Ethy1ene Oxide Research Articles

A Novel Reactive Polymeric Micelle with Aldehyde Groups on Its Surface

It is reported that amphiphilic AB block copolymers form in selective solvents micellar structures.' These nanospheric particles combine the advantages given by the hydrophobic core, which can act as a vehicle for medical drugs, and the unique properties of a hydrophilic ~ h e 1 1 . ~ ~ PEO chains attached to a surface or forming the corona of a nanospheric particle in an aqueous medium exhibit rapid chain motions and have a large excluded volume. The steric repulsion resulting from a loss of configurational entropy of the bound PEO upon the approach of a foreign particle and the low interfacial free energy contribute to the extraordinary properties of PEO-covered surface^.^-'^ The small size, apparent thermodynamic stability, and exceptional biological features of polymeric micelles favor their application in the biomedical field.11-14 Recently, a facile and quantitative synthetic method for the formation of heterobifunctional poly(ethy1ene oxide) was reported.15J6 If one of the functional end groups in the heterobifunctional PEO can selectively initiate the polymerization of a hydrophobic monomer, a new heterobifunctional AB block copolymer can be created, retaining the other functional group (acetal group) a t the PEO chain end. As a core-forming segment, polylactide (PLA) was chosen for the following reasons: (1) The ring-opening reaction of a lactide can be initiated by the living chain end of potassium ethylene oxide without any side reaction. (ii) PLAS are biodegradable and nontoxic polymers, which are widely utilized as implant materials. This is an important prerequisite considering a future application of this system in the biomedical field. (iii) Nanoparticles, consisting of block copolymers of a-methoxypoly(ethy1ene oxide) and PLA are suited for drug de1i~ery.l~ Furthermore, the micelle formation and transformation of acetal into aldehyde groups on the micelle surface were discussed. An aldehyde group reacts rapidly with primary amino groups, forming a Schiff base, a chemical path which could be employed in the hture for conjugations with proteins. Experimental Section. Materials and Methods. Commercial tetrahydrofuran (THF), 3,3-diethoxypropanol, ethylene oxide (EO), and lactide were purified conventionally.l8 Potassium naphthalene was used as a THF solution.1g GPC measurements were carried out using a Shimadzu 6A liquid chromatograph equipped with a PEO-calibrated TSK gel column (G4000HXL, G3000HXL, G2500HXL) and an internal RI detector (RID-6A). THF containing 2% of triethylamine was used as eluent a t a flow rate of 1 mumin. 'H-NMR

Effect of poly(vinylidene fluoride) on the ionic conductivity and morphology of PEO–salt polymer electrolytes

AbstractThe high dielectric constant polymer poly(vinylidene fluoride) (PVDF) was blended with PEO–Salt polymer electrolytes to improve their ionic conductivity. PVDF did improve the room‐temperature ionic conductivity of the polymer electrolytes PEO–LiCF3CO2 and PEO–LiBF4, and the ionic conductivity at room temperature went up one order of magnitude with 10−5S/cm for LIB4M–PF4 being the most prominent. PVDF exhibited strong effects on the ionic conductivity and morphology of the polymer electrolytes, such as weakening the association of poly(ethylene oxide) (PEO) with the salt, hindering the formation of the PEO–salt complex, enlarging the crystalline PEO phase in LIAnM–PFm polymer electrolytes, and reducing the crystalline PEO phase in LIBnM–PFm polymer electrolytes. Both LIA4M–PF4 and LIB4M–PF4 polymer electrolytes formed a new PEO–PVDF–salt complex. The new complex in the former was crystalline, but that in the latter was amorphous. © 1994 John Wiley & Sons, Inc.

Interactions between surfactants and uncharged polymers in aqueous solution studied by microcalorimetry

Abstract

Novel dynamic scaling hypothesis for semidilute and concentrated solutions of polymers and polyelectrolytes

We introduce a dynamic scaling hypothesis which connects the self-diffusion of a chain with the viscosity of the macromolecular solution. It applies to both semidilute and concentrated solutions and leaves the detailed motion of the chains unspecified. When it is valid, one is able to measure the density v of effective dynamic units in the transient network of entangled chains. The feasibility of the hypothesis is shown for aqueous poly(ethy1ene oxide) and sodium poly(styrenesulfonate), polymers not at all conforming to the usual scaling dynamics. Surprisingly, the density v is not very sensitive to charge or the addition of salt.

