Initiators For Anionic Polymerization Research Articles

Anionic polymerization of methyl methacrylate and chain-end modification via terminal-selective transesterification with bulky zincate

The anionic polymerization of methyl methacrylate (MMA) was investigated using dilithium tetra-tert-butylzincate (TBZL), which is a bulky zincate, as an initiator. Poly(methyl methacrylate) (PMMA) with a narrow molecular weight distribution was obtained by conducting the polymerization in toluene at −80 °C. Chain-end analysis revealed the formation of PMMA with a tert-butyl group at the α-end and a hydrogen atom at the ω-end. These results suggest the living nature of the present polymerization. However, a prolonged polymerization time or elevated temperature caused backbiting reactions. Postpolymerization modification of the formed PMMA was also investigated using TBZL as a transesterification catalyst. Chain-end analysis revealed that terminal-selective transesterification occurred only at the monomeric unit at the terminating chain end. Therefore, TBZL appears to play dual roles in the production of chain-end-modified PMMA: an initiator for anionic polymerization and a catalyst for terminal-selective transesterification.

Exotic alkyllithiums in a flash

Alkyllithiums are among the most reactive reagents synthetic chemists use. They’re reliable nucleophiles, lithiating reagents, and initiators of anionic polymerization. But because of their inherent reactivity, the conventional chemical wisdom is that it is impossible to make alkyllithiums that contain electrophilic groups. Such reagents would react with themselves long before they could react with anything else. Overturning that long-held belief, a team led by Kyoto University’s Aiichiro Nagaki and Suzuka College’s Jun-ichi Yoshida has found a way to make alkyllithiums that bear electrophilic groups, including epoxides, esters, and cyano moieties (Angew. Chem., Int. Ed. 2019, DOI: 10.1002/anie.201814088). To accomplish this feat, the researchers create and use the alkyllithiums using flash chemistry in a flow microreactor system. Controlling the temperature and time the alkyllithium reagent spends in the section of the reactor where it is formed (known as the residence time) is critical to the method’s s...

Initiation of anionic polymerization of acrylonitrile with tertiary amines and ethylene or propylene oxide: some mechanistic aspects

Fast growth of the polymer chain mechanism of the anionic polymerization of acrylonitrile under the action of bicyclic tertiary amine and ethylene oxide.

Acetylene-Functionalized Lithium Initiators for Anionic Polymerization. Powerful Precursors for “Click” Chemistry

Two novel anionic acetylene-functionalized initiators, 5-trimethylsilyl-4-pentynyllithium (TMSPLi) and 5-triethylsilyl-4-pentynyllithium (TESPLi), were synthesized and characterized by 1H NMR, 13C NMR, and GC-MS. TMSPLi was successfully used for the polymerization of styrene, but not for the polymerization of isoprene and butadiene. On the other hand, TESPLi exhibited all characteristics of an anionic initiator for the (co)polymerization of styrene, isoprene, and butadiene. TESPLi is ideal for the synthesis of living well-defined (co)polymers with acetylene end groups, perfect candidates for “click” reactions and at the same time possessing all the potential of living anionic polymerization for the synthesis of well-defined complex macromolecular architectures.

Catalytic chain transfer and its derived macromonomers

An overview is given of cobalt-catalyzed chain transfer in free-radical polymerization and the chemistry and applications of its derived macromonomers. Catalytic chain transfer polymerization is a very efficient and versatile technique for the synthesis of functional macromonomers. Firstly the mechanism and kinetic aspects of the process are briefly discussed in solution/bulk and in emulsion polymerization, followed by a description of its application to produce functional macromonomers. The second part of this review briefly describes the behavior of the macromonomers as chain transfer agents and/or comonomers in second-stage radical polymerizations yielding polymers of more complex architectures. The review ends with a brief overview of post-polymerization modifications of the vinyl endfunctionality of the macromonomers yielding functional polymers with applications ranging from initiators in anionic polymerization to end-functional lectin-binding glycopolymers.

