ABC Triblock Copolymers Research Articles

Efficient Synthesis of μ-A(BC)C Miktoarm Star Polymer Assemblies via Aqueous Photoinitiated Polymerization-Induced Self-Assembly.

In this study, green light-activated photoiniferter reversible addition-fragmentation chain transfer (RAFT) polymerization of glycerol methacrylate was performed using an ω,ω-heterodifunctional macro-RAFT agent. Because of the different RAFT controllability of two RAFT groups toward methacrylic monomers, only one RAFT group was activated under green light irradiation, leading to the formation of a diblock copolymer macro-RAFT agent with one RAFT group located at the chain end and the other RAFT group located between two blocks. The obtained diblock copolymer macro-RAFT agent was then used to mediate aqueous photoinitiated RAFT dispersion polymerization of diacetone acrylamide (DAAM), which formed μ-A(BC)C miktoarm star polymer assemblies with a diverse set of morphologies. Comparing with the ABC triblock copolymer, it was found that the architecture of the μ-A(BC)C miktoarm star polymer facilitated the formation of higher-order morphologies. Kinetic studies indicated that the aqueous photoinitiated RAFT dispersion polymerization exhibited ultrafast polymerization behavior, with quantitative monomer conversion being achieved within 5 min. Size exclusion chromatography analysis confirmed that good RAFT control was maintained during the polymerization. A morphological phase diagram for μ-A(BC)C miktoarm star polymer assemblies was constructed by varying the monomer concentration and the [DAAM]/[Macro-RAFT] ratio. We expect that this study not only develops an approach for the preparation of miktoarm star polymer assemblies but also provides mechanistic insights into the polymerization-induced self-assembly of nonlinear polymers.

Amphiphilic pH-responsive ABC triblock copolymers via RAFT-mediated aqueous PISA and comparison with their A-b-(B-co-C) diblock copolymer counterparts

The influence of the macroRAFT agent architecture on the morphology of the self-assemblies obtained by aqueous RAFT dispersion polymerization in PISA is studied by comparing amphiphilic AC, A(B-co-C) diblocks and ABC triblock copolymers, constituted of N,N-dimethylacrylamide (DMAm = A), acrylic acid (AA = B) and N-cyanomethylacrylamide (CMAm = C) monomer units. The aim of this study is to better understand the impact of the presence of pH-sensitive acrylic acid units and their spatial distribution in block copolymers. Generally, the presence of a fully protonated intermediate block of PAA between the two blocks (based on PDMAm and PCMAm) favors the formation of higher-order morphologies. These ABC triblock copolymers assemblies are pH-responsive and can undergo morphological transitions through the controlled deprotonation or protonation of the PAA segment, but do not completely dissociate at high pH (i.e. when AA units are fully ionized) unlike their A(B-co-C) diblock counterparts, where the pH-responsive monomer unit is homogeneously distributed within the solvophobic block.

Microscopic Origins of the Distinct Mechanical Response of ABA and ABC Block Copolymer Nanostructures.

It has been commonly believed that the ordered thermoplastic elastomers formed by the ABC triblock copolymer should have better mechanical performance than that by the ABA counterpart due to the higher bridging fraction. However, the thermoplastic elastomer of ABA was often observed to perform better than that of ABC. To compare the performance of two kinds of thermoplastic elastomers and unveil the underlying microscopic mechanism, we have calculated their stress-strain curves using coarse-grained molecular dynamics simulations in conjunction with self-consistent field theory. It is revealed that the stretching degree of the bridging blocks and the network connectivity play important roles in determining the mechanical properties in addition to the bridging fraction. The higher degree in the stretching of bridging blocks and network connectivity of the structure formed by the ABA triblock copolymer enables its superior mechanical performance over the ABC block copolymer.

ABC or ACB triblock copolymers? Changing the RAFT group position in diblock copolymer macro-RAFT agents leads to different PISA behaviors in RAFT dispersion polymerization

ACB and ABC triblock copolymer nanoparticles were prepared by reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization using diblock copolymer macromolecular RAFT (macro-RAFT) agents with different RAFT group positions.

Stability of Hierarchical Gyroid Structures in Frustrated ABC Triblock Copolymers

Stability of Hierarchical Gyroid Structures in Frustrated ABC Triblock Copolymers

Polymerization Induced Microphase Separation of ABC Triblock Copolymers for 3D Printing Nanostructured Materials.

