Rigid-chain Polymers Research Articles

Polymer microparticles with ultralong room-temperature phosphorescence for visual and quantitative detection of oxygen through phosphorescence image and lifetime analysis

Room-temperature phosphorescence (RTP) materials exhibiting long emission lifetimes have gained increasing attention owing to their potential applications in encryption, anti-counterfeiting, and sensing. However, most polymers exhibit a short RTP lifetime (<1 s) because of their unstable triplet excitons. Herein, a new strategy of polymer chain stabilized phosphorescence (PCSP), which yields a new kind of RTP polymers with an ultralong lifetime and a sensitive oxygen response, has been reported. The rigid polymer chains of poly(methyl mathacrylate) (PMMA) immobilize the emitter molecules through multiple interactions between them, giving rise to efficient RTP. Meanwhile, the loosely-packed amorphous polymer chains allow oxygen to diffuse inside, endowing the doped polymers with oxygen sensitivity. Flexible and transparent polymer films exhibited an impressive ultralong RTP lifetime of 2.57 s at room temperature in vacuum, which was among the best performance of PMMA. Intriguingly, their RTP was rapidly quenched in the presence of oxygen. Furthermore, RTP microparticles with a diameter of 1.63 μm were synthesized using in situ dispersion polymerization technique. Finally, oxygen sensors for quick, visual, and quantitative oxygen detection were developed based on the RTP microparticles through phosphorescence lifetime and image analysis. With distinctive advantages such as an ultralong lifetime, oxygen sensitivity, ease of fabrication, and cost-effectiveness, PCSP opens a new avenue to sensitive materials for oxygen detection.

Recent Progress of Organic Room‐Temperature Phosphorescent Hydrogels

Organic room‐temperature phosphorescent (RTP) materials have garnered significant attention owing to their unique photophysical properties. Traditionally, the stabilization of triplet excitons in RTP materials necessitates a crystalline matrix or rigid polymer chain, which limits their use in flexible materials. In contrast, hydrogels offer biocompatibility, softness, and ease of processing. Therefore, incorporating phosphorescent molecules into hydrogel systems can expand the application potential of RTP materials. This concept summarizes recent advancements in RTP hydrogels, emphasizing their synthetic strategies and diverse applications.

A polyurea capturing both high strength and rapid self-healing tailored for intelligent barrier anti-corrosion system

The long-term repair of organic coatings in underwater environments is hindered by microcracks and their poor healing performance. In this study, a high-strength and rapidly self-healing polyurea (PU3) coating that combines asymmetric dense stacking of supramolecular units with mismatched rigid and flexible polymer chains was developed. By exploiting the interaction between a 2D sheet-like Ti3C2TX MXene and finely tailored hydrogen-bonded structures of PU3, a smart biomimetic anticorrosion composite coating (PU3-1.0 wt% MXene) was produced. This coating achieved rapid (15 s), specific, and repeatable in situ repair underwater when exposed to near infrared laser light. Electrochemical tests confirmed its excellent anticorrosion capability.

Incorporating hydrogen bonding networks in microporous polymer membranes for high-flux hydrocarbon separation

Polymer membranes have been most commonly utilized in gas separations, while they often suffer from the trade-off between membrane permeability and selectivity, which arises from the inherent coupling between polymer chain rigidity and interchain spacing. Here, we propose a hydrogen bonding network strategy, where hydrogen bonding acceptors are incorporated into amidoxime-functionalized polymer of intrinsic microporosity (AO-PIM) membranes to in situ construct hydrogen bonding networks with amidoxime groups, and to modulate the interchain spacing/micropore structure in AO-PIM. Especially, 2,2′-bipyridine endows AO-PIM membranes with appropriate match between polymer chain rigidity and interchain spacing, leading to dramatically enhanced C3H6 permeability of 262 Barrer, 2.9 times higher than AO-PIM membranes, with a C3H6/C3H8 selectivity of 24 under mixed-gas tests, surpassing all the reported polymer membranes and most mixed matrix membranes. We envision this scalable, generic hydrogen bonding network strategy opens an alternative avenue for polymer membranes to break the trade-off effect.

