ABA Triblock Research Articles

Floating and Diving Loops of ABA Triblock Copolymers in Lipid Bilayers and Stability Enhancement for Asymmetric Membranes.

Hybrid membranes of lipids and AxByAz triblock copolymers can possess better biocompatibility and mechanical stability. In this work, triblock copolymer conformations and stability of asymmetric membranes are explored by dissipative particle dynamics. The triblock copolymers in the membranes exhibit either the bridge or loop conformation. As hydrophobic B-blocks interact attractively with lipid heads, bridge-shaped copolymers are significantly inhibited and loop-shaped copolymers prefer to stay at the interface between hydrophilic and hydrophobic layers. This floating loop has a flattened conformation, consistent with the experimental findings. In contrast, for repulsive interactions between B-blocks and lipid heads, bridge-shaped copolymers are abundant and loop-shaped copolymers tend to plunge into the hydrophobic layer. This diving loop displays a random coil conformation. The asymmetric membrane in which the fractions of loop-shaped copolymers in the upper and lower leaflets are different is thermodynamically unstable. Two approaches are proposed to acquire kinetically stable asymmetric membranes. First, membrane symmetrization is arrested by eliminating bridge-shaped copolymers, which is achieved by B-block/lipid head attraction and B-block/lipid tail repulsion. Second, asymmetric triblock copolymers (x ≠ z) are used to prevent the passage of the long A-block through the hydrophobic layer.

New thermoplastic elastomer triblock copolymer of PLLA for cardiovascular tissue engineering: Annealing as efficient tool to tailor the solid-state properties

A new high molecular weight aliphatic copolyester of PLLA characterized by a ABA triblock architecture was successfully synthesized by ring opening polymerization, using as initiator a low molecular weight hydroxyl terminated random copolymer of PBS, poly(butylene/triethylene succinate). To increase the final polymer molecular weight, thus ensuring both good processability and mechanical properties, chain extension reaction has been performed with hexamethylene diisocyanate (HDI) as chain extender. All the synthetic steps have been carried out in solvent-free conditions. Specifically, the A block consists of LLA sequences, whereas the B one is an aliphatic biodegradable and biocompatible random copolyester of poly(butylene succinate) containing “PEG-like” moiety. The so-obtained material was first characterized by the molecular point of view and then, prior to further characterization, subjected to two different annealing treatments. Annealing revealed to be an efficient tool to control the kind and amount of crystalline phase developed by the material, as confirmed by WAXS structural analysis, and to tailor the mechanical properties, typical of thermoplastic elastomers. Thermal treatment was found to affect also the mechanism of polymer degradation under physiological conditions. Last, but not least, in order to explore the possible use of such new PLLA-based copolymer in vascular tissue engineering, preliminary biocompatibility tests, using endothelial cells, were carried out.

Mixed micellar system for codelivery of doxorubicin and caffeic acid phenethyl ester: design and enhanced antitumor activity

Multifunctional nanocarriers of two or more anticancer drugs with different pharmacological mechanisms are being developed for combination therapy, which aims at achieving synergistic effects in cancer treatment and overcoming the increasingly common problem of drug resistance. This contribution reports the fabrication of functional nanosized micellar carriers of doxorubicin (DOX) and caffeic acid phenethyl ester (CAPE) via coassembly of two well-defined amphiphilic ABA triblock copolymers comprising identical hydrophobic poly(e-caprolactone) (PCL) blocks and different hydrophilic segments – poly(ethylene oxide) (PEO) or poly(acrylic acid) (PAA). CAPE was embedded into the PCL core via hydrophobic interactions, while DOX was loaded within a mixed PAA/PEO corona layer through complexation. The main physico-chemical properties of blank and dual drug-loaded micelles were investigated using dynamic and electrophoretic light scattering and transmission electron microscopy. Loading of CAPE and DOX increased the size and size distribution of carriers to some extent. However, the mixed micellar system was characterized by good colloidal stability and sustained release of the two drugs. The cytotoxic effect of DOX/CAPE-loaded mixed micelles in drug-resistant lymphoma cells expressing the multidrug resistance (MDR1) gene (L5178Y MDR1) was assessed. Functional micellar nanocarriers for codelivery of doxorubicin (DOX) and caffeic acid phenethyl ester (CAPE) were successfully developed via coassembly of PEO113-b-PCL35-b-PEO113 and PAA13-b-PCL35-b-PAA13. CAPE was entrapped into the PCL core via hydrophobic interactions, while DOX was loaded in the middle layer through complexation between the amino and carboxylic groups of DOX and PAA. The dual drug-loaded micelles exhibited superior colloidal stability and sustained drug release profiles. The dual drug -loaded system suppressed the proliferation of mouse T-lymphoma L5178Y MDR1 cells more effectively than the single drug-loaded micelles, suggesting a synergistic effect.

