Precise Polyethylene Research Articles

Ternary Metals in Phase Change Polymers for Efficient Thermal Management of Electronics

AbstractPhase change materials (PCMs) are paramount for the thermal management of electronics. However, the present PCMs encounter a dilemma in balancing the thermal conductivity and effective latent heat, compromising the heat dissipation function of PCMs for electronics. This work successfully integrates ternary metals and polymer science to design novel PCMs composed of a ternary metal (TM, Ga0.20In0.46Sn0.34) with precise composition and polyethylene glycol (PEG) by physical blending. Due to the introduction of PEG with high melting enthalpy, the ternary metal in PEG (TM@PEG) simultaneously has high thermal conductivity (7.086 W m−1 K−1), desirable effective latent heat (143.6 J cm−3), suitable phase change range, and durability. During thermal management, the thermal conductivity and effective latent heat of TM@PEG contribute to suppressing the working temperature and delaying the temperature rise rate of electronics, respectively. Hence, the TM@PEG effectively behaves as the thermally conductive grease for LEDs and CPU to control the working temperature of electronics in a reasonable range. This work offers a new perspective for TM applied in thermal management.

Double Gyroid Morphologies in Precise Ion-Containing Multiblock Copolymers Synthesized via Step-Growth Polymerization.

The double gyroid structure was first reported in diblock copolymers about 30 years ago, and the complexity of this morphology relative to the other ordered morphologies in block copolymers continues to fascinate the soft matter community. The double gyroid microphase-separated morphology has co-continuous domains of both species, and the minority phase is subdivided into two interpenetrating network structures. In addition to diblock copolymers, this structure has been reported in similar systems including diblock copolymers blended with one or two homopolymers and ABA-type triblock copolymers. Given the narrow composition region over which the double gyroid structure is typically observed (∼3 vol %), anionic polymerization has dominated the synthesis of block copolymers to control their composition and molecular weight. This perspective will highlight recent studies that (1) employ an alternative polymerization method to make block copolymers and (2) report double gyroid structures with lattice parameters below 10 nm. Specifically, step-growth polymerization linked precise polyethylene blocks and short sulfonate-containing blocks to form strictly alternating multiblock copolymers, and these copolymers produce the double gyroid structure over a dramatically wider composition range (>14 vol %). These new (AB)n multiblock copolymers self-assemble into the double gyroid structure by having exceptional control over the polymer architecture and large interaction parameters between the blocks. This perspective proposes criteria for a broader and synthetically more accessible range of polymers that self-assemble into double gyroids and other ordered structures, so that these remarkable structures can be employed to solve a variety of technological challenges.

Fluorine-Free Precise Polymer Electrolyte for Efficient Proton Transport: Experiments and Simulations

Designing polymers with controlled nanoscale morphologies and scalable synthesis is of great interest in the development of fluorine-free materials for proton-exchange membranes in fuel cells. This study focuses on a precision polyethylene with phenylsulfonic acid branches at every fifth carbon, p5PhSA, with a high ion-exchange capacity (4.2 mmol/g). The polymers self-assemble into hydrophilic and hydrophobic co-continuous nanoscale domains. In the hydrated state, the hydrophilic domain, composed of polar sulfonic acid moieties and water, serves as a pathway for efficient mesoscopic proton conductivity. The morphology and proton transport of p5PhSA are evaluated under hydrated conditions using in situ X-ray scattering and electrochemical impedance spectroscopy techniques. At 40 °C and 95% relative humidity, the proton conductivity of p5PhSA is 0.28 S/cm, which is four times greater than Nafion 117 under the same conditions. Atomistic molecular dynamics (MD) simulations are also used to elucidate the interplay between the structure and the water dynamics. The MD simulations show strong nanophase separation between the percolated hydrophilic and hydrophobic domains over a wide range of water contents. The percolated hydrophilic nanoscale domain facilitates the rapid proton transport in p5PhSA and demonstrates the potential of precise hydrocarbon-based polymers as processible and effective proton-exchange membranes.

Competition of Lamellar Crystal and Smectic Liquid Crystal in Precise Polyethylene Derivative Bearing Mesogenic Side-Chains

For side-chain liquid-crystalline polymers (SCLCPs) bearing calamitic mesogens, nematic and typical smectic (Sm) phases are expected. Here, using a precise polyethylene derivative with the biphenyl...

