Adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers at the silica-water interface

The adsorption of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) and poly(ethylene oxide)-b-poly(gamma-methyl-epsilon-caprolactone) copolymers in aqueous solution on silica and glass surfaces has been investigated by flow microcalorimetry, small-angle neutron scattering (SANS), surface forces, and complementary techniques. The studied copolymers consist of a poly(ethylene oxide) (PEO) block of M(n) = 5000 and a hydrophobic polyester block of poly(epsilon-caprolactone) (PCL) or poly(gamma-methyl-epsilon-caprolactone) (PMCL) of M(n) in the 950-2200 range. Compared to homoPEO, the adsorption of the copolymers is significantly increased by the connection of PEO to an aliphatic polyester block. According to calorimetric experiments, the copolymers interact with the surface mainly through the hydrophilic block. At low surface coverage, the PEO block interacts with the surface such that both PEO and PCL chains are exposed to the aqueous solution. At high surface coverage, a dense copolymer layer is observed with the PEO blocks oriented toward the solution. The structure of the copolymer layer has been analyzed by neutron scattering using the contrast matching technique and by tapping mode atomic force microscopy. The experimental observations agree with the coadsorption of micelles and free copolymer chains at the interface.     

Poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-g-poly(vinylpyrrolidone): association behavior in aqueous solution and interaction with anionic surfactants

In this work, we aimed to study the association and interaction behavior of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) block copolymers grafted with poly(vinylpyrrolidone). Critical micellization concentrations were determined using fluorescent probes (pyrene) and critical micellization temperatures characterizing temperature-dependent transitions from monomers to multimolecular micelles were measured. The thermal responsiveness of the copolymer is not affected by the grafting. The hydrodynamic radius of the graft copolymer micelles is found to be greater than that of the original copolymer micelles. The graft copolymer is found to form anisotropic aggregates. The structure of the graft copolymer micelles is less disrupted by the anionic surfactant sodium dodecyl sulfate, compared to the ungraft copolymer.     

Poly(vinyl chloride)–poly(ethylene oxide) block copolymers: Synthesis and characterization

Poly(vinyl chloride)-poly(ethylene oxide) block copolymers have been synthesized in solution and emulsion. The polymers were made by first synthesizing macroazonitriles through the reaction of 4,4′-azobis-4-cyanovleryl chloride with hydroxy-terminated poly(ethylene oxide) of varying molecular weights. These macroazonitriles had molecular weights in the range of 3000–88,000 and degrees of polymerization from 5 to 24. Thermal decomposition of the azolinkages in the presence of vinyl chloride monomer yielded block copolymers containing form 2 to 20 wt % poly(ethylene oxide). The structures of the block copolymers were characterized by spectrometric, elemental and molecular weight analyses. The possibility of some graft polymerization occurring via free-radical extraction of a methylene hydrogen from the poly(ethylene oxide) was considered. Polymerization of vinyl chloride with an azonitrile initiator in the presence of a poly(ethylene oxide) yielded predominately homopolymer with some grafted poly(vinyl chloride).     

Thermoreversible gelation of poly(ethylene oxide) biodegradable polyester block copolymers. II

Poly(ethylene oxide)-b-poly(L-lactic acid) (PEO-PLLA) diblock copolymers were synthesized via a ring opening polymerization from poly(ethylene oxide) and l -lactide. Stannous octoate was used as a catalyst in a solution polymerization with toluene as the solvent. Their physicochemical properties were investigated by using infrared spectroscopy, ¹H-NMR spectroscopy, gel permeation chromatography, and differential scanning calorimetry, as well as the observational data of gel-sol transitions in aqueous solutions. Aqueous solutions of PEO-PLLA diblock copolymers changed from a gel phase to a sol phase with increasing temperature when their polymer concentrations are above a critical gel concentration. As the PLLA block length increased, the gel-sol transition temperature increased. For comparison, diblock copolymers of poly(ethylene oxide)-b-poly(l -lactic acid-co-glycolic acid) [PEO-P(LLA/GA)] and poly(ethylene oxide)-b-poly(dl -lactic acid-co-glycolic acid) [PEO-P(DLLA/GA)] were synthesized by the same methods, and their gel-sol transition behaviors were also investigated. The gel-sol transition properties of these diblock copolymers are influenced by the hydrophilic/hydrophobic balance of the copolymer, block length, hydrophobicity, and stereoregularity of the hydrophobic block of the copolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2207–2218, 1999     