Nanocarrier-loaded block copolymer dual domain organogels

Loaded polymer gels are prevalent materials in the controlled release community and, fairly recently, have been formulated to include nanocarrier domains such as micelles and vesicles. One mechanism used to establish the solid-like characteristic of gels is block copolymer self-assembly, which can result in a system-spanning, physically-crosslinked network. The combination of nanocarrier and crosslink domain presence offers gels with a rich nanoscale phase space capable of intricate macroscopic property tuning. The current manuscript provides an overview of nanocarrier-loaded block copolymer organogels wherein nanocarriers are reverse micelles formed by sodium dioctyl sulfosuccinate (AOT), the block copolymer is a styrenic ABA triblock copolymer, and the gel solvent is aliphatic mineral oil. This introductory overview starts by identifying the envelope in ternary phase space wherein nanocarrier-loaded block copolymer organogels form (2–49 wt% triblock copolymer and 8x10−3-1 wt% AOT). Next, a detailed nanostructural description of gels varying in AOT and triblock copolymer concentration is presented. The manuscript concludes with demonstration of AOT reverse micelle release and gel uniaxial tensile response for gels containing 0–1 wt% AOT and 5–40 wt% styrenic triblock copolymer.

Effect of network connectivity on the mechanical and transport properties of block copolymer gels

AbstractEstablishing the independent tunability of transport and mechanical properties in polymer gels would significantly contribute to their implementation as transdermal drug delivery media, among other things. The work conducted herein uses facile changes in the formulation of physically crosslinked styrenic ABA/AB block copolymer organogels to alter their mechanical properties independently from the mass transport of an internally‐loaded nanocarrier. Such independent tunability is made possible by altering the relative amounts of ABA triblock and AB diblock copolymers while holding total copolymer concentration fixed. Specifically, three series of gels each with a fixed total copolymer concentration (10, 20, or 30 wt%) comprised of varying triblock copolymer concentration are studied. Small angle x‐ray scattering confirms that, at the nanoscale, only gel network connectivity changes within each series, while mechanical and release experiments show that increasing network connectivity leads to significant growth of gel moduli, but little change in nanocarrier release rate.

Architecture Effects in Complex Spherical Assemblies of (AB)n-Type Block Copolymers.

Molecular architecture plays a key role in the self-assembly of block copolymers, but few studies have systematically examined the influence of chain connectivity on tetrahedrally close-packed (TCP) sphere phases. Here, we report a versatile material platform comprising two blocks with substantial conformational asymmetry, A = poly(trifluoroethyl acrylate) and B = poly(dodecyl acrylate), and use it to compare the phase behavior of AB diblocks, ABA triblocks, and (AB)n radial star copolymers with n = 3 or 4. Each architecture forms TCP sphere phases at minority A block compositions (fA < 0.5), namely, σ and A15, but with differences in the location of order-order phase boundaries that are not anticipated by mean-field self-consistent field theory simulations. These results expand the palette of polymer architectures that readily self-assemble into complex TCP structures and suggest important design considerations when targeting specific phases of interest.

Perforated Vesicles of ABA Triblock Copolymers with ON/OFF-Switchable Nanopores

The stimuli-responsive membrane with ON/OFF-switchable pores has various applications such as targeted drug delivery and biosensor. In this work, the perforated vesicle/membrane self-assembled from...

Facile synthesis of temperature-sensitive ABA triblock copolymers by dispersion RAFT polymerization

The dispersion RAFT polymerization was applied for the first time to synthesize the well-defined ABA triblock copolymer core–shell nanoparticles of temperature-sensitive poly(N-isopropylacrylamide-co-acrylic acid)-block-poly(n-butyl acrylate)-block-poly(N-isopropylacrylamide-co-acrylic acid) and poly(n-butyl acrylate-co-N-isopropylacrylamide)-blockpoly(n-butyl acrylate)-block-poly(n-butyl acrylate-co-N-isopropylacrylamide).

