Nanostructured unsaturated polyester modified with poly[(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)] triblock copolymer

Miscibility, crystallization and morphology of unsaturated polyester (UP) matrices, nanostructured with a poly[(ethylene oxide)-b-(propylene oxide)-b-(ethylene oxide)] (PEO-b-PPO-b-PEO) block copolymer (BCP) from 0 to 50 wt% has been investigated. Additionally, the role of each block on miscibility and morphology of cured mixtures was studied. Behaviours of non-reactive mixtures of UP thermosetting precursor with two BCPs composed of similar and strong immiscible central PPO block were compared. It was found that one BCP had PEO blocks with not enough molecular weight to compatibilize the PPO block with the UP thermosetting precursor at room temperature. Transmitted light intensity study of mixtures indicated that during curing at 35 °C no macrophase separation took place, contrary to the systems cured at temperatures equal or higher than 60 °C. Curing mixtures at 35 °C produced nanostructured matrices with almost unchanged transparency. Phase separation and miscibility of BCP with UP matrix were measured by means of DSC and DMA. AFM analysis showed worm-like morphology with diameters from 10 to 20 nm and length that evolved from 50 nm to 1 μm with increase of BCP content.     

Study of the solution and aqueous emulsion copolymerization of vinylidene chloride with methyl acrylate in the presence a poly(ethylene oxide) macromolecular RAFT agent

The reversible addition-fragmentation chain transfer (RAFT) copolymerization of vinylidene chloride (VDC) with methyl acrylate (MeA) was studied in the presence of poly(ethylene oxide)-based macromolecular RAFT (macroRAFT) agents of the trithiocarbonate type (PEO-TTC) in solution and in aqueous emulsion. Firstly the formation of PEO-b-P(VDC-co-MeA) diblock copolymers was performed in toluene solution at 30 °C and a good control over the polymerization with high chain-end functionality was shown. A first aqueous emulsion copolymerization of VDC with MeA was performed using one of the amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers as macromolecular stabilizer. Then, in a series of experiments the PEO-TTC macroRAFT agents were directly tested as both chain transfer agents and stabilizing agents in similar conditions (aqueous batch emulsion copolymerization of VDC with MeA at 70 °C). The influence of the nature and concentration of the initiating system and the presence or not of a buffer were studied. We demonstrated that in simple conditions, nanometric latex particles composed of amphiphilic PEO-b-P(VDC-co-MeA) diblock copolymers formed by polymerization-induced self-assembly (PISA). It can thus be concluded that PEO-TTC macroRAFT agents are valuable non-ionic macromolecular stabilizers in the emulsion copolymerization of VDC and MeA and allow the formation of core–shell diblock copolymer particles in the absence of free surfactant. However, when rather high molar masses of the hydrophobic PVDC-based block were targeted, the determined molar masses deviated from the theoretical values.     

Vesicle formation of polystyrene-block-poly (ethylene oxide) block copolymers induced by supercritical CO2 treatment

A novel route for a preparation of polystyrene-block-poly(ethylene oxide) (PS-b-PEO) block copolymer vesicles induced by supercritical carbon dioxide (scCO₂) is demonstrated. When PS-b-PEO block copolymer solutions in tetrahydrofuran (THF) are treated with scCO₂ at 70 °C for different times, PS-b-PEO copolymers first assemble into aggregated spheres; then aggregated spheres change into large compound micelles and finally evolve into vesicles. The possible formation mechanism of the vesicles is discussed.     

Epoxy resin containing poly(ethylene oxide)-block-poly(?-caprolactone) diblock copolymer: Effect of curing agents on nanostructures

An amphiphilic diblock copolymer, poly(ethylene oxide)-block-poly(?-caprolactone) (PEO-b-PCL) was synthesized via the ring-opening polymerization of ?-caprolactone in the presence of a hydroxyl-terminated poly(ethylene oxide) monomethyl ether. The diblock copolymer was incorporated into epoxy thermosets. It is found that the formation of nanostructures of thermosetting blends is quite dependent on the uses of aromatic amine hardeners. For 4,4′-methylenebis(2-chloroaniline) (MOCA)-cured thermosetting system, the homogeneous morphology was obtained at the compositions investigated. Nonetheless, the nanostructured thermosets were obtained when the blends were cured with 4,4′-diaminodiphenylsulfone (DDS). The differential scanning calorimetry (DSC) showed that the nanostructured thermosets did not displayed any crystallinity although the subchains of the diblock copolymer are crystalline. The nanostructures were evidenced by means of atomic force microscopy (AFM), small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The dependence of morphological structures on the types of aromatic amines for epoxy and PEO-b-PCL thermosetting blends were interpreted on the basis of the difference in hydrogen bonding interactions resulting from the structure of curing agents. Considering the complete miscibility of the subchains (viz. PEO and PCL) with the precursors of epoxy resin before curing, it is judged that the formation of the nanostructures in the thermosets follows the mechanism of reaction-induced microphase separation, which is in marked contrast to the mechanism of self-assembly, i.e., micelle structures of block copolymers are formed prior to curing, followed by fixing these nanostructures via curing.     