Polymerization-induced microphase separation (PIMS) is a versatile technique for producing nanostructured materials. In previous PIMS studies, the predominant approach involved employing homopolymers as macromolecular chain transfer agents (macroCTAs) to mediate the formation of nanostructured materials. In this article, the use of AB diblock copolymers as macroCTAs to design PIMS systems for 3D printing of nanostructured materials is investigated. Specifically, the influence of diblock copolymer composition and block sequence on the resulting nanostructures, and their subsequent impact on bulk properties is systematically investigated. Through careful manipulation of the A/B block ratios, the morphology and size of the nanodomains are successfully controlled. Remarkably, the sequence of A and B blocks significantly affects the microphase separation process, resulting in distinct morphologies. The effect can be attributed to changes in the interaction parameters (χAB, χBC, χAC) between the different block segments. Furthermore, the block sequence and composition exert profound influence on the thermomechanical, tensile, and swelling properties of 3D printed nanostructured materials. By leveraging this knowledge, it becomes possible to design advanced 3D printable materials with tailored properties, opening new avenues for material engineering.

Hydrosilylation-Promoted Group Transfer Polymerization of Ethyl Sorbate: A Controlled/Living System Applied to the Synthesis of an α-End Functionalized Polymer and a Triblock Copolymer with a (Meth)acrylate Polymer

The polymerization method, preparation of well-defined (co)polymers, and controlled/living property of ethyl sorbate (ES) have been investigated using hydrosilylation-promoted group transfer polymerization (GTP). The GTP of ES with hydrosilane (R3SiH) was performed in a living manner to produce well-defined poly(ethyl sorbate) (PES) via two methods: single catalyst and catalyst switch. For the single catalyst method, B(C6F5)3 served as the catalyst for the hydrosilylation of ES and R3SiH, yielding silyl ketene acetal (SKA), as well as the polymerization of ES and PES with the trans structure. SKA was prepared using the catalyst switch method via equimolar hydrosilylation with B(C6F5)3, and the phosphazene base of t-Bu-P4 catalyzed the polymerization of ES, yielding PES with cis and trans structures. The kinetic experiments demonstrated that the propagation rate kp for t-Bu-P4-catalyzed GTP is significantly higher than that for B(C6F5)3. The α-end-functionalized PES was synthesized via the hydrosilylation-promoted GTP of ES using a sorbate ester with a functional group as the moisture-stable latent initiator via the catalyst switch method. Furthermore, the controlled/living property has enabled the hydrosilylation-promoted GTP of ES with MMA and n-butyl acrylate (nBA) to produce the AB-diblock copolymer and ABA- and ABC-triblock copolymers composed of PES, PMMA, and PnBA.

Fluorine-Containing Triblock Copolymer Vesicles with Microphase-Separated Structure

Introduction of a fluorine-containing block into block copolymers is an effective method to tune block copolymer nanoassemblies with a microphase-separated structure. However, this microphase-separated structure is difficult to clearly observe due to its nanoscale size. In this work, fluorine-containing ABC triblock copolymer vesicles of poly(ethylene glycol)-block-polystyrene-block-poly(4-vinylbenzyl pentafluorophenyl ether) (PEG-b-PS-b-PVBFP) are synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization under dispersed condition. Owing to the choice of a suitable degree of polymerization of the three blocks, the synthesized PEG45-b-PS197-b-PVBFP233 vesicles have a relatively large size of around 216 nm and a thin vesicular membrane with a thickness of around 28 nm. Ascribed to the relatively large size of the vesicles and the thin vesicular membrane, it is concluded that the fluorine-containing PVBFP block forms 9 nm columnar microdomains shielded by the PS phase in the vesicular membrane.

Asymmetric Binary Spherical Phases Self-Assembled by Mixing AB Diblock/ABC Triblock Copolymers

The self-assembly of binary blends composed of AB diblock and ABC triblock copolymers is investigated using self-consistent field theory. Specifically, the miscibility of the binary mixture is studied by tuning the concentration ϕ2 of AB diblock and the length ratio γ between AB diblock and ABC triblock. It is predicted that the sphere-forming AB diblock and binary sphere-forming ABC triblock copolymers can be compatible by coassembling into new spherical phases, even when ϕ2 is close to 50%. For relatively low γ (0.48 < γ < 1.13), the two different copolymers are accommodated into an asymmetric binary spherical phase, Li3Bi, where the A-sphere coformed by two A-blocks with similar lengths is close to the C-sphere in size. When γ is increased to larger than 1.45, the two A-blocks have considerably different lengths, and they form a core–shell distribution within the A-sphere. The core–shell distribution effectively enlarges the A-sphere. The two factors where the A-sphere is larger than the C-sphere and the volume fraction of A-blocks is larger than that of the C-block lead to the formation of NaCl phase with symmetric coordination number. Our theoretical results demonstrate that blending simple block copolymers with proper length ratio and concentration provides an efficient route for the fabrication of new binary mesocrystals.

