Anionic Polymerization Of Butadiene Research Articles

1,4-Dilithio-1,1,4,4-tetraphenylbutane in diethyl ether: An effective initiator for the living anionic polymerization of dienes

The anionic polymerization of butadiene initiated with 1,4-dilithio-1,1,4,4-tetraphenylbutane (LiTPB) in diethyl ether (DEE) gives polybutadiene (PBD) with high 1,2 content (>70%), narrow polydispersities (1.04 < Mw/Mn < 1.20), and predicted molecular weights. In THF, this polymerization does not work very well. After removal of DEE and addition of THF, the PBD dianion is end capped quantitatively by addition of 1,1-diphenylethylene (DPE) to give the diphenylalkyl end capped PBD dianion. Subsequent addition of methyl methacrylate at low temperatures results in the formation of well-defined PMMA-b-PBD-b-PMMA triblock copolymers. The results are accounted for by taking into account the effects of Li ion solvation on the BD initiation and end capping of the PBD anion by DPE. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 2198–2206, 2009

Application of online near infrared spectroscopy to study the kinetics of anionic polymerization of butadiene

Online Fourier-transform near infrared (FT-NIR) spectroscopy in combination with a fiber optic probe was utilized to study the kinetics of the anionic polymerization of butadiene. The conversion of the butadiene to methylene protons in the polymer was monitored in solution polymerization conditions by monitoring the absorbance at 1632 nm. The off-line gel permeation chromatography, GPC, technique was used to validate the online FT-NIR spectroscopy method. Butadiene polymerization kinetics in cyclohexane initiated with n-butyllithium at different initiator concentrations and temperatures was studied. A phenomenological kinetic expression for the anionic polymerization of butadiene in cyclohexane initiated with n-butyllithium was determined. The predictions of the kinetic expression were in agreement with kinetic data reported in the literature.

Modification of Model Ethylene‐Butene Copolymers Using Gamma Radiation and an Organic Peroxide

AbstractWell‐characterized linear ethylene‐butene copolymers with polydispersities lower than 1.1 were modified using gamma radiation and an organic peroxide with the purpose of assessing the relative importance and form of evolution of the chain‐linking processes with these two methods. The copolymers used in this work were obtained by hydrogenation of polybutadienes, which were synthesized by anionic polymerization of butadiene. Part of these materials were irradiated by gamma rays in a 60Co radiation facility and the rest was modified with 2,5‐dimethyl‐2,5 di(terbutyl peroxy)‐hexane in the molten state. As expected, the critical radiation dose and the critical concentration of peroxide required for the onset of gelation decreases with average molecular weight of the original copolymer. Although, the chain‐linking reactions govern the modification process, there is a fraction of molecular chains that suffers scission. The measurable fraction of molecules having molecular weights lower than the original quasi‐monodisperse copolymers is, for both processes, about 5% of the total modified polymer. On the post‐gel region, the gel amount increases continuously with the radiation dose and the peroxide concentration added to the copolymers. For the radiation modified polymers, the calculation of the evolution of the molecular weights assuming ideal network forming conditions agreed very well with the experiments both, before and after the gel point. This is not accomplished when the modification process is done with the use of peroxides. Also, the results obtained from the peroxide modification processes at low relative concentrations with respect to the critical one for gelation show that the evolution of the structural modification evolves at a considerable lower rate than that observed in the radiation results.

Viscoelastic behavior of fullerene end-capped linear polymers

Viscoelastic behavior of C 60-end-capped linear polybutadiene and C 60-end-capped poly(butadiene- co-styrene) with molecular weight ( M n) ranging from 30 to 130 kg/mol and with polydispersity index ( M w/ M n) ranging from 1.02 to 1.08 was investigated. These polymers were synthesized through anionic polymerization of butadiene and styrene in hexane, in which the living ends were capped with the C 60 via an alcoholate bridging. Rheological measurements showed that the polymer dynamics in the terminal zone were profoundly affected by the presence of fullerene, while the dynamics in the entanglement-plateau and at the terminal relaxation were nearly unaffected.

