Flexible Copolymer Research Articles

Self-Assembly of Flexible Linear–Semiflexible Bottlebrush–Flexible Linear Triblock Copolymers

Block copolymer self-assembly is a fundamental process in which incompatible blocks spontaneously form organized microstructures with broad practical applications. Classical understanding is that the domain spacing is limited by the contour length of the polymer backbone. Here, using a combination of molecular design, chemical synthesis, small/wide-angle X-ray scattering, transmission electron microscopy, and electron tomography, we discover that this molecular picture does not hold for architecturally semiflexible block copolymers. For strongly segregated linear-semiflexible bottlebrush-linear triblock copolymers, the size of the bottlebrush domain can be twice the bottlebrush backbone contour length. The mechanism of such anomalous self-assembly likely is that the interfacial repulsion between the incompatible blocks is large enough to pull a part of the linear end-blocks into the bottlebrush domain. This effectively increases the bottlebrush domain size. Moreover, the semiflexible bottlebrush widens the regime for cylinder morphology that is associated with the volume fraction of the end blocks $f_C^{SFB}\in(0.10,>0.40)$. This window is much wider than that for flexible linear block copolymers, $f_C^{F} \in(0.14,0.35)$, and that predicted by recent self-consistent field theory for linear-bottlebrush block copolymers of the same chemistry and molecular architecture. Our experimental findings reveal previously unrecognized mechanisms for the self-assembly of architecturally complex block copolymers.

Synthesis of a novel superabsorbent with slow-release urea fertilizer using modified cellulose as a grafting agent and flexible copolymer

In this work, a number of glucose unites in polymeric structure of cellulose was converted to 2,4-dihydroxy-3-(1-hydroxy-2-oxoethoxy)butanal (cellulose containing di aldehyde units (CCDAUs)) by oxidation with sodium periodate, followed by condensation with acetone to produce 5,7-dihydroxy-6-((1-hydroxy-4-oxopent-2-en-1-yl)oxy)hept-3-en-2-one unites (cellulose containing di ene units (CCDEUs)). This modified cellulose was characterized by different methods and applied as a copolymer and grafting agent to synthesize an eco-friendly (CCDEUs-g-poly(AA)/urea) superabsorbent with slow-release urea fertilizer. The created double bonds in C2 and C3 positions of β-d-glucose units increased the linkage between cellulose and acrylic acid, leading to the formation of a strong network for slow-release urea fertilizer. Also, this modification created an expanded network for storage a high amount of water by increasing the cellulose flexibility. The reaction conditions for modification and synthesis of the superabsorbent, the oxidation degree value of glucose units, kinetics models, the effect of different saline solutions, various pH and reswelling time on the water absorbency, water retention capacity, reusability, biodegradability, and slow-release property were investigated. Also, the effect of synthesized CCDEUs-g-poly(AA)/urea on plant growth was tested and excellent results were obtained.

A multi-functional coating based on acrylic copolymer modified with PDMS through copolymerization

The chemical modification of acrylic copolymer was performed through copolymerization of vinyl-terminated polydimethylsiloxane (PDMS) and acrylic monomers by solution polymerization in order to synthesize acrylic-PDMS copolymers that could possess multi-functional properties required for application in harsh industrial environments. The synthesis of acrylic-PDMS copolymers was designed to possess combined advantages of the PDMS and acrylic copolymer. The acrylic-PDMS copolymers formed dispersion particles to be stable in water and the hydrophilic groups of the acrylic copolymer was distributed outside of the particles which is intended to stabilize the copolymer particles in water, and this could make it possible to prepare water-based coatings. The acrylic-PDMS showed more flexible copolymer chains, allowing the surface of acrylic-PDMS copolymer films to form with minimum defects, compared to the acrylic copolymer film, and with significantly decreased surface energy. The copolymer coatings exhibited high hydrophobicity with contact angles of the copolymer films increased to more than 90°. The high contact angle and low surface energy contributed to the low water absorption ratio and low dirt-pick performance of the copolymer films. The enhanced anti-corrosion performance of the copolymers was verified by electrochemical impedance spectra (EIS) and salt spray tests. The incorporation of PDMS segments in the acrylic-PDMS copolymers has been shown to be an effective approach to developing multi-functional coating with high chemical, corrosion and thermal resistances.

