Kinetics of Anionic Polymerization of ε-Caprolactone (εCL). Propagation of Poly-ε=CL-K+ Ion Pairs

Kinetics of the anionic polymerization of ε-caprolactone (εCL) initiated with (CH₃)₃SiO^?K⁺ and carried out in THF solution has been studied in the temperature range from 0 to 20°C by using a calorimetric method. From the kinetic results and from conductometric measurements of the dissociation constant of the living Poly-εCL^?K⁺ ion pairs (K_D ²⁰ ? (4 ± 2) × 10^?10 mol/L), we concluded that at the conditions indicated above and for concentrations of active centers ranging from 10^?3 to 3.7 × 10^?2 mol/L, propagation proceeds on the ion pairs and is disturbed neither by dissociation nor by the formation of higher aggregates. For the polymerization of εCL proceeding on the poly-εCL^?K⁺     

Amphiphilic Biodegradable Poly(ϵ-caprolactone)-Poly(ethylene glycol) – Poly(ϵ-caprolactone) Triblock Copolymer Synthesis by Maghnite-H+ as a Green Catalyst

Amphiphilic biodegradable (PCL-PEG-PCL) triblock copolymers have been successfully prepared by the ring opening polymerization of ?-caprolactone (CL) in the presence of poly(ethylene glycol) (PEG) at 80°C employing Maghnite-H⁺ a non-toxic Montmorillonite clay as catalyst. Maghnite-H⁺ reacts as a solid source of protons to induce ?-caprolactone polymerization. The triblock architecture, molecular weight and thermal properties of the copolymers were characterized by NMR spectra, GPC and DSC analyses. The effect of Maghnite-H⁺ proportion and PEGs on the rate of copolymerization and on average molecular weight of resulting copolymers was studied. A cationic mechanism for the copolymerization reaction was proposed.     

Silolene-Bridged zirconocenium polymerization catalysts

A new silolene-bridged compound, racemic (1,4-butanediyl) silylene-bis (1-η⁵-in-denyl) dichlorozirconium ( 1 ) was synthesized by reacting ZrCl₄ with C₄H₈Si (IndLi)₂ in THF. 1 was reacted with trialkylaluminum and then with triphenylcarbenium tetrakis (penta-fluorophenyl) borate ( 2 ) to produce in situ the zirconocenium ion ( 1 ⁺). This “constraint geometry” catalyst is exceedingly stereoselective for propylene polymerization at low temperature (T_p = ?55°C), producing refluxing n-heptane insoluble isotactic poly(propylene) (i-PP) with a yield of 99.4%, T_m = 164.3°C, δH_f = 20.22 cal/g and M?_w = 350 000. It has catalytic activities of 10⁷?10⁸ g PP/(mol Zr · [C₃H₆] · h) in propylene polymerization at the T_p ranging from ?55°C to 70°C, and 10⁸ polymer/(mol Zr · [monomer] · h) in ethylene polymerization. The stereospecificity of 1 ⁺ decreases gradually as T_p approaches 20°C. At higher temperatures the catalytic species rapidly loses stereochemical control. Under all experimental conditions 1 ⁺ is more stereospecific than the analogous cation derived from rac-dimethylsilylenebis (1-η⁵-indenyl)dichlorozirconium ( 4 ). The variations of polymerization activities in ethylene and in propylene for T_p from ?55°C to +70°C indicates a Michaelis Mention kinetics. The zirconocenium-propylene π-complex has a larger insertion rate constant but lower thermal stability than the corresponding ethylene π-complex. This catalyst copolymerizes ethylene and propylene with reactivity ratios of comparable magnitude r_E ? 4r_p. Furthermore, r_E.r_p ? 0.5 indicating random copolymer formation. Both 1 and 4 activated with methylaluminoxane (MAO) exhibit much slower polymerization rates, and, under certain conditions, a lower stereo-selectivity than the corresponding 1 ⁺ or 4 ⁺ system. © 1994 John Wiley & Sons, Inc.     

Electrochemical Polymerization of Methylene Green

The electrochemical polymerization of methylene green has been carried out using cyclic voltammetry. The electrolytic solution consisted of 4° 10^?3 mol/L methylene green, 0.1 mol/L NaNO₃ and 1 × 10^?2 mol/L sodium tetraborate with pH 11.0. The temperature for polymerization is controlled at 60°C. The scan potential is set between ?0.2 and 1.2 V (vs. Ag/AgCl with saturated KCl solution). There are an anodic peak and a cathodic peak on the cyclic voltammogram of poly (methylene green) at pH≤3.8. Both peak potentials shift towards negative potentials with increasing pH value, and their peak currents decrease with increasing pH value. Poly (methylene green) has a good electrochemical activity and stability in aqueous solutions with pH≤3.8. The UV‐Visible spectrum and FTIR spectrum of poly (methylene green) are different from those of methylene green.     