High Performance Poly(styrene-b-diene-b-styrene) Triblock Copolymers from a Hydrocarbon-Soluble and Additive-Free Dicarbanionic Initiator

A new hydrocarbon-soluble (additive-free) dicarbanionic organolithium initiator, obtained by a simple halogen-lithium exchange reaction (Gilman's reaction) from a diarylhalide containing a side C15 alkyl chain, has been designed and used to initiate the anionic polymerization of butadiene and styrene. The dilithiated species formed afford well-defined poly(styrene-b-butadiene-b-styrene) (SBS) triblock copolymers with a high percentage of 1,4-microstructure polybutadiene (91%) and excellent mechanical properties, such as ultimate tensile strength higher than 30 MPa and elongation at a break of 1000%. This represents a breakthrough in the synthesis of SBS polymers, one of the most used thermoplastic elastomers.

Continuous spin fractionation and characterization by size-exclusion chromatography for styrene–butadiene block copolymers

Linear and star-shaped styrene–butadiene block copolymers synthesized by anionic polymerization of butadiene and styrene were fractionated by applying a newly developed large-scale fractionation technique, named continuous spin fractionation (CSF). Their molecular weight and polydispersity index ( d = M w/ M n) were measured with size-exclusion chromatography and static light scattering. For the linear triblock copolymer a fractionation via temperature variation turned out to be better suited than the usual isothermal procedure. The star-shaped polymer with the d value of 1.33 was fractionated in two CSF steps to get the targeted sample, which has a considerably more uniform structure and a narrower molecular weight distribution ( d = 1.11). The corresponding starting linear diblock copolymer was fractionated in one step reducing d from 1.68 to 1.17. With one set of simple laboratory equipment, 1 kg polymer can be fractionated per day. Utilizing CSF, for the first time, we fractionated successfully the block copolymers.

An in situ study of the t-butyllithium initiated polymerization of butadiene in d-heptane via small angle neutron scattering and H1-NMR

We present a combined 1H-NMR and small angle neutron scattering in situ study of the anionic polymerization of butadiene using t-butyllithium as the initiator. Both initiation and propagation phases were explored. This combined approach allows the structural and kinetic characteristics to be accessed and cross compared. The use of the D22 instrument (ILL Grenoble) permits the attainment of Q approximately equal to 2 x 10(-3) A. This, in turn, led to the identification of coexisting large-scale and smaller aggregates during all stages of the polymerization. The smaller aggregates contain most of the reacted monomers. Their structure changes from high functionality wormlike chains at early stages of the reaction to starlike aggregates where the crossover occurs at a degree of polymerization of approximately equal to 40. The initiation event involved these small, high functionality (approximately equal to 120) aggregates that apparently consisted of cross-associated t-butyllithium with the newly formed allylic-lithium head groups. As the initiation event progressed the initiation rate increased while the functionality of these small aggregates decreased and their size increased. Propagation, in the absence of initiation, was found to have a rate constant that was molecular weight dependent. At approximately 11 kg/mol the measured polymerization rate was found to increase while no further structural changes were seen.

Modification of model ethylene–butene copolymers using an organic peroxide

Well-characterized linear ethylene–butene-1 copolymers with polydispersities lower than 1.1 were modified using an organic peroxide with the purpose of assessing the relative importance of chain-linking processes. The copolymers used in this work were obtained by hydrogenation of polybutadienes, which were synthesized by anionic polymerization of butadiene. All the copolymers were modified in the molten state using 2,5-dimethyl-2,5 di(terbutyl peroxy)-hexane with concentrations varying on a ample range. The changes in the molecular structure of the polymers due to the chemical attack of the peroxide were evaluated combining selective solvent extraction and GPC-MALLS techniques. As expected, the critical concentration required for the onset of gelation, Cc, decreases with average molecular mass of the original copolymer. When concentrations of peroxide below Cc are employed, the weight-average molecular mass of the modified copolymers augments and the molecular mass distribution gets wider as the concentration of peroxide added to the copolymer increases. Although, the chain-linking reactions govern the modification process, there is a fraction of molecular chains that suffers scission. The measurable fraction of molecules having molecular mass lower than the original quasi-monodisperse copolymers ranges between 15% and 24% of the total mass when the copolymers were modified with concentrations of peroxide below Cc. Beyond the onset of gelation, the gel amount increases continuously with the peroxide concentration added to the copolymers. At a given peroxide concentration, the amount of gel produced for a given polymer is higher the greater is the initial molecular mass of the modified polymer. The limiting amount of gel was between 90% and 98% of the total mass, which was reached using concentrations 20 times larger than the critical one. The efficiency of the peroxide as cross-linking agent seems to be dependent on the concentration of peroxide.