The influence of hydrophobic substitution on self-association of poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers in aqueous media

A series of amphiphilic poly(ethylene oxide)-b-poly(n-alkyl glycidyl carbamate)s-b-poly(ethylene oxide) triblock copolymers were synthesized by reaction between poly(ethylene oxide)-b-polyglycidol-b-poly(ethylene oxide) precursor copolymer and four n-alkyl isocyanates: ethyl, propyl, butyl and pentyl. After dissolution in water at room temperature the copolymers spontaneously form micelles. The critical micellization concentrations were determined by UV-VIS spectroscopy. The dimensions of the micelles, the aggregation numbers, and in some cases the micellar shape were determined by dynamic and static light scattering in a relatively broad temperature range. Special attention has been paid to the influence of the number of the carbon atoms in the alkyl chains, and respectively, the relative hydrophobicity of the middle block upon the self-association process. Clouding transition was observed for all of the copolymers, the clouding point being dependent upon the length of the alkyl chain.     

Influence of the solvent and the end groups on the morphology of cross-linked amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) nanoparticles

The phase diagrams of nanoparticles based on self-assembled amphiphilic poly(1,2-butadiene)-b-poly(ethylene oxide) diblock copolymers (PB-b-PEO) and subsequent intra-micellar cross-linking in methanol and water show that the obtained morphology of the nanoparticles depends on: (i) the block ratio; (ii) the block length; (iii) the solvent; and (iv) the PEO-sided end group. Depending on these parameters, spherical, cylindrical and vesicle-like nanoparticles are synthesized. The PEO-sided end group is found to have an influence on the morphology of the nanoparticles and in addition, it has an impact on the characteristic dimension of the polymeric nanoparticles.     

Preparation and characterization of amphiphilic block copolymer of polyacrylonitrile‐block‐poly(ethylene oxide)

The synthesis of polyacrylonitrile‐block‐poly(ethylene oxide) (PAN‐b‐PEO) diblock copolymers is conducted by sequential initiation and Ce(IV) redox polymerization using amino‐alcohol as the parent compound. In the first step, amino‐alcohol potassium with a protected amine group initiates the polymerization of ethylene oxide (EO) to yield poly(ethylene oxide) (PEO) with an amine end group (PEO‐NH₂), which is used to synthesize a PAN‐b‐PEO diblock copolymer with Ce(IV) that takes place in the redox initiation system. A PAN‐poly(ethylene glycol)‐PAN (PAN‐PEG‐PAN) triblock copolymer is prepared by the same redox system consisting of ceric ions and PEG in an aqueous medium. The structure of the copolymer is characterized in detail by GPC, IR, ¹H‐NMR, DSC, and X‐ray diffraction. The propagation of the PAN chain is dependent on the molecular weight and concentration of the PEO prepolymer. The crystallization of the PAN and PEO block is discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1753–1759, 2003     

Behavior of aqueous solutions of poly(ethylene oxide-b-propylene oxide) copolymers containing a hydrotropic agent

The effect of the hydrotropic agent, sodium p-toluenesulfonate (NaPTS), was evaluated on the micelle formation process and on phase behavior of aqueous solutions containing poly(ethylene oxide-b-propylene oxide) (PEO–PPO) copolymers. We have studied monofunctional diblock copolymers coupled with hydrocarbons groups (R—PEO—PPO—OH and R—PPO—PEO—OH, where R length is linear C₄ and C_12–14). The critical micelle concentration (CMC) and critical micelle temperature (CMT) values of the aqueous copolymers solutions were obtained from both surface tension versus concentration plots and the dye solubilization method. The influence of the hydrocarbons groups length and PPO segment position in the structure of the copolymers were also analyzed. The same measures were obtained for the aqueous solutions of hydrotropic agent which, in turn, also presented molecular aggregation. The presence of the hydrotropic agent in the aqueous copolymers solutions altered the surface tension of these solutions and the occupied molecular area per copolymer molecule at air–water interface and CMC and CMT values of the copolymers. On the other hand, the aggregation points and the surface tension of the NaPTS solutions were dependent on the copolymer structure and composition. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 2459–2468, 1998     

