PPO Triblock Copolymers Research Articles

Shape Memory Properties of Epoxy/PPO–PEO–PPO Triblock Copolymer Blends with Tunable Thermal Transitions and Mechanical Characteristics

In this paper, we report a simple method to prepare novel, transparent, hard-tough and hard-flexible shape memory and soft-flexible epoxy polymers based on poly(propylene glycol)-block-poly(ethylene glycol)-block-poly(propylene glycol) (PPO-PEO-PPO) triblock copolymer (TBCP) and diglycidyl ether of bisphenol-A (DGEBA)/4,4'-diaminodiphenylmethane (DDM) system. The PPO-PEO-PPO triblock copolymer was used to tailor crosslink density and flexibility in epoxy thermosets and thereby their glass transition temperature (Tg). The formed blends exhibit a phase separated morphology. The phase separation was initiated by immiscible PPO blocks via self-assembly. Three types of shape memory polymers, viz. stiff, intermediate and soft-flexible epoxy systems, with entirely different physical and mechanical properties were prepared only by adjusting the blend composition. All the blends were UV resistant, thermally and dimensionally stable and could be used for various outdoor applications. To the best of our knowledge, n...

Molecular interactions between PEO–PPO–PEO and PPO–PEO–PPO triblock copolymers in aqueous solution

Abstract The molecular interactions between Pluronic F127 (PEO100–PPO65–PEO100) and Pluronic-R 25R4 (PPO19–PEO33–PPO19) in aqueous solution have been studied using micro thermal analysis and rheology, where PEO and PPO stand for poly(ethylene oxide) and poly(propylene oxide) blocks respectively through a complete thermal cycle from heating to cooling. A completely thermoreversible micellization was observed for aqueous solutions of pure F127 and F127/25R4 mixtures even if an aqueous solution of pure 25R4 was not thermally reversible. The critical micelle temperature, CMT, decreased linearly with increasing the molar ratio of 25R4/F127. The sol–gel transition temperature during heating is higher than the gel–sol transition temperature during cooling over a range of 25R4/F127 ratio. F127 dominated the gelation of F127 at the molar ratio of 25R4/F127

Role of PPO–PEO–PPO triblock copolymers in phase transitions of a PEO–PPO–PEO triblock copolymer in aqueous solution

The effects of two poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO) triblock copolymers, Pluronics-R 10R5 (PPO8–PEO22–PPO8) and 25R4 (PPO19–PEO33–PPO19), on the thermal and rheological properties as well as the phase transitions of a poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer (Pluronic F127, PEO100–PPO65–PEO100) in aqueous solution have been systematically studied. Both 10R5 and 25R4 could shift the critical micellization temperature of F127 to lower temperatures, showing a “salt-out like” effect. When F127 itself is unable to form a gel at low concentrations, 25R4 could assist micelles of F127 to be connected into a gel network. However, 10R5 is too short to be able to assist F127 to form a gel. At low contents of 10R5 or 25R4, F127 dominates its gelation but 25R4 could affect the hard gel–soft gel transition while10R5 showed a weaker effect on the hard gel–soft gel transition than 25R4. The rheological scaling law in the vicinity of the gel point was examined to obtain the critical relaxation exponent n and the critical gel strength Sg. n decreases and Sg increases with increasing 25R4 at low concentrations of F127. However, 10R5 and 25R4 affected n and Sg differently at high concentrations of F127.

Diverse effect of PEO–PPO–PEO and PPO–PEO–PPO triblock copolymers on temperature responsive behavior of luminescent hard–soft colloids

The present work introduces the interaction of hard and soft colloids in aqueous solutions at various temperatures and concentrations, as well as at critical conditions of temperature induced phase separation. Hard and soft colloids are represented by luminescent silica nanoparticles and aggregates of PEO–PPO–PEO and PPO–PEO–PPO triblock copolymers correspondingly. The formation of the mixed aggregates between hard and soft colloids in equilibrium conditions has been revealed by dynamic light scattering measurements. The distribution of silica nanoparticles between aqueous and surfactant rich phases after phase separation highlights the effect of pH, architecture and concentration of triblock copolymers on the mixed hard–soft colloids aggregation at cloud point conditions. The peculiar aggregation and phase behavior of PPO–PEO–PPO pluronics should be assumed as the main reason of the enhanced mixed aggregation with SNs at increased temperatures and concentrated conditions.

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.

