PEO Block Length Research Articles

Synthesis of polyrotaxanes consisting of multiple α-cyclodextrin rings threaded on reverse Pluronic PPO–PEO–PPO triblock copolymers based on block-selected inclusion complexation

New polyrotaxanes, in which multiple α-cyclodextrin (α-CD) rings were threaded and imprisoned on a reverse Pluronic PPO–PEO–PPO triblock copolymer chain and capped by two 2,4-dinitrophenyl groups at the two ends, were synthesized based on the block-selected inclusion complexation between the PPO–PEO–PPO triblock copolymers and α-CD. The polyrotaxanes were isolated and purified through size exclusion chromatography, and the chromatograms showed that the polyrotaxanes had high molecular masses as compared with their respective components. The polyrotaxanes were further characterized by using 13C and 1H 1D and 2D NMR spectroscopy, wide-angle X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry. It was found that the threading PPO–PEO–PPO triblock copolymers became more thermally stable because they were complexed by the imprisoned α-CD. The studies demonstrated that the numbers of α-CD rings imprisoned in the polyrotaxanes were directly related to the PEO block length, rather than to the PPO block length. In all the three polyrotaxanes synthesized in this work, the central PEO block was fully covered and complexed by α-CD stoichiometrically, while the flanking PPO bocks remained free and uncomplexed. Therefore, the new polyrotaxanes took a PPO-polyrotaxane-PPO triblock architecture. The polyrotaxanes with such block architecture may be interesting supramolecular precursor for designing novel functional materials.

Microstructural Study of a Nitroxide-Mediated Poly(Ethylene Oxide)/Polystyrene Block Copolymer (PEO- b-PS) by Electrospray Tandem Mass Spectrometry

Electrospray ionization tandem mass spectrometry has been used to characterize the microstructure of a nitroxide-mediated poly(ethylene oxide)/polystyrene block copolymer, called SG1-capped PEO-b-PS. The main dissociation route of co-oligomers adducted with lithium or silver cation was observed to proceed via the homolytic cleavage of a C-ON bond, aimed at undergoing reversible homolysis during nitroxide mediated polymerization. This cleavage results in the elimination of the terminal SG1 end-group as a radical, inducing a complete depolymerization process of the PS block from the so-formed radical cation. These successive eliminations of styrene molecules allowed a straightforward determination of the PS block size. An alternative fragmentation pathway of the radical cation was shown to provide structural information on the junction group between the two blocks. Proposed dissociation mechanisms were supported by accurate mass measurements. Structural information on the SG1 end-group could be reached from weak abundance fragment ions detected in the low m/z range of the MS/MS spectrum. Amongst fragments typically expected from PS dissociation, only beta ions were produced. Moreover, specific dissociation of the PEO block was not observed to occur in MS/MS, suggesting that these rearrangement reactions do not compete effectively with dissociations of the odd-electron fragment ions. Information about the PEO block length and the initiated end-group were obtained in MS(3) experiments.

The effect of PEO block lengths on the size and stability of complex coacervate core micelles

We report on a series of polyion complexes from mixtures of poly(ethylene oxide)- block-poly( N , N -diethylaminoethylmethacrylate) (PEO–PDEAMA) and poly(ethylene oxide)- block-poly(aspartic acid) (PEO–PAsp). As expected, the micelle size, polydispersity and stability are dependant on the relative and absolute lengths of the polyelectrolyte chains. However, we also demonstrate that whilst the length of the charged polyelectrolyte blocks is important, the length of the PEO chains is an equally relevant variable in determining both the size and stability of the final micelles as well as the degree of charge neutralisation at which micellisation occurs. We also show that the kinetics of formation can result in very different stability of the final micelles.

Direct synthesis of mesoporous silica presenting large and tunable pores using BAB triblock copolymers: Influence of each copolymer block on the porous structure