The Sequence of a Step-Growth Copolymer Can Be Influenced by Its Own Persistence Length.

Synthetic copolymer sequences remain challenging to control, and there are features of even simple one-pot, solution-based copolymerizations that are not yet fully understood. In previous simulations on step-growth copolymerizations in solution, we demonstrated that modest variations in the attractions between type A and B monomers could significantly influence copolymer sequence through an emergent aggregation and phase separation initiated by the lengthening of nascent oligomers. Here we investigate how one aspect of a copolymer's geometry-its flexibility-can modulate those effects. Our simulations show the onset of strand alignment within the polymerization-induced aggregates as chain stiffness increases and demonstrate that this alignment can influence the resulting copolymer sequences. For less flexible copolymers, with persistence lengths ≥10 monomers, modest nonbonded attractions of ∼kBT between monomers of the same type yield A and B blocks of a characteristic length and result in a polydispersity index that grows rapidly, peaks, and then diminishes as the reaction proceeds. These results demonstrate that for copolymer systems with modest variations in intermonomer attractions and physically realistic flexibilities a nascent copolymer's persistence length can influence its own sequence.

Self-assembly of cyclic grafted copolymers with rigid rings and their potential as drug nanocarriers

Enhancing the performance of polymer micelles by purposeful regulation of their structures is a challenging topic that receives widespread attention. In this study, we systematically conduct a comparative study between cyclic grafted copolymers with rigid and flexible rings in the self-assembly behavior via dissipative particle dynamics (DPD) simulation. With a focus on the possible stacking ways of rigid rings, we propose the energy-driven packing mechanism of cyclic grafted copolymers with rigid rings. For cyclic grafted copolymers with large ring size (14 and 21-membered rings), rigid rings present a novel channel-layer-combination layout, which is determined by the balance between the potential energy of micelles (Emicelle) and the interaction energy between water and micelles (Eint). Based on this mechanism, we further regulate a series of complex self-assembling structures, including curved rod-like, T-shape, annular and helical micelles. Compared with flexible copolymers, cyclic grafted copolymers with rigid rings provide a larger and loose hydrophobic core and higher structural stability with micelles due to the unique packing way of rigid rings. Therefore, their micelles have a great potential as drug nanocarriers. They possess a better drug loading capacity and disassemble more quickly than flexible counterparts under acidic tumor microenvironment. Furthermore, the endocytosis kinetics of rigid micelles is faster than the flexible counterparts for the adsorption and wrapping process. This study may provide a reasonable idea of structural design for polymer micelles to enhance their performance in biomedical applications.

Structural Changes in Hairy Nanoparticles—Insights from Molecular Simulations

Coarse-grained molecular dynamics simulations are used to study the reorganization of mobile ligands pinned to isolated nanospheres. Three types of ligands are considered: (i) freely jointed homogeneous attractive chains (H); (ii) flexible diblock copolymers composed of inert linkers and the attractive end-groups (D1); and (iii) diblock copolymers built of inert flexible linkers and end-groups being attractive rigid-rods (D2). The impact of the type of ligands, their number, and the strength of interactions on the structure of hairy nanoparticles are discussed. It is shown that the properties of ligands determine the morphology of polymer corona. For the H-particles, the one-patchy and the core–shell particles are found, while for particles D1 and D2, the ligands aggregate into a few patches. As the number of ligands increases, more patches are formed. Rigidity of attractive groups favors the formation of higher number of patches. The ligands are regularly distributed in patches on the core surface. Two patches are almost symmetrically located on the core, three patches are placed nearly at the vertices of an equilateral triangle, and four patches lie at the vertices of a regular tetrahedron.

