Triblock Copolymers In Aqueous Solution Research Articles

Using the SAFT-γ-Mie to Generate Coarse-Grained Force Fields Useable in Molecular Dynamics Simulations: Describing the Micellar Phases of Polyalkylglycols in Aqueous Solutions

In this work, we showcase the potential of the SAFT-γ-Mie equation of state to obtain, in a top-down approach, coarse-grained molecular models capable of describing micellization phenomena. For this purpose, we selected polyethylene oxide (PEO)/polypropylene oxide (PPO) triblock copolymers in aqueous solutions as a case study. The model was fitted to reproduce the thermophysical properties─liquid densities and vapor pressures─of small PEO/PPO oligomers as well as the activity coefficients or liquid–liquid phase diagrams of their binary mixtures with water. At low concentrations, the MD simulations show the formation of spherical micelles of morphology comparable to experiments, with the characteristic star-shaped or flower-shaped morphology depending on the polymer block sequence. The local structure and molecular conformations were analyzed, showing distinctions between the two types of aggregates. At higher concentrations, depending on the co-polymer sequence, the molecules form larger micelles or coalesce into larger aggregates when signs of phase separation are observed, as expected.

Unexpected influence of acrylamide on clouding behavior of PEO-PPO-PEO triblock copolymers in aqueous solution

Unexpected influence of acrylamide on clouding behavior of PEO-PPO-PEO triblock copolymers in aqueous solution

Decisive Influence of Hydrophobic Side Chains of Polyesters on Thermoinduced Gelation of Triblock Copolymer Aqueous Solutions

A series of amphiphilic triblock copolymers composed of poly(ethylene glycol) (PEG) and poly(ε-caprolactone-co-5-alkyl δ-lactone)s bearing distinct alkyl side groups were synthesized via ring-opening copolymerization of ε-caprolactone and a small amount of various 5-alkyl δ-lactones using PEG as the macroinitiator and metal-free diphenyl phosphate as the catalyst. The analysis of 1H NMR, GPC, DSC, and XRD confirmed that the synthetic copolymers had similar molecular weights and bulk properties; nevertheless, they exhibited quite different aqueous behaviors in response to temperature variations. While the polyesters without side chains simply presented a free-flowing sol over the entire examined temperature range, those bearing methyl or n-propyl side groups underwent a sol–gel transition upon heating and harvested a reversed thermosensitive hydrogel (T-Gel). Meanwhile, the sol–gel transition temperature of the polymer/water system could be easily tailored by adjusting the content of the n-propyl side group. In contrast, the polyesters containing longer n-amyl side groups formed a normal hydrogel (N-Gel) exhibiting a gel–sol (suspension) transition upon heating. Their different aqueous behaviors stemmed from the difference in the hydrophilic–hydrophobic equilibrium of the amphiphilic copolymers. The sol–gel transitions of the thermosensitive hydrogels were attributed to the aggregation of micelles and the dehydration of PEG. The copolymers bearing n-propyl side groups had good cytocompatibility and were fairly stable in a phosphate buffered saline for 80 days, whereas the formed thermosensitive hydrogel (20 wt %) was rapidly degraded via surface erosion within half a month after subcutaneous injection into mice. Consequently, this study indicates that subtle variation in the length of hydrophobic side chains plays a decisive role in the physical gelation of PEG/polyester copolymers. In addition, the thermosensitive hydrogels have the potential for drug and cell delivery based on their good biocompatibility and biodegradability.

Rheological signatures of gel–glass transition and a revised phase diagram of an aqueous triblock copolymer solution of Pluronic F127

In this work, we study temperature-induced state change of an aqueous solution of triblock copolymer composed of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), PEO-PPO-PEO (Pluronic F127), at different concentrations using rheology. While this temperature-dependent state change visually appears like a liquid–soft solid transition, and the soft solid state has been termed as a gel in the literature, there is a debate regarding the precise microstructure of the soft solid state. We observe that over a concentration domain of interest, an aqueous solution of F127 overwhelmingly demonstrates all the characteristic rheological features of not just a sol–gel–glass transition at low temperatures and glass–liquid transition at high temperatures, but also that associated with the individual states, such as sol, post-gel, and glass. The temperature at which the gel–glass transition is observed decreases while the temperature associated with glass–liquid transition increases with an increase in the concentration of F127. Based on the observed behavior, we propose a mechanism that considers the change in micelle volume fraction and alteration of the hydrophilicity of PEO corona as a function of temperature. Finally, we construct a phase diagram and discuss the similarities and differences with respect to various phase diagrams of F127 solution available in the literature.