Aluminate and Magnesiate Complexes as Propagating Species in the Anionic Polymerization of Styrene and Dienes

AbstractThe influence of MgR2 and AlR3 additives on alkyllithium initiators in the anionic polymerization of butadiene has been investigated in non polar solvents. A strong decrease of the diene polymerization rate in the presence of the two Lewis acids was observed, similarly to that observed in the retarded anionic polymerisation of styrene. With n,s‐Bu2Mg, the percentage of 1,2 vinyl units increases with the [Mg]/[Li] ratio. This behavior is specific to magnesium derivatives bearing secondary alkyl groups and likely results from the additional complexation of lithium species by free dialkylmagnesium and/or a 1,4‐ to 1,2‐ chain end isomerization process during chain exchanges between polybutadienyl active chains and dormant ones attached to magnesium species. These reversible exchanges also lead to the formation of one supplementary chain by initial dialkyl magnesium which acts as reversible chain transfer agent. On the contrary with the R3Al/RLi systems the number of chains is only determined by the concentration of initial alkyllithium and no modification of the polybutadiene microstructure compared to lithium initiators (1,4 units = 80%) is noticed.Dialkyl magnesiate complexes with alkali metal derivatives (i.e. alkoxide) are also able to influence the stereochemistry of the styrene insertion during the propagation reaction. Polystyrenes with different tacticities ranging from predominantly isotactic (85% triad iso) to syndiotactic (80% triad syndio) can be obtained with these initiators.

A New View of the Anionic Diene Polymerization Mechanism

AbstractWe investigated the anionic polymerization of butadiene in d‐heptane solvent using tert‐butyl lithium as initiator. Two complementary techniques were used to follow the polymerization processes: 1H NMR and small angle neutron scattering (SANS). The time resolved 1H NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The initiation event commences slowly and then progressively accelerates. This indicates an autocatalytic mechanism. The microstructure of the first monomer units attached is to a high extent 1,2. The disappearance of initiator ‐‐‐ at about 10% monomer conversion ‐‐‐ signals the onset of the normal ∼6% vinyl content of the chain. Small angle neutron scattering was used to study the aggregation behavior of the carbon lithium head groups. It is well known that the polar head groups aggregate and form micellar structures. For dienes in non‐polar solvents the textbook mechanism assumes the formation of only tetramers during the propagation reaction. By combining 1H NMR and SANS results we were able to determine quantitatively the aggregation number during all stages of the polymerization. Our measurements show the existence of large‐scale structures during the initiation period. The initial degree of aggregation of more than 100 living polymer chains diminished as the polymerization progressed. In addition, even larger, giant structures with Nagg &gt;&gt;1000 and Rg ≈ 1000Å were found.

Diblock Copolymers with Azobenzene Side‐Groups and Polystyrene Matrix: Synthesis, Characterization and Photoaddressing

AbstractSummary: Diblock copolymers with a photoaddressable dispersed phase containing p‐methoxy substituted azobenzene side groups and a polystyrene matrix were synthesized and characterized. The block copolymers were prepared by a sequential living anionic polymerization of butadiene and styrene. The poly(1,2‐butadiene) segment was hydroborated and the hydroxy‐functions converted by a polymeranalogous reaction with the azo chromophore as side groups. The block copolymers were synthesized with different compositions by varying the length of the polystyrene segment and the length of the functionalized segment in order to obtain different morphologies. In this paper, for the first time a comparison of the cis‐trans photo‐isomerization behavior and photoaddressing with respect to different morphologies of the block copolymers is presented. To complete the comparison, the corresponding homopolymer and a statistical copolymer were also synthesized and investigated. A different photoaddressing behavior between homopolymer, statistical copolymer and the block copolymers was observed. One principal difference and advantage for photo addressable block copolymers is the lack of a formation of surface gratings which occurs in homopolymers and statistical copolymers.TEM of a poly(1,2‐butadiene)‐block‐polystyrene copolymer containing azobenzene side‐groups.magnified imageTEM of a poly(1,2‐butadiene)‐block‐polystyrene copolymer containing azobenzene side‐groups.