Thermoplastic polyimide with low dielectric properties enabled by the 2,2′‐spirobifluorene group

AbstractThermoplastic polyimides (TPIs) have melt‐processability and adhesive ability, besides the intrinsic advantages of polyimides. To meet the requirements of applications in high‐frequency communication, TPIs with low dielectric constant (Dk)/dielectric loss factor (Df) at high frequency are also desirable. Enhancing the rigidity of polymer chains and simultaneously intermolecular interaction are effective ways to ensure low Dk/Df, which also benefit to heat resistance. However, it is not conducive to thermoplasticity, due to limited movement of polymer chains. To balance the trade‐off between them, we introduce noncoplanar 2,2′‐spirobifluorene groups to modify the rigidity of polymer chains and regulate the twist between electron‐donor moieties (diamine units) and electron‐acceptor moieties (dianhydride units). It leads to rigid polymer chains, which benefits to good heat resistance and dielectric properties. Meanwhile, the resultant irregular chain structure is difficult to crystallize, which results in thermoplasticity.

Ionic Cross-Linked MOF-Polymer Mixed-Matrix Membranes for Suppressing Interfacial Defects and Plasticization Behavior.

To address the plasticization phenomenon and MOF-polymer interfacial defects, we report the synthesis of ionic cross-linked MOF MMMs from a dual brominated polymer and MOF components by using N,N'-dimethylpiperazine as the cross-linker. We synthesized brominated MIL-101(Cr) nanoparticles by using mixed linkers and prepared brominated polyimide (6FDA-DAM-Br) to form ionic cross-linked MMMs. The gas permeation properties of the polyimide, ionic cross-linked MOF-polymer MMMs, and non-cross-linked MOF-polymer MMMs with various MOF weight loadings were investigated systematically to effectively understand the effects of MOF weight loading and ionic cross-linking. The ionic cross-linked 40 wt % MOF-polymer MMM exhibited significantly enhanced gas permeability with an H2 permeability of 1640 Barrer and CO2 permeability of 1981 Barrer and slightly decreased H2/CH4, H2/N2, CO2/CH4 and CO2/N2 selectivities of 16.9, 15.4, 20.5, and 18.6, respectively. The H2 and CO2 permeabilities are approximately 2-3 fold higher than those of the pure polyimide (6FDA-DAM) membrane. Moreover, the ionic cross-linked 40 wt % MOF-polymer MMM exhibited significantly increased resistance to plasticization. This is because the brominated MOF incorporation boosted molecular transport and polymer chain rigidity, and ionic cross-linking further reduced the number of interfacial defects and polymer chain mobility.

Low-Temperature Alignment of Conjugated Polymers by Plasticizer-Aided Physical Rubbing.

Rubbing-induced alignment of conjugated polymers issystematically investigated in terms of intra- and inter-molecular interaction. Various polymer films with a broad range of polymer chain rigidity arerubbed, and the degree of polymer chain alignment isquantitatively characterized. The rubbing technique effectively aligns crystalline domains in conjugated polymer films when the temperature approaches the critical rubbing temperature ( ), at which the rearrangement and the slip of polymer chains are possible. A polymer with significant intra-/inter-molecular interactions exhibits higher , though quantitative analysis reveals an intermediately aligned state at temperature Tr ' lower than . This state originates from polymer chain aggregation in an amorphous domain. The intermediately aligned state can be controlled by plasticizer, which enables low-temperature alignment of high-mobility polymer film by reducing Tr ' to near 100 °C, increases the crystallinity, and improves the alignment effect at this state comparable to that of the completely aligned state obtained at extremely high temperatures.

Nanoclusters and sol–gel transition in water solutions of rigid-chain polymers

We describe a mechanism of pre-transition process near the sol-gel transition temperature in the sol-phase of water solutions of rigid-chain polymers. During this process the water boundary layer is disordered, and voids are formed in it. The variation of density of the hydroxypropyl methylcellulose with temperature is measured experimentally for temperatures between 25 and 80 °C. The experiment supports the proposed mechanism.

Decoupling Planarizing and Steric Energetics to Accurately Model the Rigidity of π-Conjugated Polymers.

The π-conjugated backbone of semiconducting polymers gives rise to both their electronic properties and structural rigidity. However, current computational methods for understanding the rigidity of polymer chains fail in one crucial way. Namely, standard torsional scan (TS) methods do not satisfactorily capture the behavior of polymers exhibiting a high degree of steric hindrance. This deficiency in part stems from the method by which torsional scans decouple energy related to electron delocalization from that related to nonbonded interactions. These methods do so by applying classical corrections of the nonbonded energy to the quantum mechanical (QM) torsional profile for polymers that are highly sterically hindered. These large corrections to the energy from nonbonded interactions can substantially skew the calculated QM energies related to torsion, resulting in an inaccurate or imprecise estimation of the rigidity of a polymer. As a consequence, simulations of the morphology of a highly sterically hindered polymer using the TS method can be highly inaccurate. Here, we describe an alternative, generalizable method by which the delocalization energy can be decoupled from the energy associated with nonbonded interactions─the "isolation of delocalization energy" (DE) method. From torsional energy calculations, we find that the relative accuracy of the DE method is similar to the TS method (within 1 kJ/mol) for two model polymers (P3HT, PTB7) when compared to quantum mechanical calculations. However, the DE method significantly increased the relative accuracy for simulations of PNDI-T, a highly sterically hindered polymer (8.16 kJ/mol). Likewise, we show that comparison of the planarization energy (i.e., backbone rigidity) from torsional parameters is significantly more precise for both PTB7 and PNDI-T when using the DE method as opposed to the TS method. These differences affect the simulated morphology, with the DE method predicting a significantly more planar configuration of PNDI-T.

