The Experts below are selected from a list of 108522 Experts worldwide ranked by ideXlab platform
Jun Li - One of the best experts on this subject based on the ideXlab platform.
-
biodegradable hyperbranched amphiphilic polyurethane multiblock Copolymers consisting of poly propylene glycol poly ethylene glycol and polycaprolactone as in situ thermogels
2012Co-Authors: Zibiao Li, Zhongxing Zhang, Xiping Ni, Jun LiAbstract:This paper reports the synthesis and characterization of new hyperbranched amphiphilic polyurethane multiblock Copolymers consisting of poly(propylene glycol) (PPG), poly(ethylene glycol) (PEG), and polycaprolactone (PCL) segments as in situ thermogels. The hyperbranched poly(PPG/PEG/PCL urethane)s, termed as HBPEC Copolymers, were synthesized from PPG-diol, PEG-diol, and PCL-triol by using 1,6-hexamethylene diisocyanate (HMDI) as a coupling agent. The compositions and structures of HBPEC Copolymers were determined by GPC and 1H NMR spectroscopy. We carried out comparative studies of the new hyperbranched Copolymers with their linear counterparts, the linear poly(PPG/PEG/PCL urethane) (LPEC) copolymer and Pluronic F127 PEG-PPG-PEG block copolymer, in terms of their self-assembly and aggregation behaviors and thermoresponsive properties. HBPEC Copolymers were found to show thermoresponsive micelle formation and aggregation behaviors. Particularly, the lower critical solution temperature (LCST) of the copol...
-
synthesis and water swelling of thermo responsive poly ester urethane s containing poly e caprolactone poly ethylene glycol and poly propylene glycol
2008Co-Authors: Jun LiAbstract:Abstract Thermo-responsive multiblock poly(ester urethane)s comprising poly(e-caprolactone) (PCL), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) segments were synthesized. The Copolymers were characterized by GPC, NMR, FTIR, XRD, DSC and TGA. Water-swelling analysis carried out at different temperatures revealed that the bulk hydrophilicity of the Copolymers could be controlled either by adjusting the composition of the copolymer or by changing the temperature of the environment. These thermo-responsive copolymer films formed highly swollen hydrogel-like materials when soaked in cold water and shrank when soaked in warm water. The changes are reversible. The mechanical properties of the copolymer films were assessed by tensile strength measurement. These Copolymers were ductile when compared to PCL homopolymers. Young's modulus and the stress at break increased with increasing PCL content, whereas the strain at break increased with increasing PEG content. The results of the cytotoxicity tests based on the ISO 10993-5 protocol demonstrated that the Copolymers were non-cytotoxic and could be potentially used in biomedical applications.
Karin Schillen - One of the best experts on this subject based on the ideXlab platform.
-
the interaction between peo ppo peo triblock Copolymers and ionic surfactants in aqueous solution studied using light scattering and calorimetry
2004Co-Authors: Jorgen Jansson, Karin Schillen, Gerd Olofsson, And Rodrigo Cardoso Da Silva, Watson LohAbstract:Properties of nonionic triblock Copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) (EOnPOmEOn) in aqueous solution and their interaction with the ionic surfactants sodium dodecyl sulfate and hexadecyltrimethylammonium chloride have been investigated by static and dynamic light scattering, high sensitivity differential scanning, and isothermal titration calorimetry. The studied Copolymers (denoted P123 and F127) have the same hydrophobic PPO central block (m = 68), but different length of the endblocks, n = 20 and 97. At 40 °C, the Copolymers are associated into micelles with hydrodynamic radius of 9.8 nm (P123) and 12.5 nm (F127) composed of a hydrophobic PPO core and a water-swollen PEO corona. The different copolymer/surfactant systems have been investigated at a constant copolymer concentration of 1 wt % and with varying surfactant concentration up to about 120 mM. When ionic surfactants are added to the PEO−PPO−PEO block copolymer micellar systems, three concentration regimes are...
