Dual influence of lithium chloride on the reactivity of polystyryllithium in ethereal solvents

Addition of LiCl to ethereal solutions of polystyryllithium retards propagation of the polymerization at low polymer concentration, but accelerates it at higher polymer concentrations. This phenomenon is accounted for by the dual action of LiCl. Its dissociation yielding free common Li⁺ ions which diminish the concentration of the reactive free polystyryl anions dominates at low electrolyte concentrations. However, at their higher concentrations the Li⁺ scavenging action of LiCl, resulting in the formation of LiClLi⁺ triple ions, becomes important, it reduces the concentration of the free Li⁺ ions and increases, therefore, the proportion of the reactive free polystyryl anions.     

Kinetic study of anionic oligomerization of styrene by quantitative SEC

By the method of the absolute quantitative SEC, a process of anionic oligomerization of styrene, initiated by n-butyl lithium, was followed. The concentration of 1–5-mer monodisperse species in different reaction times can be obtained by HPSEC separation. The results showed that the propagation rate constants increased with increasing chain length and converged to a constant. © 1996 John Wiley & Sons, Inc.     

Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters

Lithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at –78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (<1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO₄. Number-average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (>2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent-separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.     

Absolute propagation constants in vinyl polymerization

The determination of the individual rate constants in a reaction involving more than a single step is part of the basic knowledge required to understand the process itself. The history of the chain mechanism of vinyl polymerization is presented briefly. The techniques needed to measure the chain propagation step are discussed for the three basic mechanisms: free-radical, cationic, and anionic polymerization. Illustrative examples of the rate constants obtained are given, with stress placed on the monomers styrene and methyl methacrylate, which have the advantage of being able to be polymerized by all three or two of the mechanisms, respectively. This allows a comparison of propagation constants between mechanisms. Some factors influencing the magnitudes of the constants are mentioned, and some problems involved in specific cases are discussed. © 1999 Government of Canada. Exclusive worldwide publication rights in the article have been transferred to John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4467–4477, 1999     

Recent advances in the anionic synthesis of chain-end functionalized polymers

Recent results for the preparation of chain-end functionalized polymers using alkyllithium-initiated anionic polymerization are described. Termination with 4-chloro-1,1,1-trimethoxybutane has been used to prepare trimethoxy ortho ester (carboxyl)-functionalized polymers. Functionalization with the oxiranes, glycidoxypropyltrimethoxysilane, 3,4-epoxy-1-butene and 1,1,1-trifluoro-2,3-epoxypropane, has been investigated to prepare trimethoxysilyl-functionalized polymers, 1,3-diene-functionalized macro monomers and trifluoromethyl-functionalized polymers, respectively. Secondary amine-functionalized polymers have been prepared by termination with N-(benzylidene)methylamine and also using an N-benzyl tertiary amine-functionalized alkyllithium initiator followed by hydrogenolysis of the benzyl group.     

Comments on the determination of absolute rate constants in anionic polymerization

Claims have recently been made that absolute rate constants for chain propagation of the unassociated active centers can be made in systems where a high degree of association is present. Anionic polymerization of styrene in nonpolar solvents with lithium as counterion is a typical case. The conditions required to obtain these constants (and the associated aggregate dissociation constants) are described using data from styrene polymerization with lithium and potassium as counterions and data from o-methoxystyrene polymerization. The conclusion reached must be that the k_p and K_ds values obtained for styrene with counterion lithium cannot be obtained from existing literature data and are simply artifacts of the computer analysis. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1065–1068, 1998     

Anionic ring-opening polymerization behavior of trans-cyclohexene carbonate using metal tert-butoxides: Construction of living anionic ring-opening polymerization by lithium tert-butoxide

Anionic ring-opening polymerization (ROP) behavior of trans-cyclohexene carbonate (CHC) using metal alkoxides as initiators was investigated. As a result, lithium tert-butoxide-initiated ROP of CHC with a high-monomer concentration (10 M) at low temperature (−15 to −10°C) proceeded to afford a poly(trans-cyclohexene carbonate) (PCHC) without undesired side reactions such as mainly backbiting. The suppression of side reactions enables the control of the molecular weight (M_n = 2400–6100) of PCHC with low molar-mass dispersity values (M_w/M_n = 1.16–1.22). Furthermore, by increasing the feed ratio of the monomer to the initiator, the molecular weight increases proportionally, indicating a controllable polymerization. The results of a matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis, a kinetic study, and a chain extension experiment suggested a living nature of this ROP using lithium tert-butoxide.     

