Block Copolymer Solutions Research Articles

Visualization study on the dry devolatilization characteristics of styrene-butadiene-styrene block copolymers

Dry devolatilization is a promising method for saving energy, but understanding the devolatilization process has been challenging. A static devolatilizer was designed to study the devolatilization process of a Styrene-butadiene-styrene (SBS) block copolymer solution at different temperatures using visualization technology. The study found that temperature, Reynolds number, and heat flux are key factors influencing the devolatilization process. The optimal residence time was determined to be 196 s and the suitable feed coefficient is 0.17. Additionally, a new dimensionless parameter (the LZ number) was introduced. A value closer to 1 indicated a more effective devolatilization process. The obtained thermodynamic parameters and LZ number can guide the design of industrial devolatilization devices.

Hydrodynamic Properties and LCST Behavior of Six-Armed Star-Shaped Polymers with Arms of a Diblock Copolymer of Poly-2-Ethyl-2-Oxazine and Poly-2-Isopropyl-2-Oxazine

Star-shaped six-arm polymers with arms of the block copolymers of poly-2-ethyl-2-oxazine and poly-2-isopropyl-2-oxazine were synthesized. The branching center was hexaase[26]cyclophane. The prepared samples differed in the order of block attachment to the core. Molar masses of the two samples were 14200 and 21500 g⋅mol−1. The fractions of poly-2-ethyl-2-oxazine monomers in the arms were 61 and 65%, respectively. It was shown that the arms were strongly folded. Water-salt solutions of the star-shaped block copolymers exhibited thermoresponsiveness. The difference in the phase separation temperatures for the studied samples was caused by the differences in their molar masses and the different contents of poly-2-ethyl- and poly-2-isopropyl-2-oxazine blocks. The concentration dependences of the phase separation temperatures for the synthesized star-shaped copolymers coincided with those for the arms, despite the fact that the molecular masses of the stars and their arms differed by factor of near 6. The addition of NaCl to the aqueous of solutions of the star copolymers did not lead to significant changes in their characteristics. No influence of the order of the block attachment to the core on the molecule conformation and on the thermoresponsive behavior was found.

Kinetically Controlled and Nonequilibrium Assembly of Block Copolymers in Solution.

Covalent polymers are versatile macromolecules that have found widespread use in society. Contemporary methods of polymerization have made it possible to construct sequence polymers, including block copolymers, with high precision. Such copolymers assemble in solution when the blocks have differing solubilities. This produces nano- and microparticles of various shapes and sizes. While it is straightforward to draw an analogy between such amphiphilic block copolymers and phospholipids, these two classes of molecules show quite different assembly characteristics. In particular, block copolymers often assemble under kinetic control, thus producing nonequilibrium structures. This leads to a rich variety of behaviors being observed in block copolymer assembly, such as pathway dependence (e.g., thermal history), nonergodicity and responsiveness. The dynamics of polymer assemblies can be readily controlled using changes in environmental conditions and/or integrating functional groups situated on polymers with external chemical reactions. This perspective highlights that kinetic control is both pervasive and a useful attribute in the mechanics of block copolymer assembly. Recent examples are highlighted in order to show that toggling between static and dynamic behavior can be used to generate, manipulate and dismantle nonequilibrium states. New methods to control the kinetics of block copolymer assembly will provide endless unanticipated applications in materials science, biomimicry and medicine.

High χ P2PFBEMA-b-P2VP Block Copolymers Forming 6-8 nm Domains for Semiconductor Lithography.

We leveraged the potential of high χ-low N block copolymer (BCP), namely, poly[2-(perfluorobutyl) ethyl methacrylate]-block-poly(2-vinylpyridine) (P2PFBEMA-b-P2VP), and demonstrated its utility in next-generation nanomanufacturing. By combining molecular dynamics simulations with experiments, the χ value was calculated to be as high as 0.4 (at 150 °C), surpassing similar structures. Highly ordered features suitable for application were observed, ranging in periods from 19.0 nm down to 12.1 nm, with feature sizes as small as 6 nm. Transmission electron microscopy images of the BCP solutions indicated that preformed micelles in the solution facilitated the self-assembly process of the thin film. In addition, the vertical or parallel orientation of the cylindrical structure was determined by manipulating the solvent, substrate, and annealing conditions. Finally, guided by a wide topographical template, nearly defect-free directed self-assembly (DSA) lines with a resolution of 8 nm were achieved, highlighting its potential practical application in DSA lithography technology.