Incorporation of NaCI into polyelectrolyte complex of poly(acrylic acid)/poly(4-vinylpyridine)

Abstract Much attention is being devoted to polymer/salt hybrids prepared by dispersing inorganic salts in polymers, because the hybrids have high ionic conductivities (1,2). Many of the investigations have concentrated on the system polyester-alkali metal salts, such as poly(ethy1ene oxide)-NaI (3). A few other polymers, such as poly(viny1idene fluoride) and poly(ethy1ene imine), have been examined as the polymer matrix for dissolving the salts (4, 5). In the field of solid state ionics, an active area of research is the attempt to obtain polymer/salt hybrids with higher conductivity. Most of the investigations have been directed toward the evaluation of conductivity for new polymer-salt systems.

Adsorption of Peo-b-Ps Copolymers on Surfaces. Infrared and Surface Force Measurements at XRCC

Abstract Surface force and IR data on polystyrene-b-poly(ethy1ene oxide) block copolymers adsorbed on mica from toluene will be presented. The copolymers were selected to have a wide range of asymmetry radius radio (β = RF,PE,O)3/5 as defined by Marques and Joanny. The extended length L the block copolymers has been measured with the Surface Force Apparatus and shown to scale as L∼NNPSNPEO 1/3 for moderately asymmetric copolymers (1 ≪ β ≫ NNPEO 1/2). Deviations are observed when the nonadsorbing block is either much larger than the anchor block or approximately the same size. A general method using infrared spectroscopy has been developed which can measure the quantity of adsorbed polymers on mica. A FTIR operated in a dual beam mode has been used to increase the sensitivity to a point where it is possible to easily obtain spectra of adsorbed polymers. Thin mica sheets and a transmission-reflectance device are used to suppress optical interference fringes which otherwise dominate the spectrum and mask the infrared bands due to adsorbed polymers. The Alexander-de Gennes scaling law for the surface density, LNBσ1/3, has been found to be roughly obeyed over a wide range of copolymer molecular weights and radius ratios p. The Marques and Joanny scaling laws for σ, σ 1/Na, describe well the behaviour of the moderately asymmetric materials. However, their model does not appear to predict the proper surface density for material at the cross over point between the 3D and 2D regimes, near β ≈ NA 1/2. Recently we have extended our infrared studies of PEO-b-PS adsorption to high surface area silica particles. The adsorption of the PEO and PS units with the surface of the silica can be measured independently by observing the perturbation in the infrared band due to surface hydroxyl groups. 8pecial infrared cells have been designed to allow for thermal pretreatment of the silica and subsequent polymer addition under vacuum conditions. An overview of our initial findings will be discussed.

Phase transitions in poly(ethylene oxide) and polystyrene at high pressure

Abstract The temperature and enthalpy of melting for poly(ethy1ene oxide) have, for the first time, been studied as a fuction of pressure up to 1 GPa by means of differential scanning calorimetry. The initial increase of the temperature of melting with increasing pressure is 64 K/GPa, whereas the enthalpy decreases by 40% in the 1 GPa pressure range. Using Clausius-Clapeyrons equation the volume change on melting is estimated to be 1.5 cm3/mol. The glass transition temperature Tg for polystyrene has also been studied by the same technique for pressures up to 0.1 GPa. The measurements show that Tg increases with increasing pressure by 250 K/GPa.

Phosphorescence from a bromonaphthalene lumophore as a photophysical probe of polymer conformation and interpolymer interactions

A bromonaphthalene-labeled poly(acry1ic acid), BNPAA, was synthesized and found to be phosphorescent in solution at room temperature. The phosphorescence of the polymer was employed to investigate (1) the influence of pH on the conformations of the polymer in aqueous solutions, (2) the interactions of BNPAA with complementary polymers (poly( 1-vinyl-2-pyrrolidinone) and poly(ethy1ene oxide)), and (3) conformations of the polymer adsorbed on a solid-liquid interface. The phosphorescence lifetimes of BN- PAA provide a probe of changes in polymer conformations that result from inter- and intrapolymer interactions. The results suggest an unusual pH dependence for BNPAA conformations in dilute solutions; e.g., significant breaks in the lifetime/pH profile are found at pH 4 and pH 10. These unexpected results were confirmed by the observation of the same two breaks at pH 4 and pH 10 with the use of two independent photolu- minescence probes, a pyrene-labeled poly(acry1ic acid), PyPAA, and a ruthenium complex, Ru(byp)gZ+. The two breaks in the conformation/pH profile are explained in terms of combination of hydrogen bonding and a hydrophobic substituent effect at low pH and charge screening at high pH. Phosphorescence lifetime measurements are also used to probe the interactions of the BNPAA with complementary macromolecules such as poly( 1-vinyl-2-pyrrolidinone) and poly(ethy1ene oxide) and with a solid alumina surface. Finally, the interaction of BNPAA with a low molecular weight substance, the cationic surfactant dodecyltrimethylam- monium bromide, was also investigated by employing the phosphorescent probe.

