Anionic polymerization initiated by lithium diethylamide in organic solvents. II. Investigation of the polymerization of isoprene

The polymerization of isoprene, initiated by lithium diethylamide has been investigated in the presence of a number of additives. Kinetic results are interpreted on the basis of simultaneous initiation and propagation reactions. The effect of additives, particularly diethyl either, has a profound effect on both the rate of initiation and propagation. The active centers are believed to be ion-pairs with the lithium counterions solvated by both ether and monomer molecules, and the actual propagation reaction is believed to involve a rearrangement of the monomer, complexed to the lithium, and the growing polymeric chain.     

Anionic polymerization initiated by lithium diethylamide in organic solvents. III. Investigation of the polymerization of styrene

The polymerization of styrene, initiated by lithium diethylamide in mixtures of benzene and THF, has been investigated. Kinetic and molecular weight measurements are interpreted on the basis of simultaneous initiation and propagation steps, and the effect of solvation and coordination processes on these reactions is discussed. Initiation of polymerization is thought to involve addition of solvated lithium diethylamide ion-airs to styrene, giving species with diethylamide end groups. The possible influence of these end groups on the initiation is considered in terms of an intramolecular cyclization process. Propagation of polymerization is believed to involve polystyryllithium ion-pairs, solvated to varying extents by THF. No evidence has been found to suggest that chain transfer, or termination, reactions are an integral part of the polymerization process. The polymerization has a number of similarities to the alkyllithium-initiated polymerization of styrene, but also exhibits some interesting differences.     

Anionic polymerization with alkaline-earth counterion. II. Polymerization of styrene initiated by dicarbanionic oligostyrylbarium in THF

The propagation kinetics of anionic polymerization of styrene initiated by dicarbanionic oligostyrylbarium (PS⁼Ba⁺⁺) in THF are described. The apparent propagation rate constant k_p increases drastically with the degree of polymerization (DP) of living chains and tends at 20°C, for the highest molecular weight (DP ? 5000), to the value determined for monocarbanionic polystyrylbarium(PS^?)₂Ba⁺⁺. At given DP, the propagation step follows usual first-order kinetics with respect to monomer, and k_p is inversely proportional to carbanion concentration; as observed for (PS^?)₂Ba⁺⁺. Similar behavior is observed in the temperature range from ?60 to +20°C. The activation energy of the propagation is 4–5 kcal/mole (16.7–21 kJ/mole). It is shown that k_p may be considered as directly proportional to the dissociation constant K_d of ion pairs (～S^?Ba^++?S～ is considered as an ion pair ～(SBa)⁺S^?～). The striking variation of k_p with the DP living chains is interpreted in terms of cyclic living chains, in which both carbanionic ends are bound to the same cation. Values of the intramolecular dissociation constant K_d of ion pairs included in such a model are computed as a function of DP, and their variation is found to fit rather well with experimental data.     

Kinetics of polymerization initiated by peroxides containing heterocyclic groups. I. Kinetics of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide

The rate and degree of bulk polymerization of styrene and vinyl acetate initiated by difuroyl peroxide and, for comparison, by dilauroyl and dibenzoyl peroxides were measured at several temperatures as a function of the initiator concentration. Also the rates of initiation were determined by the inhibition method with Banfield's radicals. The rate of polymerization initiated by difuroyl peroxide appears to be lower than could be expected from the rate of initiation determined by the inhibition method and from the decomposition of difuroyl peroxide. In the case of polymerization of vinyl acetate there are significant deviations from the proportionality between R_p and the square root of the initiator concentration, which follows from the conventional kinetic scheme. The degrees of polymerization are also low, and the plots of P _n^?1 versus R_p are not linear. These deviations can be accounted for by postulating a retardation effect of the furan cycle and chain transfer to difuroyl peroxide.     

Anionic polymerization of acrylates. I. Polymerization of 2-ethylhexylacrylate in nonpolar solvents

Initiation with a combined initiator n-butyllithium/lithium tert-butoxide in the ratio 1:6 brings the anionic polymerization of 2-ethylhexylacrylate (EtHA) in toluene and n-heptane at temperatures between ?78 and ?20°C up to a quantitative conversion. In the initial stages of the process the molecular weight distribution (MWD) of the products is polymodal as a result of the stablizing function of the alkoxide; MWD of the final product after a complete consumption of the monomer is medium, being visibly dependent on the reaction temperature and without any distinct content of low-molecular weight components, which suggests a sufficient activity of all growth centers, and thus an essential restriction of side termination reactions.     

Emulsion polymerization of styrene. II. Effect of Ag(I) and Fe(II) on the polymerization of styrene initiated by potassium persulfate

The emulsion polymerization of styrene initiated by potassium persulfate catalyzed by Ag(I) and/or ferrous ions Fe (II) was studied. It was found that silver ions in conjunction with potassium persulfate accelerate the polymerization of styrene. Ferrous ions reduce the polymerization rate by termination reaction with primary radicals. Both silver ions and ferrous ions act as transfer agents with the result of lowering of the average molecular weight of the polymer.     