Polymer defect engineering – conductive 2D organic platelets from precise thiophene-doped polyethylene

Synthesis and crystallization of polyethylene with precisely positioned thiophene groups were used to produce polymer crystals with a conductive surface.

Vitamin C Loaded Polyethylene: Synthesis and Properties of Precise Polyethylene with Vitamin C Defects via Acyclic Diene Metathesis Polycondensation.

A polyethylene-like polymer with an in-chain vitamin C group was synthesized by olefin metathesis polymerization. Here, we describe both the synthesis and a comprehensive physical characterization. Because of the olefin metathesis synthesis, the vitamin C groups are equidistantly arranged in the polyethylene (PE) main chain. Their separation was adjusted to 20 CH2 units. After hydrogenation, a semicrystalline polymer is obtained that is soluble in polar solvents. Because of its size and steric effect, the vitamin C acts as a chain defect, which is expelled from the crystal lattice, yielding a lamellar crystal with a homogeneous thickness corresponding to the interdefect distance. The physical properties were examined by various methods including differential scanning calorimetry, X-ray scattering, and transmission electron microscopy. We show that vitamin C retains its radical scavenger properties despite being incorporated into a polyethylene chain. Furthermore, we demonstrate that it is degrading in alkaline conditions. To complete its suitability as a biocompatible material, cytotoxicity and cell uptake experiments were performed. We show that the polymer is nontoxic and that it is taken up in nanoparticular form via endocytosis processes into the cytoplasm of cells.

Precise polyethylene derivatives bearing mesogenic side-chains: delicate self-assembly depending on graft density

Precise polyethylene derivatives bearing mesogenic side-chains demonstrate a sophisticated side-chain spacing effect on the local coupling and spatial arrangement of the backbone and side-chains.

Chain and Ion Dynamics in Precise Polyethylene Ionomers

We analyze the dynamics from microsecond-long, atomistic molecular dynamics (MD) simulations of a series of precise poly(ethylene-co-acrylic acid) ionomers neutralized with lithium, with three diff...

Anisotropic Extended-Chain Polymer Nanocrystals

As a concept for distinct shape polymer nanoparticles, nanoscale single crystals composed of a crystallizable chain with lyophilic end groups are explored. This differs from much studied block copolymer nanoparticles and nanostructures, in which the second (noncrystalline) blocks’ spacial demand impacts the overall structure and blurs the cores’ anisotropic shape. For precise C48 polyethylene telechelics X(CH2)46X (X = COO–M+ or CH2SO3–M+, with M+ = Na+, K+, or Cs+) as a relevant model system, a combined experimental and atomistic-level simulation study reveals them to form extended-chain, single-crystalline nanoparticles sandwiched by a layer of head groups. Their microscopic structure, order, and the resulting overall shape are decisively impacted by the mutual repulsion of the head groups, itself determined by the degree of ion pairing with the counterions and the size of the head groups. This leads to the bending of the chains at the lateral side of the crystal, preventing the particles from agglomera...

Proton Transport within Acid Aggregates in a Hydrated Precise Sulfophenylated Polyethylene

Hydrated acid aggregates in a precise sulfophenylated polyethylene exhibit high proton conductivity. This study focuses on a new precise polymer synthesized by ring-opening polymerization, p5PhSA, that has a polyethylene backbone with a sulfonated phenyl group pendant on every 5th carbon. The structure of p5PhSA is characterized with X-ray scattering and the proton conductivity is measured by electrical impedance spectroscopy. Experiments are performed as a function of relative humidity and temperature. Water uptake in p5PhSA is determined by sorption measurements as a function of humidity. Atomistic molecular dynamics simulations are used to elucidate the structure of the acid aggregates in the amorphous polymer matrix and are directly compared to absolute X-ray scattering data. At 40°C and 90% relative humidity, the proton conductivity of p5PhSA is 0.23 S/cm, exceeding that of Nafion at the same conditions. At room temperature, the interaggregate distance nearly doubles from 1.8 nm at 0% relative humidity to 3.4 nm at 100% relative humidity. The swelling of these acid aggregates with water is reversible and facilitates the proton transport through p5PhSA. Figure 1

Comparing Morphological Evolution during Tensile Deformation of Two Precise Polyethylenes via 2D Fitting of in Situ X-ray Scattering

Some types of precise polyethylenes, or linear polyethylenes containing precisely periodic functional groups, exhibit significant strain hardening under tensile deformation. Here we perform in situ X-ray scattering during tensile deformation of two precise polyethylenes: one with pendant carboxylic acid groups every 21st carbon (p21AA) and another with pendant imidazolium bromide groups every 15th carbon (p15ImBr). p21AA exhibits significant strain hardening and its layered structure orients with the layer normal along the tensile axis, while p15ImBr does not exhibit strain hardening and its layer normal orients perpendicular to the tensile axis. Quantitative evaluation of the 2D fiber patterns shows that p21AA undergoes a morphological transition, from a semicrystalline structure to a nanofibrillar structure, while the morphology of p15ImBr reorients and the chain folding structure is preserved. This suggests that fibrillization plays an important role in the strain hardening mechanism.