Polymerization of Methyl Methacrylate in the Presence of Imidazole Derivatives. Kinetics and Polymer Structure

The kinetics of the polymerization of methyl methacrylate (MMA) in the presence of imidazole (Im), 2-methylimidazole (2MIm), or benz-imidazole (BIm) in tetrahydrofuran (THF) at 15–40°C was investigated by dilatometry. The rate of polymerization, R_p , was expressed by R_p = k[Im] [MMA]², where k = 3.0 × 10^?6 L²/(mol² s) in THF at 30°C. The overall activation energy, E_a , was 6.9 kcal/mol for the Im system and 7.3 kcal/mol for the 2MIm system. The relation between logR_p and 1 T was not linear for the BIm system. The polymers obtained were soluble in acetone, chloroform, benzene, and THF. The melting points of the polymers were in the range of 258–280°C. The ¹H-NMR spectra indicated that the polymers were made up of about 58–72% of syndiotactic structure. The polymerization mechanism is discussed on the basis of these results.     

Synthesis and rheology of biodegradable poly(glycolic acid) prepared by melt ring‐opening polymerization of glycolide

Ring‐opening polymerization (ROP) of glycolide was studied in melt conditions and in the presence of two different initiators: 1‐dodecanol and 1,4‐butanediol and tin(II) 2‐ethylhexanoate as catalyst. Its subsequent polymerization provided poly(glycolic acid) with controlled molar masses ranging from 2000 to 42,000 g/mol with well‐defined structures characterized by NMR. Their thermal properties were evaluated by DSC analysis, and a glass transition temperature at infinite molar mass (T_g∞) of 44.8 °C was thus calculated. From rheological data, the critical molar mass for entanglement, M_c, was estimated to be near 11,000 g/mol. Furthermore, in situ polymerizations were also performed between the plates of the rheometer within a same temperature range from 210 to 235 °C. The variation of the storage and loss moduli during the polymerization step have been monitored by time sweep oscillatory experiments under an angular frequency ω = 10 rad/s. Finally, the development of an inverse rheological method allowed to calculate the bulk polymerization kinetics in the temperature range 200–230 °C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1440–1449, 2009     

Kinetics of anionic polymerization of α-methylstyrene in tetrahydrofuran and toluene mixed solvents

The kinetics of anionic polymerization of α-methylstyrene with Na⁺ as counterion have been studied in mixed solvents of tetrahydrofuran (THF) and toluene in various compositions at ?25 to 5°C. The ion-pair rate constant k(_±) increases by about a factor of 50 at ?10°C, whereas the activation energy decreases from 5.1 to ?2.2 kcal/mole, when THF in the mixed solvent increases from 30 to 100 vol-%. The plot of log k(_±) against (D ? 1)/(2D + 1) is a curve, where D is the dielectric constant of the medium. This deviation from linearity is explained in terms of propagation by two types of ion-pairs.     

Anionic Polymerization of α-Methylstyrene. IX. Nature of the Propagating Species

Abstract

The nature of the initiating and propagating species involved in the anionic polymerization of α-methylstyrene has been explored. The earlier hypothesis that multimodal GPC molecular weight distributions in polymers arise solely out of different reaction steps or different ion-pair mechanisms being involved has been modified for poly-α-methylstyrene. Multimodal GPC molecular weight distributions in poly-α-methylstyrene initiated with potassium at 25°C and polymerized at 25°C or higher in THF, p-dioxane, or cyclohexane as solvents have been ascribed to the presence of two different types of tetramers which grow simultaneously but at different rates, each responding to its own well-defined thermodynamic equilibrium and yielding dormant and living polymers. Reaction schemes describing the initiation (at 25°C) and propagation reactions (between -25 and 60°C) in the polymerization (in solution of THF as well as in bulk) of α-methylstyrene initiated with potassium-naphthalene, butyl-lithium, and butyllithium-tetramethylethylenediamine (TMEDA) have been presented. The role of coordinating agents naphthalene and TMEDA in changing irreversible propagations into reversible ones has been emphasized.     