Mesoporous silicas with large and tunable (from 4 to 40 nm) accessible pores have been successfully synthesized using laboratory-made BAB (A: hydrophilic block, B: hydrophobic block) type triblock copolymers as templates. A direct synthesis is carried out in the absence of swelling agent and without any further treatment. The polystyrene- b–poly(ethylene oxide)- b–polystyrene (PS- b–PEO- b–PS) copolymers were synthesized using living/controlled radical polymerization. The porous structure (mesopore size, size distribution and microporous volume) was characterized using electron transmission microscopy and nitrogen sorption measurements. This study is focused on the control of the porous structure as a function of the hydrophobic PS block length and the hydrophilic block length (whilst keeping the other block length constant). It was found that when the PS block length increases: (i) the mesopore size increases linearly with PS block length which thus proffers a fine tuning of the pore diameter from 4 to 40 nm, (ii) the micropore volume decreases. When the PEO block length increases, (i) the mesopore size decreases (ii) the micropore volume increases. All these results were explained considering (i) that both PS and PEO block lengths have an influence on the degree of stretching of the PS chains, thus on the micellar core radius (ii) that the mesopore size is directly connected to the micellar core radius, i.e. that PEO chains do not directly participate to mesoporosity (due to its particular loop configuration) but only to microporosity.

Nonfouling biomaterials based on polyethylene oxide‐containing amphiphilic triblock copolymers as surface modifying additives: Protein adsorption on PEO‐copolymer/polyurethane blends

Surface modification of a segmented polyurethane was achieved by blending with novel PEO-containing amphiphilic triblock copolymers (PEO-polyurethane-PEO). Three copolymers having different PEO MW (550, 2000, 5000) were used as surface modification additives. The protein resistance of the blend surfaces was evaluated using radiolabeling methods. On the blends of copolymers with PEO blocks of MW 2000 and 5000, fibrinogen adsorption from physiologic buffer decreased with increasing copolymer content up to 20 wt%. On the blends with PEO blocks of MW 550, resistance to adsorption for a given copolymer content was much greater. For all three blend types at 20% copolymer content, reductions in adsorption compared to the unmodified PU matrix were greater than 95%. Reductions in adsorption were similar for the 20% blends and surfaces prepared by coating the copolymers directly on the matrix, suggesting that the 20% blend surfaces were completely covered by copolymer. At low copolymer content (< or =10 wt %), fibrinogen adsorption decreased with decreasing PEO block length. This was probably due to increasing surface coverage of the copolymers with decreasing block length. It is therefore concluded that surface density of PEO is more important than PEO MW for the protein resistance of these surfaces. Lysozyme, a much smaller protein, showed adsorption trends similar to fibrinogen. The adsorption of fibrinogen and lysozyme from binary solutions to blends of the copolymer with PEO blocks of 2000 MW was investigated to probe the effects of protein size on adsorption resistance. Fibrinogen and lysozyme showed similar fractional decreases in adsorption relative to the PU matrix independent of the surface density of PEO. However lysozyme was enriched in the surface relative to the solution, that is, it was adsorbed preferentially to fibrinogen.

A Systematic Study of the Stabilization in Water of Gold Nanoparticles by Poly(Ethylene Oxide)−Poly(Propylene Oxide)−Poly(Ethylene Oxide) Triblock Copolymers

Poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO)x−(PPO)y−(PEO)x triblock copolymers have been efficiently used for the stabilization of gold nanoparticles (AuNps) in NaCl aqueous solutions. The effects of concentration and structure of the block copolymer (i.e., PEO block length, PPO block length, and overall length of the polymer) have been systematically investigated, using well-defined AuNps (diameter ∼12 nm) synthesized through a standard citrate reduction procedure. Aggregation and precipitation processes were assessed separately using empirical parameters calculated from optical absorbance spectra. Increasing the concentration, PEO and PPO block lengths, or the overall length of the polymer enhanced the nanoparticles colloidal stability. Among all these parameters, the paramount one appeared to be the length of the PPO block. Different aggregation states were observed and characterized by the displacement of the plasmon resonance band. A correlation between the displacement of t...

Synthesis and micelle formation of triblock copolymers of poly(methyl methacrylate)- b-poly(ethylene oxide)- b-poly(methyl methacrylate) in aqueous solution

Amphiphilic triblock copolymers of poly(methyl methacrylate)- b-poly(ethylene oxide)- b-poly(methyl methacrylate) (PMMA- b-PEO- b-PMMA) with well-defined structure were synthesized via atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) initiated by the PEO macroinitiator. The macroinitiator and triblock copolymer with different PMMA and/or PEO block lengths were characterized with 1H and 13C NMR and gel permeation chromatography (GPC). The micelle formed by these triblock copolymers in aqueous solutions was detected by fluorescence excitation and emission spectra of pyrene probe. The critical micelle concentration (CMC) ranged from 0.0019 to 0.016 mg/mL and increased with increasing PMMA block length, while the PEO block length had less effect on the CMC. The partition constant K v for pyrene in the micelle and in aqueous solution was about 10 5. The triblock copolymer appeared to form the micelles with hydrophobic PMMA core and hydrophilic PEO loop chain corona. The hydrodynamic radius R h,app of the micelle measured with dynamic light scattering (DLS) ranged from 17.3 to 24.0 nm and increased with increasing PEO block length to form thicker corona. The spherical shape of the micelle of the triblock copolymers was observed with an atomic force microscope (AFM). Increasing hydrophobic PMMA block length effectively promoted the micelle formation in aqueous solutions, but the micelles were stable even only with short PMMA blocks.

