PEO Arms Research Articles

Oscillatory and Relaxation Study of the Interfacial Rheology of Star Polymers with Low-Grafting-Density PEO Arms and Hydrophobic Poly(divinylbenzene) Cores.

Star polymers have been gaining interest due to their tunable properties. They have been used as effective stabilizers for Pickering emulsions. Herein, star polymers were synthesized via activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP). Poly(ethylene oxide) (PEO) with terminal α-bromoisobutyrate ATRP functionality was used as a macroinitiator and divinylbenzene as a crosslinker for the arm-first star synthesis. Stars with PEO arms with a molar mass of either 2 or 5 kDa had a relatively low density of grafted chains, i.e., ca. 0.25 chain/nm2. The properties of PEO stars adsorbed at oil-water interfaces were investigated using interfacial tension and interfacial rheology. The magnitude of interfacial tensions at oil-water interfaces depends on the nature of the oil phase, being lower at the m-xylene/water interface than at the n-dodecane/water interface. Small differences were observed for stars with different molecular weights of PEO arms. The overall behavior of PEO stars adsorbed at an interface can be considered as an intermediate between a particle and a linear/branched polymer. Obtained results offer an important insight into the interfacial rheology of PEO star polymers in the context of their application as stabilizers for Pickering emulsions.

(PVDF)2(PEO)2 miktoarm star copolymers: Synthesis and isothermal crystallization leading to exclusive β-phase formation

In this work, we study how chain topology can induce different polymorphic behaviors in poly(vinylidene fluoride) (PVDF)-based materials. A linear PVDF precursor with two azido groups at the junction point, (PVDFx-N3)2 and three 4-miktoarm star copolymers (PVDFx)2-b-(PEOy)2 with two poly(ethylene oxide) (PEO) and two PVDF arms were synthesized and employed in this study. The amphiphilic miktoarm copolymers were prepared by a combination of anionic ring-opening polymerization, iodine transfer radical polymerization (ITP), and copper-catalyzed azide-alkyne cycloaddition (CuAAC). They have practically similar overall molar mass but different compositions, ideal for performing bulk morphology and crystallization investigations. The isothermal overall crystallization kinetics of the PVDF and PEO arms of the 4-miktoarm star copolymers and representative PEO and PVDF precursors was determined by Differential Scanning Calorimetry (DSC). The results indicate that the star arms crystallized faster than the equivalent precursors as the kinetics are dominated by nucleation effects. The phases formed by the PVDF components in the materials examined were analyzed by studying their melting behavior by DSC, their superstructural morphology by Polarized Light Optical Microscopy (PLOM), and the phase structure by Fourier Transform Infrared Spectroscopy (FTIR). The linear PVDF and (PVDF29-N3)2, exhibited α, β and γ-phases (with a majority of β-phase formation) during melting after isothermal crystallization. The ratio of the different phases depends on the crystallization temperature. An analysis of the multiple melting behavior indicated that the sample forms both α and β-phases initially, and the α-phase partially transforms into the γ-phase during isothermal crystallization when the temperature of crystallization increases. We found a remarkable behavior for the 4-miktoarm star copolymers, as the PVDF arms only form the ferroelectric β-phase when all three materials were isothermally crystallized regardless of the crystallization temperature employed. The presence of the polymorphism in the PVDF was detected by DSC, PLOM, and FTIR. Hence, we have shown that tailoring chain topology in PVDF copolymers can lead to exclusive β-phase formation, a path that can be exploited for future piezoelectric applications.

Controlled block-polymerization of styrene, divinylbenzene and ethylene oxide. Intermolecular cross-linking towards well-defined miktoarm copolymer stars

• Synthesis of well-defined miktoarm copolymer stars. • Control over the molecular weight and composition for both arm species. • Controlled polymerization of poly(divinylbenzene). • Intermolecular cross-linking of linear triblock terpolymers. A novel approach for the synthesis of miktoarm copolymer stars with divinylbenzene cross-linked core, via anionic polymerization is reported. This synthetic route gives access to polymers, characterized by low dispersity values and improved structural homogeneity for both arm species. Specifically, miktoarm copolymer stars of A n B n type, with cross-linked divinylbenzene (DVB) core and arms of polystyrene (PS) and poly(ethylene oxide) (PEO), are synthesized via anionic polymerization and sequential monomer addition, employing high vacuum techniques. Analytically, the first step involves the synthesis of a triblock terpolymer PS- b -PDVB- b -PEO. Then, in the presence of a free radical initiator the pending vinyl groups of the middle DVB block cross-link intermolecularly, leading to the final miktoarm copolymer star. The novelty of the proposed synthetic route, lies in the potassium alkoxide co -initiator, which is responsible for the controlled polymerization of both DVB and EO in one pot, without the need for end group modification between the two steps. Concerning the final polymer, there are numerous benefits advancing from this synthetic protocol, such as the control of the molecular characteristics of both arms, as well as the easily confirmed structural integrity of the precursor triblock which is inherited to the resulting miktoarm star. For comparison reasons, another batch of (PS)(PEO) miktoarm copolymers was synthesized, following the “in-out” synthetic route. For this reason, styrene was polymerized using s -BuLi, which is used as macroinitiator for the polymerization/cross-linking of DVB, resulting PS star with DVB cross-linked core. With the addition of EO, in the presence of p4 t -Bu phosphazene base, PEO arms are polymerized, initiating from the core’s active cites outwards.