Controlling the thermal response of poly(N-isopropylacrylamide)-poly(ethylene glycol)- poly(N-isopropylacrylamide) triblock copolymers in aqueous solution by means of additives

The present work describes how the thermal response of some thermosensitive poly(N-isopropylacrylamide)-poly(ethylene glycol)-poly(N-isopropylacrylamide) (PNIPAM-PEG-PNIPAM) triblock copolymers of different compositions, in aqueous solution, estimated by the cloud point (CP) method, can be controlled by factors like polymer concentration (0.05–5 wt%) and composition (PNIPAM and PEG blocks length, overall polymer hydrophilicity), as well as by the nature and concentration (0.1–0.4 M) of some water-soluble additives. The experiments showed that CP decreased with polymer concentration and molecular weight (MW) of the PNIPAM block and increased with the MW of the PEG block. The influence of inorganic and organic salts through both their anion and cation, and short-alkyl chain organic nonelectrolytes through their alkyl chain architecture (linear or branched) and polarity of the functional group (alcohol, aldehyde, amine, carboxyl) was also investigated. Neither the composition nor the hydrophilicity of our triblock copolymers displayed any appreciable influence upon CP increase/decrease in the presence of additives. It was proved by hysteresis loop area measurements that NaCl addition increased the hysteresis effect of the polymer soluble - insoluble reversible transition.

Aqueous solutions of triblock copolymers used as the media affecting the magnetic relaxation properties of gadolinium ions trapped by metal-oxide nanostructures

The present work introduces the optimization of the oxidative degradation, complex formation and aggregation of the water-soluble metal oxide nanostructures (the so-called keplerates) [{W6O21(H2O)5(OAc)0.5}12{Mo2O4(OAc)}30]48− (W72Mo60), [{Mo6O21(H2O)3(SO4)}12(VO)30(H2O)20]26− (Mo72V30), and [{Mo6O21}12Fe30(OAc)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91] (Mo72Fe30) in aqueous solutions containing Gd3+ ions and triblock copolymers, which can be used as a tool to enhance magnetic relaxivity of the gadolinium-bound nanostructures. The particularly significant enhancement in the magnetic relaxivity of the Gd3+ ions bound with W72Mo60 versus Mo72Fe30/V30 is due to the more convenient size of the external pores in the keplerate framework, which are the binding sites for Gd3+ aqua ions. The structure of the W72Mo60 keplerate is also responsible for the high stabilities of its gadolinium complexes against oxidative degradation in the solutions. The aggregation of the gadolinium-bound W72Mo60 keplerates controlled by the Gd:keplerate molar ratio is a factor in addition to the structure affecting the relaxivity. The assembly of the gadolinium-bound keplerates with the triblock copolymers enhances the relaxivity values by limiting the size of the aggregates, while the relaxivity of the molecular complexes is insignificantly affected by the assembly with the triblock copolymers. The gadolinium complexes exhibiting competitively high magnetic relaxivity values, coupled with their high chemical stability and low cytotoxicity, are introduced herein as the result of the structural optimization, both on molecular and supramolecular levels.

Dispersion of Boron Nitride Nanotubes by Pluronic Triblock Copolymer in Aqueous Solution.

Boron nitride nanotubes (BNNTs) have been of interest for their excellent thermal, electrical, and mechanical properties, and they have a broad spectrum of potential applications, such as in piezoelectric materials, reinforcement of materials, and electrothermal insulation materials. For practical use of BNNTs, it is desirable to disperse them in aqueous solution, which improves convenience of handling. However, it is still difficult to make a homogenous and stable BNNT dispersion in aqueous solution, due to their strong van der Waals interactions and hydrophobic surface. To solve these problems, we used Pluronic P85 and F127, which have both hydrophilic groups and hydrophobic groups. Here, we report the wrapped structure of a Pluronic polymer-BNNT dispersion by using small-angle neutron scattering, UV–Vis spectroscopy, thermogravimetric analysis, and atomic force microscopy.

