Random Block Copolymers Research Articles

Nanocomposites Based on Coil-Comb Diblock Copolymers

The polymer chain architecture is an important factor determining the phase behavior of nanoparticle (NP) assembly in polymer matrices. Block copolymers (BCPs) containing a random copolymer (RCP) block present a convenient variation on traditional BCPs to tune the interaction parameters between the polymer blocks and the nanofillers as well as to evaluate the effect of the chain architecture on the NP arrangements within BCP microdomains. Here, we synthesized BCPs with a coil polystyrene (PS) block and a comb RCP block through reversible addition-fragmentation chain transfer polymerization. The RCP block consists of methyl- and lauryl acrylates, the latter of which confers a long-chain alkyl moiety to favorably interact with alkyl-passivated NPs. BCPs showing lamellar, cylindrical, and mixed morphologies were obtained by varying the volume fractions of the RCP block (fRCP). In comparison to coil-coil BCP, the coil-comb BCPs show highly asymmetric phase behavior with respect to fRCP, where lamellar morphologies were observed at fRCP from 0.31 to 0.51. NPs in the size of 4–5 nm were successfully incorporated in the RCP block of the BCPs with periodicities of 30–60 nm. An order-to-order phase transition from lamellae to PS cylinders was observed after the addition of only 1–2 vol % 5 nm NPs into the BCP with a periodicity of 25 nm and fRCP of 0.51. Self-consistent field theory-density functional theory simulations qualitatively described the observed morphologies and phase transitions in the nanocomposites. The current study presents a platform to fabricate nanocomposites with NP assemblies in coil-comb BCPs that contain a random copolymer block and provides insight into how polymer chain architectures can affect the phase behavior of BCPs and nanocomposites.

Nonionic UCST-LCST Diblock Copolymers with Tunable Thermoresponsiveness Synthesized via PhotoRAFT Polymerization.

Nonionic double thermoresponsive diblock copolymers with both upper critical solution temperature (UCST) and lower critical solution temperature (LCST) phase transitions are synthesized via eco-friendly photoiniferter reversible addition-fragmentation chain transfer polymerization. While the biocompatible random copolymer of di(ethylene glycol) methyl ether methacrylate and oligo(ethylene glycol) methacrylate accounts for the LCST transition, the block of polymethacrylamide from an easily accessible monomer with low health hazard is responsible for the UCST transition. Temperature-dependent dynamic light scattering measurements confirm the formation of micellar aggregates in water at the temperatures below UCST- and above LCST-type cloud points. Additionally, the temperature interval between UCST and LCST, where both blocks are dissolved, can be tailored by varying the comonomer ratio in the random copolymer block. With these unique advantages, the presented work introduces a new polymer system for the design of schizophrenic polymers.

Tuning Composition of Polymer and Porous Silicon Composite Nanoparticles for Early Endosome Escape of Anti-microRNA Peptide Nucleic Acids.

Porous silicon nanoparticles (PSNPs) offer tunable pore structure and easily modified surface chemistry, enabling high loading capacity for drugs with diverse chemicophysical properties. While PSNPs are also cytocompatible and degradable, PSNP integration into composite structures can be a useful approach to enhance carrier colloidal stability, drug-cargo loading stability, and endosome escape. Here, we explored PSNP polymer composites formed by coating of oxidized PSNPs with a series of poly[ethylene glycol-block-(dimethylaminoethyl methacrylate-co-butyl methacrylate)] (PEG-DB) diblock copolymers with varied molar ratios of dimethylaminoethyl methacrylate (D) and butyl methacrylate (B) in the random copolymer block. We screened and developed PSNP composites specifically toward intracellular delivery of microRNA inhibitory peptide nucleic acids (PNA). While a copolymer with 50 mol % B (50B) is optimal for early endosome escape in free polymer form, its pH switch was suppressed when it was formed into 50B polymer-coated PSNP composites (50BCs). We demonstrate that a lower mol % B (30BC) is the ideal PEG-DB composition for PSNP/PEG-DB nanocomposites based on having both the highest endosome disruption potential and miR-122 inhibitory activity. At a 1 mM PNA dose, 30BCs facilitated more potent inhibition of miR-122 in comparison to 40BC (p = 0.0095), 50BC (p < 0.0001), or an anti-miR-122 oligonucleotide delivered with the commercial transfection reagent Fugene 6. Using a live cell galectin 8-based endosome disruption reporter, 30BCs had greater endosomal escape than 40BCs and 50BCs within 2 h after treatment, suggesting that rapid endosome escape correlates with higher intracellular bioactivity. This study provides new insight on the polymer structure-dependent effects on stability, endosome escape, and cargo intracellular bioavailability for endosomolytic polymer-coated PSNPs.

