Random Block Copolymers Research Articles

Control of Solution Phase Behavior through Block–Random Copolymer Sequence

Control of Solution Phase Behavior through Block–Random Copolymer Sequence

Effective Interaction between Homo- and Heteropolymer Block of Poly(n-butyl acrylate)-b-poly(methyl methacrylate-r-styrene) Diblock Copolymers.

We investigated the segregation behavior of a molten diblock copolymer, poly(n-butyl acrylate)-b-poly(methyl methacrylate-r-styrene) (PBA-b-P(MMA-r-S)), wherein styrene (S) is incorporated as a comonomer in the second block to modulate the effective interaction between homopolymer and a random copolymer block. The temperature dependence of the effective interaction parameter χeff between n-butyl acrylate (BA) and the average monomer of the MMA-r-S random block was evaluated from small-angle X-ray scattering (SAXS) analysis using the random phase approximation (RPA) approach. The calculated χeff, as a function of the styrene fraction in the random copolymer block, shows a good agreement with the mean-field binary interaction model. This consistency indicates that the effective interaction between component BA and the average monomer of the random copolymer block is smaller than the interactions between pure components (χBA,MMA,χBA,S). The present study suggests that the introduction of a random copolymer block to a block copolymer can effectively reduce the degree of incompatibility of the block copolymer system without altering the constituent species, which may serve as a viable methodology in designing novel thermoplastic elastomers based on triblock or multiblock copolymers.

Diblock versus block-random copolymer architecture effect on physical properties of Gd3+-based hybrid polyionic complexes

HypothesisRandom insertion of vinylphosphonic acid (VPA) units into a of PEG-PAA block copolymer improves the chemical stability and properties of hybrid nanoobjects obtained from the complexation of the copolymer with metal ions. ExperimentsBlock polymers based on poly(acrylic acid) (PAA) and poly(ethylene glycol) (PEG) are modified by random insertion of 0 to 100 % of phosphonic acid functions in PAA block by a RAFT polymerization process. These polymers are then used to form hybrid polyionic complexes (HPICs) by complexation with gadolinium or europium ions. The properties of the obtained assemblies are evaluated by magnetic relaxivity, fluorescence and light scattering measurements. FindingsThe insertion of VPA units within the PAA block increases the chemical stability of the hybrid micelles by maintaining their integrity even at low pH. This insertion also minimizes the exchange of ions between HPICs and the surrounding medium thanks to a strengthening of interactions toward lanthanide ions. When such systems are used as MRI contrast agents or luminescent probe, 50/50 AA/VPA composition appears to be a good compromise to achieve optimal relaxivity or luminescent properties while ensuring a good chemical stability.

Temperature Transferable and Thermodynamically Consistent Coarse-Grained Model for Binary Polymer Systems

For the simulations of polymer systems, coarse-grained (CG) models are often developed to tackle the length and time scale limitations that are not feasible by all-atom molecular dynamic simulations. However, due to the necessary simplification or reduction in atomistic degrees of freedom, CG models usually have poor transferability over various temperatures, compositions, or thermodynamic states. In this work, the structure-based iterative Boltzmann inversion (IBI) method is further developed to obtain temperature transferable and thermodynamically consistent CG potentials for binary polymer systems. In particular, the conventional IBI procedure is first utilized to optimize single-component CG potentials from homopolymer systems while cross-interaction potentials from a random block copolymer system. Afterward, a thermodynamic integration method is applied to refine the cross-interaction potential between two constituent components in binary systems until the Flory–Huggins parameter (χ) between two components is matched with experimental value. We apply the above optimization procedure for the polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) as an example, which is widely studied experimentally, and the χ value can be easily obtained in the literature. To validate the transferability of the obtained CG potential, systems of both PS and PMMA homopolymers, random block copolymers, diblock copolymers, and PS/PMMA blends with various compositions are simulated. Many properties, including the mass density, radius distribution function, and bonded distribution functions, between CG beads generated from CG simulations match very well with those from atomistic simulations in the simulated temperature range, i.e., from 453 to 500 K. More importantly, phase morphologies of diblock copolymers and phase diagram of PS/PMMA binary blends over wide temperature and compositional ranges generated from CG simulations using our model are in good agreement with experimental results and predictions from self-consistent field theory.

