Ring-opening Polymerization Of Ethylene Oxide Research Articles

Linear- and star-brush poly(ethylene glycol)s: Synthesis and architecture-dependent crystallization behavior

Linear-brush and star-brush poly(ethylene glycol)s (PEGs) with tunable branching degree and side chain length were successfully obtained via metal-free ring-opening polymerization of ethylene oxide using hydroxylated polybutadiene (HPB) as a macroinitiator and t-BuP4 as a catalyst. The branching degree and side chain length of brush PEGs can be tailored simply by controlling the number of hydroxyl groups ([OH]) on backbone and the feed ratio of ethylene oxide/[OH], respectively. The effects of molecular weight and macromolecular architecture on crystallization behavior were systematically investigated through crystallization kinetics and morphologies. In all cases, the thermal parameters, including Tc, ΔHc, and ΔHm, increase with increasing molecular weight of side chains, while decrease with an increasing the branching degree, suggesting an increased or reduced crystallinity. According to the Avrami equation, the rate constant K decreases while the n values increase with branching degree increasing. POM observations suggested that the spherulites growth rate G decreases with branching degree increasing under the same supercooling. Nonetheless, with increasing the side chain length, the spherulites growth rate G decreases for linear and star PEGs while increases instead for brush PEGs, suggesting that the crystal growth rate of PEGs is influenced by topological structure and supercooling simultaneously. Consequently, with increasing the side chain length, Kg and σe increase for linear and star PEGs, while Kg and σe decrease for brush structures. Both Kg and σe increase regardless of macromolecular architecture with an increasing branching degree. Based on Hoffman-Lauritzen analysis, the transition of regime II to regime III for brushed PEG (ΔT = 15 K) require larger supercooling than linear and star PEGs (ΔT = 10 K).

Fast Access to Amphiphilic Multiblock Architectures by the Anionic Copolymerization of Aziridines and Ethylene Oxide.

An ideal system for stimuli-responsive and amphiphilic (block) polymers would be the copolymerization of aziridines with epoxides. However, to date, no copolymerization of these two highly strained three-membered heterocycles had been achieved. Herein, we report the combination of the living oxy- and azaanionic ring-opening polymerization of ethylene oxide (EO) and sulfonamide-activated aziridines. In a single step, well-defined amphiphilic block copolymers are obtained by a one-pot copolymerization. Real-time 1H NMR spectroscopy revealed the highest difference in reactivity ratios ever reported for an anionic copolymerization (with r1 = 265 and r2 = 0.004 for 2-methyl- N-tosylaziridine/EO and r1 = 151 and r2 = 0.013 for 2-methyl- N-mesylaziridine/EO), leading to the formation of block copolymers with monomodal and moderate molecular weight distributions ( Mw/ Mn mostly ≤1.3). The amphiphilic diblock copolymers were used to stabilize emulsions and to prepare polymeric nanoparticles by miniemulsion polymerization, representing a novel class of nonionic and responsive surfactants. In addition, this unique comonomer reactivity of activated-Az/EO allows fast access to multiblock copolymers, and we prepared the first amphiphilic penta- or tetrablock copolymers containing aziridines in only one or two steps, respectively. These examples render the combination of epoxide and aziridine copolymerizations via a powerful strategy for producing sophisticated macromolecular architectures and nanostructures.

Synthesis and Properties of SEPS-g-PEO Copolymers with Varying Branch Lengths

Poly(ethylene oxide) (PEO) was controllably grafted from styrene-b-(ethylene-co-propylene)-b-styrene (SEPS) backbones by combining lithiation of styrenic units and living monomer-activated anionic ring-opening polymerization of ethylene oxide (EO) monomers with the aid of co-initiators triisobutyl aluminum. The as-synthesized SEPS-g-PEO copolymers were characterized by SEC, 1H-NMR, FTIR, SAXS, AFM and DSC. When the branch length is relatively small, increase of PEO fraction leads to the increase of the correlation length between neighboring hard domains, but the degree of correlation reduces. When the branch length is relatively large, the phase-separated structures become random both in terms of size and spatial correlation, and macro-phase separated structures appear. The crystallization behavior of the PEO branches can be effectively inhibited in SEPS-g-PEO, so no significant crystallization takes place until the fraction of PEO branches is 20.1 wt%, which greatly promotes the rapid delivery of hydrophilic drugs in the hot-melting pressuresensitive adhesives (HMPSAs) based on SEPS-g-PEO. Their cumulative release amount of a model drug could achieve 80%, more than twice the value in the HMPSAs based on linear PEO-containing styrenic block copolymers.