-
vesicles formed from a poly ethylene oxide poly propylene oxide poly ethylene oxide triblock copolymer in dilute aqueous solution
1999Co-Authors: Karin Schillen, Karin Bryskhe, Yuliya S MelnikovaAbstract:Micelle formation of block Copolymers in selective solvents (organic solvent or water) has been studied for many years.1-3 The morphology of polymeric micelles has been the subject of more recent investigations both theoretically and experimentally.4-8 Diblock Copolymers with a long soluble block compared to the nonsoluble block may self-assemble into micelles of a starlike structure while Copolymers with a short soluble block often form so-called crew-cut micelles.3,9 One class of water-soluble block Copolymers that has attracted great interest in the literature is the triblock Copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), often abbreviated as PEOPPO-PEO or EOa-POb-EOa. These Copolymers exist in a wide range of different compositions and display a rich phase behavior in water depending on their relative block lengths.10,11 It is well established that the more hydrophilic Copolymers associate into micelles, composed of a PPO core and a PEO corona, with a spherical or rodlike shape depending on temperature.7,12-14 The present work focuses on the investigation of one of the most hydrophobic PEO-PPO-PEO Copolymers (L121) in dilute water solutions. New interesting structures found in the L121/water system are presented and visualized by the cryogenic transmission electron microscopy (cryo-TEM) technique. For the first time, to our knowledge, unilamellar vesicles are shown to exist in a triblock copolymer system of this type. Vesicles of branched PEO-PPO block Copolymers in water have only been predicted as a metastable state in earlier model calculations.15 There are only a few reports in the literature on vesicle formation of diblock and multiblock Copolymers in dilute solutions of selective solvents.16-21 Vesicles were one among several different crew-cut aggregates found in polystyrene-poly(acrylic acid) (PS-PAA) and PS-PEO diblock copolymer aqueous systems.9 These vesicular aggregates were prepared by a dialysis method. Both Copolymers form so-called glassy vesicles, which are preserved in water since the water-insoluble PS block is in a glassy state at ambient temperatures. However, a recent study on a polybutadiene-PAA (PBD-PAA) copolymer/water system has concluded that the vesicular morphology is not controlled by the glass temperature of the nonsoluble block.22 Other publications have reported the existence of multilamellar block copolymer vesicles in a homopolymer-rich matrix as a selective solvent and in a concentrated ternary block copolymer system exposed to a shear flow.23-27 This communication presents a different and new preparation procedure of block copolymer vesicles than described in earlier work. The method uses an extrusion method often utilized for the preparation of single-tailed and double-tailed surfactant (or lipid) vesicles, during which the dispersed bilayers close into a spherical structure with a water interior.28 The formation of unilamellar surfactant vesicles normally requires the input of energy by extrusion, ultrasonication, or dialysis, although it has been suggested that they may form spontaneously in some mixed cationic and anionic surfactant systems.29 The PEO-PPO-PEO triblock copolymer, denoted Pluronic L121, was a gift from BASF corporation and used without further purification. It has a nominal molecular weight of 4400 g/mol, and the average composition is EO5PO68EO5, which corresponds to 10 wt % of PEO. L121 Copolymers do not form micelles. At low concentrations and temperatures, unimers (individual copolymer chains) coexist with larger unimer aggregates (an L1 phase). The hydrodynamic radii (RH) of the unimers and the aggregates, obtained using dynamic light scattering (DLS) at 10 °C, are 1.9 and 44 nm, respectively. Figure 1 displays one part of the binary phase diagram of L121 in water. Because of the short hydrophilic PEO chains, and therefore the small headgroup area, the Copolymers can easily pack into a lamellar phase (LR) which appears at higher copolymer concentrations (>55 wt %). The lamellar phase boundaries, as preliminary determined by small-angle X-ray scattering (SAXS), are also indicated in the figure. At low concentrations and at ambient temperatures, the system phase separates, and the phase separation curve determined by visual inspection is shown in Figure 1. The two-phase region is an equilibrium between the lamellar phase and the L1 phase. The L121 block copolymer vesicles were prepared at 25 °C from dilute block copolymer solutions in this L1/LR two-phase regime by repeated extrusion of the * To whom correspondence should be addressed. E-mail address: Karin.Schillen@fkem1.lu.se. Figure 1. Schematic phase diagram of L121 in water. The vesicles were prepared in the two-phase region (2φ) at 25 °C from aqueous L121 solutions with concentrations of 0.2, 0.4, 0.6, and 1.2 wt %. 6885 Macromolecules 1999, 32, 6885-6888
Yuliya S Melnikova - One of the best experts on this subject based on the ideXlab platform.