Cross-Linkable Polyion Complex Micelles from Polypept(o)ide-Based ABC-Triblock Copolymers for siRNA Delivery.

ABC-type triblock copolymers are a rising platform especially for oligonucleotide delivery as they offer an additional functionality besides the anyhow needed functions of shielding and complexation. The authors present a polypept(o)ide-based triblock copolymer synthesized by amine-initiated ring-opening polymerization (ROP) of N-carboxyanhydrides (NCAs), comprising a shielding block A of polysarcosine (pSar), a poly(S-ethylsulfonyl-l-cystein) (pCys(SO2 Et)) block B for bioreversible and chemo-selective cross-linking and a poly(l-lysine) (pLys) block C for complexation to construct polyion complex (PIC) micelles as vehicle for small interfering RNA (siRNA) delivery. The self-assembly behavior of ABC-type triblocks is investigated to derive correlations between block lengths of the polymer and PIC micelle structure, showing an enormous effect of the β-sheet forming pCys(SO2 Et) block. Moreover, the block enables the introduction of disulfide cross-links by reaction with multifunctional thiols to increase stability against dilution. The right content of the additional block leads to well-defined cross-linked 50-60nm PIC micelles purified from production impurities and determinable siRNA loading. These PIC micelles can deliver functional siRNA into Neuro2A and KB cells evaluated by cellular uptake and specific gene knockdown assays.

Polymerization-induced self-assembly and disassembly during the synthesis of thermoresponsive ABC triblock copolymer nano-objects in aqueous solution.

Polymerization-induced self-assembly (PISA) has been widely utilized as a powerful methodology for the preparation of various self-assembled AB diblock copolymer nano-objects in aqueous media. Moreover, it is well-documented that chain extension of AB diblock copolymer vesicles using a range of hydrophobic monomers via seeded RAFT aqueous emulsion polymerization produces framboidal ABC triblock copolymer vesicles with adjustable surface roughness owing to microphase separation between the two enthalpically incompatible hydrophobic blocks located within their membranes. However, the utilization of hydrophilic monomers for the chain extension of linear diblock copolymer vesicles has yet to be thoroughly explored; this omission is addressed for aqueous PISA formulations in the present study. Herein poly(glycerol monomethacrylate)-poly(2-hydroxypropyl methacrylate) (G-H) vesicles were used as seeds for the RAFT aqueous dispersion polymerization of oligo(ethylene glycol) methyl ether methacrylate (OEGMA). Interestingly, this led to polymerization-induced disassembly (PIDA), with the initial precursor vesicles being converted into lower-order worms or spheres depending on the target mean degree of polymerization (DP) for the corona-forming POEGMA block. Moreover, construction of a pseudo-phase diagram revealed an unexpected copolymer concentration dependence for this PIDA formulation. Previously, we reported that PHPMA-based diblock copolymer nano-objects only exhibit thermoresponsive behavior over a relatively narrow range of compositions and DPs (see Warren et al., Macromolecules, 2018, 51, 8357–8371). However, introduction of the POEGMA coronal block produced thermoresponsive ABC triblock nano-objects even when the precursor G-H diblock copolymer vesicles proved to be thermally unresponsive. Thus, this new approach is expected to enable the rational design of new nano-objects with tunable composition, copolymer architectures and stimulus-responsive behavior.

Synthesis of an ABC triblock copolymer by a bilateral Click reaction using α,ω-bifunctionalized poly(3-hexylthiophene) as an inner segment

A novel A-b-poly(3-hexylthiophene)(P3HT)-b-C type triblock copolymer was successfully synthesized by the bilateral Cu-catalyzed azide alkyne cycloaddition reaction using α,ω-bifunctionalized P3HT.

Linear ABC amphiphilic triblock copolymers for complexation and protection of dsRNA

We herein report the synthesis and characterisation of linear ABC triblock copolymers, investigation of their self-assembly in aqueous solution, and complexation with and protection of double stranded-RNA (dsRNA).

