Triblock Copolymer Solutions Research Articles

Biodegradable and thermoreversible hydrogels of poly(ethylene glycol)‐poly(ε‐caprolactone‐co‐glycolide)‐poly(ethylene glycol) aqueous solutions

The aqueous solutions of triblock copolymers of poly(ethylene glycol)-poly(epsilon-caprolactone-co-glycolide)-poly(ethylene glycol) [PEG-P(CL-GA)-PEG] undergoing sol-gel transition as the temperature increases from 20 to 60 degrees C were successfully prepared. The thermogelling block copolymers were synthesized by subtle control of the hydrophilic/hydrophobic balance and the chain microstructures. The amphiphilic block copolymer formed micelles in aqueous solution, and the micelle aggregated as the temperature increased. The sol-gel transition of the copolymer aqueous solutions was studied focusing on the structure-property relationship. GA was incorporated into the polymer chain to prevent crystallization of PCL component and increase the polymer degradation. It is expected to be a promising long-term delivery system for pH-sensitive drugs, proteins, and genes.

Effects of unidirectional and mutual interactions between microstructures and azo dyes as “kinetic” probe molecules on cis→trans isomerization rate constants in aqueous P85 and F88 triblock copolymer solutions

AbstractRate constants of the thermal cis → trans isomerization of azo dyes have been studied in aqueous P85 and F88 triblock copolymer solutions by means of microsecond flash photolysis. Inflection points or maxima of the nonlinear Arrhenius plots indicate microstructure changes around the “kinetic” probe molecules. Unidirectional interactions of micelle formation on reactivity are reflected by discontinuous change of rate constants at temperatures near the critical micellization temperatures (cmT) determined by means of probe‐free methods. Mutual interactions have been identified by means of significant differences between cmT and temperatures, where rate constants change discontinuously. The type of interactions depends on the properties of probe molecules and amphiphiles. Systems as studied in this work might be models of more complex biological reaction systems with temperature‐dependent microstructure changes. © 2007 Wiley Periodicals, Inc. 40: 59–65, 2007

Self-Assembly and Adhesion of DOPA-Modified Methacrylic Triblock Hydrogels

Marine mussels anchor to a variety of surfaces by secreting liquid proteins that harden and form water-resistant bonds to a variety of surfaces. Studies have revealed that these mussel adhesive proteins contain an unusual amino acid, 3,4-dihydroxy-L-phenylalanine (DOPA), which is believed to be responsible for the cohesive and adhesive properties of these proteins. To separate the cohesive and adhesive roles of DOPA, we incorporated DOPA into the midblock of poly(methyl methacrylate)-poly(methacrylic acid)-poly(methyl methacrylate) (PMMA-PMAA-PMMA) triblock copolymers. Self-assembled hydrogels were obtained by exposing triblock copolymer solutions in dimethyl sulfoxide to water vapor. As water diffused into the solution, the hydrophobic end blocks formed aggregates that were bridged by the water-soluble midblocks. Strong hydrogels were formed with polymer weight fractions between 0.01 and 0.4 and with shear moduli between 1 and 5 kPa. The adhesive properties of the hydrogels on TiO2 surfaces were investigated by indentation with a flat-ended cylindrical punch. At pH values of 6 and 7.4, the fully protonated DOPA groups were highly adhesive to the TiO2 surfaces, giving values of approximately equal to 2 J/m2 for the interfacial fracture energy, which we believe corresponds to the cohesive fracture energy of the hydrogel. At these pH values, the DOPA groups are hydrophobic and have a tendency to aggregate, so contact times of 10 or 20 min are required for these high values of the interfacial strength to be observed. At a pH of 10, the DOPA groups were hydrophilic and highly swellable, but less adhesive gels were formed. Oxidation of DOPA groups, a process that is greatly accelerated at a pH of 10, decreased the adhesive performance of the hydrogels even further.

Influence of various series of additives on the clouding behavior of aqueous solutions of triblock copolymers

The cloud point (CP) studies on aqueous solutions of two ethylene oxide-propylene oxide triblock copolymers (EO)2.5(PO)31(EO)2.5 and (EO)13(PO)30(EO)13 with varying number of ethylene oxide (EO) units were carried out in the presence of series of additives, such as alkali, acids, ionic surfactants, alcohols, salts, and hydrotropes. The results of this study show that sodium hydroxide decreases the CP of the two copolymers. Acids increase the CP in the order hydrochloric acid > acetic acid > formic acid for both the triblock copolymers. Hydrotropes increase the CP, whereas salts decrease or increase the CP based on their salting-out/salting-in nature. Alcohols, which are polar organic additives, affect the CP of the two copolymers differently. The change in the CP of the triblock copolymers depends upon the structure and concentration of the additives and on the number of EO units of the two triblock copolymers.