Complex Temperature and Concentration Dependent Self-Assembly of Poly(2-oxazoline) Block Copolymers.

The effect of polymer concentration on the temperature-induced self-association of a block copolymer comprising a poly(2-ethyl-2-oxazoline) block and a random copolymer block consisting of 2-ethyl-2-oxazoline and 2-n-propyl-2-oxazoline (PEtO80-block-P(EtOxx-stat-PropO40-x) with x = 0, 4, or 8 were investigated by dynamic light scattering (DLS) and transmittance measurements (turbidimetry). The polymers reveal a complex aggregation behavior with up to three relaxation modes in the DLS data and with a transmittance that first goes through a minimum before it declines at high temperatures. At low temperatures, unassociated polymer chains were found to co-exist with larger aggregates. As the temperature is increased, enhanced association and contraction of the aggregates results in a drop of the transmittance values. The aggregates fragment into smaller micellar-like clusters when the temperature is raised further, causing the samples to become optically clear again. At high temperatures, the polymers aggregate into large compact clusters, and the samples become turbid. Interestingly, very large aggregates were observed at low temperatures when the polymer concentrations were low. The formation of these aggregates was also promoted by a more hydrophilic copolymer structure. The formation of large aggregates with an open structure at conditions where the solvent conditions are improved is probably caused by depletion flocculation of the smaller aggregates.

Synthesis of bottlebrush block copolymers from bottlebrush polystyrene and bottlebrush random copolymer of ω‐end‐norbornyl polymethacrylates and their self‐assembly

AbstractSix different bottlebrush block copolymers (BBCPs) (A‐b‐(B‐co‐C)) from bottlebrush polystyrene (A) and bottlebrush random copolymers (B‐co‐C) of polymethacrylates were synthesized through living anionic polymerization and ring‐opening metathesis polymerization. To induce the phase separation of bottlebrush polystyrene (PNB‐g‐PS) (A) and bottlebrush poly(benzyl methacrylate) (PNB‐g‐PBzMA) (C)‐based BBCP with an extremely low Flory–Huggins interaction parameter (χ), three kinds of bottlebrush polymethacrylates (B): poly(norbornene‐g‐methyl methacrylate) (PNB‐g‐PMMA), poly(norbornene‐g‐tert‐butyl methacrylate) (PNB‐g‐PtBMA), and poly(norbornene‐g‐methacrylic acid) (PNB‐g‐PMAA), respectively, were randomly combined with C. An order–disorder phase transition of the BBCPs (A‐b‐(B‐co‐C)) was observed with a change in mole ratios of PMMA, PtBMA, or PMAA to PBzMA of 25, 50, and 75% in random copolymer blocks using field‐emission scanning microscopy. While the BBCP with 25% of PMAA in the random copolymer block showed an ordered lamellar nanostructure, a disordered morphology was revealed at 75% PMAA. SEM showed that the incorporation of PtBMA and PBzMA showed better‐ordered lamellar morphologies than was the case with PMMA and PBzMA at the same mole ratios.