ABC and ABAB Block Copolymers by Electrochemically Controlled Ring-Opening Polymerization.

An electrochemically controlled synthesis of multiblock copolymers by alternating the redox states of (salfan)Zr(OtBu)2 (salfan = 1,1'-di(2-tert-butyl-6-N-methylmethylenephenoxy)ferrocene) is reported. Aided by electrochemistry with a glassy carbon working electrode, an in situ potential switch alters the catalyst's oxidation state and its subsequent monomer (l-lactide, β-butyrolactone, or cyclohexene oxide) selectivity in one pot. Various multiblock copolymers were prepared, including an ABAB tetrablock copolymer, poly(cyclohexene oxide-b-lactide-b-cyclohexene oxide-b-lactide), and an ABC triblock copolymer, poly(hydroxybutyrate-b-cyclohexene oxide-b-lactide). The polymers produced using this technique are similar to those produced via a chemical redox reagent method, displaying moderately narrow dispersities (1.1-1.5) and molecular weights ranging from 7 to 26 kDa.

Antifreeze and Rheological Properties of Injectable Triblock Copolymer Hydrogels with Supramolecular Junctions.

ABC triblock copolymers composed of hydrophobic poly(ε-caprolactone) (PCL), zwitterionic poly(carboxybetaine methacrylate) midblock, and P(PEGMA-UPy0.15 ) containing supramolecular ureidopyrimidinone moieties, poly(ε-caprolactone-block-carboxybetaine methacrylate-block-[poly(ethylene glycol) methyl ether methacrylate-co-(α-methacryloyl-ω-(6-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)hexylcarbamoyloxy)poly(ethylene glycol))]), are investigated to achieve multifunctional antifreeze hydrogels. The PCL and P(PEGMA-UPy0.15 ) blocks induce the formation of physical network with a hierarchical nanostructure comprising hydrophobic PCL cores and supramolecular junctions, respectively. The super-hydrophilic nature of polyzwitterion midblocks and the confinement effect of the supramolecular junctions enhance the antifreeze performance, where the majority of water molecules remains supercooled below sub-zero temperature. The hydrogel relaxation characterized over a wide range of timescale reveals that the facile dynamics of the supramolecular junctions lead to the self-healing and injectability of the hydrogels. In conjunction with the biodegradable PCL cores, the antifreeze and rheological characteristics of the triblock copolymer hydrogels provide significant potential to use for cryo-preservable and bio-injectable drug storage and delivery.

Recent Advances in Polyallenes: Preparation, Self-Assembly, and Stimuli-Responsiveness.

Polyallenes, as a typical type of reactive polymers, are of great significance and have aroused widespread interest because they contain double bonds that can be post-modified into other functionalities to afford varieties of functional materials. This Minireview firstly highlights the recent advances in the preparation of polyallenes, including preparation of helical polyallenes through directly polymerization of chiral allene monomers or helix-sense-selective polymerization (HSSP) of achiral allene monomers, synthesis of 1,2-regulated polyallenes and 2,3-regulated polyallenes via selective polymerization of allene monomers, polymerization of allene monomers catalyzed by Ni(II)-terminated poly(3-hexylthiophene) (P3HT), and so on. Then, latest progress on the self-assembly and stimuli-responses of polyallene-based diblock, ABA and ABC triblock copolymers is summarized. We hope this Minireview will inspire more interest in developing polyallenes and encourage further advances in functional materials.

Expanding Alternating Spherical and Cylindrical Regions by Tailoring Binary Symmetric ABC/ABC Blends

The self-assembly of a binary blend composed of two different symmetric ABC triblock copolymers has been investigated using self-consistent field theory in the grand canonical ensemble, aiming to expand the phase regions of alternating spherical and cylindrical phases by tailoring the molecular parameters. Our study confirms that the region of the spherical phase is expanded by the effect of bidispersity in which the long and short A-blocks (or C-blocks) form a core–shell distribution within the spherical domain to increase the spontaneous curvature. The bidispersity effect also expands the phase region of the alternating cylinders. In contrast to the spherical phase, the cylindrical region can be expanded by another effect of bidisperse B-blocks to release the high packing frustration of the low-coordinated tetragonal array of alternating A/C cylinders. With optimized parameters, the regions of both the spherical and cylindrical phases are tremendously expanded to such large volume fractions that the spheres and cylinders are remarkably deformed. Our work not only deepens the understanding on the self-assembly mechanism of ABC/ABC blends but also provides a valuable guide for the fabrication of alternating spherical and cylindrical morphologies with large volume fractions.