Synthesis and self-assembly of a novel amphiphilic diblock copolymer consisting of isotactic polystyrene and 1,4-trans-polybutadiene-graft-poly(ethylene oxide).

Herein, a novel amphiphilic diblock copolymer consisting of isotactic polystyrene (iPS) and 1,4-trans-polybutadiene-graft-poly(ethylene oxide) (1,4-trans-PBD-g-PEO), iPS-b-(1,4-trans-PBD-g-PEO), was synthesized by the combination of living coordination copolymerization and graft copolymerization. iPS-b-1,4-trans-PBD was firstly synthesized via sequential monomer addition in the presence of 1,4-dithiabutandiyl-2,2′-bis(6-cumenyl-4-methylphenoxy) titanium dichloride (complex 1) activated by triisobutyl aluminum modified methylaluminoxane (MMAO). Moreover, hydroboration of double bonds in the 1,4-trans-PBD blocks were performed with 9-borabicyclo[3.3.1]nonane (9-BBN) and subsequent oxidation by NaOH/H2O2 to form hydroxyls. Consequently, PEO was grafted into the hydroxylated 1,4-trans-PBD block in terms of ring-opening polymerization of ethylene oxide with potassium/naphthalide as initiatior. We also described solvent-evaporation-induced self-assembly of iPS-b-1,4-trans-PBD in n-dodecane and iPS-b-1,4-trans-PBD-g-PEO in aqueous solution, which were selective solvent for 1,4-trans-PBD and for 1,4-trans-PBD-g-PEO blocks, respectively. In these cases, tetrahydrofuran (THF) was used as good and volatile solvent. These resultant iPS-containing diblock copolymers could self-assemble into spherical nano-micelles with an iPS core as amorphous agglomeration or a very low degree of crystallinity resulting from slow crystallization rate and nanoconfinement. In addition, after isothermal crystallization of iPS in the micellar cores self-assembled in n-dodecane at 120 °C for 3 hours, the micellar morphology changed from sphere-like to platelet-like. It was believed that isothermal crystallization of iPS induced the deformation of the micelles.

Revealing the Cytotoxicity of Residues of Phosphazene Catalysts Used for the Synthesis of Poly(ethylene oxide).

We herein report a case study on the toxicity of residual catalyst in metal-free polymer. Eight-arm star-like poly(ethylene oxide)s were successfully synthesized via phosphazene-catalyzed ring-opening polymerization of ethylene oxide using sucrose as an octahydroxy initiator. The products were subjected to MTT assay using human cancer cell lines (MDA-MB-231 and A2780). Comparison between the crude and purified products clearly revealed that the residual phosphazenium salts were considerably cytotoxic, regardless of the anionic species, and that the cytotoxicity of more bulky t-BuP4 salt was higher than that of t-BuP2 salt. Such results have therefore put forward the necessity for removal of the catalyst residues from PEO-based polymers synthesized through phosphazene catalysis for biorelated applications and for the development of less or nontoxic organocatalysts for such polymers.

Synthesis of heterobifunctional polyethylene glycols: Polymerization from functional initiators

Abstract The large-scale synthesis of heterobifunctional polyethylene glycols (PEGs) with tightly controlled molecular weights ranging from 2 to 20 kDa is described. PEGs were prepared by the ring-opening polymerization of ethylene oxide (EO) initiated from a protected amine ( N -dibenzyl), and a protected alcohol ( O -trityl) initiator. Additionally, EO polymerizations from initiators bearing azide and alkyne, both prototypical “click” chemistry functionalities, are outlined. This demonstrates the first successful use of an initiator bearing either an azide or strained cycloalkyne functionality in an ethylene oxide polymerization. The key to the methodology proved to be the selection of base. The use of potassium naphthalenide or potassium hydride in paraffin wax was highly dependent on the initiator used.

Quantitative ω-amination, ω-azidolysis, and ω-thiolation of poly(ethylene oxide)s through anionic mechanism

n-Butyllithium-initiated ring-opening polymerization of ethylene oxide with potassium t-butoxide in the mixture of benzene and dimethyl sulfoxide (DMSO) at 35 °C yielded corresponding “living” polymeric alkoxide. The molecular weight was well controlled on the basis of stoichiometric balance. Quantitative chain-end functionalizations, such as the amination, the azidation, and the thiolation of polymeric alkoxide, were performed. The yields were almost quantitative (over 98 mol%). The resulting products were characterized by the combination of 1H NMR spectroscopy, UV/Visible spectroscopy, FTIR, MALDI-TOF MS analysis, and size exclusion chromatographic analysis. Open image in new window

Azide-based heterobifunctional poly(ethylene oxide)s: NaN3-initiated “living” polymerization of ethylene oxide and chain end functionalizations

Sodium azide (NaN3)-initiated “living” ring-opening polymerization of ethylene oxide and chain end functionalizations.