High strength retention of cellulose fibers crosslinking with synthesized low-molecular-weight copolymers of itaconic acid and acrylic acid

1,2,3,4-Butanetetracarboxylic acid (BTCA) can cause significant strength loss to cotton fabrics, but it has been proven that a flexible molecular structure could benefit the strength in our previous study. In this research, more flexible copolymers [P(IA–AA)] were synthesized with itaconic acid (IA) and acrylic acid (AA) and creatively used as a formaldehyde-free crosslinking reagent for cotton fabrics to replace BTCA. The optimal synthetic conditions of P(IA–AA) were recommended as that the molar ratio of IA:AA and reaction time were 1:1 and 3 h, respectively. The structure of P(IA–AA) was characterized with proton nuclear magnetic resonance spectroscopy, mass spectroscopy and Fourier transform infrared spectroscopy. Results provided evidence that the P(IA–AA) was synthesized with two IA and two AA molecules (molecular weight was 406). Through careful selection, the optimal anti-wrinkle finishing conditions were P(IA–AA) concentration of 160 g/L, pH value of 2.1, curing temperature of 180 °C, and curing time of 2 min. By comparing with IA, BTCA, citric acid (CA), and copolymers of maleic acid (MA) and AA [P(MA–AA)] in the similar conditions, the P(IA–AA)-treated fabrics showed the highest tearing strength retention of 59.30% and whiteness index of 77.60, and the wrinkle recovery angle of the P(IA–AA)-treated fabrics (245.1° ± 0.85°) was comparable with that of the CA-treated ones (244.7° ± 4.30°). Additionally, by separating the strength loss caused by degradation (TSLD) from that caused by crosslinking (TSLC), the P(IA–AA)-treated fabrics presented about 10% less TSLD than P(MA–AA)-treated ones with a comparable TSLC.

A practical method for estimating specific refractive index increments for flexible non-electrolyte polymers and copolymers in pure and mixed solvents using the Gladstone-Dale and Lorentz-Lorenz equations in conjunction with molar refraction structural constants, and solvent physical property databases

Equations for calculating the specific refractive index increment, ∂n/∂c, for polymer/solvent systems have been developed starting with either the Gladstone-Dale equation or the Lorentz-Lorenz equation for the refractive index of a dielectric medium. The resulting equations can be used to estimate ∂n/∂c as a function of polymer concentration, temperature, solvent composition, and, for copolymers, monomer composition. Simplifying assumptions have been made to generalize these equations and make them more usable: 1) molar refractions are treated as constants, 2) the density of the polymer solution, in the limit of low polymer concentration, can be approximated via the additivity of volumes approach; the densities of polymer-free solvents and solvent mixtures are not necessarily subject to this approximation, 3) the mass density of solvents and solvent mixtures can be estimated by any one of several models developed specifically for this purpose; we will consider the Rackett equation, the COSTALD equation, and the standard assumption of mass and volume additivity, and 4) the mass density of a copolymer can be obtained from a weight fraction average of the mass densities of the homopolymers from which it is comprised. Comparisons to experimental data show that (∂n/∂c)GD and (∂n/∂c)LL both yield average absolute deviations of approximately 0.009 ml/gm.

Transport of Flexible, Oil-Soluble Diblock and BAB Triblock Copolymers to Oil/Water Interfaces.

The connection between block copolymer architecture and adsorption at fluid/fluid interfaces is poorly understood. We characterize the interfacial properties of a well-defined series of polyethylene oxide/polydimethyl siloxane (PDMS) diblock and BAB triblock copolymers at the dodecane/water interface. They are oil-soluble and quite flexible because of their hydrophobic PDMS block. Rather than relying on equilibrium interfacial measurements for which it is difficult to mitigate experimental uncertainty during adsorption, we combine measurements of steady-state adsorption, dilatational rheology, and adsorption/desorption dynamics. Steady-state interfacial pressure is insensitive to interfacial curvature and mostly agrees with theory. Adsorption does not occur in the diffusive limit as is the case for many aqueous, small-molecule surfactants. Dilatational rheology reveals differences in behavior between the diblocks and triblocks, and all interfaces possess elasticities below the thermodynamic limit. Desorption dynamics show that material exchange between the interface and the neighboring fluid occurs too slowly to relax dilatational stresses. The mechanism of relaxation occurs at the interface, likely from the reorientation of adsorbed chains.