Controlled release of growth hormone from thermosensitive triblock copolymer systems: In vitro and in vivo evaluation

The purpose of this study was to design injectable controlled release polymer formulations for growth hormone using triblock copolymer PLGA–PEG–PLGA (MW 1400–1000–1400). Porcine growth hormone (pGH) formulations were prepared by adding pGH into 30% (w/v) aqueous solution of triblock copolymer. pGH concentrations in the released samples were determined using a standard MicroBCA method. In vitro release studies demonstrated that there were no initial burst of pGH from both formulations containing a low dose (0.12%, w/v) and a high dose (0.42%, w/v) of pGH. In vivo absorption study of pGH in rabbits showed that constant serum levels of exogenous pGH (3–7 ng/mL from high dose and 2–4 ng/mL from low dose) were detected for nearly 4 weeks from delivery systems upon single subcutaneous injection. The absolute bioavailability of pGH enhanced from the thermosensitive polymer-based systems, which was ∼5–15-fold those of subcutaneous aqueous solution. MTT assay and light microscopy were used to investigate the in vitro and in vivo biocompatibility of thermosensitive polymer delivery systems, respectively. Both in vitro and in vivo results support the biocompatible nature of these polymer delivery systems. Thus, the triblock copolymer used in this study was able to control the release of incorporated pGH in vitro and in vivo for longer duration and the delivery system was biocompatible.

Effect of Copolymer Architecture on the Micellization and Gelation of Aqueous Solutions of Copolymers of Ethylene Oxide and Styrene Oxide

The micellar properties and solubilization capacity of poorly water soluble drugs of several micellar and gel solutions of diblock and triblock copolymers of styrene oxide/ethylene oxide have been measured and compared with block copolymers of butylene oxide/ethylene oxide, showing that the solubilization capacity of the styrene oxide block is approximately four times that of a butylenes oxide block for dilute solutions. To continue establishing the correlation between micellar characteristics and solubilization capacity, we have found it interesting to compare the micellar and gelation properties of the diblock and triblock copolymers PSO10PEO135 and PEO69PSO8PEO69 (subindexes are the number-average block lengths), with different architecture but similar average block lengths. Surface tension measurements allowed the determination of the critical micelle concentrations at several temperatures and, so, to calculate standard enthalpies of micellization. Static and dynamic light scattering data permitted us to determine micellar parameters and to obtain qualitatively the extent of hydration of the copolymer micelle. A tube inversion method was used to define the mobile-immobile (soft-hard gel) phase boundary. To refine the phase diagram and observe the existence of additional phases, rheological measurements were done. The results are in good agreement with previous values published for PSOnPEOm and PEOmPSOnPEOm copolymers.

Fabrication of PbS microstructures with different shapes in aqueous solutions of amphiphilic triblock copolymer

Hollow PbS nanospheres and branch-like PbS microstructures have been successfully synthesized by the reaction of Pb(Ac) 2 with the S 2− ions released slowly from thioacetamide (TAA) in Pluronic F127 aqueous solutions at room temperature. The obtained hollow PbS nanospheres have a wall thickness of about 40 nm, and the branch-like PbS microstructures have an average size of 0.7–2.2 μm. Both the wall of the hollow PbS nanospheres and the branch-like structures consist of cubic PbS nanocrystallites. It has been found that a minimum F127 concentration is required for the formation of hollow and branch-like PbS structures. With increasing F127 concentration, the diameter of the obtained hollow spheres increases gradually, whereas the size of the branch-like structures decreases. The addition of cyclohexane makes the diameter of hollow spheres decrease, but has little effect on the branch-like structures. Increasing the temperature of the solutions can significantly decrease the sizes of the hollow and branch-like structures. The complex micelles formed by Pb(Ac) 2 and F127 micelles act as soft templates for the formation of hollow PbS nanospheres, and the complex monomeric F127 aggregates formed by Pb(Ac) 2 and monomeric F127 chains play a structure-directing role in the formation of branch-like PbS microstructures.

