Copolymer Phase Research Articles

Hydrolysis of poly(ester urethane): In-depth mechanistic pathways through FTIR 2D-COS spectroscopy

The hydrolysis of thermoplastic poly(ester urethane) (PEU) is convoluted by its block copolymer phase structure and competing hydrolytic sensitivities of multiple functional groups. The exact pathways for water ingress, water interaction with the material and ultimately the kinetics and order of functional group hydrolysis remain to be refined. Additional diagnostics are needed to enable deeper insight and deconvolution of material changes. In combination with GPC results, a promising analytical technique – two-dimensional correlation spectroscopy (2D-COS) – has been reviewed and applied to analyze FTIR spectra of hydrolyzed PEUs aged under various conditions, such as exposure time, temperature, and relative humidity. 2D-COS allows the complex role of water with distinct intermediate steps to be established, plus it emphasizes the initial stages of PEU hydrolysis at more susceptible functional groups. As a complication for the raw material, ATR IR detected some talc on the surface of commercial PEU beads and pressed sheets thereof, which can interfere with water ingress and thereby retards PEU hydrolysis, particularly in its natural form or moderate aging at lower temperatures (e.g., below the melting point of PEU). As aging temperature increases above the melting temperature, even traces of water trapped inside the PEU are sufficient to initiate the hydrolysis, which then progresses strongly with increasing temperatures. Feedback from 2D-COS analysis confirms that PEU hydrolysis starts at esters in the soft-segments before those in the urethane linkage become susceptible. Only when the molecular weight of PEU is below a critical molar mass (Mc) will the hydrolysis occur in parallel in the hard-segments since protective morphological phase structures are then absent. The current observations demonstrate unexpected behavior that may result from 'unknown' additives in polymer degradation, the temporal and group-specific hydrolysis of PEU as a function of locally available water molecules, the order of reactivity of susceptible functional groups, and the importance of changes in molecular weight coupled with the phase structure of the polymer.

Accessing the Frank–Kasper Phase of Block Copolymer via Selective Incorporation of Metal Salt

Accessing the Frank–Kasper Phase of Block Copolymer via Selective Incorporation of Metal Salt

Preparation and melt-spun applications of PA6-based Poly(Amide-Ether) copolymers phase change fibers with passive temperature management

Phase change fiber, as an intelligent fiber material used in passive thermal management, can balance the temperature of the microenvironment near human skin. However, the traditional blending method makes phase change material prone to leakage during the processing and applications. Herein, this work introduces the phase change material PTMEG into the polyamide 6 (PA6) chain through melt polymerization to prepare a series of PA6-based poly(amide-ether) copolymers. Copolymers exhibit an obvious microphase separation structure, with the PA6 segments and the PTMEG segments can form independent crystalline and amorphous regions. PTMEG in copolymers through polymerization method exhibits better thermal stability compared with the blended way, which effectively solves the leakage problem of phase change materials. The copolymers can be directly melt-spun (1500 m/min) to prepare PA6-based phase change fibers. The fiber can maintain excellent mechanical properties (breaking strength of 2.12 cN/dtex). Meanwhile, the crystallization enthalpy and melting enthalpy of the PTMEG in the fiber are 10.59 J/g and 12.44 J/g, respectively. The thermal management time of the fiber in the hot environment is 349 s, and the maximum temperature difference is lower 5.6 ℃ from the PA6 fiber. In addition, the exothermic duration in a cold environment is 536 s, and the maximum temperature difference is higher 1.1 °C from the PA6 fiber. Meanwhile, the thermal enthalpy of the fiber remained stable (fluctuation within 2 %) after 20th thermal cycles, and the loss rate is less than 2 % after washing at 25 ℃, 50 ℃ and 90 ℃. The fiber exhibits good thermal stability, water washability and cyclic stability. Preparation of high enthalpy polymers directly by copolymerization will provide new ideas for phase change fibers for apparel.

Synthesis and Characterization of β-Myrcene-Styrene and β-Ocimene-Styrene Copolymers.