Precision Polyelectrolytes with Phenylsulfonic Acid Branches at Every Five Carbons.

A precision polyethylene containing phenyl branches at every fifth carbon (p5Ph) is nearly quantitatively functionalized (≈95%) with sulfonic acid groups on the para-position of each phenyl branch (p5PhS-H). Unlike polystyrene sulfonate (PSS), p5PhS-H has a glass transition temperature (Tg = 109 °C) well below its thermal decomposition temperature (Td ≈ 200 °C), making this new material capable of thermal processing into molds and films at temperatures between these thermal limits. Neutralization of the sulfonic acid groups with varying counter cations (Li+ , Na+ , Cs+ ) produces a new class of precision polyelectrolytes. Neutralization and increasing size of the counter cation improves the thermal decomposition temperature (Td ) to over 400 °C for the Cs+ form. Neutralization causes Tg to increase above Td for the Li+ and Na+ form. The Cs+ form is found to have an accessible Tg = 294 °C. Further investigations of water absorption and the polyelectrolyte effect of these systems are discussed.

Solution-grown crystals of precise acid- and ion-containing polyethylenes

Crystals of precise acid- and ion-containing polyethylenes were prepared from solution. While large pendant groups on polyethylene backbones are typically excluded from the crystalline domain, the precisely-placed acid and ionic functional groups are accommodated into the solution-grown crystals. Polyethylene containing carboxylic acid pendant groups on every 21st carbon atom (p21AA) grows into rectangular shaped crystals with an average thickness of 9 nm, which is 3–4 times the all-trans chain length between the functional groups. This thickness indicates that the carboxylic acid groups are incorporated within the crystals. Electron diffraction images and Raman spectra indicate that p21AA backbones are hexagonally packed with more gauche chain conformations than the polyethylene orthorhombic phase. The precise polyethylene containing geminal carboxylic acid groups placed every 21 carbon atoms (p21gAA) forms irregular-shaped crystals with an average thickness 8 nm. Similar to p21AA, p21gAA incorporates the geminal acid groups into its solution-grown crystals. Surprisingly, the polymer with imidazolium bromide groups on every 21st carbon (p21ImBr) produces remarkably large crystals with thicknesses of 200–900 nm, and widths of 6–12 μm. Finally, we propose a multi-layer stack of adjacent reentry structures that is consistent with the incorporation of large functional groups into the solution-growth crystals of these precise polyethylenes. Interestingly, this stacked structure is distinct from our recent results in melt-crystallized p21AA, where the layers are nearly transverse to the lamellae.

Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene

AbstractStarting from common monounsaturated fatty acids, a strategy is revealed that provides ultra‐long aliphatic α,ω‐difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω‐dicarboxylic fatty acid self‐metathesis products is shifted selectively to the statistically much‐disfavored α,β‐position in a catalytic dynamic isomerizing crystallization approach. “Chain doubling” by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co‐reagents, yields ultra‐long‐chain α,ω‐difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm=120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self‐assembly to polyethylene‐like single crystals.

Chain Multiplication of Fatty Acids to Precise Telechelic Polyethylene.

Starting from common monounsaturated fatty acids, a strategy is revealed that provides ultra-long aliphatic α,ω-difunctional building blocks by a sequence of two scalable catalytic steps that virtually double the chain length of the starting materials. The central double bond of the α,ω-dicarboxylic fatty acid self-metathesis products is shifted selectively to the statistically much-disfavored α,β-position in a catalytic dynamic isomerizing crystallization approach. "Chain doubling" by a subsequent catalytic olefin metathesis step, which overcomes the low reactivity of this substrates by using waste internal olefins as recyclable co-reagents, yields ultra-long-chain α,ω-difunctional building blocks of a precise chain length, as demonstrated up to a C48 chain. The unique nature of these structures is reflected by unrivaled melting points (Tm =120 °C) of aliphatic polyesters generated from these telechelic monomers, and by their self-assembly to polyethylene-like single crystals.