Coarse-grained simulations of ABA amphiphilic triblock copolymer solutions in thin films

We study a coarse-grained model of A(10)-B(20)-A(10) amphiphilic triblock copolymers in aqueous solution under confinement. We focus on the influence of the wall interaction on the morphology of the ensuing self-assembled structures. We also study the dynamics of the polymers. All our simulations are confined between two walls. We study three different combinations of walls: hydrophobic and hydrophobic, hydrophobic and hydrophilic, hydrophilic and hydrophilic. We moreover elucidate the concentration influence. The conformation and behavior of the copolymer in strongly confined systems depend on the type of wall interaction and concentration.

Control of the confined and unconfined crystallization in glassy-crystalline poly(vinylcyclohexane)- b-poly(ethylene)- b-poly-(vinylcyclohexane) triblock copolymer in solution

The influence of the solvent evaporation rate on the crystallization of the poly(vinylcyclohexane)- b-poly(ethylene)- b-poly(vinylcyclohexane) (PVCH–PE–PVCH) triblock copolymer with the high T g of PVCH segment in chloroform was investigated. The competition between the crystallization of PE block and the vitrification of PVCH in the triblock copolymer was controlled through changing the solvent evaporation rate in the solution system at different temperatures ( T e). It was found that the melting temperature ( T m) of PVCH–PE–PVCH samples increased with increasing the T e when the T e was lower than the solvent boiling point (bp), depending on the crystalline temperatures. However, when T e was just a little above the solvent bp, two melting peaks, which corresponding to the fusion of the confined and unconfined crystals, respectively, were observed on the DSC curves of the samples. As T e increased to be higher temperature, only one lower melting peak, which corresponding to the fusion of the confined crystals, existed for each samples. It was also found that the crystallinity ( X c) of the samples decreased gradually when T e was lower than the solvent bp, and then decreased suddenly when T e was just a little above the solvent bp, finally reached a plateau (about 13.5%) at higher T e. The changes in X c of the samples depend on the evaporating time in the solution. The results should be related to the competition between the crystallization of PE block in solvent and the vitrification of PVCH block with the solvent evaporation. Furthermore, the competition was controlled through changing the solvent evaporation rate. The confined and unconfined crystallization of the samples could be freely adjusted.

Effect of “inverse melting transition” of aqueous triblock copolymer solutions on solute rotational dynamics

Rotational dynamics of two structurally similar hydrophobic solutes, 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and 1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DPP), has been investigated in 30% wv aqueous solution of triblock copolymer, poly(ethylene oxide)(20)-poly(propylene oxide)(70)-poly(ethylene oxide)(20) as a function of temperature. This study has been undertaken in an attempt to explore how the dynamics of a solute molecule solubilized in a copolymer solution is influenced when it undergoes sol-to-gel transition. It has been observed that the anisotropy decays of both DMDPP and DPP can be described by biexponential functions in the sol as well as in the gel phase. This observation has been rationalized on the basis of the probe molecule undergoing two different kinds of motion rather than being located in two different regions of the micelle. Even in the gel phase, which results as a consequence of micelle-micelle entanglement due to an increase in their volume fraction, the rotational relaxation of the solutes is similar to that observed in the micellar solution. The outcome of this work indicates that even though these gels have very high macroscopic viscosities and hence do not flow, the microenvironments experienced by the solutes are akin to that of a micellar solution.

Large amplitude oscillatory shear behavior of PEO-PPO-PEO triblock copolymer solutions

Rheological properties of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymer solution in both linear and nonlinear regions have been investigated. PEO-PPO-PEO triblock copolymer solution shows a dramatic change in mechanical properties as temperature changes. PEO-PPO-PEO triblock copolymer undergoes a transition from sol to gel with increase of temperature. During this transition the copolymer solution passes through three different stages, namely sol, soft gel, and hard gel. In our previous research (Hyun et al. in J Non-Newtonian Fluid Mech 55:51–65, 2002), large amplitude oscillatory shear (LAOS) behavior was found to be very sensitive to the generated microstructures. In this study, we investigated the relationship between the LAOS type and the microdomain structure. Newtonian behavior is observed in sol region, while there appear two kinds of LAOS types in the soft gel region. One is type I (G′, G′′ decreasing) and the other is a combination of type I and type IV (G′, G′′ increasing followed by decreasing). Type III (G′ decreasing, G′′ increasing followed by decreasing) is observed in the hard gel region. We compared the shape of stress curves, Lissajous pattern, and Fourier transform (FT) rheology of hard gel and soft gel under LAOS, and tried to relate the complex LAOS behavior with the microstructural change. From these investigations, it was found that the LAOS behavior and the stress pattern at large strain are closely related to the microdomain structure of PEO-PPO-PEO triblock copolymer, and provide a lot of useful information on the microstructures induced by large deformation.