The structure-properties relationships of sustainable materials derived from biomass-based monomers are investigated, focusing on hybrid styrene/terpene-based copolymers with blocky microstructures, such as β-myrcene- and β-ocimene-styrene copolymers. The samples show complex glass transition dynamics, as evidenced by the physical aging experienced by the amorphous phase in styrene-rich copolymers. The tendency of styrene- and terpene-rich sequences to give heterogeneous morphologies with correlation strength extending over 10-40nm is outlined, through small-angle X-ray scattering analysis. A new class of terpene-based hybrid systems, holding promise for applications in surface coating technologies, is identified.

A Super-Ionic Solid-State Block Copolymer Electrolyte.

Polymer solid-state electrolytes offer great promise for battery materials with high energy density, mechanical stability, and improved safety. However, their low ion conductivities have so far limited their potential applications. Here, it is shown for poly(ethylene oxide) block copolymers that the super-stoichiometric addition of lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) as lithium salt leads to the formation of a crystalline PEO block copolymer phase with exceptionally high ion conductivities and low activation energies. The addition of LiTFSI further induces block copolymer phase transitions into bi-continuous Fddd and gyroid network morphologies, providing continuous 3D conduction pathways. Both effects lead to solid-state block copolymer electrolyte membranes with ion conductivities of up to 1·10-1Scm-1 at 90°C, decreasing only moderately to 4·10-2Scm-1 at room temperature, and to >1·10-3Scm-1 at -20°C, corresponding to activation energies as low as 0.19eV. The co-crystallization of PEO and LiTFSI with ether and carbonate solvents is observed to play a key role to realize a super-ionic conduction mechanism. The discovery of PEO super-ionic conductivity at high lithium concentrations opens a new pathway for fabrication of solid polymer electrolyte membranes with sufficiently high ion conductivities over a broad temperature range with widespread applications in electrical devices.

Stabilizing hexagonally close-packed phase in single-component block copolymers through rational symmetry breaking

Despite being predicted to be a thermodynamically equilibrium structure, the absence of direct experimental evidence of hexagonally close-packed spherical phase in single-component block copolymers raises uncomfortable concerns regarding the existing fundamental phase principles. This work presents a robust approach to regulate the phase behavior of linear block copolymers by deliberately breaking molecular symmetry, and the hexagonally close-packed lattice is captured in a rigorous single-component system. A collection of discrete A1BA2 triblock copolymers is designed and prepared through an iterative growth method. The precise chemical composition and uniform chain length eliminates inherent size distribution and other molecular defects. Simply by tuning the relative chain length of two end A blocks, a rich array of ordered nanostructures, including Frank−Kasper A15 and σ phases, are fabricated without changing the overall chemistry or composition. More interestingly, hexagonally close-packed spherical phase becomes thermodynamically stable and experimentally accessible attributed to the synergistic contribution of the two end blocks. The shorter A blocks are pulled out from the core domain into the matrix to release packing frustration, while the longer ones stabilize the ordered spherical phase against composition fluctuation that tends to disrupt the lattice. This study adds a missing puzzle piece to the block copolymer phase diagram and provides a robust approach for rational structural engineering.

Accelerated discovery and mapping of block copolymer phase diagrams

Block copolymers are widely used in many applications due to their spontaneous self-assembly into a variety of nanoscale morphologies. However, a grand challenge in navigating this diverse and ever-growing array of possible structures is the accelerated discovery, design, and implementation of materials. Here, we report a versatile and efficient strategy to accelerate materials discovery by rapidly building expansive, high-quality, and detailed block copolymer libraries through a combination of controlled polymerization and chromatographic separation. To illustrate the potential of this approach, a family of 16 parent diblock copolymers was synthesized and separated, leading to over 300 distinct and well-defined samples at the multigram scale. The resulting materials span a wide range of compositions with exceptional resolution in volume fraction and domain spacing that allows for the impact of monomer design on polymer self-assembly to be elucidated. Phase behavior that can be gleaned from these libraries includes the precise location of order-order boundaries and the identification of morphologies with extremely narrow windows of stability. This user-friendly, scalable, and automated approach to discovery significantly increases the availability of well-defined block copolymers with tailored molecular weights, molar-mass dispersities, compositions, and segregation strengths, accelerating the study of structure-property relationships in advanced soft materials. Published by the American Physical Society 2024