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

Green Stereoregular Polymerization of Poly(methyl methacrylate)s Through Vesicular Catalysis

Interfacial dilatational rheology as a bridge to connect amphiphilic heterografted bottlebrush copolymer architecture to emulsifying efficiency

HypothesisMolecular architecture and composition of amphiphilic bottlebrush copolymers will dictate the dominant interfacial relaxation modes and the corresponding dilatational rheology for adsorbed layers at oil/water interfaces in a way that will correlate with the emulsifying efficiency of different bottlebrush copolymers. ExperimentsAmphiphilic, xylene-soluble poly(ethylene oxide)-poly(n-butyl acrylate) (PEO-PBA) heterografted bottlebrush copolymers with controlled differences in backbone length, hydrophilicity and arm length were synthesized by atom transfer radical polymerization. Dilatational rheology of adsorbed layers at the xylene/water interface was probed via pendant drop tensiometry by measuring the interfacial stress response to either large-amplitude strain cycling or small-amplitude strain oscillation. The rheological response was recorded as a function of interfacial pressure for adsorbed layers under different compression states. Emulsifying efficiency was determined as the lowest copolymer concentration that yielded water-in-xylene emulsions with at least one-month stability against coalescence. FindingsThe more hydrophilic copolymers with longer PEO arms exhibited non-hysteretic stress-strain response curves in large-amplitude strain cycling and a tendency for the modulus to increase with increasing interfacial pressure. These were more efficient emulsifiers than less hydrophilic copolymers that exhibited hysteretic interfacial rheology. Mere existence of significant moduli did not correlate with high emulsifying efficiency, while an increase in modulus with increasing interfacial pressure did so.

H-Shaped Copolymer of Polyethylene and Poly(ethylene oxide) under Severe Confinement: Phase State and Dynamics.

The self-assembly and the dynamics of an H-shaped copolymer composed of a polyethylene midblock and four poly(ethylene oxide) arms (PE-b-4PEO) are investigated in the bulk and under severe confinement into nanometer-spaced LAPONITE clay particles by means of small- and wide-angle X-ray diffraction (SAXS, WAXS), differential scanning calorimetry (DSC), polarizing optical microscopy (POM), rheology, and dielectric spectroscopy (DS). Because of the H-shaped architecture, the PE midblock is topologically frustrated and thus unable to crystallize. The superstructure formation in the bulk is dictated solely by the PEO arms as inferred by the crystallization/melting temperature relative to the PEO homopolymer. Confinement produced remarkable changes in the interlayer distance and PEO crystallinity but left the local segmental dynamics unaltered. To reconcile all structural, thermodynamic, and dynamic effects, a novel morphological picture is proposed with interest in emulsions. Key parameters that stabilize the final morphology are the severe chain confinement with the associated entropy loss and the presence of interactions (hydrophobic/hydrophilic) between the LAPONITE and the PEO/PE blocks.

PEO-based electrolytes blended with star polymers with precisely imprinted polymeric pseudo-crown ether cavities for alkali metal ion batteries

Tailor-made star polymers comprised of cross-linked cores containing polymeric pseudo-crown ether cavities and linear poly(ethylene oxide) (PEO) arms are designed via cation template-assisted cyclopolymerization. The pseudo-crown ether cavities in cross-linked cores can coordinate with alkali metal cations and offer more cation diffusion channels. Moreover, the functional linear PEO arms are beneficial to the conductivity of cations and increase the compatibility with the PEO matrix. By selecting monomers with different chain lengths and cation templates, the tailor-made star polymers can be employed as efficient conductors for lithium-ion, sodium-ion, and potassium-ion batteries. The lithium-ion conductivity of the solid-state polymer electrolytes obtained from a potassium cation template and poly(ethylene glycol) dimethacrylate (PEGDMA750) monomer (K-SPE750-Li) is 2.82 × 10-5 S cm-1 at 20 °C. Furthermore, the cell of Li|K-SPE750-Li|LiFePO4 shows stable cycling performance and a good rate property.