Synthesis of poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene triblock copolymers by two-step atom transfer radical polymerization

The synthesis of ABC triblock copolymer poly(ethylene oxide)-block-poly(methyl methacrylate)-block-polystyrene (PEO-b-PMMA-b-PS) via atom transfer radical polymerization (ATRP) is reported. First, a PEO-Br macroinitiator was synthesized by esterification of PEO with 2-bromoisobutyryl bromide, which was subsequently used in the preparation of halo-terminated poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-b-PMMA) diblock copolymers under ATRP conditions. Then PEO-b-PMMA-b-PS triblock copolymer was synthesized by ATRP of styrene using PEO-b-PMMA as a macroinitiator. The structures and molecular characteristics of the PEO-b-PMMA-b-PS triblock copolymers were studied by FT-IR, GPC and ¹H NMR.     

Poly(ethylene oxide)-grafted poly(N-isopropylacrylamide) networks: Preparation, characterization and rapid deswelling and reswelling behavior of hydrogels

Poly(ethylene oxide)-grafted poly(N-isopropylacrylamide) networks (PNIPAAm-g-PEO) were prepared via the reversible addition-fragmentation chain transfer polymerization (RAFT) of N-isopropylacrylamide with trithiocarbonate-terminated poly(ethylene oxide) and N,N′-methylenebisacrylamide as the chain transfer agent and the crosslinking agent, respectively. It was found that the PNIPAAm-g-PEO copolymer networks were microphase-separated and that PEO microdomains were dispersed in the PNIPAAm matrix. The hydrogel behavior of the PNIPAAm-g-PEO networks was investigated using swelling, deswelling and reswelling tests. The PNIPAAm-g-PEO hydrogels displayed faster responses to external temperature changes than did the control PNIPAAm hydrogel.     

Amphiphilic polysilane with poly(ethylene oxide) side chains

The synthesis of an amphiphilic polysilane with poly(ethylene oxide) grafted segments (PS-g-PEO) through the addition of an allyl-terminated poly(ethylene oxide) (AT-PEO) to poly[diphenylsilane-co-methyl(H) silane] (PSH) in a homogeneous system and using catalyst platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane is reported The process involves the activation of the polymer by microwave irradiation as a preliminary stage with the view to perform the subsequent addition stage at room temperature, when side reactions are prevented. The PS-g-PEO structure was characterized by NMR, FT-IR spectral analysis and GPC methods. The amphiphilic properties were estimated by comparison of the water sorption isotherms of the PS-g-PEO copolymer with those of the component segments. The core-shell micellization in water and the morphological aspects of the self-assembled structures were investigated by DLS and SEM. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Toughening of epoxy thermosets with nano-sized or micron-sized domains of poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) triblock copolymers synthesized using room temperature ester coupling reaction

Poly(ethylene oxide)-b-poly(butadiene-co-acrylonitrile)-b-poly(ethylene oxide) (PEO-b-PBN-b–PEO) triblock copolymers with three different compositions were synthesized from poly(ethylene glycol) methyl ethers and carboxylic acid-terminated poly(butadiene-co-acrylonitrile) (CTBN) by ester coupling reaction at room temperature. The PEO-b-PBN-b-PEO was incorporated into anhydride cured epoxy thermosets to improve the fracture toughness by the formation of either nano-sized spherical micelles or micron-sized vesicles. The polymer chemical structure was confirmed by Fourier transform infrared spectroscopy, nuclear magnetic resonance, and gel permeation chromatography. The morphology of PEO-b-PBN-b–PEO within the epoxy thermosets was investigated using a transmission electron microscope, an atomic force microscope, and a scanning electron microscope. Also, we conducted impact testing and plane-strain fracture toughness testing to evaluate the fracture toughness in terms of the impact strength and the critical stress intensity factors (K_IC) for the modified epoxy thermosets. The results revealed that all the PEO-b-PBN-b-PEO triblock copolymers are more effective in the toughening of epoxy thermoset compare to CTBN. We found that the 5 wt% PEO-b-PBN-b-PEO modified epoxy thermoset containing micron-sized vesicles exhibited the highest K_IC, which was 3.23 times as high as the K_IC of pristine epoxy thermoset. Besides, the glass transition temperature remained and the tensile modulus did not reduce remarkably when the amount of PEO-b-PBN-b-PEO added into epoxy was 5 wt%.     