Composition Dependence of the Crystallization Behavior and Morphology of the Poly(ethylene oxide)-poly(ε-caprolactone) Diblock Copolymer

The crystallization behavior and morphology of the crystalline-crystalline poly(ethylene oxide)-poly(epsilon-caprolactone) diblock copolymer (PEO-b-PCL) was studied by differential scanning calorimetry (DSC), wide-angle X-ray diffraction (WAXD), Fourier transform infrared spectroscopy (FTIR), small-angle X-ray scattering (SAXS), and hot-stage polarized optical microscope (POM). The mutual effects between the PEO and PCL blocks were significant, leading to the obvious composition dependence of the crystallization behavior and morphology of PEO-b-PCL. In this study, the PEO block length was fixed (Mn = 5000) and the weight ratio of PCL/PEO was tailored by changing the PCL block length. Both blocks could crystallize in PEO-b-PCL with the PCL weight fraction (WFPCL) of 0.23-0.87. For the sample with the WFPCL of 0.36 or less, the PEO block crystallized first, resulting in the obvious confinement of the PCL block and vice versa for the sample with WFPCL of 0.43 or more. With increasing WFPCL, the crystallinity of PEO reduced continuously while the variation of the PCL crystallinity exhibited a maximum. The long period of PEO-b-PCL increased with increasing WFPCL from 0.16 to 0.50 but then decreased with the further increase of WFPCL due to the interaction of the respective variation of the thicknesses of the PEO and PCL crystalline lamellae. Only the PEO spherulites were observed in samples with WFPCL of 0.16-0.36 by POM, in contrast to only the PCL spherulites in samples with WFPCL of 0.56-0.87. For samples with WFPCL of 0.43 and 0.50, a unique concentric spherulite was observed. The morphology of the inner and outer portions of the concentric spherulites was determined by the PCL and PEO spherulites, respectively. The growth rate of the PEO spherulites reduced rapidly with increasing WFPCL from 0 to 0.50. However, when increasing WFPCL from 0.43 to 0.87, the variation of the growth rate of the PCL spherulites exhibited a maximum rather than a monotonic change.

Dynamic and Static Light Scattering Studies on Self-Aggregation Behavior of Biodegradable Amphiphilic Poly(ethylene oxide)−Poly[(R)-3-hydroxybutyrate]−Poly(ethylene oxide) Triblock Copolymers in Aqueous Solution

The self-aggregation behavior of two amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer samples with nearly identical PHB block lengths but different PEO block lengths, PEO-PHB-PEO(2000-810-2000) and PEO-PHB-PEO(5000-780-5000), was studied with dynamic and static light scattering (DLS and SLS), in combination with fluorescence spectroscopy and transmission electron microscopy (TEM). The formation of polymeric micelles by the two PEO-PHB-PEO triblock copolymers was confirmed with fluorescence technique and TEM. DLS analysis showed that the hydrodynamic radius (R(h)) of the monodistributed polymeric micelles increased with an increase in PEO block length. The relative thermostability of the triblock copolymer micelles was studied by SLS and DLS at different temperatures. The aggregation number and the ratio of the radius of gyration over hydrodynamic radius were found to be independent of temperature, probably due to the strong hydrophobicity of the PHB block. The combination of DLS and SLS studies indicated that the polymeric micelles were composed of a densely packed core of hydrophobic PHB blocks and a corona shell formed by hydrophilic PEO blocks. The aggregation numbers were found to be approximately 53 for PEO-PHB-PEO(2000-810-2000) micelles and approximately 37 for PEO-PHB-PEO(5000-780-5000) micelles. The morphology of PEO-PHB-PEO spherical micelles determined by DLS and SLS measurements was further confirmed by TEM.