Segregation of fluids with polymer additives at domain interfaces: a dissipative particle dynamics study.

This paper investigates the phase separation kinetics of ternary fluid mixtures composed of a polymeric component (C) and two simple fluids (A and B) using dissipative particle dynamics simulations with a system dimensionality of d = 3. We model the affinities between the components to enable the settling of the polymeric component at the interface of fluids A and B. Thus, the system evolves to form polymer coated morphologies, enabling alteration of the fluids' interfacial properties. This manipulation can be utilized across various disciplines, such as the stabilization of emulsions and foams, rheological control, biomimetic design, and surface modification. We probe the effects of various parameters, such as the polymeric concentration, chain stiffness, and length, on the phase separation kinetics of the system. The simulation results show that changes in the concentration of flexible polymers exhibit perfect dynamic scaling for coated morphologies. The growth rate decreases as the polymeric composition is increased due to reduced surface tension and restricted connectivity between A- and B-rich clusters. Variations in the polymer chain rigidity at fixed composition ratios and degrees of polymerization slow the evolution kinetics of AB fluids marginally, although the effect is more pronounced for perfectly rigid chains. Whereas flexible polymer chain lengths at fixed composition ratios slow down the segregation kinetics of AB fluids slightly, varying the chain lengths of perfectly rigid polymers leads to a significant deviation in the length scale and dynamic scaling for the evolved coated morphologies. The characteristic length scale follows a power-law growth with a growth exponent ϕ that shows a crossover from the viscous to the inertial hydrodynamic regime, where the values of ϕ depend on the constraints imposed on the system.

Durable, Low-Cost, and Efficient Heat Spreader Design from Scrap Aramid Fibers and Hexagonal Boron Nitride

Aramid, chemically known as para phenylene terephthalamide or PPD-T, has been widely used in the reinforcement of telecommunication cables, rubber materials (transmission belts, pneumatic belts), ballistic clothing, and frictional materials primarily due to their high tensile resistance, high elastic modulus, and excellent thermal stability (−80–200 °C). These unique properties of aramid originate from its chemical structure, which consists of relatively rigid polymer chains linked by benzene rings and amide bonds (-CO-NH-). Here, in this work inspired by these properties, a heat spreader called Thermal Interface Material (TIM) is developed by synthesizing a resin from scrap aramid fibers. When hexagonal boron nitride (h-BN) as filler is introduced into the as-synthesized aramid resin to form a thin film of thermal sheet (50 μm), an in-plane thermal conductivity as high as 32.973 W/mK is achieved due to the firmly stacked and symmetric arrangement of the h-BN in the resin matrix. Moreover, the influence of h-BN platelet size is studied by fabricating thermal sheets with three different sizes of h-BN (6–7.5 μm, 15–21 μm, and 30–35 μm) in the aramid resin. The results of the study show that as platelet size increases, thermal conductivity increases significantly. Since the resin reported herein is developed out of scrap aramid fibers, the cost involved in the manufacture of the thermal sheet will be greatly lower. As the thermal sheet is designed with h-BN rather than graphene or carbonaceous materials, this high heat spreading sheet can be employed for 5G antenna modules where properties like a low dielectric constant and high electrical insulation are mandated.

Intrinsic low-dielectric constant and low-dielectric loss aliphatic-aromatic copolyimides: The effect of chemical structure

Low-dielectric polymer materials are becoming essential for 5 G mobile communication to achieve mass transport information without signal loss. Herein, we present an aliphatic–aromatic copolyimide using Priamine 1075 (aliphatic) and m-tolidine (aromatic) as diamines. The branched bulky aliphatic units enlarge the free volume, effectively reducing the dipole moment density, while the aromatic diamine was introduced to prevent polymer chain relaxation under the operating conditions. We observed that there is an optimal composition that regulates the chain movement and density of dipole moments through the control of the polymer chain rigidity and nanostructure. Thus, by tuning the composition, we succeeded in achieving a low-dielectric copolyimide with a dielectric constant ( D k ) of 2.63 and dielectric loss ( D f ) of 0.0017 at 28 GHz. Combining molecular design and composition control, this study suggests a design factor for advanced copolymers for telecommunication applications with fast signal transport speed and minimum signal loss. The optimal molecular design for arresting chain motions achieves the lowest dielectric loss while minimizing the increase in the dielectric constant of copolyimide.