Peculiarities of complexation of sodium cations by star-shaped polymers with core formed from diepoxides and poly(ethylene oxide) arms

23Na NMR spectroscopy was used to study complexation of sodium cations (NaClO4) with a few of star-shaped polyethers. The bonding of sodium ions by these polymers having PEO arms and with model compounds has been studied in anhydrous methanol solutions. In this paper the preliminary studies are presented, indicating that star polymers built from PEO arms and core formed from diepoxides, containing cyclic structures, are good polydentate complexing agents of sodium cations. Core cyclic structures hinder exchange of the complexed sodium cation with free cations.

Temperature sensitive supramolecular self assembly of per-6-PEO-β-cyclodextrin and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) in water.

The host/guest interactions in water of a star polymer consisting of a β-cyclodextrin (β-CD) core bearing six poly(ethylene oxide) arms linked to the C6 positions of β-CD (β-CD-PEO7, Mn 5000 g mol(-1)) and α,ω-di-(adamantylethyl)poly(N-isopropylacrylamide) (Ad-PNIPAM-12K, Mn 12,000 g mol(-1)) were studied by 1D and 2D (1)H and (13)C NMR spectroscopy, isothermal calorimetry (ITC), and light scattering (LS). In cold water (T < 26 °C) supramolecular "dumbbell" assemblies, consisting of PNIPAM chains with β-CD/Ad inclusion complexes at each end, formed viaβ-CD-insertion of the terminal Ads through the β-CD secondary face. Light scattering, microcalorimetry (DSC), and DOSY NMR studies indicated that mixed aqueous solutions of β-CD-PEO7 and Ad-PNIPAM-12K undergo a reversible heat-induced phase transition at ∼32 °C, accompanied by a release of a fraction of the Ad-bound β-CD-PEO7 into bulk solution and the formation of aggregated Ad-PNIPAM-12K stabilized by a β-CD-PEO7 shell.

Synthesis, Self‐Assembly, and Properties of Homoarm and Heteroarm Star‐Shaped Inorganic–Organic Hybrid Polymers with a POSS Core

AbstractNovel homoarm and heteroarm star‐shaped inorganic–organic hybrid polymers with a polyhedral oligomeric silsesquioxane (POSS) core are prepared via click chemistry of azide POSS [POSS‐(N3)8], alkynyl poly(L‐lactide) (PLLA), and alkynyl poly(ethylene oxide) (PEO). The melting and crystallization behaviors of the polymers can be adjusted by altering the PLLA to PEO ratio. The hybrid polymers reveal unique crystalline morphology due to the influence of the star‐shaped structure and the mutual influence of PLLA and PEO. The hybrid polymers show different thermostabilities, owing to the different compositions of the polymers. The hydrophilicity can be adjusted by alternating the composition of the PLLA and PEO segments. In addition, the sizes of the polymer micelles change with the change of the ratio of PLLA and PEO arms in the hybrid polymers.magnified image

Three-arm star compounds composed of 1,3,5-tri(azobenzeneethynyl)benzene cores and flexible PEO arms: synthesis, optical functions, hybrid Ormosil gel glasses

A three-arm star rod-coil block conjugated compound composed of 1,3,5-tri(azobenzeneethynyl)benzene core and flexible poly(ethylene oxide) arms was synthesized. For comparison, two others with the same core but different end groups were also prepared. The compounds show thermotropic discotic liquid crystalline phase behavior and properties of optical limiting and photo-induced trans–cis isomerization. The star-shaped compound with poly(ethylene oxide) arms can be homogeneously dispersed into Ormosil gel glass monoliths up to 12 wt% without any compatibilizer. The glasses are mechanically stable and highly transparent in the visible and near IR region. The nonlinear optical and optical limiting properties of the gel glasses are comparable or superior to those of the corresponding solutions. The photochromic property of the azobenzene units can be maintained in the gel glass state.

PEO-Based Star Copolymers as Stabilizers for Water-in-Oil or Oil-in-Water Emulsions

A series of well-defined poly(ethylene oxide) (PEO)-based star copolymers with controlled number of arms, compactness, and compositions were prepared by atom transfer radical polymerization using a simple “arm-first” method. Tuning the composition of the arms allowed these star polymers to stabilize either oil-in-water or water-in-oil emulsions. Stable oil-in-water emulsions were obtained with star copolymers containing only hydrophilic PEO arms due to their better affinity to the aqueous phase. In contrast, the insertion of a fraction of hydrophobic poly(butyl acrylate) arms into the star structure significantly changed the surfactant behavior of the star copolymers, leading to the formation of stable water-in-oil emulsions. Additionally, in both cases, an extremely low surfactant concentration, <0.01 wt % vs total weight of water and xylene used for emulsion formation, was sufficient to generate stable emulsions.