Mesogenic Ordering-Driven Self-Assembly of Liquid Crystalline Block Copolymers in Solution.

With the development of nanotechnology, the preparation of polymeric nanoparticles with nicely defined structures has been well-developed, and the functionalization and subsequent applications of the resultant nanostructures are becoming increasingly important. Particularly, by introducing mesogenic ordering as the driving force for the solution-state self-assembly of liquid crystalline (LC) block copolymers (BCPs), micellar nanostructures with different morphologies, especially anisotropic morphologies, can be easily prepared. This review summarizes the recent progress in the solution-state self-assembly of LC BCPs and is mostly focused on four main related aspects, including an in-depth understanding of the mesogenic ordering-driven self-assembly, precise assembly methods, utilization of these methods to fabricate hierarchical structures, and the potential applications of these well-defined nanostructures. We hope not only to make a systematic summary of previous studies but also to provide some useful thinking for the future development of this field.

Solvent effect on the self-assembly of polyisobutylene-based glycopolymers

Investigation of polymeric conformations in different solvents is critical because block copolymer solution morphology is not only associated with the architecture but also with its characteristic features which depend upon the solvent polarity. A series of double hydrophobic diblock copolymers comprising polyisobutylene (PIB) segment and varying sugar pendant units have been prepared by a combination of living cationic and reversible addition-fragmentation chain transfer (RAFT) polymerizations. After the deprotection of the acetate from sugar pendants, the synthesized water-soluble amphiphilic block copolymers showed morphological transformations in both aqueous and organic media. A conformational transition due to a change in solvent polarity from polar protic to nonpolar was supported by 1H NMR spectroscopy. The dynamic light scattering (DLS) experiments demonstrated that the hydrodynamic diameters of aggregates varied with solvent polarity. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) evidenced the morphological changes from micellar to tubular orientation. Finally, the self-assembly behavior of PIB-based glycopolymers due to changes in solvent polarity is proposed.

Direct-ink-write cross-linkable bottlebrush block copolymers for on-the-fly control of structural color

Additive manufacturing capable of controlling and dynamically modulating structures down to the nanoscopic scale remains challenging. By marrying additive manufacturing with self-assembly, we develop a UV (ultra-violet)-assisted direct ink write approach for on-the-fly modulation of structural color by programming the assembly kinetics through photo-cross-linking. We design a photo-cross-linkable bottlebrush block copolymer solution as a printing ink that exhibits vibrant structural color (i.e., photonic properties) due to the nanoscopic lamellar structures formed post extrusion. By dynamically modulating UV-light irradiance during printing, we can program the color of the printed material to access a broad spectrum of visible light with a single ink while also creating color gradients not previously possible. We unveil the mechanism of this approach using a combination of coarse-grained simulations, rheological measurements, and structural characterizations. Central to the assembly mechanism is the matching of the cross-linking timescale with the assembly timescale, which leads to kinetic trapping of the assembly process that evolves structural color from blue to red driven by solvent evaporation. This strategy of integrating cross-linking chemistry and out-of-equilibrium processing opens an avenue for spatiotemporal control of self-assembled nanostructures during additive manufacturing.

Synthesis and self-assembly of dendritic-linear block copolymers containing poly(mandelic acid) with discrete molecular weights and stereochemical structures.

In this work, we present the synthesis of uniform PMAs, where the number of repeat units and their stereochemical arrangement are precisely defined. Utilizing an iterative convergent approach with orthogonally protected dimandelic acid building blocks, we achieved high molecular weight PMAs with the desired number of repeat units, extending up to 144 mandelic acids. Additionally, stereochemically defined poly(l-mandelic acid)s with up to 32 repeat units were successfully synthesized. These uniform PMAs were subsequently coupled with uniform branched poly(ethylene glycol) blocks to create uniform dendritic-linear block copolymers. The self-assembly of these block copolymers in solution was systematically investigated. In solution self-assembly, the synthesized block copolymers showed multiple phases from cylinder to inverse cubic as the molecular weight of PMA increased. In the case of solvent diffusion-evaporation-mediated self-assembly, the block copolymers underwent a phase transition as the rate of water addition decreased.