Amphiphilic Copolymers of Acrylic Acid and n-Butyl Acrylate with the Predetermined Microstructure: Synthesis and Properties

Features of the synthesis of n-butyl acrylate copolymers with acrylic acid in 1,4-dioxane by free radical reversible addition-fragmentation chain transfer (RAFT) polymerization mediated by symmetric trithiocarbonates are considered. It is shown that the living mechanism of polymerization is realized in the studied systems. The chemical nature of the RAFT agent dictates different chain microstructures (random block or random) of the copolymers. The effect of chain microstructure on the properties of the copolymers containing about 90 mol % of acrylic acid units is studied by differential scanning calorimetry, contact angle measurements, turbidimetry, potentiometric titration, and dynamic light scattering. It is demonstrated that all the copolymers in the solid phase have similar properties: a single glass transition temperature close to the glass transition temperature of polyacid and a good water wettability. In dilute aqueous solutions, the properties of the copolymers are different: at the inherent pH, random copolymer macromolecules form large associates, while random block copolymers are dispersed into individual coils or micelles. All the copolymers are weaker polyacids compared with PAA; the random block copolymers are characterized by the compaction of macromolecules at small degrees of ionization. Our studies provide evidence that reversible addition-fragmentation chain transfer polymerization is an efficient tool for the targeted insertion of nonpolar units into a polyelectrolyte chain and it can be used for the fine-tuning of its properties.

Amphiphilic water soluble cationic ring opening metathesis copolymer as an antibacterial agent

AbstractBacterial infection is a global problem, especially resistance acquired by bacteria against to antibiotics; there is urgent need for the development of antibiotics. Here, we proposed dendron‐grafted polymers via ring opening metathesis polymerization (ROMP) featuring different with tailored hydrophobicity/hydrophilicity and cationic charges. Dendritic oxanorbornene derivatives were synthesized having two and six carbon linkers and their corresponding random and block copolymers were prepared having pendant pyridinium salt moieties via ROMP. In total, 12 different water‐soluble dendronized cationic polymers featuring hexyl pyridinium moieties were prepared and investigated. Six carbon linker possessing triple charge density and hexyl pyridinium functionality each repeating unit copolymers exhibited high antibacterial activity against Gram‐positive bacteria (S. aureus). However, all the polymers were inactive against Gram‐negative bacteria (E. coli). Most of the copolymers are non‐hemolytic (&gt;HC 50 = 1,000 μg/ml). It was also observed that, there is no significant effect between block copolymers and random copolymers keeping hydrophobicity and cationic charge density constant. Zeta potential was measured to investigate the mechanism in solution via the interaction of polymers with S. aureus, while scanning electron microscope (SEM) measurements image confirms damage of the bacterial cell wall after implementation of biocidal polymer.

Precisely Synthesized Sequence‐Controlled Amino Acid–Derived Vinyl Polymers: New Insights into Thermo‐Responsive Polymer Design

Thermo-responsive block copolymers are of great interest in biomedical and nanotechnological fields. These polymers achieve a versatile and complex responsiveness through a sophisticated and intricate combination of different thermo-responsive blocks. While their utility is clear, the fundamental design principles of such vinyl polymers are not yet thoroughly understood. Herein, a precise synthesis of sequence-controlled amino-acid-derived vinyl polymers and their unique thermal response in water are reported. Seven distinct block (random) copolymers that contain two kinds of amino acid blocks (poly(N-acryloyl alanine(A)- or glycine(G)-methyl ester)) with the same total chain length (degree of polymerization [DP] ≈30) and chemical composition (A/G ≈1), but with systematic variations in the block sequence and length, with an accuracy target of DP ± 1, are prepared. By specifying the primary structure, the thermal responses including transition temperature, thermo-sensitivity, and microenvironment in the dehydrated state can be finely tuned. These findings offer new directions in the design of structurally and functionally diverse thermo-responsive vinyl polymers.

Mechanisms of Ion Transport in Block Copolymeric Polymerized Ionic Liquids.