Quantitative amine functionalization of polymeric organolithium compounds with 3‐dimethylaminopropyl chloride in the presence of lithium chloride

The addition of lithium chloride promoted the coupling reaction of hydrocarbon solutions of poly(styryl)lithium (PSLi) and poly(isoprenyl)lithium (PILi) with 3‐dimethylaminopropyl chloride to form the corresponding ω‐dimethylamino‐functionalized polymers. Quantitative amine functionalization was achieved for PSLi and PILi in the presence of 1 and 10 equivalents, respectively, of LiCl in benzene; the functionalization efficiency was only 67% for PSLi and 85% for PILi in the absence of LiCl. The polymer products were characterized by size exclusion chromatography, thin‐layer chromatography, and amine end‐group titration. The pure amine‐functionalized polymers were isolated by silica gel column chromatography. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 145–151, 2000     

Estimation of activation parameters for the propagation rate constant of styrene

For a temperature range of −11.8–92.6°C, the propagation rate constant k_p of styrene has been determined with the use of pulsed-laser polymerization (PLP). The temperature dependency of the obtained k_p data was evaluated using the Arrhenius equation. The NLLS error-in-variables method (EVM) is recommended for this fit. The resulting activation energy is 32.6 kJ mol⁻¹ and the pre-exponential factor is 10^7.66 dm³ mol⁻¹ s⁻¹. A joint confidence interval for these parameters is given. © 1996 John Wiley & Sons, Inc.     

119Sn-NMR evidence for 2,1-initiation in the anionic polymerization of butadiene with trialkyltin lithium

Low molecular weight polybutadienes and styrene butadiene copolymers were anionically prepared with trialkyltin lithium initiator and end-capped with either hydrogen or a trialkyltin group. These polymers were prepared with a variety of microstructures. Analysis by ¹¹⁹Sn-NMR and comparison to model compounds showed no cis-1,4-initiation of the butadiene. The initiation sites found were trans-1,4- and both 2,1- and 1,2-additions of the tin-lithium bound to a 1,3-butadiene. At low levels of added polar modifier, the 2,1-addition predominated. The ¹¹⁹Sn-NMR spectra allowed the assignment of the sequence distribution associated with the nearest eight main chain carbon atoms (2-4 monomer units) adjacent to the tin end groups. No initiation could be detected involving the styrene comonomer, but incorporation of styrene was detected as the first or second unit after initiation. The reaction of the allyl-tin end groups of these polymers with 1,2-napthoquinone was followed by NMR and was used to assign the peaks associated with 1,2-addition of the trialkyltin lithium to 1,3-butadiene. © 1995 John Wiley & Sons, Inc.     

提高聚环氧丙烷分子量的研究

本文采用丙二醇—钾、丙二醇引发环氧丙烷（PO）的阴离子聚合，同时加入络合剂，发现聚合反应速度加快，同时能有效提高聚环氧丙烷（PPO）的分子量。通过探索合成工艺条件，得到了■为4，000的线型聚环氧丙烷。     