Sweep-type triboelectric linear motion sensor with staggered electrode

For use in modern industrial automation, a sweep-type triboelectric linear motion sensor (ST-TLMS) is demonstrated that can monitor the position, displacement, velocity and direction of sliding objects. The ST-TLMS consists of a slider, a stator, and an acrylic groove box for housing them. They are configured allowing a flexible copolymer film to be fixed on the slider and moves with it and the stator to be coated with three pairs of copper electrode arrays arranged uniformly. The phases of adjacent pairs of electrodes are staggered by one third. Three periodic friction electrical signals are generated on the copper electrode by the back and forth sweeping of the stator and film. The experimental results show that the output amplitude after voltage amplification and signal processing remains basically unchanged at different sliding velocities, showing good stability. More importantly, the dominant frequency of the signal is consistent with the sliding velocity. Through real-time noise reduction and the signal transformation of the three output signals, the resolution and accuracy of the motion perception are effectively improved. Additionally, after 32 h of continuous operation, the output signal of the sensor had not decayed, which meets the requirements of durability in practical applications.

Modeling the Reactivity of Aged Paper with Aminoalkylalkoxysilanes as Strengthening and Deacidification Agents

Aminoalkylalkoxysilane (AAAS) flexible copolymer networks can be used to deacidify and strengthen paper in a one-step operation. The treatment is versatile and can be tailored to convey a balanced ...

Silsesquioxane-Polythiophene Hybrid Copolymer as an Efficient Modifier for Single-Walled Carbon Nanotubes

One silsesquioxane-polythiophene hybrid copolymer, with combined star-like structure and intramolecular heterogeneity, was synthesized and sufficiently characterized via various methods, including FTIR, NMR, and SEC measurements. According to the exploration and characterization results, it was much more efficient at modifying SWNTs than its linear analogs in aqueous solution. The hydrophobic silsesquioxane core and PEDOT chains could locally anchor to the surface of the nanotubes, while the soluble flexible copolymer chains extended into the solution and rigid conjugated chains provided some π-π stacking effect to enhance adhesive force with the conjugated structure of the carbon nanotube, imparting steric stabilization to nanotube dispersion. The noncovalent interaction with SWNTs and solubility in aqueous solution improved the electrochemical characteristics of the modified-SWNT composite and availed for the preparation of a flexible and transparent electroactive film. Accordingly, this kind of silsesquioxane-polythiophene hybrid copolymer will be forwarded to apply to the assembling of flexible optoelectronic devices.

Nanopiezoelectric Devices for Energy Generation Based on ZnO Nanorods/Flexible-Conjugated Copolymer Hybrids Using All Wet-Coating Processes.

In this study, nanopiezoelectric devices based on ZnO nanorod array/conducting polymers are fabricated for wearable power generation application. To replace the inorganic rigid indium-tin oxide (ITO) conducting coating commonly used in the nanogenerator devices, a series of flexible polyaniline-based conducting copolymers underlying the perpendicularly-oriented ZnO nanorod arrays has been synthesized with improved electric conductivity by the copolymerization of aniline and 3,4-ethylenedioxythiophene (EDOT) monomers in order to optimize the piezoelectric current collection efficiency of the devices. It is found that significantly higher conductivity can be obtained by small addition of EDOT monomer into aniline monomer solution using an in-situ oxidative polymerization method for the synthesis of the copolymer coatings. The highest conductivity of aniline-rich copolymer is 65 S/cm, which is 2.5 times higher than that for homopolymer polyaniline coating. Subsequently, perpendicularly-oriented ZnO nanorod arrays are fabricated on the polyaniline-based copolymer substrates via a ZnO nanoparticle seeded hydrothermal fabrication process. The surface morphology, crystallinity, orientation, and crystal size of the synthesized ZnO nanorod arrays are fully examined with various synthesis parameters for copolymer coatings with different monomer compositions. It is found that piezoelectric current generated from the devices is at least five times better for the device with improved electric conductivity of the copolymer and the dense formation of ZnO nanorod arrays on the coating. Therefore, these results demonstrate the advantage of using flexible π-conjugated copolymer films with enhanced conductivity to further improve piezoelectric performance for future wearable energy harvesting application based on all wet chemical coating processes.