The effect of organic nitriles on the radiation induced polymerization of styrene

The effect of a range of 10 organic nitriles on the radiation-induced polymerization of styrene was studied. A dose rate of 4.4 rad s^?1 was used. A rate of polymerization of styrene (1.744 mol L^?1 of toluene solution) of 5.0 × 10^?7 mol L^?1 s^?1 was found. With organic nitriles present (styrene:nitrile ratio of 1:0.28) the rate of polymerization increased. Rates in the range of 5.5 × 10^?7 ?5.2 × 10^?6 mol L^?1 s^?1, depending on the nitrile present, were obtained. The polymers were partially characterized and evidence of involvement of each of the nitriles in the polymer chains was revealed. The increase in rate of polymerization has been attributed to the part played by nitrile radicals in the initiation of styrene polymerization. Radical yield values [as G(nitrile radical)] were derived from the relevant rate expressions. Values ranged from 2.7 to 49.5, depending on the particular nitrile. Corresponding values of G(nitrile radical) in the range of 5.1–129.4 were obtained by the manipulation of number-average molar mass data. Values of k_pk_t of approximately 2 × 10^?5 L mol^?1 s^?1 were found. Trommsdorff types of effect are absent from these systems.     

Anionic polymerization of lactones initiated by alkali graphitides. I. Polymerization of ϵ-caprolactone initiated by KC24

The influence of the reaction conditions (time, temperature, concentrations of the monomer, and the initiator) on the amount and composition of the oligomers and high molecular products formed during the heterogeneous anionic polymerization of ?-caprolactone was investigated. The polymerization was initiated by KC₂₄ in xylene or tetrahydrofuran. Conditions were found under which intra- and intermolecular transesterification was strongly suppressed, thus providing the opportunity for the formation of polyesters with viscometric molecular masses of more than 300,000 and good yields (80% and higher). The total quantity of products with a viscometric molecular mass below 2500 did not exceed 15%; that of the cyclic dimer was not in excess of 5%. Peculiar features of the KC₂₄ initiated polymerization are the insignificant rise in the number of oligomers and the formation of high polymers even in strongly diluted solutions of ?-caprolactone (0.2 mol/L and lower). The quantity and molecular mass of the polymers obtained decreased as the temperature increased. It was also established that the polymerization of the cyclic dimer of ?-caprolactone is not initiated by KC₂₄.     

The effect of the disperse composition of a titanium catalyst on the kinetic heterogeneity of isoprene polymerization centers

The kinetic heterogeneity of centers of isoprene polymerization on fractions of titanium catalyst particles is studied. It is found that the isoprene polymerization with a catalyst consisted of particles 0.03–0.14 μm in diameter involves centers of one type with low reactivity. On catalyst particles 0.15–4.50 μm in diameter, the active centers of polymerization of two types with high reactivity may be formed. The addition of modifiers, a reduced temperature of catalyst formation, and the hydrodynamic effect result in the appearance of a narrow fraction of particles 0.15–0.18 μm in diameter with one type of surface active center that generates high-molecular-mass cis-1,4-polyisoprene. The obtained results are in accordance with the concept of particles 0.15–4.50 μm in diameter as aggregates of the elementary crystallites of β-TiCl₃ connected via additional Al-Cl bonds to surface titanium atoms. At the same time, catalyst particles 0.03–0.14 μm in diameter are formed by the minimum number of elementary crystallites, where titanium atoms are bound to a smaller number of chlorine atoms.     

Block copolymers of styrene,isoprene, and ethylene oxide prepared by anionic polymerization. I. Synthesis and characterization

Anionic polymerization has been used as a technique for the synthesis of five-block copolymers of polystyrene (PS), polyisoprene (PI), and poly(ethylene oxide) (PEO). Two types of such polymers, PEO-PI-PS-PI-PEO and PEO-PS-PI-PS-PEO with varying PEO block length, have been prepared, using potassium naphthalene as the initiator and tetrahydrofuran as the solvent. The polymers were purified by extraction with ethyl acetate, diethyl ether, and water. After the addition of each monomer, a sample from the living polymer solution was taken and analyzed by spectroscopy (infared (IR) and proton magnetic resonance (PMR)), osmometry, and gel-permeation chromatography (GPC) to obtain information about composition, molecular weight and molecular weight distribution of the intermediate polymers. The five-block copolymers have also been characterized by the same techniques and by elemental analysis.     