Methacrylic acid‐based amphiphilic block‐random copolymer stabilizers for emulsion polymerization

AbstractThe emulsion polymerization of styrene was investigated using polystyrene‐b‐[polystyrene‐r‐poly(methacrylic acid)] amphiphilic block‐random copolymers (BRCs) of different compositions as stabilizers. These stabilizers with molar masses <20,000 g/mol, which possess unique dispersion behaviour (i.e., self‐assembly with low aggregation numbers) when dissolved in aqueous medium at alkaline pH, were prepared by the nitroxide‐mediated bulk polymerization of styrene to achieve a desired molar mass followed by chain extension by batchwise addition of styrene and methacrylic acid monomers to obtain the stabilizing group. Emulsion polymerizations of styrene stabilized by these BRCs yielded stable latexes with particle diameters that range between 30 and 150 nm. When different concentrations of the stabilizer (2–3.5 mM) were utilized for emulsion polymerization of styrene, a similar novel emulsion polymerization mechanism observed previously by our group for the acrylic‐acid based amphiphilic BRCs was also seen, further validating the difference between this class of polymeric surfactants and conventional small molecule surfactants, block copolymers, or alkali soluble resins. The performance of methacrylic‐acid based BRCs was more efficient and yielded higher surface coverage of the polystyrene latexes when compared to the acrylic‐acid based BRCs as a result of the more hydrophobic nature of the former.

Self-Aggregation in Aqueous Media of Amphiphilic Diblock and Random Block Copolymers Composed of Monomers with Long Side Chains.

Amphiphilic diblock copolymers and hydrophobically modified random block copolymers can self-assemble into different structures in a selective solvent. The formed structures depend on the copolymer properties, such as the ratio between the hydrophilic and the hydrophobic segments and their nature. In this work, we characterize by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS) the amphiphilic copolymers poly(2-dimethylamino ethyl methacrylate)-b-poly(lauryl methacrylate) (PDMAEMA-b-PLMA) and their quaternized derivatives QPDMAEMA-b-PLMA at different ratios between the hydrophilic and the hydrophobic segments. We present the various structures formed by these copolymers, including spherical and cylindrical micelles, as well as unilamellar and multilamellar vesicles. We also examined by these methods the random diblock copolymers poly(2-(dimethylamino) ethyl methacrylate)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) (P(DMAEMA-co-Q6/12DMAEMA)-b-POEGMA), which are partially hydrophobically modified by iodohexane (Q6) or iodododecane (Q12). The polymers with a small POEGMA block did not form any specific nanostructure, while a polymer with a larger POEGMA block formed spherical and cylindrical micelles. This nanostructural characterization could lead to the efficient design and use of these polymers as carriers of hydrophobic or hydrophilic compounds for biomedical applications.

Amphiphilic Block-Random Copolymers: Shedding Light on Aqueous Self-Assembly Behavior

The aqueous solution and aggregation behavior of polystyrene-b-poly[styrene-r-(acrylic acid)] block-random copolymers have been examined. Previous work conducted by our group showed that these materials exhibit an unanticipated ease of dispersion in water compared to polystyrene-b-poly(acrylic acid) block copolymers of similar molecular weight and composition. Herein, fluorescence labeling experiments and the presence of a critical aggregation concentration suggest the self-assembly of these materials into multichain aggregates as opposed to the self-folding behavior that was previously hypothesized. In our analysis, we demonstrate that caution must be used when interpreting particle size data from dynamic light scattering with polyelectrolyte solutions and that other characterization methods should be used to confirm findings. The fundamental understanding of block-random copolymer solution properties enables the widespread application of these easily dispersible materials in fields where amphiphilic copolymers are of interest, including biomedicine, catalysis, and stabilizers in emulsion polymerization.