Morphology and NMR Self-Diffusion in PBA/PEO Miktoarm Star Copolymers

Abstract Morphology and NMR self-diffusion of two miktoarm star copolymers differing in fraction of poly(n-butyl acrylate) and poly(ethylene oxide) (PBA and PEO) arms were under investigation. Structural characteristics of copolymers was obtained on the basis of Small Angle X-Ray Scattering (SAXS) investigations. The phase separated nanoscale morphology of the miktoarm star copolymer with a high fraction of PEO arms was confirmed by Scanning Probe Microscopy (SPM) studies. The modified Avrami approach was used to obtain the information on the non-isothermal crystallization kinetics of the studied systems. It was observed that the crystallization in the system with a higher content of PBA, occurring at higher undercooling, was characterized by a higher crystallization rate. It was also found that increase in PBA arms fraction leads to the reduction in the size of PEO domains. The activation energy of the crystallization process, estimated with Kissinger's method, is lower for miktoarm star copolymer with higher PBA content, which results from facilitation of the transport of PEO chains in the direction of the growing crystal due to the presence of mobile PBA arms. The self-diffusion studies of miktoarm star copolymers melts, carried out with the Pulsed-Gradient STimulated-Echo (PGSTE) Nuclear Magnetic Resonance (NMR) technique, reveals the existence of at least two types of diffusion mechanisms in these systems.

Effect of Degree of Branching on the Thermoresponsive Phase Transition Behaviors of Hyperbranched Multiarm Copolymers: Comparison of Systems with LCST Transition Based on Coil-to-Globule Transition or Hydrophilic−Hydrophobic Balance

This work reports for the first time the influence of degree of branching (DB) on the thermoresponsive phase transition behaviors of hyperbranched multiarm copolymers. Two series of PEHO-star-PEOs (series A) and PEHO-star-PDMAEMAs (series B) with the hydrophobic DB-variable PEHO core and different kinds of linear arms (PEO arms or PDMAEMA arms) were synthesized. It was found these two series demonstrate thermoresponsive phase transitions with the lower critical solution temperature (LCST). The studies on the LCST transition mechanism indicate that series A belongs to the thermoresponsive polymer system with LCST transition based on hydrophilic-hydrophobic balance, while series B belongs to the thermoresponsive polymer system with LCST transition based on coil-to-globule transition. Correspondingly, there is a big difference in the DB dependence of LCST transition between series A and series B. For series A, the LCST phase transition is highly dependent on the DB of the PEHO core in copolymers. For series B, the LCST phase transition is independent of the DB but dependent on solution pH. Such results may extend the knowledge on the structure-activity relationship of thermoresponsive highly branched polymers.

Rapid Synthesis and MALDI‐ToF Characterization of Poly(ethylene oxide) Multiarm Star Polymers

AbstractMultiarm PEO star polymers with a purely aliphatic polyether structure have been synthesized using hyperbranched polyglycerol (PG) with different molecular weights as a multifunctional initiator. Different degrees of deprotonation of the initiator were studied with respect to molecular weight control. The results show that the degree of deprotonation is a crucial parameter for the synthesis of well‐defined polymers with controlled molecular weights. Partial deprotonation of the PG hydroxyl groups (5–8%) was proven to represent an optimum for the synthesis of star polymers with molecular masses close to the theoretical values. Molecular weights of the stars ranged between 9 000 and 30 000 g · mol−1. MALDI‐ToF spectra confirmed that the PEO arms in the star polymers possess homogeneous lengths.magnified image

One‐pot preparation of 3‐miktoarm star terpolymers via “click chemistry” and atom transfer nitroxide radical coupling reaction

A new strategy for preparation of 3-miktoarm star terpolymer was suggested. The fully-defined precursors PtBA-N3 (poly(tert-butyl acrylate) with azide end group), TEMPO-PEO or TEMPO-PCL (poly(ethylene oxide) or poly(ε-caprolactone) with TEMPO end group) and PS-alkyne/Br (polystyrene with ω-propargyl and ω′-(2-bromoiso butyryl) groups) are designed and prepared first, then the star terpolymers composed of PtBA, PS, and PEO (PCL) arms could be obtained via combination of “click chemistry” and ATNRC reaction using a one-pot. [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.]