Grafting Poly(ethylene glycol) Onto Single-Walled Carbon Nanotubes by Living Anionic Ring-Opening Polymerization.

Recent years, many methods have been developed to widen the practical application of single-walled carbon nanotubes (SWCNTs). Among them, PEGylation is a general strategy to endow functionality, biocompatibility as well as its good solubility. In this paper, poly(ethylene glycol) (PEG) is successfully grafted onto SWCNTs through living anionic ring-opening polymerization of ethylene oxide (EO). By controlling the amount of monomer and initiator, a series of PEGylated SWCNTs with different PEG molecular weight and density are prepared. Then, the as-prepared SWCNTs have been verified by thermogravimetric analyses (TGA), Raman spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS). Finally, the protein resistance property of the PEGylated SWCNTs is investigated. It is found that these PEGylated SWCNTs have a good protein resistance property and the higher the content of PEG grafted on the SWCNTs, the less adsorption amount of BSA and the larger capacity to resist protein absorption. This work provides a novel method to prepare PEGylated SWCNTs.

Controlled Nanopores by Supramolecular Assembly of End-Functionalized Dendrimer and Homopolymer Blend.

Supramolecular assembly of end-functionalized polymers, forming block copolymer-like supramolecules based on ionic interaction, has been utilized as a simple and facile method for generating functionalized nanoporous thin film. Here, the binary blend film of aminated poly(ethylene oxide) dendrimer (APEO-G) and sulfonated polystyrene (SPS) at a stoichiometric composition after benzene/water solvent vapor annealing exhibits spherical domains in multilayers over a large area. By controlling the number of end-functional arms of dendrimer via divergent ring-opening polymerization of ethylene oxide as well as the molecular weights of SPS, the domain sizes can be controlled ranging from mainly 34 to 54 nm, even to 131 nm. Our supramolecular-assembly system provides an alternative approach to fabricating a functional nanotemplate by easily etching domains with selective solvent treatment and leaving functional groups at the pore surfaces.

Phosphazene-Promoted Metal-Free Ring-Opening Polymerization of Ethylene Oxide Initiated by Carboxylic Acid

The effectiveness of carboxylic acid as initiator for the anionic ring-opening polymerization of ethylene oxide was investigated with a strong phosphazene base (t-BuP4) used as promoter. Kinetic study showed an induction period, i.e., transformation of carboxylic acid to hydroxyl ester, followed by slow chain growth together with simultaneous and fast end-group transesterification, which led to poly(ethylene oxide) (PEO) consisting of monoester (monohydroxyl), diester, and dihydroxyl species. An appropriate t-BuP4/acid ratio was proven to be essential to achieve better control over the polymerization and low dispersity of PEO. This work provides important information and enriches the toolbox for macromolecular and biomolecular engineering with protic initiating sites.

Anionic Polymerization of para-(1-Ethoxy ethoxy)styrene: Rapid Access to Poly(p-hydroxystyrene) Copolymer Architectures.

Living anionic polymerization of para-(1-ethoxy ethoxy)styrene (pEES) resulting in molecular weights between 2700 and 69 000 g mol-1 and polydispersity indices ≤1.09 is introduced. PpEES can be used as a precursor for the synthesis of well-defined poly(p-hydroxystyrene) (PHS) architectures, enabling facile and rapid acidic deprotection at room temperature within a few minutes. In addition, a series of block copolymers containing pEES and 2-vinylpyridine (2VP) have been synthesized by anionic block copolymerization, with varied block ratios (X2VP) between 0.13 and 0.83. Characterization by 1H NMR spectroscopy, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) was carried out, and all polymers have been deprotected, leading to the respective PHS-b-P2VP block copolymers. Furthermore, PHS-b-P2VP has been used as a macroinitiator for the anionic ring-opening polymerization of ethylene oxide (EO) to generate ((PHS-g-PEO51)13-b-P2VP40) graft-block copolymers.

Enlarging the Toolbox: Epoxide Termination of Polyferrocenylsilane (PFS) as a Key Step for the Synthesis of Amphiphilic PFS-Polyether Block Copolymers.

