Equilibrium anionic polymerization of n-valeraldehyde

This paper describes an anionic polymerization of n-valeraldehyde (VA) in tetrahydrofuran (THF) initiated by benzophenone-monolithium complex in a high vacuum system. In spite of the deposition of the resulting polymer an equilibrium state between the monomer and the polymer was observed at a temperature range of ?90 to ?68°C. From the linear relationship between the equilibrium monomer concentration and the polymerization temperature, values of ?5.3 ± 0.3 kcal/mole and ?25.7 ± 1.4 cal/mole-deg, respectively, were evaluated for the enthalpy change and the entropy change in the present system. The effect of polar substituents on the polymerizability of aldehydes is discussed from the comparison of these values with those in the case of β-methoxypropionaldehyde.     

Equilibrium anionic polymerization of β-methoxypropionaldehyde

Anionic polymerization of β-methoxypropionaldehyde (MPA) was carried out in tetrahydrofuran (THF) by using benzophenone–monolithium complex as an initiator. An equilibrium between polymerization and depolymerization was observed at a temperature range of ?90 to ?70°C. From the temperature dependence of the equilibrium monomer concentration, thermodynamic parameters for the polymerization of MPA in THF were evaluated as follows: ΔH_ss = ?4.8 ± 0.2 kcal/mole, ΔH_SS = ?22.4 ± 1.3 cal/mole-deg, and (T_c)_ss = ?59°C. The thermodynamic change upon the conversion of liquid monomer to condensed polymer was computed from both the partial mixing energy of MPA with THF and the linear relationship between the equilibrium volume fraction of MPA monomer and that of the resulting polymer: ΔH_1c = ?4.7 ± 0.2 kcal/mole, ΔS_1c = ?19.5 ± 1.3 cal/mole-deg, and (T_c)_1c = ?35°C.     

Anionic polymerization of acrylates. III. Polymerization of 2-ethylhexyl acrylate initiated by lithium-tert-butoxide

The polymerization of 2-ethylhexyl acrylate (EtHA) initiated with lithium-tert-butoxide (t-BuOLi) in tetrahydrofuran (THF) and in the temperature range between ?60 and 20°C was investigated. The reaction rate is distinctly temperature-dependent and at ?60°C is already very low, similarly to the polymerization of methacrylates. Molecular weights of the polymers thus formed, particularly at higher temperatures, are inversely proportional to conversion of the monomer due to the slow initiation reaction. This is documented by the low consumption of alkoxide even at long reaction times, which also depends on the reaction temperature. At higher temperatures the polymerization stops spontaneously, due to the greater extent of autotermination reactions. The weak initiating efficiency of the alkoxide decreases still more with decreasing concentration of the monomer during the polymerization, as confirmed by the concentration dependence of the reaction rate in toluene at ?20°C. The results suggest a negligible initiating effect of alkoxides in complex bases, particularly at lower polymerization temperatures. © 1992 John Wiley & Sons, Inc.     

Equilibrium anionic polymerization of the isopropenyl monomers containing aromatic heterocycles

The anionic polymerization of three monomers, 2-isopropenyl-4,5-dimethyloxazole(I), 2-isopropenylthiazole(II), and 2-isopropenylpyridine(III), was studied in THF. These monomers produced red-colored living polymers on addition of sodium naphthalene or living α-methylstyrene tetramer as an initiator. It was observed that a considerable amount of monomer remained in the respective living polymer–monomer system, indicating that an equilibrium between the polymer and the monomer existed as in the case of α-methylstyrene. At lower temperatures, the conversion of the monomer to the polymer increased. The equilibrium monomer concentrations [M_e] were determined at different temperatures, and the heats (ΔH) and the entropies (ΔS°) of polymerization were obtained by plotting In(1/[M_e]) against 1/T as ΔH = ?9.4, ?6.8, and ?6.2 kcal/mole, ΔS°S = ?22.9, ?16.5, and ?16.6, eu for I, II, and III, respectively.     

