Anionic Initiators Research Articles

Synthesis of well-defined poly(p-alkoxystyrene) by anionic polymerization in the presence of di-n-butylmagnesium

This study demonstrates the necessity of introducing di-n-butylmagnesium (n-Bu2Mg) additives to synthesize precisely controlled polymers through anionic polymerization of p-alkoxystyrene monomers at -40°C. Without additives, 4-tert-butoxystyrene (BSt) and 4-(1-ethoxy ethoxy)styrene (EESt) are polymerized using sec-butyllithium (s-BuLi) in tetrahydrofuran (THF) solvent, yielding a molecular weight distribution (MWD) of 1.36. However, the MWD is strictly controlled to 1.05–1.06 after adding n-Bu2Mg in more than 30 times the amount of s-BuLi, resulting in an accurately designed molecular weight. Therefore, n-Bu2Mg effectively suppresses side reactions that could occur at the polymerization temperature of -40°C in the Schlenk reactor. Interestingly, the polymerization reaction of styrene monomer proceeds when n-Bu2Mg is mixed in THF solvent at -40°C for an extended period, even without s-BuLi. This result suggests that, despite being a weak anionic initiator, n-Bu2Mg can initiate polymerization due to the lower electron density of the styrene double bond compared to BSt or EESt. Based on these results, a precise copolymer with a narrow molecular weight distribution can be synthesized by initiating polymerization with s-BuLi within 20 seconds of adding n-Bu2Mg to the mixed monomers of styrene and EESt.

Unraveling the Complexities of Silica Nanoparticle Adsorption onto Polymer Latexes in Pickering Emulsion Polymerization.

Incorporating unmodified silica nanoparticles onto polymer latexes to fabricate aqueous polymer dispersions without relying on electrostatic attraction during the Pickering emulsion polymerization process still faces challenges. For negatively charged silica nanoparticles to successfully adsorb onto polymer latexes, particularly in an anionic initiator emulsion polymerization system, they have remained elusive without the use of auxiliary monomers and cationic initiators. This study investigates various experimental parameters, such as emulsion polymerization temperature, monomer solubility, salt concentration, and cation type, to elucidate the factors influencing the adsorption of unmodified silica nanoparticles in Pickering emulsion polymerization. While poly(methyl methacrylate) (PMMA)/SiO2 hybrid latexes can be obtained under pH conditions of 5-6 and at temperatures of 65 °C or below, the loading rate of silica nanoparticles decreases as the reaction temperature increases, resulting in bare PMMA latexes without silica nanoparticle adsorption at temperatures exceeding 70 °C. Introducing styrene (St) into the monomer mixture with methyl methacrylate in a ratio of up to 10 wt % leads to a gradual decrease in silica nanoparticle loading rate, from 27.3 to 8.2 wt %, attributed to the low solubility of St in water. Furthermore, the presence of sodium ions (Na+) is found to be crucial for silica nanoparticle adsorption onto PMMA latexes, as the sodium ions have a stabilizing effect on both the silica nanoparticles and the silica nanoparticle-armored latexes. These findings highlight the complex nature of Pickering emulsion polymerization in the presence of unmodified silica nanoparticles, demonstrating that the loading rate of silica nanoparticles onto polymer latexes is influenced by various factors. These insights pave the way for developing aqueous polymer dispersions with high silica nanoparticle loading rates onto polymer latexes, which is a desirable trait in the coating industry.