Radical polymerization behavior of trimethoxyvinylsilane

Trimethoxyvinylsilane (TMVS) was quantitatively polymerized at 130 °C in bulk, using dicumyl peroxide (DCPO) as initiator. The polymerization of TMVS with DCPO was kinetically studied in dioxane by Fourier transform near‐infrared spectroscopy. The overall activation energy of the bulk polymerization was estimated to be 112 kJ/mol. The initial polymerization rate (R_p) was expressed by R_p = k[DCPO]^0.6[TMVS]^1.0 at 120 °C, being closely similar to that of the conventional radical polymerization involving bimolecular termination. The polymerization system involved electron spin resonance (ESR) spectroscopically observable polymer radicals under the actual polymerization conditions. ESR‐determined apparent rate constants of propagation and termination were 13 L/mol s and 3.1 × 10⁴ L/mol s at 120 °C, respectively. The molecular weight of the resulting poly(TMVS)s was low (M_n = 2.0–4.4 × 10³), because of the high chain transfer constant (C_mtr = 4.2 × 10^?2 at 120 °C) to the monomer. The bulk copolymerization of TMVS (M₁) and vinyl acetate (M₂) at 120 °C gave the following copolymerization parameters: r_l = 1.4, r₂ = 0.24, Q₁ = 0.084, and e₁ = +0.80. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5864–5871, 2005     

Ring opening polymerization of tetrahydrofuran catalysed by maghnite-H+

The cationic ring-opening polymerization of tetrahydrofiiran using maghnite-H~+ is reported.Maghnite-H~+,is a non-toxic solid catalyst issued from proton exchanged montmorillonite clay.Polytetrahydrofuran,also called "poly(butandiol) ether",with acetate and hydroxyl end groups was successfully synthesized.Effects of reaction temperature, weight ratio of initiator/monomer and reaction time on the conversion of monomer and on the molecular weight are investigated.A cationic mechanism of the reaction was proposed.This chemistry can be considered as a suitable route for preparing poly(THF) as a soft segment for thermoplastic elastomers.     

Synthesis of poly(D,L‐lactic acid‐alt‐glycolic acid) from D,L‐3‐methylglycolide

D ,L ‐3‐Methylglycolide (MG) was synthesized via two step reactions with a good yield (42%). It was successfully polymerized in bulk with stannous octoate as a catalyst at 110 °C. The effects of the polymerization time and catalyst concentration on the molecular weight and monomer conversion were studied. Poly(D ,L ‐lactic acid‐co‐glycolic acid) (D ,L ‐PLGA50; 50/50 mol/mol) copolymers were successfully synthesized from the homopolymerization of MG with high polymerization rates and high monomer conversions under moderate polymerization conditions. ¹H NMR spectroscopy indicated that the bulk ring‐opening polymerization of MG conformed to the coordination–insertion mechanism. ¹³C NMR spectra of D ,L ‐PLGA50 copolymers obtained under different experimental conditions revealed that the copolymers had alternating structures of lactyl and glycolyl. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4179–4184, 2000     

Controlled synthesis of poly(dimethylsiloxane) homopolymers using high‐vacuum anionic polymerization techniques

The controlled synthesis of poly(dimethylsiloxane) homopolymers (PDMS) using hexamethyl(cyclotrisiloxane) monomer (D₃), a mixture of ciclohexane/tetrahydrofuran 50/50 v/v and sec‐Bu^–Li⁺ as initiator was studied using different experimental conditions, and whole‐sealed glass reactors according to standards procedures in high‐vacuum anionic polymerization. It was observed that polydispersity indexes (PD) and conversions strongly depend on temperature and reaction times. For PDMS homopolymers with molar masses below 100,000 g/mol, high conversion (>90%) and PD < 1.1 can be achieved at long reaction times (24 h) and mild temperature conditions (below or up to 30 °C). On the other hand, to synthesize PDMS homopolymers with molar masses higher than 100,000 g/mol and PD < 1.1 it is necessary to increase the temperature up to 50 °C and decrease the reaction time (8 h). However, under these reaction conditions, it was observed that the conversion decreases (about 65–70% conversion is achieved). Apparently, the competition between propagation and secondary reactions (redistribution, backbiting, and reshuffling) depends on the molar masses desired. According to the results obtained in this study—which were compared with others found in the scientific literature—propagation is favored when M_n < 100,000 g/mol, whereas secondary reactions seem to become important for higher molar masses. Nevertheless, model PDMS homopolymers with high molar masses can still be obtained increasing the reaction temperature and shortening the total reaction time. It seems that the combined effect of these two facts favors propagation against secondary reactions, and provides model PDMS homopolymers with molar masses quite close to the expected ones. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4774–4783, 2009     