Ultrasmall 3D network morphologies from biobased sugar–terpenoid hybrid block co-oligomers in the bulk and the thin film states

Nanoscale three-dimensional (3D) network morphologies, such as those represented by gyroids accessed by the self-assembly of block copolymers, are highly attractive platforms for the fabrication of nanostructured materials. However, it remains challenging to access such morphologies, especially in the sub-10 nm domain spacing region. Herein, we systematically investigated the microphase separation behaviors of biobased sugar–terpenoid hybrid block co-oligomers (BCOs) with different molecular parameters, including their volume fractions, the linker structures between the blocks, and the stereochemistries of the terpenoid blocks. The BCOs were synthesized using the azido–alkyne click reaction of propargyl-β-d-glucopyranoside with azido-functionalized farnesol, phytol, DL-α-tocopherol, and d-α-tocopherol, to ensure a well-defined molecular structure without any molecular weight distribution. Through X-ray scattering screening, we found that tocopherols, when combined with a glucose unit, yield BCOs capable of forming gyroid and hexagonally perforated lamellar (HPL) 3D network morphologies with ultrasmall domain spacings of ∼10 nm. Remarkably, HPL, which is known as a metastable phase in block copolymers, was obtained in both the bulk and film states. The nature of the linker structure and the stereochemistry of the tocopherol hydrocarbon chain were found to influence the resulting morphology and the long-range order of the nanostructures. We expect this study to contribute to the molecular design of precise block copolymers and the construction of intricate nanostructural templates with ultrasmall feature sizes.

Flexible Block Copolymer Metamaterials Featuring Hollow Ordered Nanonetworks with Ultra-High Porosity and Surface-To-Volume Ratio.

By utilizing bicontinuous and nanoporous ordered nanonetworks, such as double gyroid (DG) and double diamond (DD), metamaterials with exceptional optical and mechanical properties can be fabricated through the templating synthesis of functional materials. However, the volume fraction range of DG in block copolymers is significantly narrow, making it unable to vary its porosity and surface-to-volume ratio. Here, the theoretically limited structural volume of the DG phase in coil-coil copolymers is overcome by enlarging the conformational asymmetry through the association of mesogens, providing fast access to achieving flexible structured materials of ultra-high porosities. The new materials design, dual-extractable nanocomposite, is created by incorporating a photodegradable block with a solvent-extractable mesogen (m) into an accepting block, resulting in a new hollow gyroid (HG) with the largely increased surface-to-volume ratio and porosity of 77 vol%. The lightweight HG exhibits a low refractive index of 1.11 and a very high specific reduced modulus, almost two times that of the typical negative gyroid (porosity≈53%) and three times that of the positive gyroid (porosity≈24%). This novel concept can significantly extend the DG phase window of block copolymers and the corresponding surface-to-volume ratio, being applicable for nanotemplate-synthesized nanomaterials with a great gain of mechanical, catalytic, and optoelectronic properties.

Stability and convergence of relaxed scalar auxiliary variable schemes for Cahn–Hilliard systems with bounded mass source

Abstract The scalar auxiliary variable (SAV) approach of Shen et al. (2018), which presents a novel way to discretize a large class of gradient flows, has been extended and improved by many authors for general dissipative systems. In this work we consider a Cahn–Hilliard system with mass source that, for image processing and biological applications, may not admit a dissipative structure involving the Ginzburg–Landau energy. Hence, compared to previous works, the stability of SAV-discrete solutions for such systems is not immediate. We establish, with a bounded mass source, stability and convergence of time discrete solutions for a first-order relaxed SAV scheme in the sense of Jiang et al. (2022), and apply our ideas to Cahn–Hilliard systems with mass source appearing in diblock co-polymer phase separation, tumor growth, image inpainting, and segmentation.