Mixed self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate in aqueous solution

Interaction of amphiphilic poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers with anionic sodium dodecyl sulfate (SDS) has been investigated in aqueous solution. Formation of mixed micelles has been confirmed by surface tension measurements, whereas the influence of the surfactant on the copolymer self-assembling has been studied by measurement of the 1H NMR self-diffusion coefficients and by small-angle neutron scattering. As a rule, the surfactant decreases the heterogeneity of the micellar structures formed by the copolymer in water. Moreover, increasing the content of SDS results in the increasingly more important extension of the poly(ethylene oxide) (PEO) corona chains and the copolymer micelle deaggregation. The stability of the micelles against SDS increases with the length of the hydrophobic block. Preliminary two-dimensional NMR measurements with nuclear Overhauser enhancement have confirmed the spatial vicinity between SDS and the constitutive blocks of the copolymer.     

Ultrafast infrared heating laser pulse-induced micellization kinetics of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) in water

The heating-induced micellization of poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide) (Pluronic PE10300) triblock copolymer chains was studied by ultrasensitive differential scanning calorimetry, laser light scattering, and fluorescence spectrometry with a fluorescent probe, 8-anilino-1-naphthalenesulfonic acid ammonium salt. The critical micellization temperatures obtained from the three methods are similar. The micellization kinetics was studied in terms of changes in the fluorescence and Rayleigh scattering intensities after an ultrafast infrared heating laser pulse (approximately 10 ns)-induced temperature jump. The increases in the fluorescence and Rayleigh scattering intensities in the millisecond range can be well described by a single-exponential equation, corresponding to the incorporation of individual triblock copolymer chains (unimers) into large spherical micelles. The increase in copolymer concentration or the initial solution temperature decreases the characteristic transition time. In general, the fluorescence measurement has a better signal-to-noise ratio but leads to a transition time that is slightly shorter than that from the corresponding Rayleigh scattering measurement for a given copolymer solution.     

Melting behavior of ethylene oxide–propylene oxide (sym-EPE) block copolymers

Melting points have been measured for several ethylene oxide–propylene oxide block copolymers (sym-EPE) chosen from the Pluronic range. Melting points of the block copolymers are lower than those of the corresponding poly(ethylene oxide) homopolymer by up to 4°C. The melting point depressions are much smaller than those observed for comparable sym-PEP block copolymers.     

Effect of temperature on the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions

In this work the intrinsic viscosity of poly(ethylene glycol)/poly(vinyl pyrrolidone) blends in aqueous solutions were measured at 283.1–313.1 K. The expansion factor of polymer chain was calculated by use of the intrinsic viscosities data. The thermodynamic parameters of polymer solution (the entropy of dilution parameter, the heat of dilution parameter, theta temperature, polymer–solvent interaction parameter and second osmotic virial coefficient) were evaluated by temperature dependence of polymer chain expansion factor. The obtained thermodynamic parameters indicate that quality of water was decreased for solutions of poly(ethylene oxide), poly(vinyl pyrrolidone) and poly(ethylene oxide)/poly(vinyl pyrrolidone) blends by increasing temperature. Compatibility of poly(ethylene oxide)/poly(vinyl pyrrolidone) blends were explained in terms of difference between experimental and ideal intrinsic viscosity and solvent–polymer interaction parameter. The results indicate that the poly(ethylene glycol)/poly(vinyl pyrrolidone) blends were incompatible.     