-
vesicles formed from a poly ethylene oxide poly propylene oxide poly ethylene oxide triblock copolymer in dilute aqueous solution
1999Co-Authors: Karin Schillen, Karin Bryskhe, Yuliya S MelnikovaAbstract:Micelle formation of block Copolymers in selective solvents (organic solvent or water) has been studied for many years.1-3 The morphology of polymeric micelles has been the subject of more recent investigations both theoretically and experimentally.4-8 Diblock Copolymers with a long soluble block compared to the nonsoluble block may self-assemble into micelles of a starlike structure while Copolymers with a short soluble block often form so-called crew-cut micelles.3,9 One class of water-soluble block Copolymers that has attracted great interest in the literature is the triblock Copolymers of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO), often abbreviated as PEOPPO-PEO or EOa-POb-EOa. These Copolymers exist in a wide range of different compositions and display a rich phase behavior in water depending on their relative block lengths.10,11 It is well established that the more hydrophilic Copolymers associate into micelles, composed of a PPO core and a PEO corona, with a spherical or rodlike shape depending on temperature.7,12-14 The present work focuses on the investigation of one of the most hydrophobic PEO-PPO-PEO Copolymers (L121) in dilute water solutions. New interesting structures found in the L121/water system are presented and visualized by the cryogenic transmission electron microscopy (cryo-TEM) technique. For the first time, to our knowledge, unilamellar vesicles are shown to exist in a triblock copolymer system of this type. Vesicles of branched PEO-PPO block Copolymers in water have only been predicted as a metastable state in earlier model calculations.15 There are only a few reports in the literature on vesicle formation of diblock and multiblock Copolymers in dilute solutions of selective solvents.16-21 Vesicles were one among several different crew-cut aggregates found in polystyrene-poly(acrylic acid) (PS-PAA) and PS-PEO diblock copolymer aqueous systems.9 These vesicular aggregates were prepared by a dialysis method. Both Copolymers form so-called glassy vesicles, which are preserved in water since the water-insoluble PS block is in a glassy state at ambient temperatures. However, a recent study on a polybutadiene-PAA (PBD-PAA) copolymer/water system has concluded that the vesicular morphology is not controlled by the glass temperature of the nonsoluble block.22 Other publications have reported the existence of multilamellar block copolymer vesicles in a homopolymer-rich matrix as a selective solvent and in a concentrated ternary block copolymer system exposed to a shear flow.23-27 This communication presents a different and new preparation procedure of block copolymer vesicles than described in earlier work. The method uses an extrusion method often utilized for the preparation of single-tailed and double-tailed surfactant (or lipid) vesicles, during which the dispersed bilayers close into a spherical structure with a water interior.28 The formation of unilamellar surfactant vesicles normally requires the input of energy by extrusion, ultrasonication, or dialysis, although it has been suggested that they may form spontaneously in some mixed cationic and anionic surfactant systems.29 The PEO-PPO-PEO triblock copolymer, denoted Pluronic L121, was a gift from BASF corporation and used without further purification. It has a nominal molecular weight of 4400 g/mol, and the average composition is EO5PO68EO5, which corresponds to 10 wt % of PEO. L121 Copolymers do not form micelles. At low concentrations and temperatures, unimers (individual copolymer chains) coexist with larger unimer aggregates (an L1 phase). The hydrodynamic radii (RH) of the unimers and the aggregates, obtained using dynamic light scattering (DLS) at 10 °C, are 1.9 and 44 nm, respectively. Figure 1 displays one part of the binary phase diagram of L121 in water. Because of the short hydrophilic PEO chains, and therefore the small headgroup area, the Copolymers can easily pack into a lamellar phase (LR) which appears at higher copolymer concentrations (>55 wt %). The lamellar phase boundaries, as preliminary determined by small-angle X-ray scattering (SAXS), are also indicated in the figure. At low concentrations and at ambient temperatures, the system phase separates, and the phase separation curve determined by visual inspection is shown in Figure 1. The two-phase region is an equilibrium between the lamellar phase and the L1 phase. The L121 block copolymer vesicles were prepared at 25 °C from dilute block copolymer solutions in this L1/LR two-phase regime by repeated extrusion of the * To whom correspondence should be addressed. E-mail address: Karin.Schillen@fkem1.lu.se. Figure 1. Schematic phase diagram of L121 in water. The vesicles were prepared in the two-phase region (2φ) at 25 °C from aqueous L121 solutions with concentrations of 0.2, 0.4, 0.6, and 1.2 wt %. 6885 Macromolecules 1999, 32, 6885-6888
Doo Sung Lee - One of the best experts on this subject based on the ideXlab platform.
-
in situ gelling stimuli sensitive block copolymer hydrogels for drug delivery
2008Co-Authors: Sung Wan Kim, Doo Sung LeeAbstract:Stimuli-sensitive block copolymer hydrogels, which are reversible polymer networks formed by physical interactions and exhibit a sol-gel phase-transition in response to external stimuli, have great potential in biomedical and pharmaceutical applications, especially in site-specific controlled drug-delivery systems. The drug may be mixed with a polymer solution in vitro and the drug-loaded hydrogel can form in situ after the in vivo administration, such as injection; therefore, stimuli-sensitive block copolymer hydrogels have many advantages, such as simple drug formulation and administration procedures, no organic solvent, site-specificity, a sustained drug release behavior, less systemic toxicity and ability to deliver both hydrophilic and hydrophobic drugs. Among the stimuli in the biomedical applications, temperature and pH are the most popular physical and chemical stimuli, respectively. The temperature- and/or pH-sensitive block copolymer hydrogels for biomedical applications have been extensively developed in the past decade. This review focuses on recent development of the preparation and application for drug delivery of the block copolymer hydrogels that respond to temperature, pH or both stimuli, including poly(N-substituted acrylamide)-based block Copolymers, poloxamers and their derivatives, poly(ethylene glycol)-polyester block Copolymers, polyelectrolyte-based block Copolymers and the polyelectrolyte-modified thermo-sensitive block Copolymers. In addition, the hydrogels based on other stimuli-sensitive block Copolymers are discussed.