Some problem questions in studying the properties of dynamically vulcanized polymer systems based on ethylene/1-hexene copolymer and nitrile butadiene rubber

The article presents the results of a study of the influence of the type and concentration of nitrile butadiene rubber on the main physical and mechanical properties of polymer compositions based on compatibilized ethylene/1-hexene copolymer (EHC*). SKN-18, SKN-26, and SKN-40 were used as nitrile butadiene rubber. The compatibilizer – polyethylene-graft-methacrylic acid was used to improve the compatibility of the mixed components of the mixture. At the first stage, the task of the study was to investigate the effect of the concentration of the considered nitrile rubbers on such properties of the compositions as yield strength, tensile strength, elongation at break, flexural strength, melt flow rate and heat resistance. It was found that, regardless of the type of used nitrile butadiene rubber, with an increase in its content in the composition of the ethylene/1-hexene copolymer, a regular decrease in strength parameters, heat resistance, and melt fluidity is observed. It is shown that with the loading of 30 wt% SKN-18 or 40 wt% SKN-26 and SKN-40 into the composition of the ethylene/1-hexene copolymer phase inversion occurs in the composite materials, according to which the dispersed phase becomes a dispersed medium. The thermomechanical properties of the considered samples were studied. It was found that in those samples in which phase inversion occurred, a region of a highly elastic plateau is formed, which increases with an increase in the content of the rubber component. This area indicates the formation of elastomer with rubber properties. The regularities of crystallization of the compositions depending on the content of the amorphous component were studied by the method of stepwise dilatometry. The mechanism of crystal formation was studied depending on the content of the amorphous component. The influence of the crosslinking agent concentration – dicumyl peroxide on the main properties of dynamically vulcanized elastomers has been studied.

Reexamine the emergence and stability of the square cylinder phase in block copolymers.

Recently, a few AB-type multiblock copolymers have been successfully designed to form stable square cylinder phase based on self-consistent field theory (SCFT) calculations. The previous works only identify the stability region of the square phase but not analyzing its stability, which is closely related to the free-energy landscape. In this work, we have reexamined the stability of the square phase in $\mathrm{B_1 A_1 B_2 A_2 B_3}$ linear pentablock and $\mathrm{(B_1AB_2)_5}$ star triblock copolymers by drawing the free-energy landscape with respect to the two dimensions of a rectangular unit cell. Our results demonstrate that the square phase continuously transfers to the rectangular phase as the degree of packing frustration is gradually released. Moreover, the prolate contour lines of the free-energy landscape indicate the weak stability of the square phase in the $\mathrm{B_1 A_1 B_2 A_2 B_3}$ copolymer. In contrast, the stability of the square phase is notably improved in the $\mathrm{(B_1AB_2)_5}$ copolymer due to its enhanced concentration of bridging configurations. Our work sheds light on the understanding of the stability of the square cylinder phase in block copolymers. Accordingly, we propose some possible strategies for further designing new AB-type block copolymer systems to obtain more stable square phase.

Toughening of alicyclic epoxy resin by in situ polymerization of modifier vinyl monomers using alkylborane as a radical initiator

AbstractIn this study, we attempted to improve the toughness of alicyclic epoxy cured resin using a vinyl polymer as a modifier which was generated with alkylborane as a radical initiator in parallel with the curing of the resin. Alkylborane has the ability to initiate radical polymerization around room temperature in the presence of oxygen, and the use of diethylmethoxyborane (DEMB) instead of a conventional peroxide radical initiator (DBPC) was found to allow copolymerization of styrene (St) and N‐phenylmaleimide (NPMI) in an alicyclic epoxy resin in the early stage of the multistep curing. As a result, only when DEMB was used as an initiator, a cured product with a phase‐separated structure at which ca. 50–100 nm St/NPMI copolymer phases were dispersed was obtained. The fracture toughness (KIC) of the modified cured resin with DEMB was 0.77 MN/m3/2, which was 30% higher than that of the modified resin with DBPC. Furthermore, the glass transition temperature of the modified cured resin with DEMB reached 247°C, which was 87 and 63°C higher than the unmodified rein and the modified resin with DBPC, respectively, since DEMB acted as a Lewis acid to promote cationic polymerization of the alicyclic epoxy resin.

Influence of additives on a Pluronic-based cubic phase

In the present work, the cubic phase of the triblock copolymer with the trade name Pluronic PE6800 is studied with and without additives. The incorporated additives are ionic linear alkylbenzosulfonate, LAS, non-ionic 1,2-propylene glycol and maltose. Small-angle X-ray scattering (SAXS) experiments are performed to characterize the cubic lattice constant and the temperature stability of the cubic phase. In addition, rheology is exploited to study the different samples. Frequency sweeps are performed to investigate the flow properties and stability of the samples at ambient temperature.