A facile synthesis of branched poly(ethylene glycol) and its heterobifunctional derivatives

Allyl-(PEG-OH)2, a dual-branched poly(ethylene glycol) (PEG) with a latent group amenable for modification at the junction, was successfully synthesized using trimethylolpropane allyl ether (TMPAE), a commercially available compound, as the initiator for anionic polymerization. To demonstrate the versatility of this approach, derivatives of the branched PEG were formed using simple modification. The chain ends of PEG were modified to inert methoxy groups and active functional groups. Using an orthogonal reaction procedure, the allyl junction was modified to carboxyl and amino group. The synthesis route was short, quantitative, and easily controlled. No cumbersome purification was needed. The branched PEG and its derivatives were characterized by SEC, 1H and 13C NMR, and MALDI-TOF mass spectroscopy.

Synthesis of Polystyrenes−Poly(alkyl methacrylates) Block Copolymers via Anionic Polymerization Using an Integrated Flow Microreactor System

The polystyrene living polymer end, which was produced by butyllithium initiated anionic polymerization of styrene in a flow microreactor system was found to be effectively trapped with 1,1-diphenylethylene. The resulting organolithium species could be used as a macro initiator for anionic polymerization of alkyl methacrylates to obtain styrene−alkyl methacrylate diblock copolymers using an integrated flow microreactor system. A high level of control of molecular weight was achieved at easily accessible temperatures such as +24 to −28 °C by virtue of the fast mixing, fast heat transfer, and residence time control. Triblock copolymers were also synthesized by sequential introduction of styrene and two different alkyl methacrylates in a similar manner.

Synthesis of heterobifunctional poly(ethylene glycol)s by an acetal protection method

A versatile synthetic route to prepare well-defined heterobifunctional poly(ethylene glycol) (PEG) derivatives via sequential modification of the hydroxyl ends was established using a newly synthesized initiator for anionic polymerization, 2-(1-ethoxyethoxy)ethanol (EEE), which contains an acid-cleavable acetal protection group. As illustrative examples, two heterobifuntional PEGs, HO–PEG–alkyne and HS–PEG–alkyne, were successfully prepared. This approach is applicable for synthesizing a wide variety of heterobifunctional PEGs.

Polymerization of epoxy resins initiated by metal complexes

AbstractBACKGROUND: Processing parameters and material properties of epoxy resins can be vastly influenced by choice of curing agent. In this work, metal complexes were investigated as initiators for anionic and cationic epoxide polymerization. Systems for thermally induced and electron beam‐induced curing are described.RESULTS: Zinc or cobalt imidazole complexes of the type [M(imidazole)2(anion)2] are efficient initiators for anionic polymerization of glycidyl‐based epoxy resins. The complexes can be employed to prepare tailored resin systems ranging from fast curing systems at slightly elevated temperatures to systems with very high thermal latencies curable at temperatures far above 150 °C. Silver complexes [Ag(L)n]SbF6 (L = crown ether or alkene) are highly efficient initiators for cationic curing and low initiator contents of around 1% are sufficient to reach high degrees of crosslinking. The complexes are excellent initiators for both thermally induced and electron beam‐induced polymerizations.CONCLUSION: Metal complexes are powerful initiators for the homopolymerization of epoxy resins and can be designed not only for anionic and cationic polymerization but also for thermal and radiation curing. Based on this study and additional work, a library can be compiled which allows retrieval of optimized metal–ligand–anion combinations and adjustment of the initiators to the respective processing and material demands. Copyright © 2009 Society of Chemical Industry

Imidazolium ionic liquids with short polyoxyethylene chains

It has been observed by us earlier that imidazolium ionic liquids ([bmim][BF4] react with paraformaldehyde giving in nearly quantitative yield imidazolium ionic liquids substituted at 2-position with hydroxymethyl group ([bhmim][BF4]). In this article, we describe the application of those ionic liquids (after converting hydroxyl group into alkoxide anion by reaction with sodium hydride) as initiators for anionic polymerization of ethylene oxide (EO). Up to DPn ∼ 30 polymerization proceeds without side reactions, and the product is exclusively low-molecular-weight polyoxyethylene containing imidazolium head group (POE-IL) with DPn equal to [EO]/[bhmim] ratio. By increasing [EO]/[bhmim] ratio further, side reaction start to interfere, and macromolecules that does not contain imidazolium head groups are also formed, as evidenced by analysis of MALDI TOF spectra. Blending of POE-IL with high-molecular-weight POE leads to significant reduction of crystallinity of POE. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6961–6968, 2008

Homogeneous Two-Electron-Transfer Initiation of Anionic Polymerization with Potassium Potassides

Alkalides are salts containing alkali metal anions and complexed metal cations. These unusual species discovered by Dye (Dye, J.L.; Andrews, C.W.; Mathews, S.E. J. Phys. Chem., 1975, 79, 3065) are strong reductants of many organic and inorganic compounds. These reactions occur rapidly under mild homogeneous conditions. In this paper we discuss new data concerning the application of potassium potassides selected from the group of alkalides to polymerization processes. Their new and corrected mechanisms for some vinyl and oxacyclic monomers are presented.