Real-time SANS and 1H-NMR studies during “living” anionic polymerization of butadiene in hydrocarbon media

Small angle neutron scattering (SANS) and high-resolution proton nuclear magnetic resonance spectra ( 1H-NMR) studies have been carried out in situ on the organolithium polymerization of butadiene in hydrocarbon media. The time resolved NMR measurements allowed us to evaluate quantitatively the kinetics of the processes involved. The combination of SANS and NMR methods offers a new way to characterize the aggregation behavior of the living chains quantitatively as a function of conversion. The present data show large-scale aggregated species exist during the initiation period. These aggregates of more than 160 living polymer chains diminished as the polymerization progressed.

Electronic excitation in anionic polymerization of butadiene: Nonempirical calculations of reaction complexes

AbstractA new mechanism of anionic polymerization of butadiene is proposed. In the elementary chemical act, the “living” polymer–monomer complex is excited into the low‐lying triplet state. This state has the character of charge (electron) and cation (Li+ or Na+) transfer from the terminal unit of the active center to the monomer molecule. In the framework of this concept, the probability of chemical bond formation is determined by spin density on radical centers of reagent molecules. Semiempirical and ab initio 6‐31G** quantum‐chemical calculations showed stable interaction between components of the complex in the ground electronic state (9–11 kcal/mol) and low energy levels of triplet excited states (&lt;14 kcal/mol). This new approach is shown to be useful in the analysis of polymerization kinetics and the microstructure of polybutadiene depending on the cation type and the ion pair state. The mechanism of cis‐trans isomerization in the terminal unit of the living polymer consists in concerted rotation about the CβCγ bond and the migration of Li between Cα and Cγ atoms. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Anionic Polymerization of Butadiene Initiated by Tributyltin Sodium. Kinetic Analysis of Induction Periods Generated by Transfer to Initiator Precursor

The kinetics of anionic polymerization of butadiene initiated by a new bimetallic initiator, tributyl-tin sodium, was studied. The mechanism was found to depend on the nature of solvent. Whereas in toluene the polymerizaton kinetics is similar to that observed with common organosodium initiators, in the presence of THF the initiation rate is two orders of magnitude lower, the polymerization rate is three orders of magnitude lower, and a marked induction period appears. The explanation and kinetic analysis of the latter phenomenon is given, based on a chain transfer reaction to the initiator precursor, hexabutyldistannane, followed by fast regeneration of initiator. This scheme enables a good fit to the experimental data. From the calculations it follows that for the appearance of a prolonged induction period two conditions should be satisfied: slow initiation, k j M o /k p I o <1, and intensive chain transfer to precursor, k tr /k p ≥10.The Scheme proposed can be used for the explanation of induction periods in other anionic and group transfer polymerization processes.

Stereospecificity of Alkaline Earth Metal Compounds in the Anionic Polymerization of N,N-Dimethylacrylamide

N,N-Dimethyllacrylamide (DMA) was polymerized with several iniators containing alkaline earth metal compounds such as dibutylmagnesium, calcium alkoxyalkoxide, bis(triphenylmethyl)barium, and magnesium and barium alkoxyalanates. The organobarium initiators, like the organolithium ones, give mainly isotactic, THF-insolube and partially crystalline polymer, whereas the structure and properties of the polymer obatined with R 2 Mg are similar to those reported for the Cs-initated polymer. The isotactic triad content is determined ny the naure of the alkaline earth metal used, and is almost independent of the presence of aluminium in the active center, and of the replacement of THF solvent by toluene. Therefore, the stereopecificity of the Group II metal compounds, with respect to the formation od isotactic poly- (DMA), increase with increasing counterion radius which is opposite to the tendency found for the polymerization with alkali metals. The situation is similar to that in the anionic polymerization of butadiene, where the effect of the counterion size on polymer structure for alkaline earth initiators is also opposite to that found with alkali meatls.