Clusterization-triggered emission of poly(vinyl amine)-based ampholytic block and random copolymers

Nonconventional stimuli-responsive luminescent polymers without aromatic units have garnered considerable attention. In this study, luminescent ampholytic block copolymer (BCP) and random copolymer (RCP) consisting of nonconjugated vinyl amine (VAm) and N-acryloyl-L-threonine (AThrOH) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequent deprotection. The ampholytic BCP and RCP display concentration-enhanced emissions, which are apparently higher than those of the VAm homopolymer and polyion complex, and wavelength-dependent emissions, thus validating clusterization-triggered emission (CTE). The intrinsic photoluminescence properties of the primary amine-containing ampholytic copolymers and corresponding polyion complexes were investigated in aqueous solution in response to the change in pH. Two noncovalent interactions, which involve electrostatic interactions between cationic VAm and anionic AThrOH units and hydrogen bonds (e.g., the amino group in VAm/hydroxyl and amide groups in AThrOH), contribute to the achievement of unique self-assembled structures and stimuli-responsive and fluorescent properties of VAm-containing BCP and RCP, which were verified by dynamic light scattering, circular dichroism, and fluorescence measurements. The ability of the copolymers to form clusterized states of the VAm unit can be governed by the comonomer sequence and external stimuli (e.g., pH change, the addition of salt and urea), leading to the manipulation of the assembled structures with CTE features.

Block–random copolymer stabilisers for semi-batch emulsion polymerisation

Polystyrene-b-[polystyrene-r-poly(acrylic acid)] block–random copolymers are efficient stabilisers in semi-batch emulsion polymerisations, yielding high-solids latexes with low viscosity.

Dewetting behavior of the spin-coated bilayer films of block copolymer and random copolymer induced by solvent vapor annealing

Dewetting behavior of the spin-coated bilayer films of block copolymer and random copolymer induced by solvent vapor annealing

Rational Optimization of Bifunctional Organoboron Catalysts for Versatile Polyethers via Ring-Opening Polymerization of Epoxides

Quaternary ammonium and phosphonium borane bifunctional catalysts have shown high catalytic performance in ring-opening polymerization (ROP) of epoxides to produce polyether. Herein, we systematically investigate a series of well-defined organoboron catalysts by varying the electronic and steric properties of the Lewis acidic boron (B) centers, manipulating the steric hindrance on the ammonium cation (N+), adjusting the distance between B and N+, and regulating the nucleic B number of the catalysts. The investigation on the dinuclear catalysts indicated that the reactivity of a given catalyst could be speculated by its B–N–B angle and the B···B distance. We found that the increase of Lewis acidity and the number of B centers of the organoboron catalysts are useful for a high catalytic activity for ROP of epoxides. The Lewis acidity of the B centers was determined using the acceptor numbers, showing an order of borinane (23.4) > BBN (21.7) > BCy2 (18.8) > Bpin (15.5). Moreover, we demonstrated the production of various telechelic polyols in the presence of different chain transfer agents using the organoboron catalysts. The produced telechelic samples have a well-defined terminal functionality with controllable molecular weight. Lastly, these organoboron catalysts were utilized to produce block copolymers, allyl-terminated macromonomers, and random copolymers.

Miscibility of isotactic polypropylene with random and block ethylene-octene copolymers studied by atomic force microscopy-infrared

Ethylene-octene random copolymers (EOCs) and block copolymers (OBCs) have been used extensively in toughening isotactic polypropylene (iPP). In this work, the miscibility of iPP/EOC and iPP/OBC blends has been investigated quantitatively using an atomic force microscopy-infrared (AFM-IR) technique. A blend of a partially deuterated iPP and EOC at 80/20 mass ratio was found to phase separate, and in situ AFM-IR analysis revealed the presence of deuterated iPP in both phases, indicating partial miscibility between the two components. Quantitation methods for phase compositions of iPP/EOC and iPP/OBC blends using AFM-IR were established, and phase separation kinetics for a solution-mixed iPP/OBC 50/50 blend at 200 °C was investigated using AFM-IR. The phase compositions reach an equilibrium state in ∼4 h, and each component exhibits a solubility of ∼10 wt% in the other one in the molten state. Moreover, an interphase of ∼1 μm thickness and transitional composition is present in between the iPP-rich and the OBC-rich phases, indicative of good compatibility between iPP and OBC. In contrast, an iPP/EOC 50/50 blend under the same conditions contains two co-existing phases, with an EOC content of 4.9 and 93.2 wt% for the iPP-rich and EOC-rich phase, respectively, with a sharp interface between, implying poorer compatibility of EOC with iPP than for OBC. Composition analyses for iPP/EOC 80/20 and iPP/OBC 80/20 blends prepared by melt-blending support these observations.