Preparation of Gelatin Grafted with Lactic Acid Oligomers

The objective of this study is to synthesize gelatins grafted with lactic acid oligomer (LAo) and lactic acid oligomer-poly(ethylene glycol)-lactic acid oligomer (LAo-PEG-LAo) triblock copolymers and to examine their gelation behavior. The grafting ratio of LAo-grafted gelatins could be changed by the feed ratio of LAo to the amino groups of gelatin for grafting reaction, while triblock copolymers with different molecular weights of LAo were prepared. The turbidity of LAo-grafted gelatin solution increased with the increased grafting ratio, although the turbidity increase was suppressed by adding guanidine hydrochloride in a dose-dependent manner. The turbidity of LAo-grafted gelatin solution further enhanced by mixing with the solution of triblock copolymers, while the enhanced extent increased with an increase in the LAo molecular weight. A mechanically firm hydrogel was formed by mixing the LAo-grafted gelatin and triblock copolymer at the higher solution concentrations, while the compression strength of the hydrogel became higher as the grafting ratio increased. No hydrogel formation was observed in the presence of guanidine hydrochloride.

The effect of solvent size on physical gelation in triblock copolymer solutions

The gelation of physically associating triblock copolymers in a good solvent was investigated by Monte Carlo simulation, and the effect of the solvent size on the gelation was discussed in detail. The solvent size can greatly affect the conformation distribution of the polymer chains, the size distribution of the micelle, and the mechanism of the gelation on microscale, mesoscale, and macroscale. Our results indicate that the effect of the solvent size on the physical gelation exhibits three distinct regions. The gelation closely couples to the chain conformation transition when the solvent size is normal or quasinormal; the gelation occurs simultaneously with phase separation when the solvent size approaches the ideal end-to-end distance of the polymer chains; the gelation follows a glass transition mechanism upon increasing the solvent size to much larger than the ideal end-to-end distance of polymer chains. We also found that the volume fraction of the gel point can shift from 0.20 to 0.06, a range much broader than that reported in the literature.

Influence of NaCl on the Behavior of PEO−PPO−PEO Triblock Copolymers in Solution, at Interfaces, and in Asymmetric Liquid Films

The solution behavior of the polymeric surfactant Pluronic F127 (PEO(99)PPO(65)PEO(99)) and its adsorption behavior on aqueous-silica and aqueous-air interfaces, as well as the disjoining pressure isotherms of asymmetric films (silica/aqueous film/air) containing F127, are studied. The interfacial properties of adsorbed F127 layers (the adsorbed amount Gamma and the thickness h) as well as the aqueous wetting film properties [film thickness (h) and refractive indexes] were studied via ellipsometry. The solution properties of F127 were investigated using surface tensiometry and light scattering. The interactions between the air-water and silica-water interfaces were measured with a thin film pressure balance technique (TFB) and interpreted in terms of disjoining pressure as a function of the film thickness. The relations between the behaviors of the asymmetric films, adsorption at aqueous air, and aqueous silica interfaces and the solution behavior of the polymeric surfactant are discussed. Special attention is paid to the influence of the concentrations of F127 and NaCl. Addition of electrolyte lowers the critical micelle concentration, diminishes adsorption on silica, and increases the thickness of the asymmetric film.

Flow control in microdevices using thermally responsive triblock copolymers

Active and passive microflow control has been demonstrated using gel formation by dilute aqueous solutions of triblock copolymers at elevated temperatures. Solutions of a poly(ethylene oxide)/sub 106/-poly(propylene oxide)/sub 70/-poly(ethylene oxide)/sub 106/ polymer, which has the trade name Pluronic/spl reg/ F127, have been used as a sample system. Flow in a microchannel has been stopped in less than 33 ms by introducing heat with an integrated electric heater. Viscous heating under high shear rates also induces gel formation, which has been used for passive automated flow control in a microchannel.