Calcium and strontium,and zinc (phenazine)−· species

Calcium and strontium react with phenazine in tetrahydrofuran (THF) at ca 20 ° C to yield red solutions containing paramagnetic species based on (phenazine)⁻· (ESR characterization). Zinc reacts in THF in the presence of zinc chloride or bromide, or without metal halide in pyridine, to yield green or red ESR-active solutions also based on (phenazine)⁻·, and then, for the reaction in pyridine, a brown paramagnetic solid of composition Zn(phenazine)(pyridine)₂.     

Direct two-step synthesis of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate–acrylic acid block copolymer by RAFT polymerization

A series of narrow-MMD polymers with the molecular mass from 33 × 10³ to 123 × 10³ (polydispersity coefficient 1.08–1.16) were synthesized by bulk polymerization of n-butyl acrylate [2,2′-azobis(isobutyronitrile), 60°C] in the presence of a low-molecular-mass RAFT agent, dibenzyl trithiocarbonate. Then, polymerization of acrylic acid was performed in aqueous-alcoholic solution (ammonium persulfate, 70°C) in the presence of the obtained polymers, and a series of n-butyl acrylate–acrylic acid block copolymers with the molecular masses from 22 × 10³ to 81 × 10³ (polydispersity coefficient 1.07–1.13) were prepared. In aqueous-alcoholic solutions of the synthesized copolymers, there are nanoparticles whose size varies from 5 tо 65 nm and increases with an increase in the molecular mass of the copolymer and in the concentration of water in the solvent.     

Molar volumes of aqueous and ethylene glycol solutions of tetrahydrofuran

The densities of ethylene glycol solutions of tetrahydrofuran (THF) with 0–20 mol % THF were measured at 20–60°C and atmospheric pressure to an accuracy of 5 × 10⁻⁵ g/cm³. The apparent molar volumes of THF in the solutions were calculated and their concentration and temperature dependences determined. The results were compared with the apparent molar volumes of THF in aqueous systems calculated from the literature data. Minima were found on the concentration dependence of the apparent volume of THF for both aqueous and ethylene glycol solutions and changed differently as the temperature increased. The data obtained were discussed from the standpoint of solvophobic effects in aqueous and ethylene glycol solutions of THF.     

Polymerization of 1,3‐dienes with functional groups. II. Free‐radical polymerization of N‐(2‐methylene‐3‐butenoyl)piperidine

The free‐radical homopolymerization and copolymerization behavior of N‐(2‐methylene‐3‐butenoyl)piperidine was investigated. When the monomer was heated in bulk at 60 °C for 25 h without an initiator, about 30% of the monomer was consumed by the thermal polymerization and the Diels–Alder reaction. No such side reaction was observed when the polymerization was carried out in a benzene solution with 1 mol % 2,2′‐azobisisobutylonitrile (AIBN) as an initiator. The polymerization rate equation was found to be R_p ∝ [AIBN]^0.507[M]^1.04, and the overall activation energy of polymerization was calculated to be 89.5 kJ/mol. The microstructure of the resulting polymer was exclusively a 1,4‐structure that included both 1,4‐E and 1,4‐Z configurations. The copolymerizations of this monomer with styrene and/or chloroprene as comonomers were carried out in benzene solutions at 60 °C with AIBN as an initiator. In the copolymerization with styrene, the monomer reactivity ratios were r₁ = 6.10 and r₂ = 0.03, and the Q and e values were calculated to be 10.8 and 0.45, respectively. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1545–1552, 2003     

Polar,functionalized diene‐based materials. V. Free‐radical polymerization of 2‐[(N‐benzyl‐n‐methylamino)methyl]‐1,3‐butadiene and copolymerization with styrene