A supramolecular gene carrier composed of multiple cationic α-cyclodextrins threaded on a PPO–PEO–PPO triblock polymer

Cationic polymers have been studied as promising nonviral gene delivery vectors. In contrast to the conventional polycations with long sequences of covalently bonded repeating units, this work reports a supramolecular gene carrier where many cationic cyclic units are threaded over a polymer chain to form a chain-interlock structured gene carrier. A series of novel supramolecular cationic polyrotaxanes consisting of multiple α-cyclodextrin (α-CD) rings grafted with various linear or nonlinear oligoethylenimine (OEI) chains, which are threaded and capped over a reverse Pluronic poly(propylene oxide)–poly(ethylene oxide)–poly(propylene oxide) (PPO–PEO–PPO) amphiphilic triblock copolymer chain, were synthesized and characterized in term of their molecular and supramolecular structures, DNA binding and condensation ability, cytotoxicity, and in vitro gene transfection efficiency in cultured cells. The supramolecular cationic polyrotaxanes were found to contain 8 cationic α-CD rings that are threaded on a PPO–PEO–PPO triblock copolymer chain. They demonstrated strong ability to bind and condense plasmid DNA into nano-sized particles which are suitable for gene delivery. In both HEK293 and COS7 cells, these polyrotaxanes show low cytotoxicity and high transfection efficiency. In particular, the cationic polyrotaxanes displayed sustained gene delivery capability in HEK293 cells in both serum and serum free condition with the increasing expression duration.

Thermoreversible micellization and gelation of a blend of pluronic polymers

Aqueous solutions of a blend consisting of a PEO–PPO–PEO triblock copolymer, Pluronic F127 (EO100–PO65–EO100) and a PPO–PEO–PPO triblock copolymer, Pluronic-R 25R4 (PO19–EO33–PO19) were studied. Thermoreversible micellization and gelation properties of the blend were examined as a function of temperature and molar ratio of 25R4 to F127 by means of micro DSC and rheology. The completely thermoreversible behaviors of micellization and gelation were observed for all the blend solutions with two F127 concentrations (10 and 15wt%) and various 25R4/F127 molar ratios (0–4) even though the pure 25R4 solution itself was not thermoreversible. At a given concentration of F127, three effects of 25R4 on F127 were found as follows. (a) The micellization temperature of F127 shifts to a lower temperature with increasing 25R4 content, implying a “salt-out like” effect of 25R4. (b) Beyond the primary peak for micellization a secondary peak appears due to the effect of 25R4. (c) At the molar ratio of 25R4/F127=3:1, the gelation of the 15wt% F127 solution occurs twice at low and high temperatures, respectively. When the ratio>3:1, the gelation occurs only at high temperatures. The possible mechanisms involved in these unique behaviors of micellization and gelation have been proposed and discussed. The effect of 25R4 on F127 was compared with another Pluronic polymer F108 (EO133–PO50–EO133).

Phase Diagram of Poly(ethylene oxide) and Poly(propylene oxide) Triblock Copolymers in Aqueous Solutions

The phase behavior of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) triblock copolymers in aqueous solutions is studied by using a self-consistent-field theory. The spectral method is extended to polymer models with internal degrees of freedom. Phase diagrams of PEO−PPO−PEO and PPO−PEO−PPO triblock copolymers in water are constructed in the concentration−temperature space. A variety of lyotropic liquid crystalline phases is found. The effects of temperature, copolymer concentration, the block (EO/PO) ratio and the chain architecture are investigated. Good agreements were found between experimental results and theory.

Effects of a PPO−PEO−PPO Triblock Copolymer on Micellization and Gelation of a PEO−PPO−PEO Triblock Copolymer in Aqueous Solution

The effects of a PPO-PEO-PPO triblock copolymer (25R4, PO(19)-EO(33)-PO(19)) on thermoreversible micellization and gelation properties of a PEO-PPO-PEO triblock copolymer (F108, EO(133)-PO(50)-EO(133)) in water were studied by means of micro-DSC and rheology. A complete, mirror-image like thermoreversible behavior has been observed for all of the samples with various molar ratios of 25R4 to F108. At a given concentration of F108, the addition of 25R4 results in the salt-out like effect on the primary micellization of F108; that is, the critical micellization temperature (CMT) of F108 shifts to lower temperatures with increasing the content of 25R4. The enthalpy changes for micellization are a linear function of the 25R4/F108 molar ratio at a fixed F108 concentration. Beyond the primary peak for the micellization of F108, a secondary peak or shoulder is observed in the DSC curves for the samples with the higher 25R4/F108 molar ratios, due to the formation of the hydrophobic aggregates from both the PPO blocks of F108 and those (i.e., PPO blocks) of 25R4. Furthermore, as an example, the dynamic viscoelastic properties of 18 wt % F108 solutions with various contents of 25R4 have been examined. It is found that, when the 25R4/F108 molar ratio < or =1, 25R4 does not affect the gelation of F108 notably. When the ratio is greater than 1, however, the formation of the 25R4-bridged micellar aggregates delays the gelation of F108 significantly. A schematic model has been proposed to explain the mechanism for the 25R4-influenced micellization and gelation of F108.