Quantum-Chemical Calculations of the Structure of the Triplet Reaction Complexes in Anionic Polymerization of Butadiene

A new mechanism of anionic polymerization of butadiene, radically changing the existing concepts on the structure and properties of the reaction complex, is suggested. It is stated that an elementary chemical process involves excitation into the low-lying triplet state of the “living” polymer–monomer complex, characterized as a transfer of a charge (electron) and cation (Li+ or Na+) from the terminal unit to the monomer molecule. In the framework of this concept, the probability of chemical bonding is determined by the spin density on the radical centers of reagent molecules. The semiempirical and ab initio 6-31G** calculations have revealed a strong interaction in the ground electronic state of the complex (5-10 kcal/mole) and low energies of the excited triplet levels (< 10 kcal/mole). A mechanism of cis-trans-isomerization in the terminal unit of the “living” polymer is suggested. The mechanism involves concerted rotation around the Cβ - Cβ bond and migration of Li between the Cα and Cγ atoms. The new approach is shown to be fruitful for microstructure analysis of polybutadiene in relation to the type of cation and the state of the terminal unit of the “living” polymer.

Effect of Lithium tert-Alkoxides on Anionic Polymerization of Butadiene Initiated with a Bifunctional Initiator

Polymerization of buta-1,3-diene initiated by bifunctional dilithium initiator in tert-butyl methyl ether, hexane and hexane-toluene mixtures was studied in the presence of Li tert-butoxide, 2-methylpentan-2-olate, 3-methylpentan-3-olate or 2,3-dimethylbutan-2-olate. The alkoxides lower the overall polymerization rate and affect, to a certain extent, microstructure of formed polymers. When applied in a concentration equal to that of the initiating centres, they lower the content of vinyl structures in polybutadiene by 10-12%. Increasing concentration of the alkoxide has no perceptible effect and, if used in 12-fold excess over the initiator, the content of 1,2-structures even increases. Polymers prepared in the presence of an alkoxide mostly have unimodal and narrow MWDs.

High-Yield Synthesis of Functionalized Alkoxyamine Initiators and Approach to Well-Controlled Block Copolymers Using Them

Reaction of ethylbenzene, 4-bromo-, 4-(ethoxycarbonyl)-, and 4-methoxyethylbenzenes with di-tert-butyl diperoxyoxalate at 35 °C in the presence of stable nitroxide radicals gave alkoxyamines in 50−91% yields. Lithiation of the 4-bromophenylalkoxyamine and subsequent treatment with DMF gave 4-formylphenylalkoxyamine in 95% yield, and the reduction of the 4-formylphenylalkoxyamine with NaBH4 yielded 4-(hydroxymethyl)phenylalkoxyamine in 89% yield. Anionic polymerization of butadiene (BD) with sec-BuLi and subsequent termination with 4-formylphenylalkoxyamine gave an end-functionalized poly(butadiene) [poly(BD)]. “Living” radical polymerization of styrene (St) initiated by the functionalized poly(BD) at 120 °C gave a poly(BD)-block-poly(St) with a Mw/Mn of 1.30. Anionic polymerization of hexamethylcyclotrisiloxane (D3) with 4-lithiophenylalkoxyamine gave poly(D3) with an alkoxyamine moiety at a polymer end. “Living” radical polymerization of St initiated by the functionalized poly(D3) gave poly(D3)-block-pol...

Classification of polar additives with respect to their influence on the microstructure in anionic polymerization of butadiene with butyllithium by transition energy measurements

Classification of polar additives with respect to their influence on the microstructure in anionic polymerization of butadiene with butyllithium by transition energy measurements

Classification of polar additives with respect to their influence on the microstructure in anionic polymerization of butadiene with butyllithium by transition energy measurements

A transition energy scale was established on the basis of di-Me indoaniline as org. dye for 23 mono- and bidentate polar additives. From polymn. expts. of isoprene with s-butyllithium in mixts. of n-hexane and the selected bases, the microstructure of polyisoprenes was detd. by 1H-NMR spectroscopy. The vinyl contents of these polymers could be satisfactorily correlated with the transition energy measurements. However, it turned out that esp. bidentate bases do not fit into this scheme. Obviously, besides their influence on the polarity of the reaction soln., they exhibit special interactions with the growing centers. The developed correlations allow the prediction of 1,2- and 3,4-linkages in polyisoprenes from anionic polymn. of isoprene with butyllithium in polar solvents in the presence of low concns., also of bases hitherto not investigated. The temp. dependence of the microstructure can likewise be estd. As in the case of butadiene, at least for weak bases, it was found that the vinyl contents depend primarily on the polarity of the reaction mixt. detd. by the base concn. and not on the molar ratio of base to initiator.