Functionalized star-shaped polymers having PEO and/or polyglycidyl arms and their properties

The introduction of methacrylic, carboxylic and phosphate functional groups on the core and at the end of the poly(ethylene oxide) (PEO) arms in the PEO star-shaped polymers is described. In the polyglycidol (PGL) star-shaped polymers phosphate groups were attached to the PGL arms as side groups. Polymers were characterized by NMR and SEC analysis with triple detection. The conversion of the unsubstituted star-shaped polymers into functionalized has been confirmed by 1H and 13C NMR spectra. The influence of the length of arms, their structure and the presence of functional groups on melting (Tm) and crystallization (Tc) temperatures and the degree of crystallinity (Xc) by differential scanning calorimetry (DSC) has been studied.

PH‐Switchable Complexation between Double Hydrophilic Heteroarm Star Copolymers and a Cationic Block Polyelectrolyte

AbstractDouble hydrophilic heteroarm star copolymers of poly(methacrylic acid) (PMAA) and poly(ethylene oxide) (PEO) were synthesized via atom‐transfer radical polymerization (ATRP) using the “in‐out” method. The synthesis consisted of three steps. Namely, ATRP was applied to the preparation of a star macroinitiator with PEO arms and a cross‐linked core resulting from the polymerization of divinylbenzene (DVB) in the first step, chain extension with tert‐butyl methacrylate (tBMA) under ATRP conditions, and subsequent hydrolysis of the tert‐butyl groups afforded (PEO)n‐PDVB‐(PMAA)n heteroarm star copolymers with a cross‐linked microgel core. This novel type of double hydrophilic heteroarm star copolymer can be considered as unimolecular micelles with hybrid coronas. The star copolymers exhibited pH‐dependent solubility in water, being soluble at high pH and insoluble at low pH, due to the formation of hydrogen‐bonded complexes between the PEO and PMAA arms. A mixed solution of the heteroarm star copolymer and a PEO‐b‐PQDMA diblock copolymer, where PQDMA is poly(2‐(dimethylamino)ethyl methacrylate) fully quaternized with methyl iodide, remained stable in the whole pH range, and exhibited an intriguing pH‐switchable complexation behavior accompanied with structural rearrangement.magnified image

Solvent induced morphologies of poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) triblock copolymers synthesized by atom transfer radical polymerization

Poly(methyl methacrylate-b-ethylene oxide-b-methyl methacrylate) (PMMA–PEO–PMMA) triblock copolymers were synthesized using atom transfer radical polymerization (ATRP) and halogen exchange ATRP. PEO-based macroinitiators with molecular weight from Mn=2000 to 35,800g/mol were used to initiate the polymerization of MMA to obtain copolymers with molecular weight up to Mn=82,000g/mol and polydispersity index (PDI) less than 1.2. The macroinitiators and copolymers were characterized by gel permeation chromatography (GPC) and nuclear magnetic resonance (NMR) spectroscopy. The melting temperature and glass transition temperature of the copolymers were measured by differential scanning calorimetry (DSC). Crystallinities of the PEO blocks were determined from the WAXS patterns of both homopolymers and block copolymers, which revealed the fragmentation of PEO blocks due to the folding of the PMMA chains. Interestingly, the fragmentation was less pronounced when cast on surfaces compared to that in bulk, as measured by GISAXS. Solvent casting was used to control the morphology of the copolymers, permitting the formation of various states including amorphous, induced micellar with a PMMA core and flower-like PEO arms, and a cross-linked gel. Atomic force microscopy (AFM) was used to visualize the different copolymer morphologies, showing micellar and amorphous states.

Synthesis of ABC-type miktoarm star polymers by “click” chemistry, ATRP and ROP

ABC-type miktoarm star polymers, poly(ethylene oxide)-block-polystyrene-block-poly ( ε-caprolactone)s (PEO- b-PS- b-PCL) were synthesized via combination of “click” chemistry, atom-transfer radical polymerization (ATRP) and ring opening polymerization (ROP). Azide ended PEO arms, PEO–N 3, and a trifunctional molecule, propargyl 2-hydroxylmethyl-2-(α-bromoisobutyraloxymethyl)-propionate (PHBP), were prepared first, respectively. A “click” reaction of PEO–N 3 and PHBP generated a PEO macroinitiator, PEO–(Br)(OH) with two functionalities, one is hydroxyl group and the other is α-bromoisobutyraloxyl group. Consecutive ATRP of styrene (St) and ROP of ε-caprolactone ( ε-CL) from the PEO macroinitiator produced the PEO- b-PS- b-PCL miktoarm stars. All the structures of the polymers were determined.