Homopolymer and ABC Triblock Copolymer Mixtures for Thermoresponsive Gel Formulations.

Our group has recently invented a novel series of thermoresponsive ABC triblock terpolymers based on oligo(ethylene glycol) methyl ether methacrylate with average Mn 300 g mol−1 (OEGMA300, A unit), n-butyl methacrylate (BuMA, B unit) and di(ethylene glycol) methyl ether methacrylate (DEGMA, C unit) with excellent thermogelling properties. In this study, we investigate how the addition of OEGMA300x homopolymers of varying molar mass (MM) affects the gelation characteristics of the best performing ABC triblock terpolymer. Interestingly, the gelation is not disrupted by the addition of the homopolymers, with the gelation temperature (Tgel) remaining stable at around 30 °C, depending on the MM and content in OEGMA300x homopolymer. Moreover, stronger gels are formed when higher MM OEGMA300x homopolymers are added, presumably due to the homopolymer chains acting as bridges between the micelles formed by the triblock terpolymer, thus, favouring gelation. In summary, novel formulations based on mixtures of triblock copolymer and homopolymers are presented, which can provide a cost-effective alternative for use in biomedical applications, compared to the use of the triblock copolymer only.

Comparative effect of thermo/pH-responsive polymer-coated gold nanocages and hollow nanostars on chemo-photothermal therapy of breast cancer cells

BackgroundCombination chemo-photothermal therapy appears to be one of the next generations of cancer treatment. In this study hollow gold nanostars (HGNSs) and gold nanocages (GNCs) were synthesized and stabilized with thermo-pH-sensitive thiol-end capped ABC triblock copolymer poly(acrylic acid)-b-poly(N isopropylacrylamide)-b-poly (e-caprolactone)-SH; PAA-b-PNIPAAm-b-PCL-SH (GNSs@Pol). Doxorubicin (Dox) was conjugated to the GNSs@Pol nanostructures via ionic interaction, covalent attachment and hydrogen bonding (GNSs@Dox-Pol). The physicochemical characteristics of prepared GNSs@Pol and GNSs were assessed using dynamic light scattering (DLS), transmission electron microscopy (TEM) and zeta potential techniques. Cytocompatibility of the GNSs@Pol was studied by hemolysis assay and MTT assay. The chemo-photothermal therapy (PTT) potential of GNSs@Dox-Pol was compared on MCF7 cells using MTT assay, cell cycle, DAPI staining and Annexin-V apoptosis assay techniques.ResultsCell internalization results showed an almost complete uptake of GNSs@Pol by MCF-7 cells in the first 3 h of treatment. The heat generation measurement results showed that both of GNSs have a potential for light to heat conversion (∆T = 23–27 ºC) and HGNSs demonstrated better efficiency than GNCs after 10-min exposure to NIR irradiation. Following chemo-photothermal treatment, the highest cell mortality (90%) and apoptotic effects (97% apoptosis) were observed in HGNSs@Dox-Pol received laser irradiation treatment group.ConclusionsThis work highlights the potential application of designed GNSs@Dox-Pol in a combinational chemo-PTT to treat breast cancer cells.Graphic abstract

Enlarged Phase Regions of Multi-Continuous 3D Network Nanostructures in ABC Triblock Copolymers.

Aiming to increase the stability region of three-dimensional (3D) multi-continuous morphologies due to great potential application in smart sensors, gas separation membranes, and photonic materials, in this paper, we control the block ratio of different channels of an ABC triblock copolymer according to the curvature of these multi-continuous nanostructures. In the small A volume fraction region, the multi-continuous gyroid nanostructure is stable when fB/fC equals 1/3, while two-domain lamellae (LB/C) and three-layer lamellae (L3) are obtained when B and C blocks have comparable volume fractions, suggesting that changing the fB/fC ratio is an effective way of forming multi-continuous polymer network nanostructures. Interestingly, a large phase region of the core-shell gyroid and O70 are found under the condition of fB/fC = 4. The mechanism of changing the ratio to enlarge the phase regimes of multi-continuous nanostructures can be ascribed to the existence of curvature in gyroid and O70 nanostructures. Therefore, the formed thin layer must be consistent with these curvatures, which can be tuned by the adjustment of the block ratio. The proposed mechanism and the calculated phase diagram can effectively guide the experimental observation of these multi-continuous nanostructures.