Simple hybrid polymeric nanostructures encapsulating macro-cyclic Gd/Eu based complexes: luminescence properties and application as MRI contrast agent.

Lanthanide-based macrocycles are successfully incorporated into hybrid polyionic complexes, formed by adding a mixture of zirconium ions to a solution of a double-hydrophilic block copolymer. The resulting nanoobjects with an average radius of approximately 10-15 nm present good colloidal and chemical stability in physiological media even in the presence of competing ions such as phosphate or calcium ions. The final optical and magnetic properties of these objects benefit from both their colloidal nature and the specific properties of the complexes. Hence these new nanocarriers exhibit enhanced T1 MRI contrast, when administered intravenously to mice.

Hybrid polyionic complexes as nanoreactors for the synthesis of iron oxide nanoparticles: From size control to modulation of magnetic and catalytic properties

Hybrid polyion complexes (HPICs) obtained from the complexation in aqueous solution of a double hydrophilic block copolymers and metal ions can act as efficient precursors for the controlled synthesis of hybrid nanoparticles. Hence, HPICs based on a mixture of ferrous and ferric ions with poly(ethylene oxide)-block-poly(acrylic acid) were used to initiate, after the addition at 70 °C of a solution of NH4OH, the formation of iron oxide nanoparticles. The careful choice of the molar ratio between polymer and metal ions within HPICs enables to tune the morphology and size of the obtained iron oxide nanoparticles while maintaining the same surface composition. This control of size and composition was further used to highlight the relationship between the size of these particles and their catalytic and magnetic properties.

Topological structure-induced self-assembly of highly asymmetric PLLA-b-QPDMAEMA block copolymers in solution: Linear versus bottlebrush

During self-assembly process of block copolymers in solution, when the volume fraction of solvophobic blocks is too low, usually below 10%, the copolymers generally tend to dissolve, which has caused trouble. Herein, a bottlebrush block copolymer composed of poly(L-lactic acid) (PLLA) and quaternized poly(N,N-dimethylaminoethylmethacrylate) (QPDMAEMA), whose content of solvophobic block PLLA was below 2 wt%, was prepared. Owing to the rigidity derived from the advantages of topological structure of bottlebrush-like molecules, the interfacial curvature between two incompatible microphases is maintained, and this highly asymmetric copolymer unexpectedly spontaneously assembles into uniform spherical micelles with diameters of tens of nanometers. The morphology of aggregates was verified by dynamic light scattering, transmission electron microscopy and atomic force microscope. This study expands the understanding of traditional theory about copolymers self-assembly in solution, which helps to design, prepare, and apply polymer micelles with various structures from a broader perspective.

Beyond the Conventional Paradigm of Radial (Normal) Stretching of Tethered Chains. Do Theories of Micellization in Solutions of Block Copolymers Need to Be Revised?

Beyond the Conventional Paradigm of Radial (Normal) Stretching of Tethered Chains. Do Theories of Micellization in Solutions of Block Copolymers Need to Be Revised?

Iron-based hybrid polyionic complexes as chemical reservoirs for the pH-triggered synthesis of Prussian blue nanoparticles

HypothesisHybrid polyion complexes (HPICs) obtained from the complexation in aqueous solution of a double hydrophilic block copolymer and metal ions can act as efficient precursors for the controlled synthesis of nanoparticles. In particular, the possibility to control the availability of metal ions by playing on the pH conditions is of special interest to obtain nanoparticles with controlled size and composition. ExperimentsHPICs based on Fe3+ ions were used to initiate the formation of Prussian blue (PB) nanoparticles in presence of potassium ferrocyanide in reaction media with varying pH values. FindingsComplexed Fe3+ ions within HPICs can be easily released by adjusting the pH value either through the addition of a base/acid or by using a merocyanine photoacid. This allows to modulate the reactivity of Fe3+ ions with potassium ferrocyanide present in solution. As a result, PB nanoparticles with different structures (core, core–shell), composition and controlled size are obtained.