Temperature and concentration effects on supramolecular aggregation and phase behavior for poly(propylene oxide)-b-poly(ethylene oxide)- b-poly(propylene oxide) copolymers of different composition in aqueous mixtures, 1

The phase behavior (temperature vs composition) and microstructure for the two binary systems Pluronic 25R4 [(PO)19(EO)33(PO)19]-water and Pluronic 25R2 [(PO)21(EO)14(PO)21]-water have been studied by a combined experimental approach in the whole concentration range and from 5 to 80 degrees C. The general phase behavior has been identified by inspection under polarized light. Precise phase boundaries have been determined by analyzing 2H NMR line shape. The identification and microstructural characterization of the liquid crystalline phases have been achieved using small-angle X-ray scattering (SAXS). The isotropic liquid solution phases have been investigated by self-diffusion measurements (PGSE-NMR method). 25R2 does not form liquid crystals and is miscible with water in the whole concentration range; with increasing temperature, the mixtures split into water-rich and a copolymer-rich solutions in equilibrium. 25R4 shows rich phase behavior, passing, with increasing copolymer concentration, from a water-rich solution to a lamellar and copolymer-rich solution. A small hexagonal phase, completely encircled in the stability region of the water-rich solution, is also present. In water-rich solutions, at low temperatures and low copolymer concentrations, the copolymers are dissolved as independent macromolecules. With increasing copolymer concentrations an interconnected network of micelles is formed in which micellar cores of hydrophobic poly(propylene oxide) are interconnected by poly(ethylene oxide) strands. In copolymer-rich solutions water is molecularly dissolved in the copolymer. The factors influencing the self-aggregation of Pluronic R copolymers (PPO-PEO-PPO sequence) are discussed, and their behavior in water is compared to that of Pluronic copolymers (PEO-PPO-PEO sequence).     

Effects of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymers on structure and stability of liposomal dioleoylphosphatidylethanolamine

The effects caused by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO; Pluronic) copolymers on the structure and stability of dioleoylphosphatidylethanolamine (DOPE) liposomes were studied by means of turbidity, leakage, and cryo-transmission electron microscopy investigations. The results show that by inclusion of Pluronics in the DOPE dispersion it is possible to stabilize the lamellar Lalpha phase and to produce liposomes that are stable and nonleaky at low pH (pH 5). The stabilizing capacity was observed to depend critically on the molecular composition of the Pluronics. Block copolymers with comparably long PPO and PEO segment lengths, such as F127 and F108, most effectively protected DOPE liposomes prepared at high pH from aggregation and subsequent structural rearrangements induced by acidification. A sufficiently long PPO block was found to be the most decisive parameter in order to obtain adequate coverage of the liposome surface at low Pluronic concentrations. Upon increasing the copolymer concentration, however, Pluronics with comparably short PPO and PEO segment lengths, such as F87 and P85, could also be used to stabilize the DOPE liposomes. Essentially the same trends were observed when the Pluronics were added to preformed DOPE liposomes instead of being included in the preparation mixture. In this case the least effective copolymers failed, however, to completely prevent the DOPE liposomes from releasing encapsulated hydrophilic markers.     

Synthesis, Purification and Characterization of Amphiphilic and Microphase Separated Graft Copolymer Polystyrene-g-Poly(ethylene oxide)

The present paper covers the poly (ethylene oxide) macromer with vinyl benzyl terminal group (PEO-VB) prepared by deactivation of the alkoxide function of mono-functional "living" PEO chains with vinyl benzyl chloride (VBC). The obtained macromers were subjected to careful purification and detailed characterization. A new kind of amphiphilic polystyrene-g-poly(ethylene oxide) (PS-g-PEO) with both mi-crophase separated and PEO side chains was synthesized from radical copolymerization of PEO-VB macromer with styrene monomer. An improved purification method, referred as "selective dissolvation", was established for the isolation of graft copolymers from the grafting products, and the purity and yield of the purified copolymers were satisfactory. The well-defined structure of the purified copolymers was confirmed by IR, 1H NMR and GPC. The bulk composition of the graft copolymers was determined by a well-established first derivative UV spectrometry. Various experimental parameters controlling the copolymeri     

Amphiphilic poly(ethylene glycol)-b-poly(ethylene brassylate) copolymers: One-pot synthesis,self-assembly,and controlled drug release

A set of amphiphilic poly(ethylene glycol)-b-poly(ethylene brassylate) (PEG-b-PEB) copolymers based on the PEB hydrophobic block was first synthesized by ring-opening polymerization of ethylene brassylate with an organic catalyst. The EB/PEGmolar ratios and reaction times were adjusted to achieve different chain lengths of PEB. Block copolymers that were characterized by ¹H NMR and GPC could selfassemble into multimorphological aggregates in aqueous solution, which were characterized by DLS and TEM. The hydrophobic doxorubicin (DOX) was chosen as a drug model and successfully encapsulated into the nanoparticles. The release kinetics of DOX were investigated.     