Micellization Phenomena of Biodegradable Amphiphilic Triblock Copolymers Consisting of Poly(β-hydroxyalkanoic acid) and Poly(ethylene oxide)

This paper reports the studies on micelle formation of new biodegradable amphiphilic poly(ethylene oxide)-poly[(R)-3-hydroxybutyrate]-poly(ethylene oxide) (PEO-PHB-PEO) triblock copolymer with various PHB and PEO block lengths in aqueous solution. Transmission electron microscopy showed that the micelles took an approximately spherical shape with the surrounding diffuse outer shell formed by hydrophilic PEO blocks. The size distribution of the micelles formed by one triblock copolymer was demonstrated by dynamic light scattering technique. The critical micellization phenomena of the copolymers were extensively studied using the pyrene fluorescence dye absorption technique, and the (0,0) band changes of pyrene excitation spectra were used as a probe for the studies. For the copolymers studied in this report, the critical micelle concentrations ranged from 1.3 x 10(-5) to 1.1 x 10(-3) g/mL. For the same PEO block length of 5000, the critical micelle concentrations decreased with an increase in PHB block length, and the change was more significant in the short PHB range. It was found that the micelle formation of the biodegradable amphiphilic triblock copolymers consisting of poly(beta-hydroxyalkanoic acid) and PEO was relatively temperature-insensitive, which is quite different from their counterparts consisting of poly(alpha-hydroxyalkanoic acid) and PEO.

Mechanism of Gold Metal Ion Reduction, Nanoparticle Growth and Size Control in Aqueous Amphiphilic Block Copolymer Solutions at Ambient Conditions

Spontaneous formation and efficient stabilization of gold nanoparticles with an average diameter of 7 approximately 20 nm from hydrogen tetrachloroaureate(III) hydrate (HAuCl4.3H2O) were achieved in air-saturated aqueous poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) block copolymer solutions at ambient temperature in the absence of any other reducing agent. The particle formation mechanism is considered here on the basis of the block copolymer concentration dependence of absorption spectra, the time dependence (kinetics) of AuCl4- reduction, and the block copolymer concentration dependence of particle size. The effects of block copolymer characteristics such as molecular weight (MW), PEO block length, PPO block length, and critical micelle concentration (cmc) are explored by examining several PEO-PPO-PEO block copolymers. Our observations suggest that the formation of gold nanoparticles from AuCl4- comprises three main steps: (1) reduction of metal ions by block copolymer in solution, (2) absorption of block copolymer on gold clusters and reduction of metal ions on the surface of these gold clusters, and (3) growth of metal particles stabilized by block copolymers. While both PEO and PPO blocks contribute to the AuCl4- reduction (step 1), the PEO contribution appears to be dominant. In step 2, the adsorption of block copolymers on the surface of gold clusters takes place because of the amphiphilic character of the block copolymer (hydrophobicity of PPO). The much higher efficiency of particle formation attained in the PEO-PPO-PEO block copolymer systems as compared to PEO homopolymer systems can be attributed to the adsorption and growth processes (steps 2 and 3) facilitated by the block copolymers. The size of the gold nanoparticles produced is dictated by the above mechanism; the size increases with increasing reaction activity induced by the block copolymer overall molecular weight and is limited by adsorption due to the amphiphilic character of the block copolymers.

Preparation and Properties of Crosslinked Polyurethane Containing Hydrophilic PEO Component for Biomaterials

A series of multiblock polyurethanes containing various poly(ethylene oxide) (PEO) contents (0-80 wt%) were prepared from hexamethylene diisocyanate (HDI)/ PEO / poly(tetramethylene oxide) (PTMO)/ polybutadiene diol (PBD)/ 1,4-butanediol (BD) and used as modifying additives (30 wt%) to improve the properties of biomedical grade PelletheneÒ. A hydrophilic PEO component was introduced by the addition of PEO-containing polyurethanes and dicumyl peroxide (DCP) as the crosslinking agents in a PelletheneÒ matrix. As the PEO content (PEO block length) increased, the hydrogen-bonding fraction of the crosslinked polyurethane also increased, indicating an increase in the phase separation with an increase in the PEO content in the crosslinked polyurethane. Using electron spectroscopy for a chemical analysis, the ratio of ether carbon to alkyl carbon in the crosslinked polyurethane film increased remarkably with an increase, in the PEO content. Meanwhile, the water contact angle of the crosslinked polyurethane film surfaces decreased with increasing PEO content. The water absorption and mechanical properties of the crosslinked polyurethane films increased with increasing and the platelet adhesion on the crosslinked polyurethane film surfaces decreased significantly. Accordingly, these results suggest that the crosslinked polyurethane containing a hydrophilic PEO component may be more effective for a biomaterial application that is in direct contact with blood.