Lithium ion complexation kinetics by cyclic and acyclic polyethers

Abstract

Application of the dynamic rotational isomeric states model to poly(ethylene oxide) and comparison with nuclear magnetic relaxation data

The dynamic rotational isomeric states (RIS) model recently developed for investigating local chain dynamics is further improved and applied to poly(ethy1ene oxide) (PEO). In general, a set of eigenvalues AI, j = 1 to Y *, characterizes the dynamic behavior of a given segment of N motional bonds, with v isomeric states available to each bond. The eigenvalues may be identified as the frequencies of the individual modes contributing to local chain relaxation. To calculate orientational autocorrelations, time correlations, and/or power spectra, Ais are combined with the weighting factors k, which are determined by the equilibrium statistics of the chain and the specific property investigated. The rates of transitions between isomeric states are assumed to be inversely proportional to solvent viscosity, leading to a linear dependence between viscosity and correlation times. Predictions of the theory are in satisfactory agreement with the isotropic correlation times and spin-lattice relaxation times from *3C and 'H NMR experiments for PEO in a variety of solvents. An activation energy of about one barrier height is theoretically calculated, in agreement with previous experimental studies.

Salt effects in free nonionic films

The thickness has been measured of macroscopic aqueous films, stabilized by nonionic surfactants consisting of a hydrophobic part and a poly(ethy1ene oxide) moiety. Special attention has been paid to the influence of electrolytes. In the fiis, the surfactants behave like coiled polymers. Addition of electrolytes increases the rate of drainage. As a function of the electrolyte concentration, the equilibrium thickness passes through a maximum. These maxima are similar to those for the Huggins constant for the corresponding micelles.

Collapse of poly(ethylene oxide) monolayers

Surface pressure ?r has been measured as a function of surface concentration for poly(ethy1ene oxide) (PEO) surface films, spread onto deionized water at temperatures T from 8 to 28 C. At fixed surface coverage, the temperature coefficient of surface pressure d?r/dT was negative at submonolayer coverages and positive at higher surface coverages. This suggests, respectively, a peculiar increase and decrease of surface entropy with increasing surface coverage. The equilibrium spreading pressure from an excess of polymer, 7rw, was achieved at surface coverage 0.8 mg/m2, approximately 1.5 times monolayer coverage. As a function of molecular weight, 7req was constant beyond molecular weight M = 1 X lo5 g/mol but fell at lesser levels for fractions of lesser molecular weight. Observation of da/dT < 0 appears to have been observed previously only for the spreading of small crystalline amphiphiles, but the reasons cannot be the same in the present system. A degree of ordering of water molecules with the PEO repeat unit in the surface layer is suggested. These findings illustrate that a polymer monolayer should not in all respects be considered as two-dimensional.

A New Ionic Conducting Polymer Based on Oligo(Ethylene Oxide) Substituted Nylon-1

Abstract The potential application of solvent-free polymer-alkali salt complexes as electrolytes in high energy density batteries1 and solid state thermoelectrochromic Displayz has stimulated considerable investigations on synthesis and characterization of poly(ethy1ene oxide) and poly(propy1ene oxide)-alkali salt complexes. These linear polymers are highly crystalline at ambient temperature and the crystalline domains are known to impede ion conduction. Thus, more recent work has focused on polymers having flexible chain structure and lower glass transition temperature (Tg). This can be accomplished for polymers with pendant oligo(ethy1ene oxide) chains on flexible polymer backbones such as poly-(methacrylate)3, poly(phospazene)4 and poly(methy1siloxane)5-6.