Characterization of polystyrene‐b‐poly(ethylene oxide) diblock copolymer and investigation of its micellization behavior in water

The recent studies deal with a diblock copolymer, polystyrene–poly(ethylene oxide). Infrared spectroscopy, proton resonance spectroscopy (¹H‐NMR), and laser light scattering techniques have been used to characterize the polymer. It has been concluded that the sample investigated is diblock copolymer polystyrene–poly(ethylene oxide) having molecular mass 1.656 × 10⁴ g/mol and blocks ratio 1 : 2. The micellization behavior is explored through ¹H‐NMR, laser light scattering, light absorption, surface tension, and conductance and viscosity measurements. The results conclude that the critical micelles concentration of copolymer is 0.0951 g/dL at 25°C. It has been observed that the surface tension of solution decreases with the temperature and its impact is maxima in dilute concentration region. In addition, new methodologies have been introduced to get accurate critical micelles concentration and critical micelles temperature. © 2010 Wiley Periodicals, Inc., J Appl Polym Sci, 2010     

Synthesis of polyether-based block copolymers based on poly(propylene oxide) and terephthalates

Poly(propylene oxide) (PPO) is a low reactive telechelic polyether and the synthesis of high molecular weight poly(propylene oxide)-based block copolymers was studied. The poly(propylene oxide) used was end capped with 20 wt % ethylene oxide and had a molecular weight of 2300 g/mol (ultra-low monol PEO-b-PPO-b-PEO). The type of terephthalic acid based precursors was varied: terephthalic acid, dimethyl terephthalate, diphenyl terephthalate, di(trifluoro ethyl) terephthalate, di(p-nitrophenyl) terephthalate) and terephthalic acid chloride. High molecular weight poly(propylene oxide) based segmented block copolymers were obtained with diphenyl terephthalate (inherent viscosity: 1.6 dl/g).The synthesis of polyether(ester-amide)s comprising PPO and isophthalamide-based segments was also studied by varying the polymerization temperature and time. High molecular weight poly(propylene oxide) block copolymers could be obtained if the reaction was carried out for 2 h at 250 °C under vacuum. Higher temperatures (280 °C) and longer times result in lower inherent viscosities, probably due to degradation of the polyether.     

Miscibility with positive deviation in Tg-composition relationship in blends of poly(2-vinyl pyridine)-block-poly(ethylene oxide) and poly(p-vinyl phenol)

Phase behavior and miscibility with positive deviation from linear T_g-composition relationship in a copolymer/homopolymer blend system, poly(2-vinyl pyridine)-block-poly(ethylene oxide) (P2VP-b-PEO)/poly(p-vinyl phenol) (PVPh), were investigated by differential scanning calorimetry (DSC), Fourier-transform infrared spectroscopy (FT-IR) and solid-state ¹³C nuclear magnetic resonance (¹³C NMR), optical microscopy (OM), and scanning electron microscopy (SEM). Optical and electron microscopy results as well as NMR proton spin-lattice relaxation times in laboratory frame () all confirmed the miscibility as judged by the T_g criterion using DSC. In comparison to the literature result on a homopolymer/homopolymer blend of P2VP/PVPh, fitting with the Kwei equation on the T_g-composition relationship for the block-copolymer/homopolymer blend of P2VP-b-PEO/PVPh blend system yielded a smaller q value (q = 120) for P2VP-b-PEO/PVPh than that for P2VP/PVPh blend (q = 160). The FT-IR and ¹³C NMR results revealed hydrogen-bonding interactions between the pendant pyridine group of P2VP-b-PEO and phenol unit in PVPh, which is responsible for the noted positive deviation of the T_g-composition relationship. Comparison of the shifts of hydroxyl IR absorbance band, reflecting the average strength of H-bonding, indicates a decreasing order of P2VP/PVPh > P2VP-b-PEO/PVPh > PEO/PVPh blends. The PEO block in the copolymer segment tends to defray the interaction strength in the P2VP-b-PEO/PVPh blends because of relative weaker interaction between PEO and PVPh than that between P2VP and PVPh pairs. A comparative ternary (P2VP/PEO)/PVPh blend was also studied as the controlling experiments for comparison to the P2VP-b-PEO/PVPh blend. The thermal behavior and interaction strength in (P2VP/PEO)/PVPh ternary blends are discussed with those in the P2VP-b-PEO/PVPh copolymer/homopolymer blend.     