Studies of higher temperature polymerization of n-butyl methacrylate and n-butyl acrylate

Free-radical acrylic polymerizations of n-butyl methacrylate and n-butyl acrylate at temperatures above 120°C show significant departure from classic free-radical kinetics. An extended model of depropagation, where the equilibrium monomer concentration varies with temperature and polymer content, is postulated and shown to adequately explain the data for n-butyl methacrylate. Intramolecular chain transfer and scission is postulated to explain the apparent reduction in molecular weight and rate of polymerization seen in n-butyl acrylate polymerization, with supporting experimental evidence found via electrospray-ionization mass spectrometry.     

Radiation-induced bulk polymerization of maleimide

Radiation-induced bulk polymerization of maleimide in both solid and liquid states was studied. Benzoquinone inhibited the liquid-state polymerization and retarded solid-state polymerization. The results of ESR study showed that solid monomer irradiated at 61°C. gave a spectrum, the concentration of which slowly decreased without changing the shape at 61°C. The radical detected at 61°C. was shown not to be the main propagating species. Overall rate polymerizations in the liquid and solid states were expressed, respectively, by first-order and zero-order rate equations with respect to the concentration of monomer. The overall rate constants in liquid and solid states were proportional to I^0.9 and I^1.0, respectively.     

Radiation-induced ionic polymerization of isobutyl vinyl ether in bulk

The radiation-induced ionic polymerization of isobutyl vinyl ether was investigated under conditions where the monomer was dried with molecular sieves. The investigation covered the temperature range from ?16°C to 90°C, and the dose-rate range from 10¹⁵ to 10²⁰ eV/g-sec, using both γ-rays and electrons. A very high overall activation energy of 15.9 kcal/mole was found for the process below 30°C. Above 30°C, however, the value of the overall activation energy dropped to 4.9 kcal/mole, a phenomenon which is ascribed to the solvation of the propagating carbonium ion below 30°C. The dose-rate dependence of the rate of polymerization was found to be 0.58 over the entire dose-rate range investigated. The molecular weight of the polymer was found to be far less sensitive to trace amounts of water than the rate of polymerization. The molecular weight of the polymer depended strongly on the irradiation temperature, reaching a maximum value of about 120,000 at 35°C. It is shown that at temperatures above 20°C regenerative chain transfer processes play an important role in determining the molecular weight of the polymer.     

p-Chlorophenyldiazonium hexafluorophosphate as a catalyst in the polymerization of tetrahydrofuran and other cyclic ethers

p-Chlorophenyldiazonium hexafluorophosphate is shown to be a convenient and effective catalyst for initiating the polymerization of tetrahydrofuran (TH) and other cyclic ethers. The polymerizations apparently proceed without any significant termination or transfer reactions (i.e., “living” polymers result), and materials of very high molecular weight can be obtained. A mobile monomer-polymer equilibrium for THF was obtained during polymerization and equilibrium conversions were determined at a number of temperatures. The ceiling temperature derived from these data was 84°C., the heat of polymerization was ?4.58 kcal./mole and the corresponding entropy change was ? 17.7 cal./°C.-mole. Hydrocarbons are suitable inert solvents for these polymerizations, but concentrated solutions must be used at ambient temperatures in order to stay above the required equilibrium monomer conceiitration and also to dissolve the catalyst which is insoluble in hydrocarbons. It was shown that acyclic ethers act as transfer agents in these polymerizations and that transfer with consequent reduction of molecular weight continues even after monomer-polymer equilibrium is reached. Cyclic ethers do not act as transfer agents but only copolymerize. Trimethyl orthoformate was shown to be a particularly effective transfer agent; it resulted in a polymer with methoxy endgroups and produced methyl formate as a by-product. The data obtained are consistent with a mechanism involving initiation by hydrogen abstraction and polymerization via tertiary oxonium ions associated with PF^?₆ gegenions. This gegenion is thought to be responsible for the “living” nature of the system.     