Epoxide termination and functionalization of living poly(ferrocenyldimethylsilane) (PFDMS) is introduced by precapping the living PFDMS with a 4/2 molar mixture of 1,1-diphenylethylene and 1,1-dimethylsilacyclobutane acting as a "carbanion pump" system. Subsequent addition of allyl glycidyl ether (AGE) leads to quantitatively functionalized PFDMS-AGE polymers with molecular weights between 1500 and 15 400 g mol-1 and polydispersity indices ≤1.10, carrying one hydroxyl group and an additional allylic double bond. PFDMS-AGE was then applied as a macroinitiator for the living anionic ring-opening polymerization of ethylene oxide (EO) to generate amphiphilic and water-soluble poly(ferrocenyldimethylsilane-b-ethylene oxide) block copolymers with a low polydispersity index. All polymers have been characterized by 1H NMR spectroscopy, DOSY 1H NMR spectroscopy, size exclusion chromatography (SEC), and MALDI-ToF mass spectrometry. In addition, for the characterization of the morphology of the PFDMS-b-PEO block copolymers transmission electron microscopy (TEM) was performed in methanol, confirming the formation of cylindrical micelles with an organometallic core and polyether corona.

Temperature-induced and crystallization-driven self-assembly of polyethylene-b-poly(ethylene oxide) in solution

In this paper, the well-defined diblock copolymers consisting a linear polyethylene (LPE) and a poly(ethylene oxide) (PEO), LPE-b-PEO, were synthesized by combining the ethylene living coordination polymerization with fluorinated bis(phenoxyimine) titanium catalyst and the living ring-opening polymerization of ethylene oxide initiated by hydroxyl-terminated polyethylene (LPE–OH) as a macromolecular initiator. We describe two methodologies for the self-assembly of LPE-b-PEO, namely temperature-induced self-assembly and crystallization-driven self-assembly. Transmission electron microscopy (TEM), atomic force microscopy (AFM) and dynamic light scattering (DLS) are employed to characterize the morphology, structure and hydrodynamic radius (Rh) of the self-assembled micelles. LPE-b-PEO is dissolved to form a molecular solution in trichlorobenzene (TCB) at 140 °C, while self-assembly could be driven when the crystallization of LPE blocks is induced by cooling to form diamond-shaped micelles with a mono-layer crystallized LPE lamella core. The resultant diblock copolymers can self-assemble into spherical micelles composed of a molten LPE core and a soluble PEO corona in DMF at 140 °C, that is above the melting temperature (Tm) of the LPE block. As the temperature decrease, the morphology changes from spherical to platelet-like micelle with a double-layer crystallized LPE lamella core sandwiched by solvent-swollen PEO corona. Furthermore, the confined crystallization of LPE block in nanosized self-assembled micelle core is investigated by differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXRD).

Anionic ring-opening polymerization of ethylene oxide in DMF with cyclodextrin derivatives as new initiators

Anionic polymerization initiated by cyclodextrins suffers from a poor solubility of those derivatives in standard polymerization solvents. The possibility to perform ethylene oxide polymerization initiated by monofunctional initiators (allyl alcohol, 2-methoxyethanol) by living ring opening polymerization in DMF, a good solvent for any CD derivative, was demonstrated by SEC, 1H and 13C NMR analyses. The study was extended to the use of native CD as initiator, leading to the synthesis of ill-defined structures, explained by the reactivity scale of the various hydroxyl functions. Two selectively modified CD derivatives are then used to synthesize a new family of star-shaped poly(ethylene oxide) polymers with CD core, having 14 or 21 arms. The polymerization was found to be living and DOSY experiments confirmed the well-defined structures for the synthesized star-polymers.

Synthesis of terpene–poly(ethylene oxide)s by t-BuP4-promoted anionic ring-opening polymerization

Terpene alcohols (menthol, retinol, cholesterol, and betulin) together with the phosphazene base t-BuP4 were used as initiating systems for anionic ring-opening polymerization of ethylene oxide. The polymerizations were conducted in a controlled manner with the initial molar ratio of t-BuP4 to hydroxyl groups of 0.01–0.2, yielding a series of biohybrid polymers comprising terpene entities and poly(ethylene oxide) (PEO) chains with low polydispersities and tunable compositions (57–87 wt% of PEO). Samples were characterized by NMR and UV/visible spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography; thermal properties were studied by differential scanning calorimetry. The concept of this study opens a new toolbox of terpene-based biohybrid polymers with variable properties and functions.