Amphiphilic polymer co‐networks: 32 years old and growing stronger – a perspective

AbstractThis brief perspective overviews amphiphilic polymer co‐networks (APCNs), polymeric chemically crosslinked hydrogels also covalently hosting a hydrophobic segment, conferring upon these materials the important property of internal self‐organization in aqueous environments. APCN synthesis is most conveniently accomplished via the random crosslinking copolymerization of a hydrophilic monomer with a hydrophobic macro‐crosslinker, whereas better structures are attained via the end‐linking of amphiphilic linear ABA triblock copolymers or amphiphilic star diblock copolymers. Microphase‐separated morphologies, translucency‐to‐transparency, biocompatibility, low to moderate aqueous swelling, fair mechanical strength and possible stimulus‐responsiveness constitute the main physicochemical properties of APCNs, with their major commercial application being in silicone hydrogel soft contact lenses. Modeling the swelling, morphological and mechanical behavior of these intriguing materials is an area where more progress is necessary in order to improve our understanding of these networks and facilitate the design of next‐generation APCNs. © 2020 Society of Industrial Chemistry

Structure and Relaxation Dynamics for Complex Coacervate Hydrogels Formed by ABA Triblock Copolymers

Complex coacervate core hydrogels were formed by simply mixing two oppositely charged polyether-based ABA triblock copolyelectrolyte solutions, where A blocks functionalized with either ammonium or...

Polymer Gel Electrolytes Based on PEG-Functionalized ABA Triblock Copolymers for Quasi-Solid-State Dye-Sensitized Solar Cells: Molecular Engineering and Key Factors.

The molecular weights and structural properties of polymers play key roles in the efficiency of gelators in polymer gel electrolytes (PGEs) for quasi-solid-state dye-sensitized solar cells (QSS-DSSCs). To find an appropriate gelator, we synthesized well-defined poly(acrylonitrile-co-N,N-dimethylacrylamide)-block-poly(ethylene glycol)-block-poly(acrylonitrile-co-N,N-dimethylacrylamide) ABA triblock copolymers with various molecular weights and copolymer compositions by reversible addition-fragmentation chain-transfer polymerization. The ratio of acrylonitrile (AN)/N,N-dimethylacrylamide (DMAA) in the triblock copolymers influences their solubility in liquid electrolytes (LEs) and thermal stability. The highest thermal stability was up to 360 °C, and this was achieved by the polymer with an AN/DMAA ratio of ≤4. The thermal stability was related to excessive randomness in the P(AN-co-DMAA) block that hinders cyclization among nitrile groups. Both the molecular weights and the AN/DMAA ratios enabled gel formation by controlling the amount of the polymer, and hence, they influence the ionic conductivity and diffusion as well. Based on the electrochemical properties, polymers with molecular weights above 100 kg/mole were efficient as PGEs in QSS-DSSCs. The overall power conversion efficiency (PCE) of 14 wt % SGT-626 PGE-based QSS-DSSCs was 9.72% under AM 1.5G solar illumination, comparable with an overall PCE of 9.79% for LE DSSCs. The overall PCE of the QSS-DSSCs further increased to 10.02% by incorporating 3 wt % TiO2 nanoparticles in the 14 wt % SGT-626 PGE. The SGT-626 PGE-based QSS-DSSC was also tested under indoor light conditions, and the best PCE of 21.26% was achieved under a white LED light of 1000 lux, which is higher than the PCE of 19.94% for the LE DSSC. The long-term device stability test under adverse conditions (50 °C and 1 sun illumination) reveals the improved stability of PGE-based QSS-DSSCs over LE DSSCs. In terms of PCE and long-term device stability, our PGE QSS-DSSCs have great potential over LE DSSCs for future indoor and outdoor applications.

"Dumb" pH-Independent and Biocompatible Hydrogels Formed by Copolymers of Long-Chain Alkyl Glycidyl Ethers and Ethylene Oxide.

