To overcome the limitations of empirical synthesis and expedite the discovery of new polymers, this work aims to develop a data‐driven strategy for profoundly aiding in the design and screening of ...novel polyester materials. Initially, we collected 695 polyesters with their associated glass transition temperatures (Tgs) to develop a quantitative structure–property relationship (QSPR) model. The model underwent rigorous validation (i.e., external validation, internal validation, Y‐random, and application domain analysis) to demonstrate its robust predictive capabilities and high stability. Subsequently, by employing an in‐silico retrosynthesis strategy, over 95,000 virtual polyesters were designed, largely expanding the available space for polyester material family. External assessments were performed, highlighting good extrapolation ability of the QSPR model. Furthermore, we experimentally synthesized 10 designed polyesters with predicted Tgs covering a large temperature range from −42.52 to 103.61°C, and characterization results gave an average absolute error of 17.40°C relative to the predicted ones. It is believed that such data‐driven approach can drive future product development of polymer industry.
Permanently cross-linked materials have outstanding mechanical properties and solvent resistance, but they cannot be processed and reshaped once synthesized. Non-cross-linked polymers and those with ...reversible cross-links are processable, but they are soluble. We designed epoxy networks that can rearrange their topology by exchange reactions without depolymerization and showed that they are insoluble and processable. Unlike organic compounds and polymers whose viscosity varies abruptly near the glass transition, these networks show Arrhenius-like gradual viscosity variations like those of vitreous silica. Like silica, the materials can be wrought and welded to make complex objects by local heating without the use of molds. The concept of a glass made by reversible topology freezing in epoxy networks can be readily scaled up for applications and generalized to other chemistries.
Weyl semimetal Td‐MoTe2 has recently attracted much attention due to its intriguing electronic properties and potential applications in spintronics. Here, Fe‐intercalated Td‐FexMoTe2 single crystals ...(0 < x < 0.15 ) are grown successfully. The electrical and thermoelectric transport results consistently demonstrate that the phase transition temperature TS is gradually suppressed with increasing x. Theoretical calculation suggests that the increased energy of the Td phase, enhanced transition barrier, and more occupied bands in 1T′ phase is responsible for the suppression in TS. In addition, a ρα–lnT behavior induced by Kondo effect is observed with x ≥ 0.08, due to the coupling between conduction carriers and the local magnetic moments of intercalated Fe atoms. For Td‐Fe0.15MoTe2, a spin‐glass transition occurs at ≈10 K. The calculated band structure of Td‐Fe0.25MoTe2 shows that two flat bands exist near the Fermi level, which are mainly contributed by the dyz and dx2−y2${{\rm{d}}_{{x^2} - {y^2}}}$ orbitals of the Fe atoms. Finally, the electronic phase diagram of Td‐FexMoTe2 is established for the first time. This work provides a new route to control the structural instability and explore exotic electronic states for transition‐metal dichalcogenides.
Fe‐intercalated Td‐FexMoTe2 single crystals (0 ≤ x ≤ 0.15) are grown successfully. The Fe intercalation significantly tunes the structural instability and brings about exotic electronic properties for the Weyl semimetal MoTe2, including the first observed Kondo effect and spin‐glass transition in its topologically nontrivial Td phase at low temperature.
Despite decades of theoretical studies, the nature of the glass transition remains elusive and debated, while the existence of structural predictors of its dynamics is a major open question. Recent ...approaches propose inferring predictors from a variety of human-defined features using machine learning. Here we determine the long-time evolution of a glassy system solely from the initial particle positions and without any handcrafted features, using graph neural networks as a powerful model. We show that this method outperforms current state-of-the-art methods, generalizing over a wide range of temperatures, pressures and densities. In shear experiments, it predicts the locations of rearranging particles. The structural predictors learned by our network exhibit a correlation length that increases with larger timescales to reach the size of our system. Beyond glasses, our method could apply to many other physical systems that map to a graph of local interaction.The physics that underlies the glass transition is both subtle and non-trivial. A machine learning approach based on graph networks is now shown to accurately predict the dynamics of glasses over a wide range of temperatures, pressures and densities.