ジエン重合における最近の動向

This review describes polymerizations of dienes such as butadiene and isoprene with radical initiators, anionic initiators and transition metal complexes with respect to recent development. In radical polymerizations, living radical polymerizations are applied to polymerization of butadiene, and the living polymerization of butadiene gave narrow molecular weights and α, ω-difunctional polymers, leading to the formation of cyclic polybutadiene by ring closure reaction using both chain ends. In anionic polymerizations, functionalizations of polymers at the chain end and inchain have been developed by use of living anionic polymerization initiator and functional monomers. Many block copolymers including polybutadiene segment are synthesized and characterized. In transition metal complexes catalyzed polymerizations, a simultaneous control of 1, 4-cis selectivity and molecular weight of the polymers was achieved in the polymerization of butadiene. In the polymerization of isoprene, a precision polymerization is also achieved using lanthanide complexes. Cyclic polybutadiene was synthesized by ring opening metathesis polymerization (ROMP) of cyclooctadiene by the well designed Ru-based catalyst. The polymer obtained from ROMP consists of only 1, 4-structure.

Potassium enolates of N,N‐dialkylamides as initiators of anionic polymerization

AbstractStable potassium enolates of N,N‐diethylacetamide [α‐potassio‐N,N‐diethylacetamide (1)], N,N‐diethylpropionamide [α‐potassio‐N,N‐diethylpropionamide (2)], and N,N‐diethylisobutyramide [α‐potassio‐N,N‐diethylisobutyramide (3)] were prepared by the proton abstraction of the corresponding N,N‐diethylamides with diphenylmethylpotassium (Ph2CHK) or potassium naphthalenide in THF. The relative nucleophilicity of 1–3 was estimated to be in the order of 1 < 3 < 2 from the results of the alkylation reaction with methyl iodide. N,N‐diethylacetamide transferred its α‐proton to 2 quantitatively in THF at 0 °C, whereas no reaction occurred between N,N‐diethylisobutyramide and 2; this indicated the relative basicity to be 1 < 2 ∼ 3. Anionic polymerizations of N,N‐diethylacrylamide (DEA) and methyl methacrylate were quantitatively initiated with 2 in THF at −78 °C, whereas the initiation efficiencies of 2 for styrene and 2‐vinylpyridine were about 2 and 67%, respectively. The initiation of DEA with 1–3 at −78 or 0 °C in THF gave poly (DEA)s having broad molecular weight distributions (MWDs; Mw/Mn = 2) and ill‐controlled molecular weights. In contrast, poly(DEA)s of narrow MWDs (Mw/Mn < 1.2) and predicted Mn's were obtained with 2 in the presence of diethylzinc (Et2Zn) at −78 °C, whereas the initiations with 1/Et2Zn and 3/Et2Zn at −78 °C resulted in poor control of the molecular weights. At the higher temperature of 0 °C, all the binary initiator systems (1–3/Et2Zn) induced controlled polymerizations of DEA in terms of the conversion, molecular weight, and MWD. The poly(DEA)s produced with 1–3/Et2Zn at 0 °C showed mr‐rich configurations (mr = 76–89%), as observed for the poly(DEA) generated with Ph2CHK/Et2Zn. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1260–1271, 2007