We present the results of a multiscale simulation framework investigating the ion transport mechanisms in multicomponent polymerized ionic liquids. Three different classes of polymeric ionic liquid systems, namely, random copolymers, lamellae forming block copolymers, and homopolymers, are constructed at the coarse-grained scale, and their atomistic counterparts are derived by using a reverse mapping method. Using such a framework, we investigate the influence of morphology on ion transport properties of such polymerized ionic liquids. Our results for ion mobilities are in qualitative agreement with experimental observations. Further analysis of random copolymer and block copolymer systems reveal that the reduced ion mobilities in such systems arise from the influence of architecture and morphology on ion coordination and intramolecular hopping events.

Amphiphilic Block-Random Copolymers: Self-Folding Behavior and Stabilizers in Emulsion Polymerization

Polystyrene-b-[polystyrene-r-poly(acrylic acid)] block-random copolymers have been synthesized at various molecular weights (7000–23 200 g/mol) and with compositions between 6 and 39 mol % acrylic ...

Orthogonal Folding of Amphiphilic/Fluorous Random Block Copolymers for Double and Multicompartment Micelles in Water.

Here, we report orthogonal folding and self-assembly systems of amphiphilic/fluorous random block copolymers for double core and multicompartment micelles in water. For this, we developed the precision folding techniques of polymer chains via the selective self-assembly of the pendant groups. Typically, A/C-B/C random block copolymers were designed: Hydrophobic dodecyl groups (A) and fluorous fluorinated octyl groups (B) were introduced into the respective blocks, while hydrophilic poly(ethylene glycol) chains (C) were randomly incorporated into all the segments. By controlling the chain length and composition of the respective blocks, the copolymers induce orthogonal single-chain folding in water to form double-compartment micelles comprising hydrophobic and fluorous cores. The copolymers were site-selectively folded in a fluoroalcohol to result in tadpole unimer micelles comprising a hydrophobic A/C unimer micelle and an unfolded fluorous B/C chain. Additionally, asymmetric A/C-B/C random block copolymers with short and highly hydrophobic or fluorous segments were effective for multicompartment micelles in water.

Copolymers with Pendant N-arylimide Groups via Atom Transfer Radical Polymerization: Synthesis, Characterization and Kinetic Study

Random and random-block copolymers of methyl methacrylate with N-arylitaconimide monomer (N-(4-chlorophenyl)itaconimide, N-phenylitaconimide, and N-(4-methoxyphenyl)itaconimide) have been synthesized via atom transfer radical polymerization process with N-arylimide as the pendant group and characterized by different techniques. A 60–80% enhancement in softening temperature of these copolymers was observed as compared to poly(methyl methacrylate). The living mechanism was confirmed by the linear rise of number average molecular weight with conversion.

Random Copolymers Allow Control of Crystallization and Microphase Separation in Fully Conjugated Block Copolymers

Thin films of fully conjugated donor–acceptor block copolymers composed of an electron donating block and an electron accepting block can be used as single component photoactive layers in organic photovoltaic (OPV) devices. In order to realize their full potential, control over microphase separation and thin-film morphology are critical. In conjugated block copolymer systems where one or more blocks can crystallize, the morphological evolution is governed by the competition between microphase separation and crystallization. In this work, we control crystallization of fully conjugated block copolymers with a random copolymer block. We suppress the crystal packing of poly(3-hexylthiophene-2,5-diyl) (P3HT) through the insertion of a small number of 3-octylthiophene (3OT) units within the chains, yielding poly(3-hexylthiophene-2,5-diyl-random-3-octylthiophene-2,5-diyl) (P[3HT-r-3OT]). While crystallization of P3HT dominates the morphology and prevents microphase separation in poly(3-hexylthiophene-2,5-diyl)-b...