•Differences in fine structure between hemicelluloses determines the functional impact of oxidation.•Oxidation of xylan reduces its glass transition temperature (Tg)•Oxidation of arabinoxylan does ...not influence its Tg at the degrees of oxidation studied•Oxidation of arabinoxylan leads to opening of primarily arabinose sidegroups
Hemicellulose from pulp mill process water and crop residuals from food production often end up in waste streams or burnt for energy contribution. These waste products contain valuable biopolymers but lack many attributes needed for use in applications such as food and medical or consumer products. This study reports on an investigation of the periodate oxidation of hardwood xylan and arabinoxylan (AX) from wheat bran to produce materials with new functionalities. The study explores how to control the oxidation degree and describes structural differences between the two xylan-based polymers. For the xylan samples, the oxidation resulted in a lowering of the glass transition temperature (Tg), indicating a more flexible chain due to ring-opening of the xylan anhydro-sugar units. For the AX samples, the arabinose side-groups were instead oxidized, hindering oxidation on part of the xylose units, which resulted in a crosslinked network with an unchanged Tg but reduced intrinsic viscosity.
A biorenewable polymer is synthesized via a green process using the RAFT principle for the first time in supercritical CO2 at 300 bar and 80 °C. α‐Methylene‐γ‐butyrolactone polymers of various chain ...lengths and molecular weights are obtained. The molecular weights vary from 10 000 up to 20 000 with low polydispersity indexes (PDI <1.5). Furthermore, the monomer conversion in supercritical CO2 is substantially higher, respectively 85% for ScCO2 compared to ≈65% for polymerizations conducted in dimethyl formamide (DMF) solvent. Chain extensions are carried out to confirm the livingness of the formed polymers in ScCO2. This opens up future possibilities of the formation of different polymer architectures in ScCO2. The polymers synthesized in ScCO2 have glass transition temperature (Tg) values ranging from 155 up to 190 °C. However, the presence of residual monomer encapsulated inside the formed polymer matrix affects the glass transition of the polymer that is lowered by increasing monomer concentrations. Hence, additional research is required to eliminate the remaining monomer concentration in the polymer matrix in order to arrive at the optimal Tg.
Biobased monomers might pave the way towards the production of more sustainable polymeric materials in the near future. However, from a sustainability point of view, the use of green solvents for the polymerization step is also a necessary condition towards “green products made via green processes”.
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•The chemical and topological structures of flame retardant were regulated at the same time.•Modified epoxy resin showed UL-94 V0 rating and LOI above 32.6 vol% with phosphorus ...content of only 0.24%.•Impact strength was increased by 113% at 25°C and by 96% at −196°C after modification.•Tg was increased from 172°C for pristine resin to 194°C for modified system determined by DMA.•Flexural strength and modulus of modified epoxy were increased by 26% and 19%.
Endowing epoxy resins with simultaneously improved flame retardancy, toughness and strength as well as glass transition temperature (Tg) is a big challenge for us. Herein, a hyperbranched flame retardant (HBFR) with rigid backbone structure was synthesized through a facile strategy. Upon the incorporation of HBFR, the modified diglycidyl ether of bisphenol A (DGEBA) with phosphorus content of only 0.24 wt% exhibited better flame retardancy beyond expectation, showing UL-94 V-0 rating and limited oxygen index (LOI) above 32.6 vol%. Meanwhile, the modified epoxy resin demonstrated superior toughness, indicated by the more than 96% increment in impact strength both at 25 and −196°C, due to the enlarged free volume originated from hyperbranched structures. Furthermore, the Tg, flexural strength and modulus of modified epoxy systems were also significantly increased because of the rigid backbone structure and high crosslinking density afforded by HBFR. This work provided us an attractive strategy for simultaneously improving the flame retardancy, toughness, Tg and strength of commercial epoxy resins.