Impact of polyethylene nanoplastics on human intestinal cells

Polyethylene (PE) is one of the most widely used plastics in the world. Its degradation leads to the production of small particles including microplastics and nanoplastics (NPs). Plastic particles’ presence poses a health risk. The aim of this work was to investigate the toxicity of two model surfactant-free PE NPs prepared by polymerization of ethylene from cationic and anionic water-soluble initiators on human cell lines Caco-2 and HT29-MTX. After physicochemical characterization, their acute and subacute toxicity profile, including cytotoxicity, oxidative stress, and genotoxicity, was evaluated on both cell lines. Results showed a size increase of PE NPs in culture medium. Zeta potential values close to −10 mV were no longer dependent on the initiator charge after adsorption of serum components in culture medium. However, the cellular toxicity of the cationic and anionic PE NPs was very different. A time-and-concentration dependent cytotoxic, oxidative, and genotoxic effects on Caco-2 cells were only observed for PE NPs prepared with cationic initiators. No toxicity was observed on HT29-MTX, likely due to the protective mucus layer. Genotoxicity correlated with oxidative stress of some PE NPs on Caco-2 cells was observed from a concentration of 0.1 mg.mL−1 after 48-h exposure.

Ring‐opening (co)polymerization strategies of selected oxacyclic monomers to control and provide tailored polymers with desired properties

AbstractRing‐opening polymerization (ROP) is a versatile synthetic method used to produce polymers from cyclic monomers, particularly oxacyclic monomers such as lactones and cyclic ethers. Oxacyclic monomers polymerize with anionic or cationic initiators. For selected monomers, such as glycidol, β‐butyrolactone and higher lactones, methods, and mechanisms of polymerization are presented, the understanding of which has allowed control of these processes. The use of appropriate polymerization techniques and methods, as well as conducting the copolymerization, mainly block copolymerization, makes it possible to control the architecture, molar mass, and end groups of the resulting polymers. These parameters determine the properties of macromolecules, such as solubility, ability to aggregate in aqueous solutions, thermoresponsiveness, and degradability. By carefully selecting monomers, catalysts, and polymerization conditions, ROP strategies can be tailored to produce polymers with precise molecular structures and desired properties for a wide range of applications. This review mainly focuses on precisely controlled syntheses that lead to well‐defined macromolecules consisting mostly of polyether and/or polyester chains.

Probing Radical Addition to 1-Phosphabutadienes by Employing Muonium as a "Light Isotope" of Hydrogen.

Understanding free radical addition to multiple bonds is important to elucidating the mechanistic details of addition polymerization reactions, albeit the fleeting radical intermediates are very difficult to detect by conventional methodologies. Muon spin spectroscopy (μSR) is a highly sensitive method that can detect radical species at 106 spins (cf. EPR: 1012 spins, NMR: 1018 spins). Herein, we employ μSR to detect the radical-addition products from three 1-phosphabutadiene monomers, P-analogues of isoprene. We show that muonium (Mu), a "light" H-atom surrogate, adds predominantly at the C4 position of the P1 =C2 -C3 =C4 moiety to give unprecedented 1-phosphaallyl radicals as the major products. Our structural assignments are supported by assignment of muon, phosphorus and proton hyperfine coupling constants using DFT-calculations. A minor radical product is also detected that is tentatively assigned to an PC3 -heterocyclic free radical. On the basis of DFT-predictions, we speculate that its formation may involve initial addition of Mu+ at the C3 position followed by electron capture. These studies provide rare insights into the prospective radical (or cationic) polymerization of 1-phosphabutadienes, which have previously been polymerized using anionic initiation.

Synthesis, Thermogravimetric Analysis, and Kinetic Study of Poly-N-Isopropylacrylamide with Varied Initiator Content.

The thermal decomposition and kinetic parameters of four polymers, PN-1, PN-05, PN-01, and PN-005, were determined by thermogravimetry (TGA/DTG) under non-isothermal conditions. N-isopropylacrylamide (NIPA)-based polymers were synthesized by the surfactant-free precipitation polymerization (SFPP) with different concentrations of the anionic initiator potassium persulphate (KPS). Thermogravimetric experiments were carried out in the temperature range of 25-700 °C at four heating rates, 5, 10, 15, and 20 °C min-1, under a nitrogen atmosphere. Poly NIPA (PNIPA) showed three stages of mass loss during the degradation process. The thermal stability of the test material was determined. Activation energy values were estimated using Ozawa, Kissinger, Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), and Friedman (FD) methods.