Synthesis of Patchy Nanoparticles with Symmetry Resembling Polar Small Molecules.

Patchy nanoparticles (NPs) show many important applications, especially for constructing structurally complex colloidal materials, but existing synthetic strategies generate patchy NPs with limited types of symmetry. This article describes a versatile copolymer ligand-based strategy for the scalable synthesis of uniform Au-(SiO2 )x patchy NPs (x is the patch number and 1 ≤ x≤ 5) with unusual symmetry at high yield. The hydrolysis and condensation of tetraethyl orthosilicate on block-random copolymer ligands induces the segregation of copolymers on gold NPs (AuNPs) and hence governs the structure and distribution of silica patches formed on the AuNPs. The resulting patchy NPs possess unique configurations where the silica patches are symmetrically arranged at one side of the core NP, resembling the geometry of polar small molecules. The number, size, and morphology of silica patches, as well as the spacing between the patches and the AuNP can be precisely tuned by tailoring copolymer architectures, grafting density of copolymers, and the size of AuNPs. Furthermore, it is demonstrated that the Au-(SiO2 )x patchy NPs can assemble into more complex superstructures through directional interaction between the exposed Au surfaces. This work offers new opportunities of designing next-generation complex patchy NPs for applications in such as biomedicines, self-assembly, and catalysis.

Amphiphilic Block-Random Copolymer Stabilizers: A “Seeded-Coagulative” Emulsion Polymerization Mechanism

Amphiphilic Block-Random Copolymer Stabilizers: A “Seeded-Coagulative” Emulsion Polymerization Mechanism

Biocompatible Nanoparticles Based on Amphiphilic Random Polypeptides and Glycopolymers as Drug Delivery Systems.

In this research, the development and investigation of novel nanoobjects based on biodegradable random polypeptides and synthetic non-degradable glycopolymer poly(2-deoxy-2-methacrylamido-d-glucose) were proposed as drug delivery systems. Two different approaches have been applied for preparation of such nanomaterials. The first one includes the synthesis of block-random copolymers consisting of polypeptide and glycopolymer and capable of self-assembly into polymer particles. The synthesis of copolymers was performed using sequential reversible addition-fragmentation chain transfer (RAFT) and ring-opening polymerization (ROP) techniques. Amphiphilic poly(2-deoxy-2-methacrylamido-d-glucose)-b-poly(l-lysine-co-l-phenylalanine) (PMAG-b-P(Lys-co-Phe)) copolymers were then used for preparation of self-assembled nanoparticles. Another approach for the formation of polypeptide-glycopolymer particles was based on the post-modification of preformed polypeptide particles with an oxidized glycopolymer. The conjugation of the polysaccharide on the surface of the particles was achieved by the interaction of the aldehyde groups of the oxidized glycopolymer with the amino groups of the polymer on particle surface, followed by the reduction of the formed Schiff base with sodium borohydride. A comparative study of polymer nanoparticles developed with its cationic analogues based on random P(Lys-co-d-Phe), as well as an anionic one—P(Lys-co-d-Phe) covered with heparin––was carried out. In vitro antitumor activity of novel paclitaxel-loaded PMAG-b-P(Lys-co-Phe)-based particles towards A549 (human lung carcinoma) and MCF-7 (human breast adenocarcinoma) cells was comparable to the commercially available Paclitaxel-LANS.

