculative analysis in terms of dissociation from paired to free ions, yielding tentative estimates for k ≈ 10⁵ and k ≈ 10⁷l·mol^?1·s^?1 in THF at 20°C. Molecular weights were all high M _n ≈ 10⁶, with M _w/M _n ≈ 2.     

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.     

Capacity flow method for determination of propagation and termination rate constants in radical polymerization

The possibility of determination of the propagation and termination rate constants k_p and k_t, resp., as well as their ratios k_p/k_t and k_p/k in homogeneous radical polymerization is shown using the capacity flow method. A theoretical analysis is carried out and relatively simple equations are introduced. The essential point is that the life time of the growing polymer chain is obtained graphically from the residence time of the reactants in the reactor vessel, which is a given quantity. As an experimental example the polymerization of methyl methacrylate initiated by benzoyl peroxide in benzene is investigated in a flow reactor with perfect mixing at 80°C. It is characteristic that the process can be followed by means usually applied for studying slow reactions. The degree of conversion is measured turbidimetrically and gravimetrically, whereas the initiation rate is analysed iodometrically. Thus, through a numerical linear approximation by the method of least squares k_p/k_t = (2,28±0,45)·10^?5, k_p/k = (1,50±0,22). 10^?1 are found from the experimental data, and hence k^p = (9,95±0,83)·10² l mol^?1 s^?1 and k_t = (4,36±0,49)·10⁷ l mol^?1 s^?1 are obtained.     

Studies on formaldehyde resins, 25. Kinetic study on the hydroxymethylation of melamine by means of HPLC

The kinetics of hydroxymethylation of melamine (2,4,6-triamino-1,3,5-triazine) with formaldehyde to form N-(hydroxymethyl)melamine (2,4-diamino-6-hydroxymethylamino-1,3,5-triazine) was investigated in aqueous hydrogen phosphate/phosphate buffer solutions in the range of pH 10,51 to 12,20 at 20°C, determining unreacted melamine by means of HPLC. As a result, this reaction is subject to a general base catalysis, and the second order rate constant k is expressed by k = k′ + k_A ? [A^?] + k[A^?]²/[HA] (or k [A^?][OH^?]), where HA and A^? denote acid and basic constituents of the buffer, and k′ is the rate constant in unbuffered media. This rate equation is compared with those reported previously.     

Anionic polymerization of 2-Oxo-1,3,2λ5-dioxaphosphorinane. Thermodynamics

Thermodynamics of the polymerization of 2-oxo-1,3,2λ⁵-dioxaphosphorinane in bulk initiated by sodium metal is described. Enthalpy (ΔH_p = 6,28 ± 0,84 kJ · mol^?1) and entropy (ΔS = 19,25 ± 2,51 J · mol^?1 · K^?1) of polymerization were evaluated from the temperature dependence of the equilibrium nomomer concentration determined directly by ³¹P{¹H} NMR. The results are compared with those obtained previously for the polymerization of other 2-alkoxy-2-oxo-1,3,2λ⁵-dioxaphosphorinanes.     

Polymerizability of methyl substituted 1,3-dioxolanes

The polymerization of 4-methyl-, 4,4-dimethyl-, cis-4,5-dimethyl-, and trans-4,5-dimethyl-1,3-dioxolanes was investigated with boron trifluoride etherate and the perchloric acid-acetic anhydride binary system as initiators. The polymerization of 4-methyl-1,3-dioxolane ( 1 ) involves an equilibrium between monomer and polymer, and the polymer consists of alternating oxypropylene and oxymethylene units. The thermodynamic parameters for the polymerization were determined from the temperature dependence of the equilibrium monomer concentrations in the temperature range from ?20 to 5°C: ΔH_1c = ?3,2±0,2kcal/mol and ΔS = ?12,7±0,8 cal mol^?1 K^?1. Dimethyl substituted 1,3-dioxolanes are very reluctant to polymerize: only a liquid oligomer was obtained in poor yield from cis-4,5-dimethyl-1,3-dioxolane, and neither polymer nor oligomer was produced from 4,4-dimethyl- and trans-4,5-dimethyl-1,3-dioxolanes at temperatures above ?;78°C. The effect of methyl substituents on the cationic polymerizability of 1,3-dioxolanes is discussed from the thermodynamic point of view.     

Determination of absolute rate constants for radical polymerization and copolymerization of ethyl α-cyanoacrylate in the presence of effective inhibitors against anionic polymerization

The absolute rate constants of propagation k_p and of termination k_t of ethyl α-cyanoacrylate (ECNA) were determined in bulk at 30°C by means of the rotating sector method under conditions to suppress anionic polymerization; k_p = 1 622 1 · mol^?1 · s^?1 and k_t = 4,11 · 10⁸ 1 · mol^?1 · s^?1 for the polymerization in the presence of acetic acid, and k_p = 1610 1 · mol^?1 · s^?1 and k_t = 4,04 · 10⁸ l · mol^?1 · s^?1 for the polymerization in the presence of 1,3-propanesultone. The magnitude of k/k_t determined was 6,39 · 10^?3 l · mol^?1 · s^?1. The absolute rate constants for cross-propagation in ECNA copolymerizations were also evaluated. Quantitative comparison of the rate constants with those of common monomers and polymer radicals shows that the strong electron-withdrawing power of the ethoxycarbonyl and cyano groups enable the poly(ECNA) radical to add to monomers as fast as the other polymer radicals. The relatively high reactivity of ECNA, regardless of the type of attacking polymer radical, is interpreted by a transition state greatly stabilized by both the ethoxycarbonyl and the cyano groups.     

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.     

The polymerization of acenaphthylene by carbocation salts in nitrobenzene

Acenaphthylene was polymerized in nitrobenzene at 25°C by NO₂SbF₆, C₂H₅COSbF₆, C₆H₅COPF₆, and (C₆H₅)₂CHSbF₆. With monomer so rigorously purified that it contained only ca. 0,01 mol-% of inhibiting impurities the reaction pattern indicated propagation by unpaired cations, and a k = 23,3 ± 2 dm³·mol^?1·s^?1 (the first for this monomer) was obtained. There are at least two chain-breaking reactions of which one is the proton transfer to monomer which has K = 2,3 dm³·mol^?1·s^?1. The kinetic irregularities and colours which develop at high conversions are probably due to the formation of non-propagating allylic cations from unsaturated end-groups.