Amphiphilic Block Copolymers of Poly(ethylene oxide) and Poly(perfluorohexylethyl methacrylate) at the Water Surface and Their Penetration into the Lipid Monolayer

Poly(ethylene oxide) (PEO) and poly(perfluorohexylethyl methacrylate) (PFMA) containing amphiphilic block copolymers have been investigated for their interfacial behavior and their penetration into 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) monolayer at the air/water interface by measuring surface pressure (π)/area (A) isotherms in conjunction with infrared reflection absorption spectroscopy (IRRAS). The π/A isotherms of the block copolymers show pressure regimes corresponding to different conformations of the polymer chains, i.e., a pancakelike conformation at low surface coverage and a brush conformation at high surface pressures. The plateau in π/A isotherms of the block copolymers, (i.e. a phase transition from the pancakelike conformation to the brush conformation) becomes less and less pronounced with a decrease in the PEO block length. The π/A isotherm of the DPhPC monolayer shows only a liquid expanded phase state at the air/water interface at all surface pressures. The DPhPC monolayer pe...

Gas-Permeation Properties of Poly(ethylene oxide) Poly(butylene terephthalate) Block Copolymers

This paper reports the gas-permeation properties of poly(ethylene oxide) (PEO) poly(butylene terephthalate) (PBT) segmented multiblock copolymers. These block copolymers allow a precise structural modification by the amount of PBT and the PEO segment length, enabling a systematic study of the relationship between polymer composition and morphology and gas-transport properties. The CO2 and N2 permeability strongly varies with the amount of PEO and the PEO segment length. The permeabilities are compared to predictions of the Maxwell model, which considers the PBT phase as impermeable. The difference between the experimental values and the Maxwell model are interpreted on the basis of chain flexibility of the PEO phase. The chain flexibility decreases with increasing amounts of PBT due to a less pronounced phase separation between the PEO and PBT phase. This is reflected in an increasing glass-transition temperature of the amorphous PEO phase. The increase of the permeability with an increasing PEO block length, at the same ratio PEO-PBT, can therefore be related to a larger chain flexibility for longer PEO segments. The permeability also depends on the degree of crystallinity and the melting temperature of the PEO phase, which increases with the amount and the PEO segment length. PEO-PBT block copolymers exhibit a high CO2/N2selectivity ( 60 at T = 35 C) due to the high solubility of CO2 in the PEO phase. However, this selectivity is structure-dependent and is higher for block copolymers with larger amounts of PBT. The CO2/He selectivity shows a different structure dependency since the permeation of CO2 occurs primarily through the PEO phase and the He permeation occurs through both the PEO and mixed PEO-PBT interphase. Therefore, block copolymers with a better phase separation between the PEO phase and the PBT phase show a higher CO2/He selectivity.

Properties of crosslinked blends of pellethene and multiblock polyurethane containing poly(ethylene oxide) for biomaterials

AbstractA series of multiblock polyurethanes, containing various poly(ethylene oxide) (PEO; number‐average molecular weight = 400–3400) contents (0–80 wt %) and prepared from hexamethylene diisocyanate/PEO/poly(dimethylsiloxane) diol/polybutadiene diol/1,4‐butanediol, were used as modifying additives (30 wt %) to improve the properties of biomedical‐grade Pellethene. Different molecular weights of PEO were used to keep poly(ethylene glycol) at a fixed molar content, if possible, although the PEO content, related to the PEO block length in the multiblock polyurethanes, was varied from 0 to 80 wt %. The hydrophilic PEO component was introduced through the addition of PEO‐containing polyurethanes and dicumyl peroxide as a crosslinking agent in a Pellethene matrix. As the PEO content (PEO block length) increased, the hydrogen‐bonding fraction of the crosslinked Pellethene/multiblock polyurethane blends increased, and this indicated an increase in the phase separation with an increase in the PEO content in the crosslinked Pellethene/multiblock polyurethane blends. According to electron spectroscopy for chemical analysis, the ratio of ether carbon to alkyl carbon in the crosslinked Pellethene/multiblock polyurethane blends increased remarkably with increasing PEO content. The water contact angle of the crosslinked Pellethene/multiblock polyurethane blend film surfaces decreased with increasing PEO content. The water absorption and mechanical properties (tensile modulus, strength, and elongation at break) of the crosslinked Pellethene/multiblock polyurethane blend films increased with increasing PEO content. The platelet adhesion on the crosslinked Pellethene/multiblock polyurethane blend film surfaces decreased significantly with increasing PEO content. These results suggest that crosslinked Pellethene/multiblock polyurethane blends containing the hydrophilic component PEO may have potential for biomaterials that come into direct contact with blood. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2348–2357, 2004