Influence of Grafted Chain Length of a Phenolic Copolymer on Its Complex Formation with Poly(vinyl Pyrrolidone) and Poly(ethylene Oxide)

A phenolic copolymer has been grafted with oligomers of different chain lengths. Polymer-polymer complexation has been studied between graft copolymers and nonionic polymers, such as polyvinyl pyrrolidone) and poly(ethylene oxide), in an acetone-methanol mixture by several methods, e.g., viscosity, conductance, and apparent pH measurements. A distinct stepwise complexation between PVP and graft copolymers has been observed. The length of the side chain also seemed to influence interpolymer complex formation. Some of these observations have been interpreted with reference to the actual structure of the graft copolymers.     

Macromolecular Architecture Based on Anionically Prepared Poly(ethylene oxide) Macromonomers

Synthesis of poly(ethylene oxide) (PEO) macromonomers carrying a methacyloyl group in one end, and N, N-dimethyl amino, thiophene, styryl and vinyl ether functional groups in the other end was desribed. The general synthetic strategy is based on the living anionic polymerization of ethylene oxide initiated with functional potassium alcoholates, followed by reaction with methacyloyl chloride. These macromonomers were further utilized in various macromolecular architectures through via concurrent or selective thermal free radical, oxidative and photoinitiated free radical and cationic polymerization methods. The use of this synthetic route to prepare graft copolymers possessing completly and perfectly alternating PEO side chains using charge-transfer-complex polymerization was also demonstrated.     

Multidimensional chromatographic techniques for hydrophilic copolymers II. Analysis of poly(ethylene glycol)-poly(vinyl acetate) graft copolymers

A large variety of hydrophilic copolymers is applied in different fields of chemical industry including bio, pharma and pharmaceutical applications. For example, poly(ethylene glycol)-poly(vinyl alcohol) graft copolymers that are used as tablet coatings are responsible for the controlled release of the active compounds. These copolymers are produced by grafting of vinyl acetate onto polyethylene glycol (PEG) and subsequent hydrolysis of the poly(ethylene glycol)-poly(vinyl acetate) graft copolymers. The poly(ethylene glycol)-poly(vinyl acetate) copolymers are distributed with regard to molar mass and chemical composition. In addition, they frequently contain the homopolymers polyethylene glycol and polyvinyl acetate. The comprehensive analysis of such complex systems requires hyphenated analytical techniques, including two-dimensional liquid chromatography and combined LC and nuclear magnetic resonance spectroscopy. The development and application of these techniques are discussed in the present paper.     

Self-assembly of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers in aqueous solution

The associative behavior of monodisperse diblock copolymers consisting of a hydrophilic poly(ethylene oxide) block and a hydrophobic poly(epsilon-caprolactone) or poly(gamma-methyl-epsilon-caprolactone) block has been studied in aqueous solution. Copolymers have been directly dissolved in water. The solution properties have been studied by surface tension, in relation to mesoscopic analyses by NMR (self-diffusion coefficients), transmission electron microscopy, and small-angle neutron and X-ray scattering. The experimental results suggest that micellization occurs at low concentration (approximately 0.002 wt %) and results in a mixture of unimers and spherical micelles that exchange slowly. The radius of the micelles has been measured (ca. 11 nm), and the micellar substructure has been extracted from the fitting of the SANS data with two analytical models. The core radius and the aggregation number change with the hydrophobic block length according to scaling laws as reported in the scientific literature. The poly(ethylene oxide) blocks are in a moderately extended conformation in the corona, which corresponds to about 25% of the completely extended chain. No significant modification is observed when poly(gamma-methyl-epsilon-caprolactone) replaces poly(epsilon-caprolactone) in the diblocks.     