Rapid oxidative fragmentation of polypropylene with pH control in seawater for preparation of realistic reference microplastics

Various tiny plastic particles were retrieved from the sea and studied using scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX) analysis to prepare realistic reference microplastics (MP). Most of the MP exhibited a diameter of < 20 × 10−6 m and 0.1–0.2 molar ratios of oxygen to carbon atoms (O/C), indicating that they primarily comprised polyethylene (PE), polypropylene (PP), and polystyrene (PS). It took a long time to reproduce such O/C ratios in standard laboratory weathering methods. For example, degrading of 30 × 30 × 0.060 mm PP film required 75 days for the 0.1 ratio, even with an advanced oxidation process (AOP) using a sulfate radical anion (SO4·−) initiator in distilled water at 65 °C. However, seawater drastically improved the PP degradation performance of AOP under a weak acid condition to achieve the 0.1 ratio of PP film in only 15 days. The combination of seawater and the SO4·− initiator accelerated the degradation process and showed that the MP’s size could be controlled according to the degradation time.

Mechanochemical solid-state vinyl polymerization with anionic initiator.

Mechanochemistry has been extended to various polymer syntheses to achieve efficiency, greenness, and new products. However, many fundamental polymerization reactions have not been explored, although anionic polymerization of vinyl compounds has been pursued under mechanochemical conditions. Two solid monomers, 4-biphenyl methacrylate and 4-vinyl biphenyl, representing methacrylate and styrenic classes, respectively, were reacted with secondary butyl lithium under high-speed ball-milling. The alkyl-anion-promoted polymerization process was established by excluding radical initiation and producing the expected polymers with good efficiency. However, the generally expected features of anionic polymerization, such as molecular weight control and narrow dispersity, were not observed. Analysis of the milling parameters, reaction monitoring, and microstructural analysis revealed that the mechanism of the mechanochemical process differs from that of conventional anionic polymerizations. The mechanical force fractured the newly formed polymer chains via anionic initiation and generated macroradicals, which participated in the polymerization process. The anionic process governs the initiation step and the radical process becomes dominant during the propagation step.

Linear not cyclic – unravelling an anionic initiation pathway for Lewis pair polymerization of lactones

Lewis pair (LP) catalysis is a powerful system for polymerizing lactone monomers into cyclic polymers. However, current work reveals that the DBU-ZnEt2 LP-catalytic system leads to the formation of linear polymers via an anionic initiation pathway.

Cover Image, Volume 139, Issue 11

This cover image by Debjyoti Banerjee and co-authors shows a facile way to ionically cyclize polyacrylonitrile fiber precursors using aldaric acid sugars as anionic initiators. Carboxylate groups in the aldaric acid sugars are responsible for lowering the activation energy barrier needed to initiate the cyclization. This image depicts simulated extended polyacrylonitrile model chains of the fiber microstructure in succession with a cyclization reaction scheme that takes place under high temperatures. The scope of the work has direct applications in the carbon fiber industry. DOI: 10.1002/app.51781

From Anionic Ring-Opening Polymerization of β-Butyrolactone to Biodegradable Poly(hydroxyalkanoate)s: Our Contributions in This Field.

The feasibility of synthesis of functionalized poly(3-hydroxybutanoic acid) analogue and its copolymers via ring-opening polymerization of β-butyrolactone mediated by activated anionic initiators is presented. Using these new synthetic approaches, polyesters with a defined chemical structure of the end groups, as well as block, graft, and random copolymers, have been obtained and characterized by modern instrumental techniques, with special emphasis on ESI-MS. The relationship between the structure and properties of the prepared polymeric materials is also discussed.