Polymer and particle adsorption at the PDMS droplet-water interface

Polymer and particle adsorption at the polydimethylsiloxane (PDMS) droplet-water interface has been investigated. Adsorption isotherms and adsorbed layer structure are reported for a range of PEO-PPO-PEO block copolymers, and hydrophilic and hydrophobic silica ‘nanoparticles’. The influence of solution conditions on the adsorption behaviour has indicated the thermodynamics of polymer-droplet and particle-droplet interactions. The influence of droplet cross-linking (deformability) has indicated the role of interfacial penetration in controlling adsorption at the droplet-water interface. The plateau adsorbed amount (Γ max) and adsorbed layer thickness ( δ max) of PEO-PPO-PEO copolymers are dependent on the copolymer structure and the level of cross-linking within droplets. For a wide range of copolymer structures, Γ max values are in the range 2 to 20 mg m −2. For δ max, values range from 2 to 20 nm and are directly proportional to the PEO block length. Droplet cross-linking significantly reduces Γ and δ values; this is considered to be due to the influence of interfacial penetrability on the adsorbed copolymer conformation. Hydrophilic silica particles adsorb onto PDMS droplets with plateau surface coverages that correspond to their hard sphere radius+double layer thickness, i.e. lateral silica-silica interactions control particle packing. Free energies of adsorption (Δ G ads) are concurrent with a physical adsorption mechanism. Surface coverages, Δ G ads and particle packing at the interface are only weakly influenced by pH, but are significantly influenced by salt addition. Droplet cross-linking reduced particle adsorption only at higher salt concentrations; this was attributed to the increased likelihood of silica particles wetting PDMS. Freeze fracture SEM revealed that individual silica particles are adsorbed at the droplet interface with negligible interfacial aggregation. Densely packed adsorbed particle layers are only observed when the double layer thickness is a few nanometers. Adsorption of hydrophobic particles at the PDMS droplet-water interface is more pronounced (greater adsorbed amounts and Δ G ads values) than for hydrophilic particles and displays a pH dependency in line with ‘DLVO behaviour’. The surface coverage values correspond to multiple close packed layers and are significantly influenced by droplet cross-linking, conferring extensive interfacial penetration (confirmed by SEM). Densely packed adsorbed particle layers with interfacial aggregation are observed over a wide range of solution conditions. Interfacial particle saturation occurred at a salt concentration two orders of magnitude less than the critical coagulation concentration (ccc) for silica in water. This phenomenon was observed for both liquid and cross-linked PDMS droplets indicating that particle interaction through the water phase plays a decisive role in particle packing at the interface. SEM indicated the presence of a rigid interfacial crust layer at the salt concentration corresponding to interfacial saturation and a multi-layered interfacial particle wall at salt concentrations ≥ ccc. The PDMS droplets under consideration, having inherent colloid stability in the absence of added stabilisers, are an excellent model system for characterising polymer and particle adsorption at the droplet-water interface. The insight gained concerning adsorption thermodynamics at the droplet-water interface is not available from more conventional emulsions.

Thermodynamics of Water Vapor Sorption in Poly(ethylene oxide) Poly(butylene terephthalate) Block Copolymers