The formation and rheological properties of hydrogels based on amphiphilic ABA triblock polyether copolymers are described, relying solely on the hydrophobic interaction of long-chain alkyl glycidyl ether (AlkGE)- based A-blocks that are combined with a hydrophilic poly(ethylene glycol) (PEG) midblock. Via anionic ring-opening copolymerization (AROP), ethylene oxide (EO) and long-chain alkyl glycidyl ethers (AlkGEs) were copolymerized, using deprotonated poly(ethylene glycol) (PEG) macroinitiators (Mn of 10, 20 kg mol-1). The polymerization afforded amphiphilic ABA triblock copolymers with molar masses in the range of 21-32 kg mol-1 and dispersities (Đ) of Đ = 1.07-1.17. Kinetic studies revealed random copolymerization of EO and AlkGE, indicating random spacing of the hydrophobic AlkGE units by polar EO units. Following this approach, the hydrophobicity of the apolar blocks of amphiphilic ABA triblock polyethers can be tailored. Detailed rheological measurements confirmed the successful formation of hydrogels at different pH values as a consequence of nonpolar interactions and alkyl chain crystallization. Hydrogel formation was also observed at different ionic strengths (i.e., varied salt concentration), based on the hydrophobic aggregates. This behavior is in contrast to other often-used supramolecular cross-linking strategies, such as Coulomb interactions, complexation, or hydrogen bonding. Micro-differential scanning calorimetry (μ-DSC) measurements of the hydrogels revealed crystalline hydrophobic domains with melting temperatures in the physiological temperature range. In 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazoliumbromide (MTT) assays, diblock copolymers possessing structural analogy to the triblock copolymers were studied to assess the general cytotoxicity of amphiphilic polyethers bearing long alkyl chains at the polyether backbone, using splenic immune cells. At intermediate polymer concentrations, no cytotoxic effects were observed. This indicates that long-chain alkyl glycidyl ethers are promising for the introduction of highly hydrophobic as well as crystalline motifs at the polyether backbone in hydrogels for biomedical purposes.

Gas-separation and physical properties of ABA triblock copolymers synthesized from polyimide and hydrophilic adamantane derivatives

In this study, ABA triblock copolymers derived from 4,4’-(hexafluoroisopropylidene)-diphthalic anhydride-2,3,5,6-tetramethyl-1,4-phenylenediamine (6FDA-TeMPD; PI) and 3-hydroxy-1-adamantyl methacrylate (HAdMA) or 3,5-dihydroxy-1-adamantyl methacrylate (DHAdMA) have been synthesized via atom transfer radical polymerization to generate mechanically tough and thermally stable gas-separation membranes with composition-tunable transport properties. Due to the inherent thermodynamic incompatibility between the chemically dissimilar blocks, these two series of triblock copolymers appear microphase-separated. While the gas permeability coefficients of these triblock copolymer membranes are consistently lower than that of PI due to the reduced fractional free volume of HAdMA and DHAdMA, the solubility coefficients of the copolymers are higher than that of PI due presumably to specific interactions between the polar hydroxyl group(s) and penetrant gas molecules. These triblock copolymers synthesized from PI and hydrophilic adamantane derivatives constitute a new class of nanostructured polymeric materials possessing excellent thermomechanical properties in conjunction with designer gas-separation properties.

Block Copolymer Pressure-Sensitive Adhesives Derived from Fatty Acids and Triacetic Acid Lactone

A method for the development of ABA triblock copolymers for high-performance pressure-sensitive adhesives from the biorenewable chemicals lauryl acrylate and triacetic acid lactone (TAL) is present...

(Invited) Interactions of Block Co-Polymer Ionomers on Metal Surfaces for Tuned Electrocatalysis