Chain Folding Produces a Multilayered Morphology in a Precise Polymer: Simulations and Experiments.

Precise control over polymer architecture unlocks the potential for engineered self-assembled crystal structures with useful features on the nanometer length scale. Here we elucidate the structure of the ordered phase of a semicrystalline, functional polyethylene having a precise linear architecture, namely, pendant carboxylic acid groups precisely every 21st backbone carbon atom. By comparing the results of atomistic molecular dynamics simulations with experimental X-ray scattering and Raman spectroscopy data, we find that the polymer chains are folded in a hairpin manner near each carboxylic acid group, giving rise to multiple embedded layers of functional groups that have an interlayer distance of 2.5 nm. This is in contrast to other precise polyethylenes, where the chains are mostly trans within the crystals. Such layers could act as two-dimensional pathways for ionic or molecular transport given an appropriate choice of functional group.

Heterogeneous Chain Dynamics and Aggregate Lifetimes in Precise Acid-Containing Polyethylenes: Experiments and Simulations

Melt state dynamics for a series of strictly linear polyethylenes with precisely spaced associating functional groups were investigated. The periodic pendant acrylic acid groups form hydrogen-bonded acid aggregates within the polyethylene (PE) matrix. The dynamics of these nanoscale heterogeneous morphologies were investigated from picosecond to nanosecond timescales by both quasi-elastic neutron scattering (QENS) measurements and fully atomistic molecular dynamics (MD) simulations. Two dynamic processes were observed. The faster dynamic processes which occur at the picosecond timescales are compositionally insensitive and indicative of spatially restricted local motions. The slower dynamic processes are highly composition dependent and indicate the structural relaxation of the polymer backbone. Higher acid contents, or shorter PE spacers between pendant acid groups, slow the structural relaxation timescale and increase the stretching parameter (β) of the structural relaxation. Additionally, the dynamics ...

Role of Periodicity and Acid Chemistry on the Morphological Evolution and Strength in Precise Polyethylenes

We report the morphology evolution under tensile deformation for strictly linear polyethylenes with associating functional groups. In situ X-ray scattering measurements during elongation reveal that periodic acid group placement along the backbone is required to form hierarchical layered morphologies that lead to strain hardening. This phenomenon was observed in both semicrystalline and amorphous precise acid polyethylenes with acrylic, geminal acrylic, and phosphonic acids. Polymers with nonperiodic (pseudorandom) acid placement fail to form layered morphologies and instead retain a liquidlike distribution of acid aggregates. Acid chemistry and acid concentration influence morphological evolution in both periodic and nonperiodic polymers predominately through the modification of Tg and percent crystallinity, which subsequently impact the mechanical properties. Our results indicate that hierarchical acid-rich layered structures, commensurate with improved mechanical properties, form in polymers with stric...

Epitaxial crystallization of precisely fluorine substituted polyethylene induced by carbon nanotube and reduced graphene oxide

Crystallization of well-defined precision polyethylene with fluorine substituent on every 21st backbone carbon (PE21F) induced by low-dimensional carbonaceous nanofillers (carbon nanotube (CNT) and reduced graphene oxide (RGO)) via solution crystallization and supercritical CO2 assisted solution crystallization were investigated. Transmission electron microscopy was used to investigate the morphology of carbonaceous nanofiller-induced PE21F crystals. The kebab-like and rod-like crystals formed on the CNT and RGO, respectively. Selected area electron diffraction (SAED) pattern revealed that the c-axis of polymer chain is parallel to the surface of the RGO. Differential scanning calorimetry (DSC) revealed the melting temperatures (Tm) of PE21F lamellae nanocomposites increased with crystallization temperature increasing. The X-ray diffraction (XRD) results showed that the incorporation of nanofillers did not influence the crystal structure of PE21F. The chemical composition of the PE21F nanocomposites measured by X-ray photoelectron spectra (XPS) confirmed substituent F as a defect of chain was accommodated into the crystal lattice.

Precision Polymers through ADMET Polymerization

Acyclic diene metathesis (ADMET) polymerization is a unique strategy for achieving polymers with precise control over the primary structure. This precision is obtained by specific monomer design and carefully controlled polymerization conditions. Over time, this approach has produced an array of sophisticated architectures ranging from precise polyethylenes, to hyperbranched polymers, to rotaxanes. image