Micellization and sol-gel transition of novel thermo- and pH-responsive ABC triblock copolymer synthesized by RAFT

A well-defined thermo- and pH-responsive ABC-type triblock copolymer monomethoxy poly(ethylene glycol)-b-poly(2-(2-methoxyethoxy) ethyl methacrylate-co-N-hydroxymethyl acrylamide)-b-poly(2-(diethylamino) ethyl methacrylate), mPEG-b-P(MEO2MA-co-HMAM)-b-PDEAEMA, was synthesized by reversible addition-fragmentation chain transfer polymerization (RAFT). The ABC-type triblock copolymer was endowed thermo- and pH-responsive, corresponding to the thermosensitive properties of P(MEO2MA-co-HMAM) and pH-responsive properties PDEAEMA segments, respectively. The thermo- and pH-responsive properties of copolymer aqueous solutions were studied by UV transmittance measurements, dynamic light scattering (DLS), transmission electron microscopy (TEM). The results showed that the N-hydroxymethyl acrylamide (HMAM) content in triblock copolymer affected the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution. The copolymer self-assembled into core-shell micelles, with the thermoresponsive P(MEO2MA-co-HMAM) block and the hydrophilic PEG block as the shell, the hydrophobic PDEAEMA block as the core, in alkaline solution at room temperature. While in acidic media, when the temperature above the lower critical solution temperature (LCST) of the triblock copolymer aqueous solution, the copolymer self-assembled into P(MEO2MA-co-HMAM)-core micelles with mixed hydrophilic PEG and pH-responsive PDEAEMA coronas. Sol-gel transition temperature (Tsol-gel) for the triblock copolymer determined by vial inversion test further indicated that it is dependent on the concentration of the triblock copolymers and solution pH. Copolymer hydrogel loaded with bovine serum albumin (BSA) were used for the sustained release study. The results indicated that the hydrogel was a promising candidate for controlling protein drug delivery.

Rheological study of the effect of polyethylene oxide (PEO) homopolymer on the gelation of PEO-PPO-PEO triblock copolymer in aqueous solution

The effects of polyethylene oxide (PEO) homopolymer on the gelation behavior of a PEO100-PPO65-PEO100 triblock copolymer (Pluronic F127) were explored in aqueous solution under non-isothermal and isothermal conditions. Under non-isothermal conditions (temperature sweep test), two transition points were observed on increasing temperature, that is, at lower and upper gelation temperatures (LTgel and UTgel, respectively). Between LTgel and UTgel, F127 aqueous solutions maintained a hard gel state. Both molecular weight (MW) and PEO concentration affected these two gelation temperatures. In particular, relative molecular weight (MWrel ≡ molecular weight of PEO homopolymer/PEO segment of F127) affected LTgel. LTgel decreased on increasing PEO concentration at MWrel values of 1. On the other hand, UTgel decreased with increasing PEO concentration regardless of MWrel. Under isothermal conditions (fixed temperature between LTgel and UTgel), the effects of PEO homopolymer on the mechanical properties of F127 hard gel were systemically investigated using small and large amplitude oscillatory shear tests. In the linear viscoelastic regime, total intra-cycle stress and elastic intra-cycle stress were similar, and viscous response increased on increasing PEO concentration. However, at large strain amplitudes, hard gels showed intra-cycle stiffening but inter-cycle softening behavior. In addition, on increasing PEO concentrations, viscous nonlinearities underwent strain-rate thickening followed by strain-rate thinning.

Self-Assembled CNT-Polymer Hybrids in Single-Walled Carbon Nanotubes Dispersed Aqueous Triblock Copolymer Solutions

We have carried out scanning electron microscopy (SEM), differential scanning calorimetry (DSC), small angle X-ray scattering (SAXS), electrical conductivity, and 1H NMR studies as a function of temperature on single-walled carbon nanotubes (SWCNTs) dispersed aqueous triblock copolymer (P123) solutions. The single-walled carbon nanotubes in this system aggregate to form bundles, and the bundles aggregate to form net-like structures. Depending on the temperature and phases of the polymer, this system exhibits three different self-assembled CNT-polymer hybrids. We find CNT-unimer hybrid at low temperatures, CNT-micelle hybrid at intermediate temperatures wherein the polymer micelles are adsorbed in the pores of the CNT nets, and another type of CNT-micelle hybrid at high temperatures wherein the polymer micelles are adsorbed on the surface of the CNT bundles. Our DSC thermogram showed two peaks related to these structural changes in the CNT-polymer hybrids. Temperature dependence of the 1H NMR chemical shifts of the molecular groups of the polymer and the AC electrical conductivity of the composite also showed discontinuous changes at the temperatures at which the CNT-polymer hybrid’s structural changes are seen. Interestingly, for a higher CNT concentration (0.5 wt.%) in the system, the aggregated polymer micelles adsorbed on the CNTs exhibit cone-like and cube-like morphologies at the intermediate and at high temperatures respectively.