A rapid‐injection NMR study of the effect of lithium alkoxides on the butyllithium‐initiated polymerization and propagation of styrene

In studies carried out in THF at −80°C, lithium n‐butoxide was found to speed up the initiation and to an even greater extent the rate of propagation in the alkyllithium‐initiated polymerization of styrene. Bulky alkoxides were found to slow down the rate of polymerization by slowing both initiation and propagation although initiation was decreased to a greater extent than propagation. Five equivalents of lithium tert‐butoxide stopped the initiation completely under these reaction conditions when n‐butyllithium was used as an initiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1157–1168, 1999     

Emulsion polymerization of styrene. III. Effect of Ti(III) and Cl(1) on the polymerization of styrene initiated by potassium persulfate

The emulsion polymerization of styrene initiated by potassium persulfate catalyzed by Ti⁺³ ions was studied. Two sources of Ti⁺³ ions were used: the titanium trichloride and titanium sulfate. It was found that the titanium ions used in conjunction with potassium persulfate decrease both the reaction rate and the average molecular weight. An even greater drop of reaction rate was noted when chlorine anions (TiCl₃) were present. The presence of these ions had a stabilizing effect on the polydispersity.     

Anionic polymerization of lactones initiated by alkali graphitides. II. Changes in the KC24 structure during polymerization of lactones

The structural changes in the potassium graphitide KC₂₄ in its interaction with ?-caprolactone, γ-butyrolactone and pivalolactone are examined by profilometric measurement and electron scanning microscopy. The interaction of KC₂₄ with a nonpolymerizable lactone-γ-butyrolactone proceeds without delamination of the graphitide. The polymerization of ?-caprolactone and pivalactone in the interlayer spaces of KC₂₄ leads to destruction of the initiators structure. An increase in the temperature and monomer concentration enhances the delamination of the graphitide.     

Kinetics and mechanism of emulsion polymerization initiated by oil-soluble initiators. II. Kinetic behavior of styrene emulsion polymerization initiated by 2,2′-azoisobutyronitrile

In order to clarify the general kinetic behavior of emulsion polymerization initiated by oilsoluble initiators, the emulsion polymerization of styrene initiated by 2,2′-azoisobutyronitrile was as a typical example, investigated thoroughly. The variations of the polymerization rate and the number of polymer particles produced with changes in emulsifier (sodium lauryl sulfate), initiator, and monomer concentrations initially charged and the reaction temperature were determined. It is shown from these experimental results that the kinetic behavior of this emulsion polymerization system is quite similar to that of styrene emulsion polymerization initiated by the water-soluble initiator, potassium persulfate despite the difference in the principal loci of radical production in both systems.     

Lipase-lipid complex as a resolution catalyst of racemic alcohols in organic solvents

A lipid-coated lipase was newly prepared and vigorously catalyzed the reaction of enantioselective esterification (resolution) of racemic alcohols in anhydrous and homogeneous organic solvents.     

The effects of aromatic solvents on the photopolymerization rates of isoprene,ethyl methacrylate,and styrene

The photochemical polymerization rates of isoprene, ethyl methacrylate, and of styrene in various aromatic solvents were measured. The average lifetimes of propagating radicals were measured by the rotating sector method. The polymerization rate constants, K_p, were determined and compared with dipole moments (μ) and Hammett σ constants for the aromatic solvents. Linear correlations of log(k_p/k_{p, benzene}) vs. μ and σ were obtained.     

Anionic polymerization of methyl methacrylate and tert-butyl acrylate initiated with the YCl3/lithium amide/nBuLi systems

The anionic polymerization of methyl methacrylate (MMA) was initiated with a mixture of lithium amide of various secondary amines and nBuLi in the presence of YCl₃, where an Y-ate complex was formed and an amide ligand on Y attacked MMA nucleophilically. In THF at −78 °C, PMMAs with narrow molecular weight distributions were obtained in high yields. The presence of a secondary amino group derived from the initiator at the polymer chain end was confirmed by MALDI-TOF-MS analyses. The initiating system using indoline as a secondary amine was effective for block copolymerization of MMA with tert-butyl acrylate (tBA), giving poly(MMA-b-tBA)s with narrow molecular weight distributions.     

The microwave radiation effect on the polymerization of styrene

Styrene was cured by microwave radiation at two different powers: 300 and 500 W. The temperature profile of the sample during the microwave curing process was determined to select a suitable temperature for comparison with the conventional method of cure. The results indicate a similar comparable temperature of about 80°C irrespective of the microwave power used. The percentage conversion of the cure was followed by Fourier transform infrared (FTIR) spectroscopy. The thermal polymerization at 79(±1)°C displayed a gradual increase in the rate of reaction at the gel effect from about 30 to 50% conversion of the reaction. The microwave cure at 300 and 500 W displayed a large and sharp gel effect from about 20 to 69 and 64% conversion of the reaction, respectively. The limiting conversion decreased with increase in microwave power which was also observed in the polymerization of methyl methacrylate (MMA). Based on similarity in temperature and reaction conditions, the 500 W cure was found to show a reaction rate enhancement of 190% and the 300 W cure 120%. A comparison of microwave induced reactions with thermal methods, therefore, must also specify the microwave power used. © 1996 John Wiley & Sons, Inc.