In acidic fuel cells, the ionomer and catalyst layer were developed empirically, and only recently studies have begun investigating the success of the heterogeneous microstructure and triple-phase boundary. Currently, the catalyst layer is not well understood due to its complexity; however, model interfaces between ionomers and catalyst particles have been used to provide valuable insight on ionomer-catalyst interfacial interactions. It is known from studies with Nafion® that restructuring of the polymer morphology can occur when it exists as an ionomer thin film at a catalyst interface. The behavior of the thin film ionomer changes compared to its bulk characteristics, which ultimately affects electrode kinetics by altering ionic and water transport networks. In the field of alkaline fuel cells, there is limited research published on ionomer developments in general or on specific interactions between ionomers and catalysts. The few fuel cell studies that compare the effects of ionomer chemistry have conflicting conclusions, which likely arise because the ionomer chemistries interact with Pt in different ways. Overall, this provides the motivation for our work to study idealized structures in the electrode, specifically to elucidate and modify interactions occurring at the interface between ionomers and non-PGM catalysts. This insight will enable the rational and systematic development of ionomer chemistry with the ultimate goal of improving electrode kinetics for a variety of important electrochemical reactions.We have synthesized a large number of model cationic block co-polymers, diblocks, triblocks and pentablocks (AB, ABA, ABABA). Where the hydrophobic block is either polyisoprene or polycyclooctadiene, or their hydrogenated analogues, polymethylbutylene or polyethylene. The other block is polychloromethylstyrene that can be quaternized with a variety of amines to vary the interaction with the surface, inmost of work we use the relatively simple benzyltrimethylammonium (TMA) cation or the reportedly more stable and more bulky benzylmethylpyrolidinium (MPRD) cation. Our initial studies using commercial Ag nano powders showed that the olefinic groups of the polymers interacted wit the Ag and that the interaction of the cations with the Ag surface could completely remove the crystallinity from the entire sample in the case of the polyethylene block. Probing the effects of these interactions on electrocatalysis of the oxen reduction reaction is on going and we will report our progress in this paper.To further constrain the polymers we have also studied them as thin films on flat Si wafers and the same substrate coated with thin metallic films and studied by GISAXS. When block co-polymers are spin coated on plain silicon wafers we almost always see no scattering as there is no alignment of the polymer on the silicon surface. When a thin layer of silver is coated onto the silicon, discrete alignment of features perpendicular to the surface are observed for many of the polymers we have synthesized on the nanoscale. The size of these features in the thin films is not always correlated with the block sizes observed in the bulk films by SAXS. AFM imaging of the polymer air interface suggests that these vertically aligned features persist throughout the film, a property presumably needed for transport, but that the size can vary. The data shown below is typical of aligned vertical triblock ABA polymers on Ag. We have also investigated these thin films as a function of temperature and hummidity and observed transients of the changes in the morphology of these materials. In this paper we will show how these interactions can be utilized for the beneficial development of electrocatalysts. Figure 1

ABA triblock copolyesters composed of poly(l-lactide) A hard blocks: comparison of amorphous and crystalline unsaturated aliphatic polyesters as B soft blocks

The property profiles of ABA triblock copolymers can be precisely customized by changing the chemical structure of the components. The identification of the midblock is the key point in the development of PLLA-containing ABA triblock copolymers. Two kinds of unsaturated aliphatic polyesters, crystalline poly(cis-butene succinate) (PcBS) and amorphous poly(cis-butene glutarate) (PcBG) with dihydroxyl end groups were prepared by polycondensation reactions. Then, dihydroxyl-terminated PcBS and PcBG were used as macroinitiators to initiate ring opening of polymerization of L-lactide toward two series of fully biobased biodegradable PLLA-b-PcBS-b-PLLA and PLLA-b-PcBG-b-PLLA triblock copolymers with PLLA as hard end-blocks. The influences of the midblocks and the endblocks length on microstructure, thermal and tensile properties of the triblock copolymers were studied. Compared to homopolymer PLLA, all the triblock copolymers had a much higher elongation at break with lower tensile strength and tensile modulus, depending on the length of PLLA blocks. It was found that the amorphous PcBG midblock plays a greater role than the crystalline PcBS midblock in enhancing the tensile toughness of ABA triblock copolymers. PLLA-b-PcBG-b-PLLA composed of shorter PLLA hard block displayed typical elastomeric behavior without yield, which is a promising aliphatic polyester-based thermoplastic elastomer. The unsaturated carbon–carbon double bonds in these polyesters backbone provide a variety of opportunities for further modifications.