Molecular Architecture Effect on Self-Assembled Nanostructures of a Linear-Dendritic Rod Triblock Copolymer in Solution

ADVERTISEMENT RETURN TO ISSUEPREVCommunication to the...Communication to the EditorNEXTMolecular Architecture Effect on Self-Assembled Nanostructures of a Linear-Dendritic Rod Triblock Copolymer in SolutionCai-Xia Cheng, Yun Huang, Ru-Pei Tang, Er-qiang Chen, and Fu XiView Author Information State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials, Institute of Chemistry, The Chinese Academy of Sciences, Beijing 100080, China, and Department of Polymer Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China Cite this: Macromolecules 2005, 38, 8, 3044–3047Publication Date (Web):March 25, 2005Publication History Received30 January 2005Revised6 March 2005Published online25 March 2005Published inissue 1 April 2005https://doi.org/10.1021/ma050196tCopyright © 2005 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views640Altmetric-Citations43LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit Read OnlinePDF (419 KB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Chemical structure,Copolymers,Micelles,Self organization,Solvents Get e-Alerts

Excitation Dynamics in Anisotropic Nanostructures of Star-Shaped CdS

Unique starlike CdS particles were prepared from the lyotropic triblock copolymer solution system. The starlike CdS consists of a spherical core and dozens of the attached conical nanolobes. From the comparative studies with the spherical and rod-shaped CdS nanoparticles, the unique photophysical property is presented for the starlike CdS particle. The experimental results suggest that the photogenerated charge carriers at the tip-edge region of the conical nanolobe in the starlike CdS system diffuse into the thicker inner part including the core region, which is possibly due to the decreasing excited state potential gradient from the tip edge to the thicker inner part. This type of charge carrier diffusion dynamics from the surrounding to the thicker inner part in this anisotropic morphology of the starlike CdS semiconductor closely resembles the energy transfer dynamics in the organic dendrimers.

Sodium Chloride and Ethanol Induced Sphere to Rod Transition of Triblock Copolymer Micelles

Dynamic light scattering (DLS), small-angle neutron scattering (SANS), and viscosity studies have been carried out to examine the influence of NaCl and ethanol on the structure of triblock copolymer [(EO)20(PO)70(EO)20] (EO = ethylene oxide; PO = propylene oxide) micelles in aqueous medium. The studies show that while the pure triblock copolymer solutions do not show any significant growth of the micelles on approaching the cloud point, the presence of a small amount of ethanol (5-10%) induces a sphere to rod shape transition of micelles at high temperatures. Interestingly, this ethanol induced sphere to rod transition of micelles can be brought down to room temperature (25 degrees C) with the addition of NaCl. It is also found that NaCl alone cannot induce such sphere to rod transitions and excess ethanol suppresses them by increasing their transition temperature.

Surface Light-Scattering at the Air−Liquid Interface: From Newtonian to Viscoelastic Polymer Solutions

The dynamics of the liquid-air interface of aqueous solutions of a tensioactive triblock copolymer (Pluronic F-68) has been studied using surface quasielastic light scattering over a broad range of concentrations and temperatures. Ancillary surface tension and bulk rheometry data have been obtained for the same system. The results show that the classical theoretical spectrum for monolayers on a Newtonian fluid can be applied only for concentrations below 4.10(-2) mM. For concentrations above c = 14 mM a clear peak centered at zero frequency appears in the spectrum. This feature is incompatible with the classical theoretical spectrum. The SQELS spectra have been described in terms of the theory of Wang and Huang [Wang, C. H.; Huang, Q. R. J. Chem. Phys. 1997, 107, 5898] considering that the loss modulus of the concentrated solutions shows the existence of two relaxation modes even at low frequencies. The theory is able to explain the existence of a peak centered at zero frequency in the spectra, and the theoretical spectra point out the existence of an elastic peak together with the capillary one. There is a reasonable agreement between the relaxation times and the product Gtau obtained from the fits of the SQELS spectra to the theory of Wang and Huang and those obtained from bulk rheology.

Solubilisation in aqueous micellar solutions of block copoly(oxyalkylene)s

The solubilisation capacities of micellar solutions of diblock and triblock copolymers composed of hydrophilic poly(ethylene oxide) and hydrophobic poly(styrene oxide) have been compared using the poorly water-soluble drug griseofulvin as a model solubilisate. Our results showed an increase of solubilisation capacity (expressed as mg griseofulvin per gram of hydrophobic block) with temperature and, for spherical micelles, with core volume before reaching limiting values. A change of micelle shape from spherical to cylindrical (or worm-like) resulting from an increase in micelle aggregation number was accompanied by a further enhancement of solubilisation capacity. Comparison with the solubilisation of the same drug in micellar solutions of block copolymers of poly(ethylene oxide) and poly(1,2-butylene oxide) showed that the solubilisation capacity of a poly(styrene oxide) block was approximately four times that of a poly(1,2-butylene oxide) block for spherical micelles. Solubilisation capacity at 25 °C was approximately doubled when griseofulvin was incorporated into a copolymer melt and micelles initially formed from the drug-loaded melt at 65 °C rather than by loading the drug into pre-micellised solution at 25 °C in the usual manner.