Preparation and characterization of stable DQ silicone polymer sols

Stable DQ silicone polymer sols composed of di (D)- and tetra (Q)-functional alkoxysilanes were prepared by the following methods: (i) co-hydrolysis–condensation between diethoxy(dimethyl)silane (DEDMS) and tetraethoxysilane (TEOS) (DEDMS–TEOS as random copolymer sols), (ii) co-hydrolysis–condensation between poly(dimethylsiloxane) (PDMS) and TEOS (PDMS–TEOS as random block copolymer sol), and (iii) triethoxysilylation of a PDMS-lithium salt (PDMS–TES). The polymer sols were characterized by GPC, NMR, and FT-IR. The differences in properties between the structures were analyzed from their thermal stabilities and by using the swelling test. Thermal stabilities of these polymer sols were increased with the increase in the chain length of the D domain and with decrease in hydrolyzability. The swelling of films via polymer sols was decreased with the increase in the degree of crosslinking in sols.

Energy-Intensive Random Block Copolymers of 3,3-Bis (Nitratomethyl) Oxetane and 3-Azidomethyl-3- Methyloxetane

Energy-Intensive Random Block Copolymers of 3,3-Bis (Nitratomethyl) Oxetane and 3-Azidomethyl-3- Methyloxetane

Effects of incorporation of polyester on the electrical resistivity of polycarbonate/multi-walled carbon nanotube nanocomposite

In this work, we present the effect of incorporation of polyester on the electrical properties of injection-molded polycarbonate/multi-walled carbon nanotube nanocomposites. The study was conducted by melt-mixing polycarbonate, multi-walled carbon nanotube, and three types of polyesters: polybutylene terephthalate, polyethylene terephthalate, and liquid crystal polymer. It was found that the volume resistivities of injection-molded composites containing 2 phr polyester significantly decreased because of the transesterification reaction between the polycarbonate and polyester. The resulting polycarbonate-polyester random block copolymer kept the conductive networks intact because of the preferential affinity of multi-walled carbon nanotubes with polyester. This study showed that incorporating polyester with polycarbonate–multi-walled carbon nanotube increases the electrical conductivity of injection-molded polycarbonate/multi-walled carbon nanotube nanocomposites to a great extent.

(Invited) The Effects of Water Binding and Morphology on Proton Transport in Polymer Membranes

The effects of water binding and morphology will be reported in the context of designing new proton exchange membranes (PEMs). While much has been learned about the function of proton exchange membranes by studying perfluorosulfonic acid and sulfonated aromatic polymers, new generations of proton-conducting polymers for aqueous applications are being developed. Key to these advancements have been block copolymers and random copolymers with new sulfonic-acid bearing headgroups. Sulfonated aromatic block copolymers are a known route to high-performing proton exchange membranes. Compared to their random sulfonated copolymer counterparts, the organization of the sulfonate groups in a concentrated ionic domain has demonstrable benefits to proton conductivity. However, the relative humidity effects on the specific headgroup chemistry still often lead to lower conductivity than desirable at low RH. Using FTIR, we have explored the water binding in aromatic random copolymers with a number of new sulfonate groups. Our data shows that superacid groups on aromatic backbones can give comparable conductivities to perfluorosulfonic acid membranes. The interaction of these headgroups with water is one of the important factors for high proton conductivity – even though their morphologies can be much different than block copolymers or perfluorosulfonic acid materials. This talk will discuss the morphology and water binding factors that influence the proton conductivity of a number of unique aromatic polymer-based proton exchange membranes. Figure 1

Synthesis of statistical PET/PEN random block copolymers and their crystallizability in the bulk and at the surface