Equilibrium anionic polymerization of β-methoxycarbonylpropionaldehyde

β-Methoxycarbonylpropionaldehyde (MCPA) was polymerized in tetrahydrofuran (THF) with benzophenone–monolithium complex as the initiator. An equilibrium between the monomer and its polymer was observed in the temperature range of ?96 to ?78°C. MCPA had lower polymerizability than ether-substituted aldehydes and their corresponding unsubstituted aliphatic aldehydes in the temperature range. The thermodynamic parameters were evaluated from the temperature dependence of the equilibrium monomer concentration: ΔH_ss = ?4.3 ± 0.2 kcal/mole, ΔS_ss = ?21.9 ± 1.0 cal/mole deg, Tc_ss = ?76°C. Not only an ether substitution but also an ester substitution in propionaldehyde caused the decrease in the absolute values of the thermodynamic parameters for the aldehyde polymerization. These substituent effects may have been the result mainly of the strong intermolecular dipole–dipole interactions of polar groups in monomer states.     

Electroinitiated polymerization of 1,3-dioxolane in chlorinated hydrocarbons

The electrochemically initiated polymerization of 1,3-dioxolane has been investigated in 1,2-dichloroethane with tetrabutylammonium perchlorate as background electrolyte.The anode process is due to the monomer, and its intermediate oxidation products are probably the initiating species; once initiated, the polymerization reaches an equilibrium which is largely independent of the amount of the initially furnished charge.The conversion at equilibrium on the contrary depends on temperature and initial monomer concentration. The kinetic curves at 50° do not exhibit induction and acceleration periods but autocatalysis becomes important at lower temperature.The polymerization seems slower in dichloromethane, but the process trends to the same equilibrium conversion.The molecular weight of the polymers depends on temperature, monomer concentration and amount of initiating charge: apart from some chain transfer acting in the first stage of polymerization, the process exhibits “living” features in the increase of molecular weight with conversion.     

Anionic ring-opening polymerization of silacyclobutane derivatives

Anionic polymerizations of 1,1-dimethylsilacyclobutane, 1,1-diethylsilacyclobutane and 1-methyl-1-phenylsilacyclobutane were investigated. Addition of 5 mol % of butyllithium to a solution of 1,1-dimethylsilacyclobutane in THF-hexane (1 : 1) at −48°C provided poly(1,1-dimethylsilabutane) in 99% yield. M_n and M_w/M_n of the obtained polymer were 2400 and 1.10. This polymerization proceeded with a living nature. M_n increased in proportion as the yield of polymer increased. Addition of the second fresh feed of the monomer to the reaction mixture restarted polymerization of the second monomer at the same rate as in the initial stage. Addition of styrene to the living poly(1,1-dimethylsilabutane) provided a poly(1,1-dimethylsilabutane-b-styrene) block copolymer. It was also found that a polymerization of 1,1-diethylsilacyclobutane in THF-hexane at −48°C showed a living nature. In contrast, a polymerization of 1-methyl-1-phenylsilacyclobutane in THF at −78°C did not show a living nature. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3207–3216, 1997     

Living cationic polymerization of dihydrofuran and its derivatives

Cationic polymerization of 2,3‐dihydrofuran (DHF) and its derivatives was examined using base‐stabilized initiating systems with various Lewis acids. Living cationic polymerization of DHF was achieved using Et_1.5AlCl_1.5 in toluene in the presence of THF at 0 °C, whereas it has been reported that only less controlled reactions occurred at 0 °C. Monomer‐addition experiments of DHF and the block copolymerization with isobutyl vinyl ether demonstrated the livingness of the DHF polymerization: the number–average molecular weight of the polymers shifted higher with low polydispersity as the polymerization proceeded after the monomer addition. Furthermore, this base‐stabilized cationic polymerization system allowed living polymerization of ethyl 1‐propenyl ether and 4,5‐dihydro‐2‐methylfuran at ?30 and ?78 °C, respectively. In the polymerization of 2,3‐benzofuran, the long‐lived growing species were produced at ?78 °C. The obtained polymers have higher glass transition temperatures compared to poly(acyclic alkyl vinyl ether)s. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4495–4504, 2008     