Kinetics of Micellization and Liquid-Liquid Phase Separation in Dilute Block Copolymer Solutions.

A lattice theory for block copolymer solutions near the boundary between the micellization and liquid-liquid phase separation regions proposes a new kinetic process of micellization where small concentrated-phase droplets are first formed and then transformed into micelles in the early stage of micellization. Moreover, the thermodynamically stable concentrated phase formed from metastable micelles by a unique ripening process in the late stage of phase separation, where the growing concentrated-phase droplet size is proportional to the square root of the time.

Molecular Insight into 6FD Polyimide-Branched Poly(phenylene) Copolymers: Synthesis, Block Compatibility, and Gas Transport Study

A series of 6FDA-DABA (6FD) polyimide and branched poly(phenylene) (PP) block copolymers and homopolymers were successfully synthesized using Diels–Alder and polycondensation reactions. PP and 6FD homopolymer blends in tetrahydrofuran were immiscible. The result coincides with their large chemical dissimilarity and theoretical solubility parameter differences of 25.47 and 33.17 (MJ/m3)1/2. However, 6FD-PP block copolymer solutions were clear, and thin films were robust and creasable. Densities and fractional free volumes (FFV) (0.162–0.346) largely obeyed the rule of mixing, suggesting a “blend-like” morphology. At moderate PP block lengths, two distinct glass transition temperatures (340 and 420 °C) were evident, while large PP block lengths suppressed first-order polyimide transitions entirely. A small-angle X-ray scattering and atomic force microscopy morphological analysis revealed two distinct domains, with separation lengths increasing with the PP block length. Their gas permeation, diffusion, sorption, and separation properties were thoroughly investigated and exhibited a strong correlation with polymer chemistry, block length, and FFV. A block copolymer had an O2 permeability roughly between 6FD and PP, resulting in a 30% increase in O2/N2 selectivity. The N2/CH4 selectivities ranged from 4.2 to 0.58, suggesting that this 6FD-PP system could be efficiently tuned from highly N2-selective to CH4-selective performance. Five structural models, rule-of-mixture, Maxwell, equivalent box model, laminate, and blend, were used to predict gas transport properties. Compared with experimental data, the miscible blend model provided the best results for the 6FD-PP block copolymer system. Block copolymerization by combining highly selective polyimide and highly permeable branched poly(phenylene) provides an opportunity for gas separation tunability and improvement in selected gas pairs.

Stimuli‐responsive polypeptoid block copolymers containing o‐nitrobenzyl groups with extremely sharp transition

AbstractBioinspired thermoresponsive polymers have received increasing attention for many applications. Here, we report a series of thermoresponsive polypeptoid block copolymers containing o‐nitrobenzyl groups, that is, poly(ethylene glycol)‐b‐poly[N‐[2‐[N‐(o‐nitrobenzyloxycarbonyl)‐amino]‐ethyl]‐glycine] (PEG‐b‐PN[oNB]G), prepared by ring‐opening polymerization. The polypeptoid block copolymers show reversible lower critical solution temperature (LCST)‐type behavior in water with tunable phase transition properties dependent on the pH values, chemical compositions, and concentrations of the copolymers. The dynamic light scattering results reveal the formation of spherical micelles and temperature‐induced aggregation of PEG‐b‐PN(oNB)G. Notably, the phase transition of the block copolymer solution upon heating appears extremely sharp (∆T < 1°C), superior to bench mark poly(N‐isopropylacrylamide). In addition, we present the removal of photo‐responsive o‐nitrobenzyl groups can result in the increased clouding point and even the loss of phase transition properties, acting as an excellent regulator to tune the LCST behavior. We demonstrate that the hydrogen‐bonding interaction may play a critical part on the LCST behavior. The prepared diblock copolymers show great potential for many applications and its structure–property may shed light on highly designable stimuli‐responsive polymeric materials.