2‐[(N‐Benzyl‐N‐methylamino)methyl]‐1,3‐butadiene (BMAMBD), the first asymmetric tertiary amino‐containing diene‐based monomer, was synthesized by sulfone chemistry and a nickel‐catalyzed Grignard coupling reaction in high purity and good yield. The bulk and solution free‐radical polymerizations of this monomer were studied. Traditional bulk free‐radical polymerization kinetics were observed, giving polymers with 〈M_n〉 values of 21 × 10³ to 48 × 10³ g/mol (where M_n is the number‐average molecular weight) and polydispersity indices near 1.5. In solution polymerization, polymers with higher molecular weights were obtained in cyclohexane than in tetrahydrofuran (THF) because of the higher chain transfer to the solvent. The chain‐transfer constants calculated for cyclohexane and THF were 1.97 × 10^?3 and 5.77 × 10^?3, respectively. To further tailor polymer properties, we also completed copolymerization studies with styrene. Kinetic studies showed that BMAMBD incorporated into the polymer chain at a faster rate than styrene. With the Mayo–Lewis equation, the monomer reactivity ratios of BMAMBD and styrene at 75 °C were determined to be 2.6 ± 0.3 and 0.28 ± 0.02, respectively. Altering the composition of BMAMBD in the copolymer from 17 to 93% caused the glass‐transition temperature of the resulting copolymer to decrease from 64 to ?7 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3227–3238, 2001     

Kinetics of the Copolymerization of Methyl Vinyl Ketone and Acrylamide Initiated by the Adduct of Methyl Vinyl Ketone and Imidazole

N-(Butyl-3-one)imidazole acts as an initiating adduct which is formed in the anionic polymerization of methyl vinyl ketone (MVK) induced by imidazole (Im) and is directly formed from Im and the MVK monomer. The kinetics of the anionic homopolymerization of MVK and acrylamide (AAm) under argon in the presence of the adduct were investigated in tetrahydrofuran (THF). The rate of polymerization for the MVK system is expressed as R_p = k[Adduct] [MVK], where k = 3.1 × 10^?6 L/(mol·s)in THF at 30°C. The overall activation energy, E_a , was found to be 5.34 kcal/mol. The R_p for the AAm system is expressed as R_p = k[Adduct] [AAm], where k = 6.8 × 10^?6 L/(mol·s) in THF at 30°C, with E_a 7.78 kcal/mol. The mechanism of the polymerization induced by the initiator adduct is discussed on the basis of these results.     

Calorimetric Measurements of the Complexation of Cyclosporin A,Ascomycin, Fujimycin,and Rapamycin with Lithium Chloride and with an Immunophilin

Solutions (2 ml) of small linear and cyclic peptides ( 4–11 ), of a peptolide containing nine amino acids and a lactate moiety ( 12 ), of the cyclic undecapeptide cyclosporin A (CS, 1 ), and of the macrolides ascomycin, fujimycin, and rapamycin ( 13–15 ) in THF were added to excess LiCl, LiBr, or LiClO₄ (up to 3000 equiv. in 40 ml THF) in a calorimeter (calorimetric titration). The enthalpies of interaction measured are in the range of ΔH = ?8 to ?37 kcal/mol. A similar experiment was carried out with one of the binding proteins of cyclosporin, the human cyclophilin A, to give the thermodynamic parameters for the complexation ΔH = ?16, ΔG° = ?10 kcal/mol, and ΔS° = ?20 cal/mol·deg. at 25° which corresponds to an equilibrium constant K = 2·10⁷ l/mol, in good agreement with the result of independent measurements using different methods. NMR Measurements of the macrolides in (D₈)THF containing LiCl show strong down-field shifts of signals of the H-atoms next to C?O and C–OH groups in these molecules.     

RAFT copolymerization of methacrylic acid and poly(ethylene glycol) methyl ether methacrylate in the presence of a hydrophobic chain transfer agent in organic solution and in water

RAFT polymerization of poly(ethylene glycol) methyl ether methacrylate (PEGMA, 1100 g mol^?1) was first performed using cyanoisopropyl dithiobenzoate (CPDB). The control of PEGMA homopolymerization, carried out in THF ([PEGMA] = 40 wt %) at 65 °C (reflux) using 2,2′‐Azobis(isobutyronitrile) (AIBN) as initiator, was shown by the linear increase of molar masses and the low polydispersity indices (PDI) observed with conversion and also by the determination of a high chain transfer constant (C_tr = 9.1) for CPDB in this system. Copolymerization of PEGMA with methacrylic acid (MAA) ([PEGMA]/[MAA] = 40/60) was then undertaken first in dioxane at 85 °C. High conversion (89%) was obtained in 3 h without any composition drift and with a good level of control (PDI < 1.40). When the polymerization was performed in water, a strong increase in polymerization rate was observed with almost quantitative conversion (98%) in 2 h without affecting the level of control of the final copolymers (PDI ～ 1.30). These last results were tentatively explained by the formation of hydrophobic domains in which the polymerization occurred as in bulk. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3045–3055, 2009