Synthesis of polystyrene-grafted carbon nanocapsules

A novel polymeric composite material, polystyrene (PS)-grafted carbon nanocapsules (CNCs), has been prepared. sec-butyllithium was first used to introduce negative charges on CNCs, and these CNC carbanions acted then as initiators for anionic polymerization of styrene. Based on a weight loss at the decomposition temperature of the butyl groups, the quantity of the butyls attached to the CNC surface was determined as 1.18 wt%, corresponding to 0.25 mol% initiator per mol of carbon atom on the CNC surface. Furthermore, the decomposition temperature of butylated CNCs was lower than that of the pristine CNCs by nearly 200 °C. The polystyrene content in our PS-grafted CNC sample was approximately 20%, and the molecular weight of the grafted PS on the surface of CNCs was calculated as 1200 gmol−1. Compared with the molecular weight of the ungrafted PS, the molecular weight of grafted PS was lower, thus indicating rates of initiation and/or propagation for CNC-bound carbanions lower than those of the free sec-butyllithium. The PS-grafted CNCs had good dispersion in toluene, tetrahydrofuran, cyclohexane, and other common organic solvents in which polystyrene was dissolvable and thus indicated good compatibility when further blended with other styrenic polymers. The PS-grafted CNCs were characterized and examined by Fourier transform infrared, thermogravimetric analysis, atomic force microscopy, differential scanning calorimetry, ultraviolet-visible spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electron microscopy images indicated that the PS-grafted CNCs were homogeneous composites containing uniform polymer/CNC ratios.

Application of poly(3-ethyl-3-hydroxymethyloxetane) as macroinitiator for the synthesis of star polymers of ethylene oxide. Efficiency of initiation

Macromolecules of poly(3-ethyl-3-hydroxymethyloxetane) (poly-EHMOX) may act as convenient multifunctional initiators for the synthesis of star polymers in polymerizations initiated by -OH (or -O(-)) groups. It is desirable, that all functional groups of the initiator are indeed involved in initiation because in such case the number of arms is equal to the number of functional groups. We have used poly-EHMOX as macroinitiator for anionic and cationic polymerization of ethylene oxide (EOX) leading to star polymers containing poly-EHMOX core and poly-EOX arms. Using 1H NMR method it has been shown that the efficiency of initiation of anionic polymerization by -O(-) groups derived from poly-EHMOX is not quantitative. On the other hand, in the cationic polymerization of EOX in the presence of poly-EHMOX (proceeding by Activated Monomer mechanism) efficiency of initiation is quantitative and the number of arms is equal to the number of functional groups in poly-EHMOX even at the early stages of reaction.

Dual Reactivity of Magnesium Compounds as Initiators for Anionic and Cationic Polymerization

AbstractOrganomagnesium compounds are well known initiators of anionic polymerization of polar monomers. However, we have found recently that in the presence of compounds with labile halogen atoms, e.g., benzyl chloride, they are also active initiators of cationic polymerization of isobutylene and styrene in hydrocarbon media. The tentative scheme of cationic initiation is suggested assuming the formation of benzyl cation connected with Mg2Cl5− counter‐ion. The scheme is confirmed by quantum‐chemical calculations and 1H NMR analysis of polyisobutylene. On addition of a polar monomer, N,N‐dimethylacrylamide or 2‐vinylpyridine, to Bu2Mg‐BzCl‐isobutylene polymerizing mixture, the former readily polymerizes. The mixture of homopolymers rather than block copolymers is formed in this case, however, this fact proves the co‐existence of anionic and cationic centers in the system.

Poly(phenylene ether)/epoxy thermoset blends based on anionic polymerization of epoxy monomer

AbstractLow molar mass poly (phenylene ether) (LMW‐PPE) with phenol‐reactive chain ends was used as modifier of epoxy thermoset. The epoxy monomer was diglycidylether of bisphenol A (DGEBA), and several imidazoles were used as initiators of anionic polymerization. The curing and phase separation processes were investigated by different techniques: Differential Scanning Calorimetry, Size Exclusion Chromatography, and Light Transmission measurements. The final morphology of blends was observed by Environmental Scanning Electron Microscopy and Transmission Electron Microscopy. The epoxy network is obtained by imidazole initiated DGEBA homopolymerization. Initial LMW‐PPE/DGEBA mixtures show an UCST behavior with cloud point temperatures between 40 and 90°C. PPE phenol end‐groups can react with epoxy, leading to a better interaction between phases. The curing mechanism and phase separation process are not influenced by the chemical structure of initiators, except when reactive amine groups are present. The phase inversion is observed at 30 wt % of PPE. The mixtures with amine‐substituted imidazole present important differences in the initial miscibility and curing process interpreted in terms of fast room temperature amine‐epoxy reaction during blending. Final domain size is affected by this prereaction. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2678–2687, 2004

Synthesis and structural characterization of double metal cyanides of iron and zinc: catalyst precursors for the copolymerization of carbon dioxide and epoxides.