Light-mediated one-pot synthesis of an ABC triblock copolymer in aqueous solution via RAFT and the effect of pH on copolymer self-assembly

We present the triblock copolymer self-assembly resulting into different morphologies that occurred during the polymerization of a hydrophobic third block in aqueous solution.

Phase behaviors of a mixture of two kinds of Pluronic triblock copolymers in aqueous solution

A new method to easily derive the phase transition of amphiphilic block copolymer in aqueous solution is suggested in this study. Using two kinds of Pluronic triblock copolymers, which have different mass fractions of the hydrophilic part of the block copolymer, the mixed block copolymers in aqueous solution self-assembled into a variety of nanostructures. Small angle neutron scattering revealed that the block copolymer complex formed spheres, cylinders, and vesicles depending on both the concentration of another Pluronic block copolymer (Pluronic PE6200) as an additive and temperature. This phase behavior can be easily explained in terms of the hydrophobicity of the block copolymer by increasing its effective hydrophobic moiety and temperature.

CO2-sensitive amphiphilic triblock copolymer self-assembly morphology transition and accelerating drug release from polymeric vesicle

A series of triblock copolymers, containing a CO2-switchable block poly(2-(dimethylamino)ethyl methacrylate) (PDM) block and two symmetrical hydrophilic blocks polyacrylamide (PAM), were synthesized using atom transfer radical polymerization (ATRP) method. The pH and conductivity tests showed that the triblock copolymer exhibited switchable responsiveness to CO2, i.e. a relatively low conductivity of solution could be switched on and off by bubbling and removing of CO2, and the triblock copolymer aqueous solution displayed a CO2-switchable viscosity variation. The changes were all attributed to protonation of tertiary amine groups in PDM blocks and proven by 1H-NMR. Cryogenic transmission electron microscopy and dynamic light scattering characterization demonstrated that the viscosity variation was the result of a unilamellar vesicle-network aggregate structure transition. The release of rhodamine B from the vesicles with and without CO2 stimuli showed the potential application in drug delivery domains; after CO2 bubbling, the drug release rate could be accelerated. Finally, reasonable mechanism of CO2-switchable morphology changes and CO2-induced drug release was proposed.

Gelation of Triblock Copolymers in Aqueous Solution through CO2 -Triggered Electrostatic Interaction

Polymer systems displaying CO2-triggered rheology alteration are widely investigated in recent years, which can change from nonviscous liquid to high-viscosity solution or even gel by passing CO2 through. Among those polymer systems, a previous study of the group shows that a rationally designed ABA-type triblock copolymer with a hydrophilic middle block and two CO2-responsive end blocks can undergo either gel–sol or sol–gel transition triggered by CO2 as a result of increase or decrease in lower critical solution temperature of A blocks, respectively. This paper describes a new and more flexible approach to achieving CO2-induced gelation of polymer aqueous solution at much lower polymer concentrations. It consists in mixing two water-soluble ABA triblock copolymers that have the same B block but different A blocks: for one polymer, the A blocks are a negatively charged polyelectrolyte, and for the other polymer, the A blocks can be turned positively charged under CO2 stimulation. In this way, CO2 bubbling through an aqueous solution of the two constituent triblock copolymers can induce complexation of the oppositely charged A blocks and, as a result, gelation of the solution of mixed triblock copolymers.

Synthesis and solution properties of a temperature-responsive PNIPAM–b-PDMS–b-PNIPAM triblock copolymer

In this paper, we report the synthesis and self-assembly of a novel thermoresponsive PNIPAM60–b-PDMS70–b-PNIPAM60 triblock copolymer in aqueous solution. The copolymer used a commercially available precursor modified with an atom transfer radical polymerization (ATRP) initiator to produce an ABA triblock copolymer via ATRP. Small-angle neutron scattering (SANS) was used to shed light on the structures of nanoparticles formed in aqueous solutions of this copolymer at two temperatures, 25 and 40 °C. The poly(dimethylsiloxane) block is very hydrophobic and poly(N-isopropylacrylamide) (PNIPAM) is thermoresponsive. SANS data at 25 °C indicates that the solutions of PNIPAM–b-PDMS–b-PNIPAM copolymers form well-defined aggregates with presumably core–shell structures below cloud point temperature. The scattering curves originating from nanoparticles formed at 40 °C in 100% D2O or 100% H2O were successfully fitted with the Beaucage model describing aggregates with hierarchical structure.