Selective Destruction of Soluble Polyurethaneimide as Novel Approach for Fabrication of Insoluble Polyimide Films.

Polymeric coatings and membranes with extended stability toward a wide range of organic solvents are practical for application in harsh environments; on the other hand, such stability makes their processing quite difficult. In this work, we propose a novel method for the fabrication of films based on non-soluble polymers. The film is made from the solution of block copolymer containing both soluble and insoluble blocks followed by selective decomposition of soluble blocks. To prove this concept, we synthesized copolymer [(imide)n-(polyurethane)]m, in which the imide blocks were combined with polyurethane blocks based on polycaprolactone. By selective hydrolysis of urethane blocks in the presence of acid, it was possible to obtain the insoluble polyimide film for the first time. It was shown that the combination of thermal and acid treatment allowed almost complete removal of urethane blocks from the initial copolymer chains. IR spectroscopy, TGA, DSC and DMA methods were used to study the evaluation of the structure and properties of polymeric material as a result of thermal oxidation and hydrolysis by acid. It was shown that the polymeric films obtained by controlled decomposition were not soluble in aprotic solvent, such as dimethylformamide, n-methylpyrrolidone and dimethyl sulfoxide, and showed very close similarity to the homopolymer consisting of the same imide monomer, poly-(4,4′oxydiphenylene)pyromellitimide, confirming the feasibility of the proposed concept and its perspectives for fabrication of organic solvent-resistant membranes.

Temperature Variation Effect on Behavior of Block Copolymer of 2- Isopropenylnaphthalene and Methacrylic Acid in Ethanol

Fluorescence spectra of dilute solution of blockcopolymer of 2- Isopropenylnaphthalene and methacrylic acid ( 2- IPN – MA) in ethanol have been measured in temperature range of 9.5 – 50˚C . The fluorescence spectra show two emission bands at 342 nm and 387nm corresponding to monomer and excimer bands, respectively. From temperature dependent fluorescence measurements a plot of excimer to monomer intensity ratio ( IE/IM ) versus temperature was obtained , which shows that ( IE /IM ) value increases linearly in the temperature range of 9.5-25˚C and sharp increasing at a bout 35˚C ,then IE/IM increases smoothly above 35˚C . These results Indicate that the conformational change of the polymer chain from contraction form to expansion form takes place at about 35˚C.

Mean-field models of size selection in polymer vesicles with and without interdigitation

ABSTRACT Block copolymers in solution can form vesicles with a preferred size when the degree of polymerisation of the hydrophobic block is significantly greater than that of the hydrophilic block. In an earlier publication, we introduced a mean-field theory that treats the vesicle membrane as a bilayer. Here, a model is presented in which the hydrophobic blocks form a single interdigitated layer. In the model with interdigitation, the vesicles still have a preferred radius, but this increases more slowly as a function of than in the bilayer model, in better agreement with experiment. However, the predictions of the bilayer model for the relationship between and the vesicle membrane thickness are consistent with the experimental result over a wide range of parameters, while the model with interdigitation predicts an exponent of around . This suggests that the structure of the vesicles may lie between these two cases.

Aggregate behavior in amphiphilic coil/rod block copolymer solutions

The self-assembly in coil/rod/coil BAB amphiphilic symmetric triblock copolymer solutions was investigated using lattice self-consistent field theory. At low concentrations, some peaks emerge on the heat capacity curve, i.e., multiple rearrangements (MRs) of micelles. For short hydrophobic rod blocks (HRBs), MRs are concerned with the emergences of vesicles, stellate, rod, and lamellar micelles (LMs), and the breakup and formation of LMs. At high concentrations with HRBs of intermediate length HRBs, MRs are associated to a few (quasi-)order/disorder transitions of micelles. For long HRBs, although only one quasi-order/disorder transition emerges, MRs do occur. It is found that the aggregation behavior of high concentrations with HRBs of intermediate length is similar to that of low concentrations compared with high concentrations with long HRBs. These results are explained by the reappearing behavior and dissolution, and the cooperative growth of micelles, where the micellar cores and coronas are rearranged alternately with temperature. This work is helpful for further interpreting the cooperativity and dynamics of self-assembly.