Structure and Phase Transitions in PEO-KI Complexes

Abstract In the 1970's Wrightl1-2 and later Armand et aL3 suggested that poly(ethy1ene oxide) (PEO) complexed with alkali metal salts could be used as thin film polymeric solid electrolytes. Since this original work we have witnessed a rapid expansion of research and development of this class of conducting polymers.

Ionic Conductive Polymers Based on Crosslinked Elastic Siloxane-Ethylene Oxide Copolymers

Abstract Solvent-free polymer electrolytes have generated much interest because of their potential applications in such areas as high energy density batteries1, solid state electrochromic display2, photoelectrochemical cells3. Early investigations were focused on alkali metal ion conduction in poly(ethy1ene oxide) (PEO) and polyfpropylene oxide) (PPO)4. Recent work has utilized various polymers such as poly(ethylenimine)5 and poly(ethy1ene succinate)6 as well as macromolecules with pendant methoxy-oligo(oxyethy1ene) chains anchored to polymethacrylate7, polyphosphazene8, and methylsiloxane9 backbones.

Photoluminescent probes for water soluble polymers. Pressure and temperature effects on a polyol surfactant

Five photoluminescent probes have been employed to investigate the behavior of a poly(ethy1ene oxide)-poly(propy1ene oxide) block copolymer in aqueous solution. The measured fluorescence probe parameters, at fied probe concentration, were found to be dependent on the concentration of copolymers and to demonstrate a low-, medium-, and domain. In the high-concentration domain the parameters were found to be extremely sensitive to temperature and pressure. The results are interpreted in terms of intramolecular and intermolecular micelle formation by the copolymer.

Binding of (arylmethyl)ammonium cations by polyelectrolytes. Evidence for hydrophobic and electrostatic interactions

The associative interactions of several cationic probes, Le., bis(a-naphthylmethy1)a”onium chloride (DNMAC), (a-naphthylmethy1)a”onium chloride (NMAC), dibenzylammonium chloride (DBAC), and (benzy1)a”onium chloride (BAC), with anionic polyelectrolytes, Le., sodium poly(ethy1enesulfonate) (PES), sodium poly(styrenesulfonate) (PSS), and sodium poly(2-acrylamido-2-methyl-l-propanesulfonate) (PAMPS), and with a neutral polymer, poly(ethy1ene oxide) (PEO), have been investigated by fluorescence techniques. Evidence is presented that the probe conformation in both the ground and the excited singlet states depends on the type of interaction (hydrophobic or electrostatic) that dominates in determining the binding strength. For example, the predominately hydrophobic binding of DNMAC and PEO in aqueous solution produces a decrease in the ratio of excimer to monomer emission of the probe, relative to that in aqueous solution. The predominately electrostatic binding of DNMAC and PAMPS in methanol produces a sharp increase in the ratio of excimer to monomer emission of the probe relative to that of the probe in methanol solution. The binding of the probes to the polyelectrolytes PAMPS, PSS, and PES in aqueous solution results in an enhancement of excimer emission of the probe. The dependence of such enhancement of the excimer emission on the probe and/or polyelectrolyte concentration suggests that, in spite of the low effective charge of the probes, electrostatic interactions of the probe and the polyelectrolyte are not negligible with respect to the hydrophobic interactions.

An ion-exchange process with thermal regeneration. III. Properties of weakly acidic ion-exchange resins

A series of cross-linked poly(acrylic acid) and poly(methacrylic acid) resins has been synthesized. Their titration curves, and those of similar commercial resins, show that at c. 20� the pH value at half neutralization may be varied within about one unit by using acrylic or methacrylic acid monomers, or by changing the degree of cross-linking. The titration curves of such resins do not have a pronounced plateau although the acidity is due only to carboxyl groups. Resins with flatter titration curves can be made by copolymerizing acrylic or methacrylic acids with methyl methacrylate. Copolymerization reduces the effective acid strength of carboxylic acid resins but does not always produce a resin with a flatter titration curve. The effects of salt concentration, calcium ions, and temperature on the titration curves of a poly(acry1ic acid) resin have been studied. Heating the resins in a salt solution from c. 20 to 80� decreases their effective acidity slightly. A bigger reduction in acidity with heating is observed with several polymers in which a "snake" polymer, such as a poly(ethy1ene oxide), is incorporated within a cross-linked poly(acrylic acid) resin cage.