Stereoregulation in the polymerization of methyl α-ethylacrylate by n-BuLi in toluene

The polymerization of methyl α-ethylacrylate was carried out in toluene by n-BuLi at various temperatures. The yield of the polymer decreased with increase in the polymerization temperature and at 30°C and above no polymer was obtained, indicating that the ceiling temperature of this monomer lay between 0 and 30°C. The isotacticity increased with an increase in the polymerization temperature and at 0°C a highly isotactic polymer was obtained. The fractionation of the polymer obtained at ?78°C showed that the polymer was a mixture of isotactic and syndiotactic ones. Upon the addition of a small amount of methanol or water in the polymerization mixture the isotacticity of the polymer increased while the yield decreased. Syndiotactic polymer was obtained in the polymerization by n-BuLi in tetrahydrofuran as well as by diisobutyl aluminum diphenylamide in toluene.     

Permanganate/glycine-initiated polymerization of acrylamide

The kinetics of aqueous polymerization of acrylamide with KMnO₄/glycine redox pair was studied in an atmosphere of nitrogen at 35 ± 0.2°C. The rate of polymerization was found to be first power on monomer, activator, and catalyst concentration. The overall energy of activation was calculated to be 15.66 kcal/deg mol (65.54 kJ/mol) between 30 and 50°C. The effects of various additives (alcohols, neutral salts, complexing agents, addition of catalyst) were studied. The dependence of the polymerization rate on the activator and catalyst concentration was studied in DMF-water mixture also. The molecular weight of polymer was determined at various temperatures of the reaction medium.     

First observation of equilibrium polymerization of cyclic sulfite

Cationic polymerization of a seven-membered cyclic sulfite ( 7CS ) was carried out with methyl trifluoromethanesulfonate as a catalyst in chlorobenzene. The final conversions of 7CS were 22, 41, 52, and 60% in the polymerizations at 25°C with the initial monomer concentrations of 3, 4, 5, and 6M, respectively. The calculated monomer concentration at equilibrium was evaluated as 2.4M in any case. The conversion of 7CS decreased as the polymerization temperature rose. These results support the fact that this polymerization is an equilibrium one. ΔH⁰ and ΔS⁰ in the polymerization were evaliuated as −0.765 kcal/mol and −4.18 cal/mol by Dainton's equation, respectively. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3235–3240, 1997     

Radical ring-opening polymerization of lipoates: Kinetic and thermodynamic aspects

The radical ring-opening polymerization of a lipoate-based monomer, ethyl lipoate, in bulk and in solution was studied at various temperatures and it was found that in all cases, only limited (plateau) conversions were reached, which were lower at higher temperatures and/or at higher dilutions. It was established that a monomer-polymer equilibrium exists with a corresponding ceiling temperature of 139°C. Due to the reversibility of the lipoate polymerization, when poly(ethyl lipoate) was heated to 150°C, it degraded and within 3 h, the molecular weight decreased to less than 15% of the initial value. Likewise, when the polymer was dissolved in anisole and a radical initiator was added, degradation was observed even at 60°C and it became increasingly pronounced at higher concentrations of the radical source. Due to the presence of multiple disulfide groups in the backbone, poly(ethyl lipoate) also degraded in the presence of reducing agents, such as tributylphosphine, yielding the reduced (dithiol) form of the monomer, ethyl dihydrolipoate.     