Amphiphilic Random-Block Copolymer Micelles in Water: Precise and Dynamic Self-Assembly Controlled by Random Copolymer Association

Amphiphilic Random-Block Copolymer Micelles in Water: Precise and Dynamic Self-Assembly Controlled by Random Copolymer Association

Thermosetting epoxy resin system: Ring-opening by copolymerization of epoxide with D,L-Lactide

We examined the ring-opening copolymerization of glycidyl phenyl ether (GPE) and d,l-lactide (LAC) to afford poly(GPE-co-LAC) as a model reaction of the LAC-mediated thermal curing of epoxy resins such as 2,2-bis(4-glycidyloxyphenyl)propane (BGP), 2,2-bis(4-glycidyloxyphenyl)methane (BGM), 3,3′,5,5′-tetramethyl-4,4′-diglycidyloxybiphenyl (TDP), N,N-diglycidyl-4-glycidyloxyaniline (DGA), and oligo phenols (NC-3000 and EPPN-502H). The reaction of GPE and LAC proceeded efficiently in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) at 180 °C for 2 h. The monomer reactivities r1 of LAC and r2 of GPE calculated according to the Fineman-Ross method and the Kelen-Tüdӧs method were 0.85 and 1.26, respectively. The relatively small difference between these values suggests that the produced poly(GPE-co-LAC) would be a gradient copolymer, different from a block copolymer or random copolymer. Based on these results, we examined the thermal curing reactions of epoxy resins BGP, BGM, TDP, DGA, NC-3000, and EPPN-502H in bulk under the same conditions. The corresponding cured products were obtained quantitatively. The thermal stability of BGP, BGM, DGA, and EPPN-502H was increased by the addition of a small amount of LAC, suggesting that the cross-linking density of the cured products was increased. This new class of thermal curing system should be applicable to epoxy resins used in various industrial applications.

Effect of the macromolecular architecture on the thermoresponsive behavior of poly(N-isopropylacrylamide) in copolymers with poly(N,N-dimethylacrylamide) in aqueous solutions: Block vs random copolymers

Three samples from each type of poly(N-isopropylacrylamide)-block-poly(N,N-dimethylacrylamide) (PNIPAM-b-PDMA) block copolymers and poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (P(NIPAM-co-DMA)) random copolymers with similar chemical composition were synthesized by RAFT polymerization. The effects of DMA on the thermoresponse of its two kinds of copolymers with NIPAM were comparatively investigated by turbidity analysis, variable-temperature 1H NMR and dynamic light scattering with PNIPAM homopolymer as a control. It was discovered that the phase transition temperature, the temperature response window and the hysteresis values of the PNIPAM-b-PDMA and P(NIPAM-co-DMA) counterpart were significantly different. In particular, the temperature response window, which represents the sensitivity of response, is smaller for random copolymers than that of block copolymers in aqueous solution, indicating that the temperature response of random copolymers is more sensitive than that of block copolymers. The possible reasons leading to different thermo-responsive phase transition characteristics between block copolymers and random copolymers are discussed, and the formation of different hydrophobic structures with the temperature increasing is ascribed.

Block Random Copolymers of Styrene and Acrylic Acid: Synthesis and Properties

Block Random Copolymers of Styrene and Acrylic Acid: Synthesis and Properties

Block-Random Copolymer-Micellization-Mediated Formation of Polymeric Patches on Gold Nanoparticles.

Patchy colloidal nanoparticles are important for a broad range of applications, especially as building blocks for complex and functional structural materials, but the controllable generation of chemical patches on as-synthesized nanoparticles remains a challenge. This article describes a robust strategy for the scalable synthesis of high-quality patchy nanoparticles in high yield and solid content. A simple thermal treatment of a mixture of gold nanoparticles and thiol-terminated block-random copolymers in selected solvents produced a variety of patchy nanoparticles with a controlled morphology and number of polymeric patches (e.g., beanlike patch, one patch, two patches, three patches, multiple patches, and open-configuration patch). We show in experiments and simulations that the dynamic detachment/attachment of copolymers and the exchange of copolymers between the nanoparticle surface and free micelles in the solution-which are dictated by the architecture of copolymers-govern the formation of polymeric patches. This work not only offers an effective approach to patchy nanoparticles but also provides new insights into the phase behaviors of copolymers on nanoscale surfaces.