High strength in combination with high toughness in layered intrinsic heterocyclic aramid films via constructing liquid crystal-like structure during gelation self-assembly

The fabrication of high strength and toughness in polymeric materials, especially for rigid-chain polymers, has been a long-term technological challenge in high-performance materials design. In this work, the synthesized soluble poly (benzimidazole-terephthalamide) (PABI) acts as a rigid-chain intrinsic polymer. Then, the coordination effect of the HCl with the benzimidazole unit induces more extended PABI chains assembled into a gel network with a liquid crystal-like structure. Finally, the obtained PABI gel is further compressed into a layered film during solvent evaporation. Scanning electron microscopy images reveal that the resultant films present nacre-like morphologies. X-ray diffraction and polarized light microscopy demonstrate the formation of the liquid crystal-like structure. Owing to the highly oriented layers and the self-reinforcement of fibrils in layers, the strength (511.1 MPa) of PABI films increases by 41.7% through altering the gelation time. Ultimately, it reaches a record-high 708.7 MPa by altering HCl content. Meanwhile, the sliding and plastic deformation of amorphous interconnected layers, tearing of fibrils, crack branching, and crack deflection facilitate stable crack propagation and significantly dissipate the energy. Hence, the toughness (136.7 MJ/m3) of PABI films also increases by 23.7% through altering gelation time and remains at a high level under high HCl content. In addition, the highly oriented layered structure unexpectedly imparts PABI films with a high dielectric strength of 686.6 MV/m. Our findings provide a facile strategy for designing high-performance polymeric materials with high strength, toughness, and even more functionality.

Rigid-interface-locking of ZIF-8 membranes to enable for superior high-pressure propylene/propane separation

ZIF-8 membranes are promising for C3H6/C3H8 separation due to its proper pore size between C3H6 and C3H8. However, challenges from the defective grain-boundary (poor reproducibility), inferior pressure-resistant, and insufficient synthesis parameters regulation hinder its advancement. Herein, we demonstrate an interface engineering method that can simultaneously deal with these two issues by coating a polymeric layer on the surface of ZIF-8 membrane which can seal the grain boundaries and lock the pressure-induced linker rotation. Accordingly, by optimizing the polymer chain rigidity and the corresponding thickness layer, the resultant membrane with locked rigid interface demonstrates desired C3H6 permeance and C3H6/C3H8 separation factor above 45 GPU and 105, respectively, and stabilized performance up to 7 bar. Such performance is superior to most of the recently reported work in the literature. This strategy provides inspiration for considering the polymer chain rigidity regulation in the membrane coating layer and its effect on developing advanced composite membranes for energy-efficient separations.

Relaxation and Amorphous Structure of Polymers Containing Rigid Fumarate Segments.

The physical properties of polymers are significantly affected by relaxation processes. Recently, we reported that poly(diethyl fumarate) (PDEF) shows two thermal anomalies on DSC measurement, despite the fact that it is a homopolymer. We attribute these two relaxations α relaxation and β relaxation, respectively. In this study, we investigate the two relaxations of fumarate-containing polymers by DSC, solid-state NMR, and X-ray scattering. The two relaxations are present even in a copolymer of diethyl fumarate and ethyl acrylate with fumarate segments of 30%. We used poly(methyl methacrylate) (PMMA) as a model polymer for comparison, since there are detailed investigations of its dynamics and physical properties. Solid-state NMR indicates that the very local relaxation of poly(fumarate)s is not significantly different from that of PMMA. The tensile test showed that PDEF is still brittle at above β relaxation temperature and below α relaxation temperature. It was revealed that a structural anisotropy appeared when PDEF was extended at around α relaxation temperature. We discuss the effect of the glassy packing of the rigid polymer chain including the DEF segments on the strong β relaxation behavior. Our data provide insight into the microscopic mechanism of β relaxation of vinyl polymers.

Lattice conformation of theta-curves accompanied with Brunnian property

A theta-curve is an embedding of the Greek letter Θ shaped graph in three-dimensional space. This is a useful physical model for polymer chains since theta-curve motifs are often present in many circular proteins with internal bridges. A Brunnian theta-curve is a nontrivial theta-curve with the property that if we remove any one among three edges, then the remaining knot can be laid in the plane without crossings. We focus on the rigidity of polymer chains with the Brunnian theta-curve shape by using the lattice stick number which is the minimal number of sticks glued end-to-end that are necessary to construct the theta-curve in the cubic lattice. The authors have already shown in a previous research that at least 15 lattice sticks are needed to construct Brunnian theta-curves. In this paper, we improve the lower bound of the lattice stick number for Brunnian theta-curves to 16.