Equilibrium polymerization behavior in the cationic single ring‐opening polymerization of bicyclo orthoesters

The synthesis and cationic polymerization of the following bicyclo orthoesters were examined: 4‐ethyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 1,4‐diethyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 4‐ethyl‐1‐phenyl‐2,6,7‐trioxabicyclo[2.2.2]octane, 4‐ethyl‐1‐(4‐methoxyphenyl)‐2,6,7‐trioxabicyclo[2.2.2]octane, and 4‐ethyl‐1‐(4‐nitrophenyl)‐2,6,7‐ trioxabicyclo[2.2.2]octane. All the monomers underwent equilibrium polymerization, which was confirmed by the relationships between the polymerization temperature and monomer conversion. The obtained polymers afforded the original monomers via an acid‐catalyst treatment with a low reagent concentration in CH₂Cl₂ at 20 °C. The equilibrium monomer concentration was constant, regardless of the initial reagent concentration, in both polymerization and depolymerization. The bicyclo orthoesters with a bulky and electron‐withdrawing substituent showed a larger equilibrium monomer concentration. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3159–3167, 2001     

Analysis of DSC curve of dodecyl methacrylate polymerization by two-peak deconvolution method

Free radical polymerization of n-dodecyl methacrylate (DDMA) in bulk has been investigated by differential scanning calorimetry (DSC). Autoacceleration of reaction was observed at the temperatures 70, 80, and 90 °C, with 0.25, 0.5, and 1 wt% of initiator, and was absent at 100 °C. DSC curves obtained at the temperatures below 100 °C were characterized by two maxima. Two-peak deconvolution was used to separate DSC curve into two constitutive unimodal curves, i.e., to calculate the contribution of polydodecyl methacrylate formed before (first maximum) and after (second maximum) the onset of autoacceleration. The share of second maximum decreases as the polymerization temperature and initiator concentration are increased. As the organization of monomer is known to decrease with increasing temperature, it can be expected that the fraction of polymerized disordered phase of monomer (first maximum in DSC curve) is the highest at 90 °C. Our results confirm this prediction and are in good agreement with those observed from conversion versus time curves of DDMA polymerization.     

Preparation of functional polymers by living anionic polymerization: Polymerization of allyl methacrylate

The anionic polymerization of allyl methacrylate was carried out in tetrahydrofuran, both in the presence and in the absence of LiCl, with a variety of initiators, at various temperatures. It was found that (1,1-diphenylhexyl)lithium and the living oligomers of methyl methacrylate and tert-butyl methacrylate are suitable initiators for the anionic polymerization of this monomer. The temperature should be below −30°C, even in the presence of LiCl, for the living polymerization to occur. When the polymerization proceeded at −60°C, in the presence of LiCl, with (1,1-diphenylhexyl)-lithium as initiator, the number-average molecular weight of the polymer was directly proportional to the monomer conversion and monodisperse poly(allyl methacrylate)s with high molecular weights were obtained. ¹H-NMR and FT-IR indicated that the α CC double bond of the monomer was selectively polymerized and that the allyl group remained unreacted. The prepared poly(allyl methacrylate) is a functional polymer since it contains a reactive CC double bond on each repeating unit. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2901–2906, 1997     

Stereospecific polymerization of o-methoxystyrene by anionic initiators

o-Methoxystyrene was polymerized with n-butyllithium (n-BuLi), Na naphthalene, and K dispersion as initiators in tetrahydrofuran (THF) and toluene. The stereoregularity of the polymer was investigated by means of the NMR spectroscopy. The methoxy resonance of the spectrum split into ten components due to the tactic pentads. It was found by x-ray examination that the polymer obtained by n-BuLi in toluene at ?45°C was crystalline and highly isotactic. In THF, the stereospecificity of the polymerization was independent of the initiator, and the isotacticity of the polymer increased with increasing reaction temperature. In toluene, the stereospecificity depended on the initiator; i.e., n-BuLi gave a polymer with higher isotacticity than that given by phenylsodium. The fraction of isotactic triad of the polymer obtained by n-BuLi in toluene at ?78°C was more than 90%, but 50% at 50°C. The presence of ca. 1% THF in toluene led to a steep decrease in the isotacticity even at ?78°C. The tacticity of the polymer given by Na naphthalene was not affected by the existence of NaB(C₆H₅)₄ in THF. The polymerization in THF could be explained by Bovey's “single σ” process, while a penultimate effect was observed in the polymerization by n-BuLi in toluene.