ABSTRACTA series of PET/PEN copolyesters were synthesized by molten transesterification. The degree of randomness and the sequence length of the copolymers were determined by 1H NMR spectroscopy, and the changes in the bulk glass transition temperature (TgB), bulk crystallization temperature (TcB), and bulk melting temperature (TmB) were observed by DSC. A clear relationship was obtained between the observed enthalpy of melting (ΔHm) and degree of randomness (B), and TmB was suppressed for the midcompositions. As with their homopolymer counterparts, there was significant depression in crystallization temperature at the surface (TcS) of the random/block copolymers compared with the bulk, and so surface‐localized crystallization could be induced in spin‐coated thick films (thickness ranging from ca. 400 to 700 nm) by annealing at a temperature in which the surface region is mobile, but the bulk is not. The formation of these clear surface crystals allows the morphology to be directly imaged by AFM, and we observed that the crystallizability and the lamellar morphology of the surface crystals deviated from those of the original homopolymers, depending on the mixing ratio of PET/PEN and degree of randomness. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46515.

Double thermoresponsive block–random copolymers with adjustable phase transition temperatures: From block‐like to gradient‐like behavior

ABSTRACTStimuli‐responsive block–random copolymers are very useful “smart” materials as their switching behavior can be tuned by simply adjusting the composition of the random copolymer block. Because of that, we synthesized double thermoresponsive poly(N‐acryloylpyrrolidine)‐block‐poly(N‐acryloylpiperidine‐co‐N‐acryloylpyrrolidine) (PAPy‐b‐P(APi‐co‐APy)) copolymers via reversible addition fragmentation chain transfer (RAFT) polymerization and investigated their temperature‐induced self‐assembly in aqueous solution. By varying the APi/APy ratio in the random copolymer block, its phase transition temperature (PTT1) can indeed be precisely adjusted while the temperature‐induced collapse upon heating leads to a fully reversible well‐defined micellization. By making the two blocks compositionally similar to more than 60%, the polymers' mechanistic thermoresponsiveness can furthermore be changed from block‐like to rather gradient‐like behavior. This means the micellization onset at PTT1 and the corona collapse at the PTT of the more hydrophilic pure PAPy block (PTT2) overlap resulting in one single broad transition. This work thus contributes to the detailed understanding of design, synthesis and mechanistic behavior of tailored “on‐demand” switchable materials. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 399–411

Investigation of the Adsorption of Amphipathic macroRAFT Agents onto Montmorillonite Clay.

Recently, there has been significant interest in the use of the reversible addition-fragmentation chain-transfer (RAFT) technique to generate a variety of organic/inorganic colloidal composite particles in aqueous dispersed media using the so-called macroRAFT-assisted encapsulating emulsion polymerization (REEP) strategy. In this process, special attention should be paid to the adsorption of the macromolecular RAFT (macroRAFT) agent onto the inorganic particles, as it determines the final particle morphology and can also influence latex stability. In this work, different amphipathic macroRAFT agents were synthesized by RAFT, and their adsorption onto commercial Montmorillonite clay Cloisite Na+ (MMT) was studied by means of adsorption isotherms. Three types of macroRAFT agents were considered: a nonionic one based on poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA), anionic ones, including a block copolymer and random copolymers, based on acrylic acid (AA), BA and PEGA, and cationic ones based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), BA and PEGA. Six adsorption isotherm models (Langmuir, Freundlich, Tempkin, Redlich-Peterson, Sips, and Brunauer-Emmett-Teller) were adjusted to the experimental isotherms. The nonionic macroRAFT agent formed a monolayer on the clay surface with a maximum adsorption capacity of 400 mg g-1 at pH 8, as determined from the Sips adsorption model. Adsorption of the AA-based macroRAFT agents onto MMT was moderate at alkaline pH due to electrostatic repulsions, but increased with decreasing pH. The DMAEMA-based macroRAFT agents displayed a much stronger interaction with the oppositely charged MMT surface at acidic pH due to electrostatic interactions, and the concentration of adsorbed macroRAFT agent reached values as high as 800 mg g-1. The BET model fitted the experimental data relatively well indicating multilayer adsorption promoted by the presence of the hydrophobic BA units. In addition, the cationic macroRAFT agents afforded stable MMT/macroRAFT agent complexes as evaluated by dynamic light scattering and zeta potential analyses.