Aluminium‐based ruthenium/diamine catalysts for produce aliphatic polycarbonates from carbon dioxide and oxetanes

AbstractWe fabricated the chiral ArDPEN/Ru species within the nanoparticles of the aluminium (Al/ArDPEN/Ru). Electron microscopy photos and the anatomical properties revealed the uniformly dispersed nanoparticles with active single‐site ruthenium/diamine centres on the exterior nanoparticles shell. Al/ArDPEN/Ru showed catalytic properties for the reaction of CO2 with oxetane, to synthesize the corresponding polycarbonate with minimal amount of ether linkages. TMC is prepared by a backbiting method following ring‐opening of oxetane by the anion initiator, subsequent to carbon dioxide insertion into the ruthenium/diamine bond. The preparation of the copolymer is shown to proceed mostly by method of the anionic ring‐opening polymerization of preformed trimethylene carbonate in the presence of an anion in solution. In addition, the catalyst anatomical heterogeneity of Al/ArDPEN/Ru was characterized by various techniques, including XRD, SEM, TGA, TEM, VSM, and FT‐IR. No leaching of ruthenium into the solution was observed.

Synthesis and In Situ Gelation Behavior of Thermoresponsive Poly(N-isopropylacrylamide)/Chitosan Microgels

Thermoresponsive microgels composed of poly(N-isopropylacrylamide) (PNIPAM) and chitosan (CS) were synthesized by soap-free emulsion polymerization of N-isopropylacrylamide monomer in the presence of CS, using an anionic radical initiator and a chemical crosslinker. The resulting PNIPAM/CS microgels contracted in an aqueous phase at elevated temperature, exhibiting a negatively thermoresponsive nature with a volume phase transition temperature (VPTT) of about 34.6 °C. The microgel dispersions with a relatively high polymer content gelated when being heated across their VPTT due to their attractive hydrophobic interactions. We systematically investigated this thermo-induced in situ gelation behavior by small-deformation oscillatory rheological measurements within the linear viscoelastic region. The dynamic temperature ramp sweeps revealed that the gelation temperature was greatly influenced by the polymer content of the microgel dispersion, decreasing with increasing polymer content. The isothermal time sweeps showed that the gelation occurred more quickly at either higher polymer content or higher isothermal heating temperature. The relaxation dynamics for the as-formed gel were also studied by isothermal frequency sweeps. It was found that the gels exhibited a frequency-independent storage modulus in the lower frequency range, and the greater the polymer content of the microgel dispersions, the more elastic the gels that formed.

Chemoselective transesterification and polymer synthesis using a zincate complex

In this focused review, I present an overview of our recent research on the zincate complex dilithium tetra-tert-butylzincate (TBZL)-catalyzed ring-opening polymerization (ROP) of e-caprolactone, efficient acylation and transesterification of alcohols with vinyl acetate and carboxylic esters, and polymer synthesis with a high transesterification ability. In the first part of this report, the ROP of e-caprolactone catalyzed by TBZL in toluene is described. In a subsequent study of the ROP of e-caprolactone in the presence of 2-hydroxyethyl methacrylate (HEMA), TBZL was found to act not only as an anionic initiator but also as a transesterification catalyst. In the second part of this report, the acylation and transesterification of alcohols with vinyl acetate and carboxylic esters catalyzed by TBZL are summarized. The acylation proceeded quantitatively at 0 °C within 1 h. A wide range of combinations of esters and alcohols were suitable for the transesterification at 0 to −40 °C. In addition, the transesterification proceeded chemoselectively even in the presence of H2O and amines. Next, TBZL-catalyzed polycondensations of diphenyl carbonate (DPC) with diols are discussed. Irreversible polycondensations catalyzed by TBZL occurred to yield aliphatic polycarbonates under atmospheric pressure. In the last part of this report, the transesterifications of poly(phenyl methacrylate) (PPhMA) side chains with alcohols catalyzed by TBZL are described. The transesterification reaction not only with alkyl alcohols but also with fluoroalcohols occurred. By changing the reaction solvent and temperature, the degree of conversion could be controlled. The present system permits the partial, quantitative, or terminal conversion of polymethacrylates. Our recent studies on the zincate complex dilithium tetra-tert-butylzincate-catalyzed transesterification and polymerization are reviewed. In the first part of this report, the ROP of e-caprolactone catalyzed by TBZL is described. In the second part of this report, the acylation and transesterification of alcohols with vinyl acetate and carboxylic esters catalyzed by TBZL are summarized. Next, TBZL-catalyzed polycondensations of diphenyl carbonate (DPC) with diols are discussed. In the last part of this report, the transesterifications of poly(phenyl methacrylate) (PPhMA) side chains with alcohols catalyzed by TBZL are described.