Improve Quantum Yield of Poly(Maleic Anhydride-Alt-Vinyl Acetate) via Good Solvents.

In this study, the optical properties of poly(maleic anhydride-alt-vinyl acetate) (PMV) synthesized by different polymerization methods are studied systematically. Compared to self-stabilized precipitation polymerization (pPMV), solution polymerization produces PMV solids (sPMV) with an extraordinarily high quantum yield (QY) of 20.65%. Additionally, redissolving pPMV in good solvents (rPMV) will also help to increase QY. The rising QY of sPMV and rPMV supports the idea that good solvents will reduce the rigidity of polymer chains and promote cluster formation, which is confirmed by lower glass transition temperature (Tg ) and small angle X-ray scatterer (SAXS). The study also finds that PMV exhibits application potentials in white light-emitting diodes (WLEDs) and light conversion film.

Manipulation of clusteroluminescence in carbonyl‐based aliphatic polymers

AbstractClusteroluminogens (CLgens), nonconjugated structures with visible luminescence at the clustering state, have recently received remarkable attention due to their great theoretical significance and practical values. In carbonyl‐based aliphatic polymers, (n, π*) transition of carbonyl groups and the through‐space interactions have been demonstrated to play an important role in their clusteroluminescence (CL) properties, but it is still a big challenge to manipulate their CL at the molecular level. In this work, six nonconjugated carbonyl‐based polymers with different heteroatoms and steric hindrances were synthesized, and their photophysical properties were systematically studied. These polymers all showed CL but with different emission efficiency and wavelength. Experimental and theoretical studies indicated that the CL properties could be manipulated by changing the electronic structures of carbonyl groups and the rigidity of polymer chains. This work not only gains further insights into the CL mechanism but also provides reliable strategies to design and manipulate non‐conjugated luminescent materials.

Comparative study on selective laser sintering of aromatic and aliphatic thermoplastic polyurethanes: processability, microstructure, and mechanical properties

Selective laser sintering (SLS) of thermoplastic polyurethane (TPU) has attracted tremendous interest in producing prototypes and end-use parts for applications in mechanical energy absorption, biomedical scaffold, and wearable electronics because of the versatile properties of this material. This work aims to reveal the effects of the chemical structure on the SLS processability of TPU powders as well as the microstructure and mechanical properties of their SLS-printed parts. It was found that the aliphatic TPU exhibited better SLS processability and lower total porosity than the aromatic TPU because of its flexible polymer chains. In contrast, the aromatic TPU displayed higher tensile strength and mechanical energy absorption because of its rigid polymer chains and the increased intermolecular force. Pores in the SLS-printed parts were classified based on their morphological features, and their origins were investigated via X-ray computed tomography. This study provides guidance for the design, selection, and optimization of TPU powders for the SLS process according to different applications.

Hierarchical Amine-Functionalized ZIF-8 Mixed-Matrix Membranes with an Engineered Interface and Transport Pathway for Efficient Gas Separation

Herein, we report a facile approach to engineer a metal–organic framework (MOF) structure and polymer–MOF interface in a mixed-matrix membrane (MMM) to achieve high gas separation performance and plasticization resistance. Hierarchical ZIF-8-NH2 nanoparticles with a relatively small concentration of amine functionality (∼5 mol %) were prepared. The hierarchical MOF structure provides fast molecular transport pathways because of the MOF–MOF percolated network and high MOF packing density. Moreover, the interfacial interaction between the 6FDA-DAM:DABA(3:2) polyimide and the amine-functionalized MOF enhances the chemical stability and polymer chain rigidity. The hierarchical ZIF-8-NH2 MMMs exhibit a significantly improved gas permeability because of the accelerated molecular diffusion through the direction-oriented MOF pathway. For example, the ZIF-8-NH2 30 wt % MMM showed ∼6- and ∼4-fold enhanced H2 (761.7 Barrer) and CO2 (552.4 Barrer) permeabilities when compared to those of a pure polyimide film, with an H2/CH4 selectivity of 35.7 and CO2/CH4 selectivity of 25.9. Additionally, the MMM exhibits an improved plasticization resistance due to the connected MOF structure and MOF–polymer interaction. This strategy provides remarkable insight into the rational design of the polymer and MOF constituents in the MMM system.