Design of robust superhydrophobic coatings using a novel fluorinated polysiloxane with UV/moisture dual cure system

A novel robust and flexible superhydrophobic fluoropropyl methylsiloxane-dimethylsiloxane multi-block copolymer containing methacryloxyl group was synthesized via ring-opening polymerization, followed by macromolecular modification using 3-(trimethoxsilyl) propyl methacrylate (TMPMA). The propionyloxy group of MAc(PTFMS-alt-PDMS) could be crosslinked under UV irradiation, and its silicon methoxy group (-SiOCH3) was simultaneously condensed under moisture ambient, so as to acquire both higher crosslink density and adhesion strength duo to the dual-curing mode. After coating and curing MAc(PTFMS-alt-PDMS) on the surface of cotton fabric, a robust superhydrophobic elastomer coating was obtained. The elastomer exhibited excellent mechanical properties with a tensile strength >4.0 Mpa and an elongation at break >300%. Moreover, the elastomer exhibited superhydrophobic properties (contact angle CA > 150o) and good adhesion properties (shear strength >3.7 Mpa) on various inorganic and organic substrates such as steel, glass, paper, and polyethylene (PE) films, with the assistant of the hydrophobic silica particles. The excellent flexibility and adhesive strength of the MAc(PTFMS-alt-PDMS) allowed a PE film to be bent at a large angle (120o). The results obtained here demonstrate that this material has good application prospects where flexible superhydrophobic coatings are desired.

Controlled photoisomerization in acrylic copolymer nanoparticles based on spironaphthoxazine for reduced thermal reversion

Stimuli-responsive materials based on spirooxazines are new class of smart materials that have received great deal of attentions in the recent decades. Spirooxazine derivatives, as photochromic compounds, represent many advantages like high photofatigue resistance. But, they usually suffer from very short life time of the colored form and quick reversion to its colorless isomer which limits their application at ambient conditions. Here, spironaphthoxazine (SNO) and spironaphthoxazine acrylate (SNO-Ac, as the monomer) were synthesized and characterized by FTIR and 1H NMR spectroscopy. Then, temperature-dependent photochromic behavior of SNO solution in different solvents was studied by UV–Vis spectroscopy at room and low temperatures. The absorption band relating to the obtained meronaphthoxazine (MNO) in 500–600 nm was not clearly observed after UV irradiation (365 nm) at room temperature, while an intensive absorption was appeared at −30 and −20 °C. SNO-Ac was then copolymerized with methyl methacrylate through solution and miniemulsion polymerizations. The obtained nanoparticles (ranging from 64 to 94 nm in size) represented reduced thermal reversion in comparison with the solution-based copolymers, but still not enough for room-temperature observations. Thereafter, an evident coloration was gained at normal conditions by introducing butyl acrylate to the above-mentioned copolymeric latex. The obtained flexible copolymer chains were found to facilitate SNO to MNO isomerization and the kinetic of photoisomerization in such systems were studied comprehensively. This resulted in photothermal stability enhancement of MNO at ambient conditions by their embedding in the prepared acrylic terpolymer nanoparticle to decrease its decoloration rate as a novel approach in such systems.