•A nitrogen heterocyclic/phosphaphenanthrene derivative as reactive flame retardant named as TBO was prepared successfully.•TBO simultaneously improved the flame retardancy, Tg and dielectric ...properties of EP.•TBO/EP composites exhibited excellent potential in application of high performance polymer.
Various approaches have been successfully applied to solve the flammability of epoxy resin (EP) materials, but enhanced flame retardance of EP is often along with deteriorated glass transition temperature (Tg) and mechanical property. In order to prepare EP composites with good comprehensive performance, we synthesized a phosphorus-containing triazole derivative named TBO from 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 3,5-diamino-triazolz and salicylaldehyde, and attached it into epoxy framework. With 0.75 wt% phosphorus loading, the 0.75-TBO/EP composite had a V-0 rating and a limiting oxygen index of 33%. 1.0-TBO/EP composite also had a V-0 rating and acquired a decrease of 37.6% in peak heat release rate. In addition, the tensile strength and flexural strength of 0.75-TBO/EP increased to 63.9 MPa and 146 MPa from 59 MPa and 134 MPa of EP respectively. Meanwhile, the Tg values of TBO/EP elevated to some certain compared to EP. In a word, EP modified with TBO composites owned strong mechanical property, higher Tg and excellent flame retardance, indicating great potential for application.
Effectively tailoring the temperature coefficient of resistance (TCR) is critical for multifunctional carbon nanotube (CNT) polymer composites with sensing capability. By developing a new multiscale ...percolation network model, this work reveals theoretically that the zero-TCR could be achieved by adjusting competing contributions from thermally assisted tunnelling transport at CNT junctions and thermal expansion of matrices. On the other hand, the negative temperature coefficient of nanocomposites above glass transition temperature could be greatly enhanced because the transport mechanism at the CNT junctions experienced a transition from tunnelling to hopping. Both tube-tube and/or tube-matrix interactions at conjunction and the structural distortion of nanotubes are considered in the newly proposed model. To validate the model, CNT/polymer nanocomposites with nearly constant resistance values (zero-TCR) below the glass transition temperature and a high TCR (98% resistance change ratio) resulting from the glass transition of the polymer matrix are successfully developed. The study also suggests that the desired parameters to achieve the zero-TCR property and the potential resistance change ratio could be improved by the glass transition in nanocomposites. This could be beneficial for the development of high quality sensing materials.
When cooled or pressurized, polymer melts exhibit a tremendous reduction in molecular mobility. If the process is performed at a constant rate, the structural relaxation time of the liquid eventually ...exceeds the time allowed for equilibration. This brings the system out of equilibrium, and the liquid is operationally defined as a glass-a solid lacking long-range order. Despite almost 100 years of research on the (liquid/)glass transition, it is not yet clear which molecular mechanisms are responsible for the unique slow-down in molecular dynamics. In this review, we first introduce the reader to experimental methodologies, theories, and simulations of glassy polymer dynamics and vitrification. We then analyse the impact of connectivity, structure, and chain environment on molecular motion at the length scale of a few monomers, as well as how macromolecular architecture affects the glass transition of non-linear polymers. We then discuss a revised picture of nanoconfinement, going beyond a simple picture based on interfacial interactions and surface/volume ratio. Analysis of a large body of experimental evidence, results from molecular simulations, and predictions from theory supports, instead, a more complex framework where other parameters are relevant. We focus discussion specifically on local order, free volume, irreversible chain adsorption, the Debye-Waller factor of confined and confining media, chain rigidity, and the absolute value of the vitrification temperature. We end by highlighting the molecular origin of distributions in relaxation times and glass transition temperatures which exceed, by far, the size of a chain. Fast relaxation modes, almost universally present at the free surface between polymer and air, are also remarked upon. These modes relax at rates far larger than those characteristic of glassy dynamics in bulk. We speculate on how these may be a signature of unique relaxation processes occurring in confined or heterogeneous polymeric systems.