This paper reports on the study of the following: (a) the influence of the composition of poly(ethylene oxide)-poly(butylene terephthalate) (PEO-PBT) block copolymers on the solubility of water vapor; (b) the thermodynamic quantities governing the solubility of water vapor in these polymers. The block copolymers examined differ with respect to their hydrophilic block length (PEO segment) and the weight ratio between the hard hydrophobic PBT segment and the soft hydrophilic PEO segment. Water sorption isotherms, determined gravimetrically, are of Flory-Huggins type, exhibiting a linear relation between weight uptake and vapor activity at low activities and a sharp increase (convex shape) at higher activities. The Flory-Huggins interaction parameter decreases as the concentration of water inside the polymer increases. Its numerical value strongly depends on the polymeric structure: an increase of the soft hydrophilic PEO block length and PEO content both lead to a decrease of the interaction parameter. Solvation Gibbs energies, entropies, and enthalpies, extracted from temperature-dependent sorption data, reveal that (1) water-polymer interactions are stronger than water-water interactions in liquid water, (2) the water-polymer interactions become weaker at higher water vapor activities, and (3) the water sorption entropy increases with increasing vapor activity. The last observation (3) is responsible for the convex nature of the water sorption isotherm. Moreover, this effect depends on the structure of the polymer: the larger the PEO segment length and more PEO weight fraction the higher the solvation entropy and, consequently, the solubility of water vapor in the PEO-PBT block copolymer.

Clay Intercalation of Poly(styrene−ethylene oxide) Block Copolymers Studied by Two-Dimensional Solid-State NMR

The intercalation of poly(styrene−ethylene oxide) block copolymers (PS-b-PEO) into a smectite clay, hectorite, has been studied by multinuclear solid-state nuclear magnetic resonance (NMR). The behaviors of two copolymers with similar PEO block lengths (7 and 8.4 kDa) but different PS block lengths (3.6 vs 30 kDa) were compared. Polymer intercalation is assessed by two-dimensional 1H−29Si heteronuclear correlation (HETCOR) NMR with spin diffusion and refocused 29Si detection for enhanced sensitivity. Hydroxyl protons in the smectite layers serve as crucial spin diffusion references and 1H magnetization relay points from the polymer to the 29Si in the silicate. Experiments with CRAMPS evolution, with 1H spin diffusion, and with detection of the sharp OH proton signal after a 1H T2 filter provide excellent sensitivity for spin diffusion studies with mixing-time series. Because of the mobility of PEO, in this homonuclear experiment we can observe PEO−PS and clay−polymer spin diffusion simultaneously. While t...

New Thermoplastic Elastomers by Incorporation of Nonpolar Soft Segments in PBT-Based Copolyesters

The incorporation of hydroxy-functionalized hydrogenated polybutadienes (HO−PEB−OH, KRATON liquid polymer) into PBT-based copolyesters by a conventional two-step melt polycondensation procedure is described. The usually occurring macrophase separation with nonpolar soft segments is avoided by chain extension of HO−PEB−OH with ethylene oxide to yield the corresponding hydroxy-terminated PEO−PEB−PEO triblock copolymers. Several PEO−PEB−PEO triblock copolymers with different PEO block lengths have been synthesized by means of anionic synthesis and incorporated into PBT-based copolyesters with varying PBT content. We show that the chain extension of HO−PEB−OH with ethylene oxide compatibilizes the nonpolar KRATON with the polar reactants 1,4-butanediol and dimethyl terephthalate during melt polycondensation, leading to a complete incorporation of the triblock copolymer into the copolyester. Morphological studies using SFM as well as mechanical testing show that the morphology is strongly influenced by the soft segment leading to dispersed PBT crystallites in a matrix of the soft phase. Thermal characterization of the synthesized copolyesters by DSC exhibits a low glass transition temperature and a high PBT melting point even at high soft segment contents, making these materials suitable for low- and high-temperature range applications.

Nonaqueous emulsion copolymerization of ethyl methacrylate/lauryl methacrylate in propylene glycol. I. Evaluation of stabilizing efficiency for PEO-PS-PEO triblock copolymers

Sixteen poly(ethylene oxide)–polystyrene–poly(ethylene oxide) (PEO-PS-PEO) triblock copolymers were synthesized by anionic polymerization. They were characterized by gel permeation chromatography and proton NMR. The molecular weight of these 16 PEO-PS-PEO triblock copolymers ranged from 5100 to 13,300. The polystyrene (PS) block length was between 13 and 41. The PEO block length was between 41 and 106. The polydispersity index for these PEO-PS-PEO triblock copolymers were 1.05 ± 0.02. When using these stabilizers in the emulsion copolymerization of ethyl methacrylate and lauryl methacylate in propylene glycol, only a narrow window of stability was observed. Stable latexes were formed only when the molecular weights of the PEO blocks were within the range of 5300–7700 and the molecular weights of the PS blocks were 2000–4000. The stabilizer ability for these triblock copolymers was correlated with their molecular weight and conformation in propylene glycol. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1951–1962, 2001