-
ph temperature sensitive poly ethylene glycol based biodegradable polyester block copolymer hydrogels
2006Co-Authors: Dai Phu Huynh, Woo Sun Shim, Ji Heung Kim, Doo Sung LeeAbstract:Abstract Novel pH and temperature sensitive biodegradable block Copolymers composed of poly(ethylene glycol) (PEG), polyglycolide (GA), ɛ-caprolactone (CL) and sulfamethazine oligomers (OSMs) were synthesized by ring opening polymerization and 1,3-dicyclohexyl-carbodiimide (DCC) mediated coupling reactions. Their physicochemical properties in aqueous media were characterized by 1 H NMR spectroscopy and gel permeation spectroscopy. The sol–gel phase transition behavior of OSM–PCGA–PEG–PCGA–OSM block Copolymers was investigated both in solution and injection to PBS buffer at pH 7.4 and 37 °C. Aqueous solutions of OSM–PCGA–PEG–PCGA–OSM changed from a sol to a gel phase with increasing temperature and decreasing pH. The sol–gel transition properties of these block Copolymers are influenced by the hydrophobic/hydrophilic balance of the Copolymers, block length, hydrophobicity, stereoregularity of the hydrophobic components within the block copolymer, and the ionization of the pH functional groups in the copolymer, which depends on the environmental pH. Degradation of the triblock and pentablock Copolymers at 37 °C (pH 7.4), and at 0 °C and 5 °C both at pH 8.0, was investigated. It was demonstrated here using the in vitro test method, that the anticancer agent paclitaxel (PTX) could be loaded and released by the pH and temperature sensitive OSM–PCGA–PEG–PCGA–OSM block copolymer, such that this could be used as a suitable matrix for subcutaneous injection in drug delivery systems.
T. Alan Hatton - One of the best experts on this subject based on the ideXlab platform.
-
Poly(ethylene oxide)poly(propylene oxide)poly(ethylene oxide) block copolymer surfactants in aqueous solutions and at interfaces: thermodynamics, structure, dynamics, and modeling
1995Co-Authors: Paschalis Alexandridis, T. Alan HattonAbstract:The association properties of poly(ethylene oxide)-block-poly(propyleneoxide)-block-poly(ethylene oxide) (PEOPPOPEO) Copolymers (commercially available as Poloxamers and Pluronics) in aqueous solutions, and the adsorption of these Copolymers at interfaces are reviewed. At low temperatures and/or concentrations the PEOPPOPEO Copolymers exist in solution as individual coils (unimers). Thermodynamically stable micelles are formed with increasing copolymer concentration and/or solution temperature, as revealed by surface tension, light scattering, and dye solubilization experiments. The unimer-to-micelle transition is not sharp, but spans a concentration decade or 10 K. The critical micellization concentration (CMC) and temperature (CMT) decrease with an increase in the copolymer PPO content or molecular weight. The dependence of CMC on temperature, together with differential scanning calorimetry experiments, indicates that the micellization process of PEOPPOPEO Copolymers in water is endothermic and driven by a decrease in the polarity of ethylene oxide (EO) and propylene oxide (PO) segments as the temperature increases, and by the entropy gain in water when unimers aggregate to form micelles (hydrophobic effect). The free energy and enthalpy of micellization can be correlated to the total number of EO and PO segments in the copolymer and its molecular weight. The micelles have hydrodynamic radii of approximately 10 nm and aggregation numbers in the order of 50. The aggregation number is thought to be independent of the copolymer concentration and to increase with temperature. Phenomenological and mean-field lattice models for the formation of micelles can describe qualitatively the trends observed experimentally. In addition, the lattice models can provide information on the distribution of the EO and PO segments in the micelle. The PEOPPOPEO Copolymers adsorb on both airwater and solidwater interfaces; the PPO block is located at the interface while the PEO block extends into the solution, when Copolymers are adsorbed at hydrophobic interfaces. Gels are formed by certain PEOPPOPEO block Copolymers at high concentrations, with the micelles remaining apparently intact in the form of a "crystal". The gelation onset temperature and the thermal stability range of the gel increase with increasing PEO block length. A comparison of PEOPPO Copolymers with PEOPBO and PEO PS block Copolymers and CiEjsurfactants is made, and selected applications of PEOPPOPEO block copolymer solutions (such as solubilization of organics, protection of microorganisms, and biomedical uses of micelles and gels) are presented. © 1995.