Anionic Copolymerization of Styrene Sulfide with Elemental Sulfur (S8).

The superior ability of thiiranes (episulfides) to undergo ring-opening polymerization (ROP) in the presence of anionic initiators allows the preparation of chemically stable polysulfide homopolymers. Incorporation of elemental sulfur (S8) by copolymerization below the floor temperature of S8 permits the placement of a large quantity of sulfur atoms in the polysulfide mainchain. The utility of styrene sulfide (2-phenylthiirane; StS) for copolymerization with elemental sulfur is reported here. A few polysulfides differing depending on the initial ratio of S8 to StS and copolymerization time were synthesized. Various spectroscopic methods (1H NMR, 13C NMR, Raman spectroscopy and FTIR spectroscopy) were applied to characterize the chemical structure of the copolymers. Additionally, the phase structure and thermal stability of the synthesized polysulfides were investigated using DSC and TGA, respectively. The successful anionic copolymerization of styrene sulfide and elemental sulfur has been demonstrated.

Relationship between dispersion-forming capability of poly(4-vinylaniline) colloids and antimicrobial activity

Cationic polymers synthesized from aromatic monomers such as styrene or 4-vinylaniline, and with molecular weight less than 1000 Da display antibacterial activities against Micrococcus luteus. We prepared polymer colloids exhibiting different tendencies to form stable dispersions in order to clarify the influence of this property on their antimicrobial activity against M. luteus. 4-Vinylaniline was polymerized by a soap-free emulsion procedure using cationic and anionic initiators to prepare polymer colloids with different capacities for forming dispersions. All synthesized colloids displayed positive zeta potentials due to the presence of amino groups from the monomers and/or initiators and included polymers with molecular weights < 1000 Da. However, only colloids prepared using a cationic initiator VA-044 or V-50 and capable of forming stable dispersions were antimicrobially active. Colloids synthesized using an anionic initiator KPS or V-501, which aggregate easily due to electro-attractive forces between functional groups, were not antimicrobial. Thus, the antimicrobial activity of a polymer colloid is closely associated with its ability to form a stable dispersion.

Photolysis Mechanism of Quaternary Amidinium Salts

AbstractPhotoinduced polymerization reactions are an energy‐saving and environmentally friendly technology used in applications such as curing and coating. Photo initiators are one of the key materials which generate active species by photoirradiation. Many types of radical and cationic photo initiators (photoacid generators) have been developed. However, anionic photo initiators (photobase generators), which are more advantageous in terms of corrosion and lack of deactivation, remain under development. Cyclic amidine compounds, such as DBU® (1,8‐Diazabicyclo[5.4.0]undec‐7‐ene) and DBN (1,5‐Diazabicyclo[4.3.0]non‐5‐ene), are strong organic bases, widely used as catalysts in organic, polymerization, and crosslinking reactions. Developing a photobase initiator that can generate such a strong base is important, because there are few photobase generators with strong basicity and high reactivity for practical applications. In this study, we investigated the elementary mechanism of photolysis of quaternary amidinium borate salts by transient absorption measurements. We confirm that photoinduced electron transfer is a key step in the photo decomposition of quaternary amidinium borate salts and that the position of the sensitizing chromophore in the molecules significantly affects the decomposition efficiency.