Disubstituted pendant-functionalized insulating-conductive block copolymer with enhanced dielectric and energy storage performance

Disubstituted pendant-functionalized block copolymer consisting of insulating polynorbornene and conductive polyacetylene segments was synthesized by tandem metathesis polymerization, and displayed high dielectric constant of 30 and low dielectric loss of about 0.04, while behaved bad film-forming property, which could be improved by incorporating polycyclooctene into polynorbornene backbone. The generated flexible block copolymer with well-defined nanostructure exhibited a relatively high dielectric constant of 23, very low dielectric loss of below 0.0035, and high stored and released energy densities up to 4.52 and 4.02 J cm−3 at the electric field of 165 MV m−1, respectively, accompanied with the charge-discharge efficiency of 90%. The enhanced dielectric and energy storage capability were attributed to high permanent dipole moment and the interfacial polarization derived from the unique nanomorphology of block copolymer.

Elastic properties of liquid-crystalline bilayers self-assembled from semiflexible-flexible diblock copolymers.

The mechanical response and shape of self-assembled bilayer membranes depend crucially on their elastic properties. Most of the studies focused on the elastic properties of fluid membranes, despite the ubiquitous presence of membranes with liquid-crystalline order. Here the elastic properties of liquid-crystalline bilayers self-assembled from diblock copolymers composed of a semiflexible block are studied theoretically. Specifically, the self-consistent field theory (SCFT) is applied to a model system composed of semiflexible-flexible diblock copolymers dissolved in flexible homopolymers that act as solvents. The free energy of self-assembled tensionless bilayer membranes in three different geometries, i.e. planar, cylindrical and spherical, is obtained by solving the SCFT equations using a hybrid method, in which the orientation-dependent functions are treated using the spherical harmonics, whereas the position-dependent operators are treated using the compact difference schemes. The bending modulus κM and Gaussian modulus κG of the bilayer are extracted from the free energies. The effects of the molecular parameters of the system, such as the chain rigidity and the orientational interaction, are systematically examined.

Ambient-dried highly flexible copolymer aerogels and their nanocomposites with polypyrrole for thermal insulation, separation, and pressure sensing

Highly flexible copolymer and copolymer/polypyrrole nanocomposite aerogels have been synthesized via ambient pressure drying for superinsulation, separation and pressure sensing.

Intelligent Biomimetic Chameleon Skin with Excellent Self-Healing and Electrochromic Properties.

Animals such as chameleons possess a natural ability to adjust their skin color as a preventive measure to deter any potential threat and to self-heal damaged skin tissues. Inspired by this, we present here a copolymer film possessing biomimetic properties that simultaneously integrates electrochromic triphenylamine and self-healing Diels-Alder groups. The flexible and stretchable copolymer film acts like natural chameleon skin, which exhibits significant color variation and also possesses excellent self-healing properties. These remarkable features make it a promising material for overcoming the crack-generation issue inherited by conventional biomimetic chameleon skin. Moreover, a flexible and wearable skin device based on the copolymer film with silver fabric as a electrode has also been fabricated. The electrochromic and self-healing properties were verified for the copolymer film, and it has been elucidated that the intelligent biomimetic "chameleon skin" was a new step toward the development of highly advanced biomimetic materials and devices.

One-Step Dipping Fabrication of Fe3O4/PVDF-HFP Composite 3D Porous Sponge for Magnetically Controllable Oil–Water Separation

Industrial oil spills in various bodies of water is a worldwide environmental problem that requires effective oil absorbents with remote controllability, which would be a clear improvement upon currently used technologies. One approach for adding remote controllability is embedding magnetic particles into the oil absorbent materials; however, there are currently few reports of magnetic oil absorbents. Most of these are prepared through multistep processes or using hazardous materials, which inhibits their practical use. In this study, we introduce a single-step dipping method to simultaneously provide both magnetic and hydrophobic/oleophilic functions to melamine foam by combining hydrophobic flexible copolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and magnetic Fe3O4 nanoparticles synthesized by a method suitable for mass production. The as-fabricated coating performs effectively for oil collection of oil spilled on water, and the movement of the foam on the water’s surface can be effectively controlled under magnetic field without touching it directly. Also, the coating is capable of regenerating its oil-absorbing property by being wrung out after the initial absorption owing to its flexibility and separation of oil in a water-in-oil emulsion. Such a simple method for the creation of multifunction material could potentially be helpful for the development of commercial remediation materials.