Study of interfacial tension in poly(ethylene oxide)/polystyrene/diblock copolymer system by electric deformation method

We investigated the interfacial tension γ between poly(ethylene oxide) (PEO) and polystyrene (PS) focusing our attention on the dependence of γ on the molecular weight (M) of PEO and the surfactant effect of poly(ethylene oxide-b-styrene) diblock copolymer [P(EO-b-S)]. Measurements of γ were carried out by observing electric deformation of droplets of PEO suspended in bulk PS or in a concentrated solution of PS in dioctylphthalate (DOP). The results indicate that γ between PEO and PS is almost independent of M of PEO in the high molecular weight region, but exhibits a minimum around M = 500. Addition of 1 wt% of P(EO-b-S) to the PEO/PS system causes a decrease of γ due to the surfactant effect of the copolymer, but γ is almost independent of further addition of the copolymer. The decrement of the interfacial tension Δγ increases with increasing molecular weight of P(EO-b-S).     

Coarse-grained modelling of self-assembling poly(ethylene glycol)/poly(lactic acid) diblock copolymers

An implicit-solvent coarse-grained model for poly(ethylene glycol)/poly(lactic acid) (PEG/PLA) diblock copolymer is derived using the iterative Boltzmann inversion technique. The model is shown to be effective in reproducing the micellar core-shell structure of PEG/PLA diblock copolymer recently reported in experiments. Influence of block architecture on the aggregate morphology is investigated. Upon increasing the length of PLA block, the model predicts a morphological change from conventional spherical to anisotropic (e.g., lamellar or cylindrical) structure, in agreement with experimental findings. The current model is also noted to provide very rapid aggregation of the block copolymers, allowing observation of copolymer micelles in their equilibrium structures in a short simulation time.     

Effect of vortex-induced physical stress on fluorescent properties of dye-containing poly(ethylene glycol)-block-poly(lactic acid) micelles

The effect of vortex-induced mechanical stresses on the fluorescent properties of dye-containing poly(ethylene glycol)-block-poly(lactic acid) (PEG-b-PLA) block copolymer micelles has been investigated. PEG-b-PLA block copolymer micelles containing fluorescent dyes, 3,3′-dioctadecyloxacarbocyanine perchlorate (DiO) and/or 1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine perchlorate (DiI), are prepared by a simple one-step procedure that involves the self-assembly of block copolymers and spontaneous incorporation of hydrophobic dyes into the core of the micelles. Upon vortexing, the micelle dispersion samples showed a decrease in fluorescence intensity in a rotational speed- and time-dependent manner. The results demonstrated that the vortexing can alter the fluorescent properties of the dye-containing PEG-b-PLA block copolymer micelle dispersion samples, suggesting the potential utility of block copolymer micelles as a mechanical stress-responsive nanomaterial.     

Isothermal crystallization kinetics of poly(ethylene terephthalate)-poly(ethylene oxide) segmented copolymer with two crystallizing blocks

The isothermal crystallization kinetics and morphology of poly(ethylene terephthalate)-poly(ethylene oxide) (PET30-PEO6) segmented copolymer, and poly(ethylene terephthalate) (PET) and poly(ethylene oxide) (PEO) homopolymers have been studied by means of differential scanning calorimetry (DSC) and a transmission electron microscope (TEM). It is found that the nucleation mechanism and growth dimension of PEO in the copolymer are different from that in the homopolymer, which is attributed to the effect of the crystallizability of PET-blocks. Furthermore, the crystallization rate of PEO-blocks in the copolymer is slower than that in the homopolymer because the PET-blocks phase is always partially solidified at the temperatures when PEO-blocks begin to crystallize. In contrast, the isothermal crystallization rate of PET-blocks in the copolymer is faster than that in the homopolymer because the lower glass transition temperature of the PEO-blocks (soft blocks) increases the mobility of the PET-blocks in the copolymer.