Precisely installing gold nanoparticles at the core/shell interface of micellar assemblies of triblock copolymers

Two reduction-cleavable ABA triblock copolymers possessing two disulfide linkages, PMMA-ss-PMEO3MA-ss-PMMA and PDEA-ss-PEO-ss-PDEA were synthesized via facile substitution reactions from homopolymer precursors, where PMMA, PMEO3MA, PDEA, and PEO represent poly(methyl methacrylate), poly(tri(ethylene glycol) monomethyl ether methacrylate, poly(2-(diethylamino)ethyl methacrylate), and poly(ethylene oxide), respectively. Spherical micelles were obtained through supramolecular self-assembly of these two triblock copolymers in aqueous solutions. The resultant micelles with abundant disulfide bonds could serve as soft templates and precisely accommodate gold nanoparticles in the core/shell interface as a result of the formation of Au–S bonds.

Temperature, concentration and salt effect on F68 tri-block copolymer in aqueous solution: Rheological study

The rheology of the aqueous solution of poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO−PPO−PEO) triblock copolymer, Pluronic F68 in the presence of KF was studied in the temperature range from 15 to 60°C. The variation of the shear stress according to the shear rate shows that independently from the temperature and concentration, the F68 solutions exhibit a Newtonian behavior. The results show that the Critical Micelle Temperature of Pluronic F68 in a KF aqueous solution decreases with the increase in the salt concentration.

Positional isomeric effects of coupling agents on the temperature-induced gelation of triblock copolymer aqueous solutions

The linking angles of positional isomers in the middle of thermogelling mPEG-PLGA-mPEG polymers were found to affect their microscopic conformations and macroscopic properties.

Surface Film Adsorption and Lubricity of Soybean Oil In-Water Emulsion and Triblock Copolymer Aqueous Solution: A Comparative Study

This paper investigates the surface film adsorption and lubricity of two different types of potential environmentally friendly cold metal forming lubricants: soybean vegetable oil in water VO/W emulsions and triblock copolymer aqueous solutions. The lubricants have different visual appearance, surface film adsorption characteristic, lubricity and surface cleaning behaviour. The effects of concentration, temperature and emulsification ultrasonic energy (for VO/W emulsion) are studied. The result shows that the soybean VO/W emulsions have stronger adsorption, superior lubricity and anti-wear property compared to the copolymer solutions. The effect of temperature is investigated at 30 °C and 65 °C which are below and above cloud point of the aqueous copolymer solutions. Both lubricants show improved friction and anti-wear property at 65 °C. However, tenacious residual film remained on the discs surface after surface cleaning indicates lower cleanability of the soybean VO/W emulsions compared to the copolymer solutions, postulating the need for extra post-processing cleaning operations after cold forming process with VO/W emulsion lubricant.

Synthesis of Novel Temperature- and pH-Sensitive ABA Triblock Copolymers P(DEAEMA-co-MEO₂MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO₂MA-co-OEGMA): Micellization, Sol⁻Gel Transitions, and Sustained BSA Release.

Novel temperature- and pH-responsive ABA-type triblock copolymers, P(DEAEMA-co-MEO2MA-co-OEGMA)-b-PEG-b-P(DEAEMA-co-MEO2MA-co-OEGMA), composed of a poly(ethylene glycol) (PEG) middle block and temperature- and pH-sensitive outer blocks, were synthesized by atom transfer radical polymerization (ATRP). The composition and structure of the copolymer were characterized by 1H NMR and gel permeation chromatography (GPC). The temperature- and pH-sensitivity, micellization, and the sol–gel transitions of the triblock copolymers in aqueous solutions were studied using transmittance measurements, surface tension, viscosity, fluorescence probe technique, dynamic light scattering (DLS), zeta-potential measurements, and transmission electron microscopy (TEM). The lower critical solution temperature (LCST) of the triblock copolymer, which contains a small amount of a weak base group, (N,N-diethylamino) ethyl methacrylate (DEAEMA), can be tuned precisely and reversibly by changing the solution pH. When the copolymer concentration was sufficiently high, increasing temperature resulted in the free-flowing solution transformation into a micellar gel. The sol-to-gel transition temperature (Tsol–gel) in aqueous solution will continue to decrease as solution concentration increases.