Synthesis of Eight‐shaped Poly(ethylene oxide) by the Combination of Glaser Coupling with Ring‐opening Polymerization

The eight-shaped poly(ethylene oxide) (PEO) is synthesized by a combination of Glaser coupling with ring-opening polymerization (ROP). Firstly, the star-shaped (PEO-OH)(4) is synthesized by ROP of ethylene oxide (EO) using pentaerythritol as an initiator and diphenylmethyl potassium (DPMK) as a deprotonated agent, and then the alkyne group is introduced onto the PEO arm-end to give (PEO-Alkyne)(4) in a NaH/tetrahydrofuran (THF) system. The intramolecular cyclization is carried out by a Glaser coupling reaction in a pyridine/CuBr/N,N,N',N",N"-pentamethyldiethylenetriamine (PMDETA) system at room temperature in an air atmosphere, and eight-shaped PEO was formed with high efficiency (almost 100%). The target polymers and intermediates were well characterized by SEC, MALDI-TOF MS, (1)H NMR and FT-IR in detail.

N-Heterocyclic Carbene-Organocatalyzed Ring-Opening Polymerization of Ethylene Oxide in the Presence of Alcohols or Trimethylsilyl Nucleophiles as Chain Moderators for the Synthesis of α,ω-Heterodifunctionalized Poly(ethylene oxide)s

The present study describes innovations in the ring-opening polymerization (ROP) of ethylene oxide (EO) using N-heterocyclic carbenes (NHCs) as organocatalysts, which enables the synthesis of α,ω-heterodifunctionalized poly(ethylene oxide)s (PEOs). Two representative NHC catalysts, namely, 1,3-bis(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2), were efficiently employed in conjunction with a variety of chain regulators of general structure NuE, where Nu and E are the nucleophilic and the electrophilic part, respectively, with E = H or SiMe3 (e.g., PhCH2OH, HC≡CCH2OH, N3SiMe3, and PhCH2OSiMe3). Catalytic amounts of the NHC (typically [NHC]/[NuE]/[EO] = 0.1/1/100 in moles) were indeed utilized to trigger the metal-free ROP of EO at 50 °C in dimethyl sulfoxide, allowing the polymerization to proceed to completion. In this way, PEOs of dispersities lower than 1.2 and molar masses perfectly matching the [EO]/[NuE] ratio were obtained, attesting to the controlled/living char...

Versatile and Selective Synthesis of “Click Chemistry” Compatible Heterobifunctional Poly(ethylene glycol)s Possessing Azide and Alkyne Functionalities

Versatile route for "click chemistry" compatible heterobifunctional PEGs was established through preparation of alpha-tetrahydropyranyloxy-omega-hydroxyl poly(ethylene glycol) (THP-PEG-OH) via ring-opening polymerization of ethylene oxide using 2-(tetrahydro-2H-pyran-2-yloxy)ethanol as an initiator, followed by the functionalization of omega-OH group to either the azido or alkyne group. Quantitative azidation of THP-PEG-OH was confirmed from the analysis of molecular functionality of the derivatives. While the conversion efficiency of omega-alkynation was appropriately 70%, the unreacted THP-PEG-OH fraction was successfully removed by ion-exchange chromatography after the carboxylation of the hydroxyl group with succinic anhydride. Then, the protecting group of the alpha-end, THP, was removed in mild acidic media, followed by two- or three-step modification of the resulting alpha-hydroxyl group to primary amino or thiol groups. Consequently, "click chemistry" compatible heterobifunctional PEG derivatives (X-PEG-Y; X = NH(2) and SH, Y =Azide and Alkyne) were synthesized with high efficiency and controlled molecular weight.

Amphiphilic Polystyrene-b-poly(p-hydroxystyrene-g-ethylene oxide) Block−Graft Copolymers via a Combination of Conventional and Metal-Free Anionic Polymerization

This work presents the synthesis of polystyrene-block-poly(p-hydroxystyrene-graft-ethylene oxide), PS-b-(PHOS-g-PEO), amphiphilic block−graft copolymers. The backbone diblock copolymers (PS-b-PHOS) were prepared by lithium-based anionic polymerization, followed by postpolymerization acid hydrolysis of the poly(p-tert-butoxystyrene), PtBOS, precursor block. The PEO side chains were synthesized by metal-free anionic ring-opening polymerization of ethylene oxide (EO), using the phosphazene base (t-BuP4) and the phenolic hydroxyl groups (PhOH) in the backbones as the complex multifunctional initiating system. In all cases, starlike block−graft copolymers with high molecular weights and low polydispersities were synthesized. Well-controlled polymerization was achieved even with the molar ratio of t-BuP4 to PhOH being equal to 0.2. Dynamic and static light scattering and fluorescence spectroscopy studies were carried out to investigate the solution behavior of the amphiphilic block−graft copolymers, including t...