Activated Monomer Polymerization of an N-Sulfonylazetidine.

Previously, N-(methanesulfonyl)azetidine (MsAzet) was found to polymerize anionically via ring-opening at temperatures >100 °C to form p(MsAzet) in the presence of an anionic initiator. In the current report, potassium(azetidin-1-ylsulfonyl) methanide (KMsAzet), formed from deprotonation of the methanesulfonyl group of MsAzet by KHMDS, is shown to undergo spontaneous AROP at room temperature to form p(N-K-MsAzet). The structure of p(N-K-MsAzet) differs from that of p(MsAzet), as the sulfonyl groups are incorporated into the polymer backbone of p(N-K-MsAzet). Reaction of p(N-K-MsAzet) with MeOH produces p(N-H-MsAzet), a semicrystalline polymer with a structure like that of polyamides, but with sulfonylamides in place of the carboxamides found in polyamides. Reaction of p(N-K-MsAzet) with benzyl bromide results in the formation of amorphous p(N-Bn-MsAzet). P(N-K-MsAzet) is hypothesized to form via an activated monomer anionic polymerization; this is supported by polymerization kinetic data and structural characterization of the resulting polymers.

Simple and efficient anionic polymerization of N‐phenylmaleimide with fluorides as an initiator

ABSTRACTThe facile anionic polymerization of N‐phenylmaleimide (N‐PMI) using fluorides as an initiator has been discovered and systematically investigated. Effect of different solvents such as dioxane, tetrahydrofuran, dichloromethane (DCM), dimethyl sulfoxide (DMSO), N‐methylpyrrolidone, acetonitrile, toluene, and acetone and effect of anionic initiators such as tetra‐n‐butylammonium fluoride (TBAF), cesium fluoride, and potassium fluoride have been studied. The kinetics of polymerization using TBAF as an initiator in DMSO is also studied. Some of the resulting poly(PMI)s are characterized by gel permeation chromatography, solubility test, attenuated total reflection‐Fourier transform infrared, nuclear magnetic resonance (NMR), and 13C‐NMR spectral analysis. The thermal behaviors are studied by thermogravimetric and differential scanning calorimetric analysis. A proposed polymerization mechanism is also discussed. Our results show fluoride can effectively induce the polymerization of N‐PMI in various solvents under very mild conditions with good to excellent yields. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 137, 48909.

Curing and thermomechanical properties of off-stoichiometric anhydride–epoxy thermosets

In the present work, we report the preparation and characterization of a new family of thermosets based on off-stoichiometric anhydride–epoxy formulations in the presence of an anionic initiator. Diglycidyl ether of bisphenol A (DGEBA) and hexahydro-4-methylphthalic anhydride (HHMPA) have been used as epoxy and anhydride comonomers, respectively, and 1-methylimidazole (1MI) has been used as anionic initiator. The isothermal curing kinetics and the thermal properties of the stoichiometric and the off-stoichiometric systems have been compared. The kinetics of the isothermal curing has been analyzed by differential scanning calorimetry (DSC) using an isoconversional method and the Šesták–Berggren equation to determine the activation energy, the frequency factor and the reaction orders. The materials obtained were characterized by DSC and dynamic mechanical analysis. Gelation during epoxy–anhydride condensation was determined by thermomechanical analysis. At the same curing temperature, the reaction is faster in the system with excess of epoxy groups. However, the glass transition temperatures of the partially cured stoichiometric system are greater. The gelation time of the off-stoichiometric system is shorter than that of the stoichiometric one. The results indicate that the dual-curing character of off-stoichiometric DGEBA/HHMPA thermosets with 1MI as anionic initiator makes them suitable for multistage curing processes with easy control of degree of cure and material properties in the intermediate stage and enhanced final material properties.