Compatibilizing and toughening blends of recycled acrylonitrile-butadiene-styrene/recycled high impact polystyrene blends via styrene-butadiene-glycidyl methacrylate terpolymer

To increase the effectiveness of recovered acrylonitrile-butadiene-styrene (rABS) and recycled high impact polystyrene (rHIPS), styrene-butadiene-glycidyl methacrylate (SBG) was incorporated to the rABS/rHIPS system by melt blending for the first time. Multiple epoxy groups in SBG can combine with the butadiene ageing groups in rABS/rHIPS to generate ester groups, repairing the broken molecular chains, improving the compatibility between the two phases, and enhancing the mechanical properties of the blends. The findings demonstrated that adding SBG greatly increased the blends' molecular weight, impact strength, tensile strength, flexural strength, storage modulus, loss modulus, and complex viscosity. When SBG content was 8 wt%, the notch impact strength of the blends reached 8.84 kJ/m2, which was 108% higher than that of rABS/rHIPS. In addition, the interface between polybutadiene (PB) phase and styrene-acrylonitrile copolymer (SAN) phase became more blurred, and the compatibility of the two phases was improved, which enabled the high-value recovery of rABS/rHIPS.

Accessing the Frank–Kasper σ Phase of Block Copolymer with Small Conformational Asymmetry via Selective Solvent Solubilization in the Micellar Corona

Large conformational asymmetry has been considered as an essential ingredient for accessing the Frank–Kasper (FK) phase in a neat block copolymer (bcp) melt. This criterion can be relaxed by blending the bcp with the corresponding homopolymer, where the homopolymer is incorporated into the micellar core in the dry-brush regime. While the solubilization of the homopolymer in the micellar corona in the wet-brush regime has also been demonstrated to yield the FK σ phase in a bcp system bearing a large conformational asymmetry parameter (ε > 1.5), we demonstrate here that this is also true for the system with small conformational asymmetry. A cylinder-forming poly(ethylene oxide)-block-poly(1,2-butadiene) (PEO-b-PB) with a ε of 1.2 was blended with a small amount of selective solvent, which was either a PB homopolymer (h-PB) or dodecylbenzene (DB) to yield the mixtures forming the spherical micelles composed of the PEO core and the corona containing the wet-brush mixture of PB blocks and the selective solvents. Both types of mixtures were found to form the FK σ phase in a narrow region near the cylinder-sphere phase boundary. We argue that, under a given volume fraction (fPEO) and size of the PEO core, the shorter PB coronal blocks in the bcp/solvent mixtures are more strained than the longer PB blocks in the corresponding neat diblock; therefore, the spherical phase is accessed at a higher PEO core fraction to alleviate the excess entropic penalty. The formation of a larger core (at a higher fPEO) and the stronger propensity to alleviate the packing frustration of the more strained PB coronal blocks in the bcp/selective solvent mixture creates an effect equivalent to increasing the conformational asymmetry and hence promotes the core to adopt the polyhedral geometry templated by the Voronoi cells of the lattice. The micelles approaching the polyhedral interface limit then favor the packing in the FK σ phase to minimize the total free energy.

Phase Control of Colloid-like Block Copolymer Micelles by Tuning Size Distribution via Thermal Processing