Quick and Efficient Thermal Stability Enhancement of Micro‐Phase Separated Structure Formed from ABA Triblock Copolymers by Photo Cross‐Linking Approach

AbstractWe here report quick and efficient enhancement of the thermal stability of triblock copolymer‐based bulk morphologies by utilizing photo cross‐linking, which aims for widening the application range of block copolymer‐based materials. First, we synthesized ABA triblock copolymer bearing photo cross‐linkable groups (i. e., benzophenone groups) in the end blocks via two step atom transfer radical polymerizations (ATRP) and subsequent esterification reaction. UV‐light was irradiated for the annealed bulk films at room temperature, and the photo cross‐linking completely progressed within several minutes. Small angle X‐ray scattering (SAXS) and the model fitting analysis revealed that the original cylinder morphology of the neat sample was nicely preserved after the photo cross‐linking, which enables investigation of intrinsic effects of domain cross‐linking. The temperature ramp SAXS measurements demonstrated the photo cross‐linked cylinder structure remained up to the temperature (∼320 °C) much higher than the disordering temperature (∼240 °C) of the neat uncross‐linked structure.

ABA Triblock Copolyesters Composed of Poly(L-lactide) A Hard Blocks: Long Chain Aliphatic Polyesters as B Soft Midblocks

A series of triblock copolyesters were produced by ring-opening polymerization of l-lactide initiated by the dihydroxy-terminated poly(alkylene dodecanedioate)s as macroinitiators. The dihydroxy-terminated poly(alkylene dodecanedioate)s as low melting blocks were prepared by using 1,12-dodecanedioic acid and methyl substituted aliphatic diols. The influence of the different polyesters middle block on microstructure, thermal, crystallization and tensile properties of the triblock copolyesters was investigated. It was found that the poly(alkylene dodecanedioate)s containing methyl substitutions still exhibited crystallization and melting behavior, but the crystallization ability decreased when compared with linear poly(alkylene dodecanedioate). The diffraction peaks of soft and hard segments, measured by WAXD, showed a gentle trend after copolymerization. Through the TGA test, the results showed that thermal stability of the triblock polyesters was improved. Tensile tests exhibited that the elongation at break was improved significantly, with the highest elongation at break reaching 400%, while the tensile strength of triblock copolyesters decreased slightly compared with polylactide. The correlation between the middle block structures and their physical properties was explored and discussed.

Extraction of intrinsic cross-linking effects of A hard domains on segmental motion of B soft block for ABA triblock copolymer-based elastomers by utilizing photo cross-linking

We here shed light on effects of the A domain cross-linking for the physical properties, especially for the B middle block segmental motion, of ABA triblock copolymers with a soft B block and A glassy end blocks bearing photo cross-linkable moieties. For extraction of the intrinsic effects of cross-linking, we utilize room temperature photo cross-linking. Scattering measurements and model analysis finely confirm that the photo cross-linking proceeds without any influences on the morphology. Unexpectedly, the cross-linking of A domain affects not only the segmental motion of A block but also the B block segmental motion. Concretely, DSC and rheological measurements revealed that Tg (or α-relaxation temperature) of the B soft block decreased (ΔTg ~ 4 °C) and the apparent activation energy (Ea) of the B soft segmental motion increased (ΔEa ~90 kJ mol−1), which were discussed with assuming the rigidity change of B segment in the interfacial mixed layer.

Controlling the thermomechanical properties of biobased ABA triblock copolymers comprising polylactide (A) and poly(1,2‐propylene succinate) (B) with high molecular weight

AbstractBis‐hydroxyl‐terminated poly(1,2‐propylene succinate) (PPS‐diols) with high molecular weight (10–40 kDa) are prepared by two‐step melt polycondensation of succinic acid and 1,2‐propanediol with Ti(BuO)4 as the catalyst. By using these PPS‐diols as macroinitiators, the ring‐opening polymerization of d‐ and l‐lactides is readily conducted to obtain enantiomeric ABA triblock copolymers consisting of poly(l‐lactide) and PPS (B) (t‐l‐PPS) as well as those of poly(d‐lactide) and PPS (B) (t‐d‐PPS) which have higher PPS compositions (20–70 wt%) in addition to high molecular weight (20–80 kD). The Tg, Tm, and ΔHm values of the t‐l‐PPS copolymers as well as the stereo mixtures of t‐l‐PPS/t‐d‐PPS are controlled to linearly decrease with increasing the PPS content. The copolymers also exhibit higher elastomeric properties with increasing the PPS content. The tensile properties of the copolymer films having higher PPS contents (both the single block copolymers and stereo mixtures) are comparable to those of the oil‐based thermoplastic elastomers. It is therefore concluded that these block copolymers can afford thermoplastic elastomers or flexible plastic materials having a 100% biobased content.