Interactions of Charged Porphyrins with Nonionic Triblock Copolymer Hosts in Aqueous Solutions

The extent and locus of solubilization of guest and self-assembling surfactant host molecules in aqueous solutions are influenced by a variety of hydrophobic and hydrophilic interactions, as well as by more specific interactions between the various species present. By using a combination of two-dimensional heteronuclear 13C[1H] NMR correlation experiments with pulsed-gradient NMR diffusion and proton cross-relaxation measurements, the locations and distributions of porphyrin guest molecules have been established unambiguously with respect to the hydrophobic and hydrophilic moieties of a triblock copolymer species in solution. The interactions of tetra(4-sulfonatophenyl)porphyrin with the poly(propylene oxide) (PPO) and the poly(ethylene oxide) (PEO) segments of amphiphilic PEO-PPO-PEO triblock copolymer species have been measured as functions of solution conditions, including temperature and pH. The porphyrin/PEO-PPO-PEO interactions are established to be selective and adjustable according to the different temperature-dependent hydrophilicities or hydrophobicities of the PEO and PPO triblock copolymer components. Furthermore, such interactions influence the self-assembly properties of the block-copolymer amphiphiles in solution by stabilizing molecular porphyrin/PEO-PPO-PEO complexes well above the critical micellization temperature of the triblock copolymer species under otherwise identical conditions.

Effect of surfactants on the cloud point of amphiphilic drug solutions

Abstract The effect of cationic (alkyltrimethylammonium halide), anionic (sodium alkyl sulfate) and nonionic (Pluronic) surfactants on the cloud point (CP) of amphiphilic drug amitriptyline (AMT) solutions has been investigated in the absence and presence of sodium phosphate (SP). The CP increases on addition of ionic surfactants in the presence of small amounts of SP. Furthermore, the CP increases with the alkyl chain length of the ionic surfactants. Unexpectedly, the rate of increase in CP on addition of anionic surfactants is greater than cationic surfactants in the presence of small amounts of SP because the added anionic surfactants are adsorbed on the AMT micellar surface. The CP becomes less sensitive to addition of ionic surfactants in the presence of large amounts of SP. Addition of Pluronic F-127 (poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–PEO triblock copolymer) to the AMT solution increases the CP, whereas addition of Pluronic 10R-8 (PPO–PEO–PPO triblock copolymer) decreases the CP. These results have been discussed in terms of interactions between AMT micelles and added surfactants.

Dynamics of PEO−PPO−PEO and PPO−PEO−PPO Triblock Copolymers at the Air/Water Interface upon Thermal Stimulation

Dynamics of PEO−PPO−PEO and PPO−PEO−PPO at the air/water interface upon thermal stimulation is studied with a fast surface light scattering (SLS) technique, in terms of the dynamic surface tension recovery relaxation of the copolymer solutions in response to a short-pulsed temperature jump. The characteristic of the surface tension relaxation is examined pertaining to the structure, molecular weight, and concentration of the block copolymers at the air/water interface. The surface tension relaxation time of the copolymer surfactants is found to be monotonically related to the molecular weight of the PEO blocks suggesting that thermal sensitivity in surface tension of the copolymer solutions be due to a conformation change of PEO chains in the copolymers at the air/water interfaces upon the temperature change.

Synthesis and characterization of ABA triblock copolymers containing poly(2,6‐dimethyl‐1,4‐phenylene oxide) as A blocks and tetramethyl bisphenol‐A polysulfone as B blocks

Abstractα, β‐Bis(hydroxyphenol) tetramethyl bisphenol‐A polysulfone (PSUT) was synthesized by two different methods, one using a strong base, the other using a weak base. The bifunctional polysulfone containing tetramethyl bisphenol‐A chain ends was exploited as a model telechelic that can be used for the preparation of ABA triblock copolymers containing poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) as A segments and PSUT as B segments. PSUT and PPO were incorporated into triblock copolymers by an oxidative coupling copolymerization of PSUT with 2,6‐dimethylphenol or by the redistribution of PPO in the presence of PSUT. The mechanism of block copolymerization is discussed. DSC studies indicate that short immiscible PPO and PSUT segments incorporated into a triblock copolymer do not exhibit phase separation. Polymer blends of the PPO–PSUT–PPO triblock copolymers with PPO homopolymer were analyzed by DSC. Both miscible and phase‐separated blends can be prepared depending on the molecular weight of both PPO homopolymer and of the PPO segment present in the triblock copolymer. Polymer blends of the PPO–PSUT–PPO triblock copolymer with PSUT were miscible at all compositions.