Several synthetic approaches for the preparation of double metal cyanide (DMC) derivatives of iron(II) and zinc(II) are described. These include (1) metathesis reactions of ZnCl(2) or ZnI(2) with KCpFe(CN)(2)CO in aqueous solution, (2) reactions of KCpFe(CN)(2)CO and its phosphine-substituted analogues with Zn(CH(3)CN)(4)(BF(4))(2) and subsequent displacement of acetonitrile at the zinc centers by the addition of a neutral (phosphine) or anionic (phenoxide) ligand, and (3) reactions of the protonated HCpFe(CN)(2)(phosphine) complexes with Zn(N(SiMe(3))(2))(2), followed by the addition of phenols. All structures are based on a diamond-shaped planar arrangement of the Fe(2)(CN)(4)Zn(2) core with various appended ligands at the metal sites. Although attempts to replace the iodide ligands in [CpFe(mu-CN)(2)PPh(3)ZnI(THF)](2) with acetate using silver acetate failed, two novel cationic mixed-metal cyanide salts based on the [CpFe(PPh(3))(mu-CN)(2)Zn(NC(5)H(5))](2)(2+) framework were isolated from pyridine solution and their structures were defined by X-ray crystallography. The anionic ligand bound to zinc in these derivatives, which serve as an anionic polymerization initiator, was shown to be central to the catalytic copolymerization reaction of CO(2)/epoxide to provide polycarbonates and cyclic carbonates. The structurally stabilized phosphine-strapped complexes [CpFe(mu-CN)(2)Zn(X)THF](2)(mu-dppp), where X = I or phenolate, were shown to be thermally stable under the conditions (80 degrees C) of the copolymerization reaction by in situ infrared spectroscopy. Both of these derivatives were proposed to serve as mimics for the heterogeneous DMC catalysts in the patent literature, with the derivative where the initiator is a phenolate being more active for the production of polycarbonates.

Polymer Brushes by Living Anionic Surface Initiated Polymerization on Flat Silicon (SiOx) and Gold Surfaces: Homopolymers and Block Copolymers

The formation of homopolymer and block copolymer brushes grafted from Au and Si (SiOx) surfaces via living anionic surface-initiated polymerization (LASIP) is described. The initiator precursor 1,1-diphenylethylene (DPE) was functionalized with alkylsilane or alkylthiol and grafted onto planar Si wafer and Au surfaces, respectively, by self-assembled monolayer techniques. n-BuLi was used to activate the DPE initiator for anionic polymerization of monomers at the interface. A high-vacuum reactor was used for polymerization at surfaces under anhydrous solution conditions. By a careful sequence of monomer introduction, reaction, and termination, homopolymer and block copolymer tethered polymer brushes were obtained. The grafted polymer chains were investigated using surface sensitive techniques such as ellipsometry, contact angle measurements, atomic force microscopy, Fourier transform infrared spectroscopy, surface plasmon spectroscopy, and X-ray photoelectron spectroscopy. The importance of activation of the grafted initiator, control of polymerization conditions, and removal of excess BuLi is emphasized. Interesting differences in morphology, thickness, grafting density, and polymerization conditions contrast LASIP from solution and other surface-initiated polymerization mechanisms. The formation of block copolymer sequences highlights the unique utility of a living anionic polymerization technique on surfaces.

Understanding the Morphologies and Polymerization Mechanism of Homopolymer and Block Copolymer Brushes by Living Anionic Surface Initiated Polymerization

ABSTRACTHomopolymer and block copolymer brushes grafted from Au and Si (SiOx) surfaces via living anionic surface initiated polymerization (LASIP) has been reported. 1,1-diphenylethylene (DPE) derivative, an initiator for anionic polymerization, was grafted onto planar Si-wafer and Au surfaces by self-assembled monolayer (SAM) techniques. n-BuLi was used to activate the DPE for anionic polymerization of monomers at the interface under high vacuum. By a careful sequence of monomer introduction, reaction, and termination, homopolymer and block copolymer tethered polymer brushes were obtained. The importance of initiator activation, control of polymerization conditions, and removal of excess BuLi is emphasized. Interesting differences in morphology, thickness, grafting density, and polymerization conditions contrasts LASIP from solution and other surface initiated polymerization (SIP) mechanisms. The formation of block copolymer sequences highlights the unique utility of a living anionic polymerization technique on surfaces.