The formation of a Frank–Kasper (FK) phase in a one-component block copolymer (bcp) has been attributed to the sufficiently large conformational asymmetry parameter that leads to the deformation of the micellar core into the polyhedral shape templated by the Voronoi cells for relieving the packing frustration of the coronal blocks. Here we present the insight into the evolution of body-centered cubic (BCC) and Laves C14 phases from the corresponding metastable liquidlike packing (LLP) phases in a conformationally symmetric poly(2-vinylpyridine)-block-poly(dimethylsiloxane) (P2VP-b-PDMS) forming the colloid-like micelle with a hard P2VP core and a soft PDMS corona at the temperature of micelle ordering (Tgcorona < Ta < Tgcore). Different thermal processing conditions were applied to produce four distinct types LLP phase characterized by different average micelle size and size dispersity. The LLP phase was found to transform to BCC, C14 and a reorganized LLP phase with increasing polydispersity of particle size, showing the existence of a proper range of size dispersity for the formation of the Laves phase. The real-space analysis of the local environments of the particles revealed that the C14 phase can accommodate the particles with a broader range of interparticle distance and a less uniform local environment, such that the PDMS coronal blocks of the micelles with greater size dispersity suffered a lower degree of packing frustration when they organized into a C14 lattice. In view of the colloid-like nature of the micelle, a size fractionation process found in the crystallization of polydisperse colloidal particles was proposed as the mechanism for directing the effective development of C14 phase from the LLP phase. Due to the metastable nature of the ordered phases, their order–disorder transition temperatures were found to depend strongly on the structures of the LLP phases from which they developed and a strong memory effect underlying the phase transitions was identified.

Nematic Ordering of Anisotropic Nanoparticles in Block Copolymers

AbstractBlock copolymer melts have been previously used to control the position and alignment of anisotropic nanoparticles. In this work, 2D and 3D mesoscopic simulations are used to explore the phase behavior of block copolymer/nanoparticle systems. The method combines a time‐dependent Ginzburg‐Landau for the polymer and Brownian dynamics for the anisotropic nanoparticles. Rhomboidal and spheroidal shaped particles are simulated in two and three dimensions, respectively. It is found that the nanoparticle nematic order aligned by the block copolymer domains enhances the lamellar phase of the block copolymer, due to an anisotropy‐driven phase transition. Additionally, anisotropic nanoparticles within circular‐forming block copolymer leads to a competition between the nematic colloidal ordering and the hexagonally ordered mesophase. At large concentrations, the nematic order dominates, deforming the block copolymer mesophase.

Random Forest Predictor for Diblock Copolymer Phase Behavior.

Physics-based models are the primary approach for modeling the phase behavior of block copolymers. However, the successful use of self-consistent field theory (SCFT) for designing new materials relies on the correct chemistry- and temperature-dependent Flory-Huggins interaction parameter χAB that quantifies the incompatibility between the two blocks A and B as well as accurate estimation of the ratio of Kuhn lengths (bA/bB) and block densities. This work uses machine learning to model the phase behavior of AB diblock copolymers by using the chemical identities of blocks directly, obviating the need for measurement of χAB and bA/bB. The random forest approach employed predicts the phase behavior with almost 90% accuracy after training on a data set of 4768 data points, almost twice the accuracy obtained using SCFT employing χAB from group contribution theory. The machine-learning model is notably sensitive toward the uncertainty in measuring molecular parameters; however, its accuracy still remains at least 60% even for highly uncertain experimental measurements. Accuracy is substantially reduced when extrapolating to chemistries outside the training set. This work demonstrates that a random forest phase predictor performs remarkably well in many scenarios, providing an opportunity to predict self-assembly without measurement of molecular parameters.

Valorization of Recycled Tire Rubber for 3D Printing of ABS- and TPO-Based Composites.

Vulcanized and devulcanized ground tire rubber microparticles have been used as a minor phase in acrylonitrile butadiene styrene copolymer (ABS) and thermoplastic polyolefins (TPO) for the development of materials with desired functionalities by 3D printing. These polymers have been selected because they (i) present part of the plastic waste generated by the automotive industry and (ii) have totally different properties (ABS for its stiffness and robustness and TPO for its softness and ductility). The study aims to improve the circular economy of the automotive industry by proposing a promising route for recycling the generated tire rubber waste. In this respect, emergent technology for plastic processing such as 3D printing is used, as part of the additive manufacturing technologies for the prolongated end of life of recycled plastics originated from automotive waste such as ABS and TPO. The obtained results revealed that (i) the composites are suitable for successful filament production with desired composition and diameter required for successful 3D printing by fused deposition modeling, and that (ii) the optimization of the composition of the blends allows the production of materials with interesting mechanical performances. Indeed, some of the investigated ABS-recycled rubber tire blends exhibit high impact properties as TPO-based composites do, which in addition exhibits elongation at break higher than 500% and good compression properties, accompanied with good shape recovery ratio after compression.