Block copolymers prepared by emulsion polymerization with poly(ethylene oxide)–azo-initiators

Poly(ethylene oxide)-b-poly(styrene) block copolymers were prepared in the form of latex particles by emulsion polymerization of styrene with poly(ethylene glycol)–azo-initiators as well as with the redox initiation system poly(ethylene glycol)/Ce⁴⁺. The emulsion polymerization can be carried out in the absence of additional stabilizers if the chain length of the poly(ethylene glycol) is greater than 40. The latex particles as well as the copolymers were characterized by capillary hydrodynamic fractionation, ¹³C-nuclear magnetic resonance (NMR) spectroscopy and Fourier transform infrared spectroscopy. By ¹³C-NMR spectroscopy a side reaction of the primary radicals arising from the azo-initiator was found which can contribute to the low efficiency of azo-initiators in emulsion polymerization.     

Concomitant adsorption of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers and sodium dodecyl sulfate at the silica-water interface

Upon addition of silica to aqueous solutions of poly(ethylene oxide)-b-poly(epsilon-caprolactone) copolymers (PEO-b-PCL) and sodium dodecyl sulfate (SDS), adsorption of the solutes occurs at the silica-water interface. The amount of the adsorbed constituents has been measured by the total concentration depletion method. Small-angle neutron scattering experiments (SANS) have been carried out to investigate the structure of the adsorbed layer. Although SDS is not spontaneously adsorbed onto hydrophilic silica, adsorption is observed in the presence of PEO-b-PCL diblocks, in relation to the relative concentration of the two compounds. Conversely, SDS has a depressive effect on the adsorption of the copolymer, whose structure at the interface is modified. Copolymer desorption is however never complete at high SDS content. These observations have been rationalized by the associative behavior of PEO-b-PCL and SDS in water.     

Assessment of the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles under biological conditions: a fluorogenic-based approach

The integrity of block copolymer micelles is important for their effectiveness and successful delivery of the incorporated drugs. Here we evaluate the integrity of poly(caprolactone)-b-poly(ethylene oxide) micelles in media of varying chemical complexity and in cells by using fluorogenic micelles. Fluorogenic dye fluorescein-5-carbonyl azide diacetate was covalently attached to the micelle-core-forming part of the block copolymer, poly(caprolactone). The fluorescence was not detectable unless the poly(caprolactone)21-b-poly(ethylene oxide)45 micelles were destroyed and the fluorogenic dye was activated by deesterification. The fluorescence of the activated dye from destroyed micelles was easily detectable in various media and in cells. Micelles were stable in simple media such as phosphate-buffered saline but disassembled to varying extents with increasing chemical complexity of the media and addition of serum. The integrity of the internalized micelles within the cells showed a time-dependent decrease but remained largely preserved (80%) after 20 h of incubation with cells. A proof of principle was also demonstrated in vivo in mice. The fluorogenic approach to micelle integrity assessment presented herein should lend itself to other block copolymer micelles and assessments of their integrity in complex biological systems in vitro and in vivo.     

Thermal degradation behavior of a carboxylic acid-terminated amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)

The thermal degradation of an amphiphilic block copolymer poly(ethylene)-b-poly(ethylene oxide)-carboxylic acid terminated (PE-b-80%PEO–CH₂COOH) and its salt obtained as intermediary product from chemical oxidation of the end group of poly(ethylene)-b-poly(ethylene oxide) (PE-b-80%PEO) has been studied using a thermogravimetric mass spectrometry (TG/MS) coupled system. The isothermal fragmentation of PE-b-80%PEO–CH₂COOH showed a more complex fragmentation pattern than PE-b-80%PEO owing to the simultaneous occurrence of the polyether block and the carboxylic end group fragmentations. This led to the appearance of four overlapping ion current peaks of fragments with m/z 44 and two peaks relative to m/z 18 at different times by acid-terminated copolymer. For the PE-b-80%PEO copolymer, two ion current peaks associated to m/z 44 and one large peak relative to m/z 18 fragments were detected. The intermediary product (PE-b-80%PEO–CH₂COO⁻ K⁺) showed differences related to the fragmentation behavior. It has more defined ion current signals and presented characteristic peaks attributed to m/z 43 fragment at the very beginning of the thermal degradation process, which it not detected in the acid copolymer.