苯乙烯阴离子本体聚合引发剂缔合及其机理的研究

分别以正丁基锂和叔丁基锂为引发剂,采用自制管式流动反应装置,对较高温度下苯乙烯阴离子本体聚合动力学进行了研究.证实了正丁基锂主要以六元缔合结构形式引发聚合,并导致超分子团聚体的形成,从而使进一步的聚合因单体扩散受阻而受到限制,并伴随聚合转化率停滞平台（SCP）的产生.随后由于前期聚合累积的能量,使超分子结构完全解离.聚合温度越高,SCP持续时间越短.结果还表明,在正丁基锂引发剂中,存在一个以六元缔合结构为基础形成的更大的缔合体结构.原子力显微镜照片显示,超分子结构的直径分别为20～30nm和50～60nm.此外,在阴离子聚合过程中活性种的缔合结构只决定于初始引发剂的分子结构,而不同活性种缔合结构对阴离子聚合的链增长存在很大影响,从而解释了采用不同结构的锂系引发剂引发苯乙烯单体聚合时聚合速率存在巨大差异的原因.     

An evaluation of the concept of unreactivity arising from head-group aggregation in anionic polymerizations

The long-standing presumption that aggregated organolithium species are unreactive in hydrocarbons has been examined for styryllithium head-groups. A computer based curve-fitting evaluation of the equilibrium constants assumed to govern the perceived dimer: singlet equilibria for polystyryllithium in benzene, cyclohexane, and toluene was done. From the calculated concentrations of singlet head-groups and the experimental propagation rates, the rate constant (k_p) values were obtained. Some values were approximately equal to or larger than those measured for the ion-pair in etherial solvents. These hydrocarbon solution values are improbably large, raising serious doubts about the validity of the mechanism upon which they are based. The data for the styrenic monomers in toluene also failed to lend support to that mechanism. © 1996 John Wiley & Sons, Inc.     

Controlled anionic synthesis of star‐shaped polystyrene by the incremental addition of divinylbenzene

Star polystyrenes were synthesized from polystyryllithium with an incremental procedure in which equally divided portions of divinylbenzene (DVB) were added periodically. When the addition of DVB was repeated, the content of the unreacted polystyryllithium dramatically decreased, and complete conversion was readily achieved. In the conventional linking reaction, however, in which all the required amounts of DVB were added at once, there was an incomplete conversion of the arm polymer. The arm number of star polymers also continuously increased upon the subsequent addition of DVB. The incremental‐addition method effectively synthesized star polystyrene, minimizing uncoupled polystyrene and reproducibly controlling the arm number of star polystyrene without the formation of gel polymers. The intrinsic viscosity of star polystyrene was measured to determine the highly branched structure of star polystyrene prepared by incremental or one‐shot addition. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 870–878, 2005     

Polymerization of butyl acrylate in anionic microemulsion

Butyl acrylate was initiated with KPS or BPO to polymerize at high monomer concentration in the microemulsions with SBOA (sodium 12-butinoyloxy-9-octadecenate) as emulsifier. The microemulsion remained clear or reddish. It was found that the constant polymerization period appeared in most microemulsions and the length of it varied with the concentration of monomer and the initiating rate. When microemulsions were initiated with KPS, the overall polymerization rate increased with the emulsifier concentration; while initiator was BPO, it showed the inverse tendency. It was attributed to the difference between the initiating mechanism of the two initiators. © 1996 John Wiley & Sons, Inc.     

Mechanism of the anionic polymerization of methyl methacrylate initiated by tetramethylammonium–triphenylmethide in tetrahydrofuran

A tetramethylammonium (TMA)–triphenylmethide (TPM) initiator generated in situ by the reaction of trimethyltriphenylmethylsilane with tetramethylammonium fluoride in tetrahydrofuran was found to have greater stability than the corresponding tetrabutylammonium or tetrahexylammonium derivatives. The predominant mode of degradation of TMA–TPM was found to be the TMA‐mediated methylation of TPM anions. The initiation of methyl methacrylate by TMA–TPM in tetrahydrofuran at ?78 °C was demonstrated to produce quantitative yields of poly(methyl methacrylate) with polydispersities of less than 1.1. Although the initiator efficiencies were low (9–40%) because of relatively slow initiation on the polymerization timescale, the initiation appeared to be rapid enough to give relatively narrow molecular weight distributions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 237–244, 2004     

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

A 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 (<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 C_β? C_γ bond and the migration of Li between C_α and C_γ atoms. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002