In order to reduce greenhouse gas emissions, developing flame retardants from bio-based resources has aroused extensive interest in recent years. In this work, we utilized furfural (biomass) and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) to synthesize a bio-based co-curing agent (FGD) to combine with 4,4’-diaminodiphenyl methane (DDM) for obtaining a low-phosphorus loading flame-retardant epoxy thermosets. The introduction of FGD decreased the activation energy of the curing progress, enhanced the mechanical properties of the epoxy thermosets, and did not affect the glass transition temperature of the epoxy thermosets. EP-5.0 had a lower thermal degradation rate and a doubled char yield compared with EP-0. The phosphorus content of EP-5.0 was only 0.45 wt%, while EP-5.0 reached the UL-94 V-0 rating with a high LOI value of 32%. Compared with EP-0, the PHRR of EP-2.5 and EP-5.0 decreased by 22.3% and 31.3%, respectively. The SEM results showed that the addition of FGD made the char residues more uniform and denser, which could effectively prevent combustible volatiles from escaping from the degradation area to the flame area and isolate the heat transfer so that the epoxy thermosets had an excellent flame-retardant performance.

To address the issue of hemilabile catalyst in olefin polymerization catalysis, a cyclizing strategy was used to construct novel N-bridged phosphine-carbonyl palladium and nickel catalysts, resulting in improvements on ethylene (co)polymerizations. The N-bridged phosphine-carbonyl Pd catalysts (Pd1−Pd5) and Ni catalysts (Ni1−Ni5) bearing five- to eight-membered-ring structures were designed and synthesized. Catalytic performance for ethylene (co)polymerization became better as the size of N-containing bridge increased. The seven-membered-ring bridged catalysts Pd4 and Ni4 exhibited the best performance in terms of catalytic activity, polymer molecular weight and incorporation of acrylates and acrylic acid. The better performance of these catalysts bearing larger-size bridges was tentatively attributed to the methylene-induced higher electron density around nitrogen, which strenghtens the coordination of carbonyl group to metal center, and also to the steric effect offered by this cyclization. This work provides a new strategy to enhance hemilabile polymerization catalysts.

This work proposes a facile fabrication strategy for thermally conductive graphite nanosheets/poly(lactic acid) sheets with ordered GNPs (o-GNPs/PLA) via fused deposition modeling (FDM) 3D printing technology. Further combinations of o-GNPs/PLA with Ti₃C₂T_x films prepared by vacuum-assisted filtration were carried out by “layer-by-layer stacking-hot pressing” to be the thermally conductive Ti₃C₂T_x/(o-GNPs/PLA) composites with superior electromagnetic interference shielding effectiveness (EMI SE). When the content of GNPs was 18.60 wt% and 4 layers of Ti₃C₂T_x (6.98 wt%) films were embedded, the in-plane thermal conductivity coefficient (λ_||) and EMI SE (EMI SE_||) values of the thermally conductive Ti₃C₂T_x/(o-GNPs/PLA) composites significantly increased to 3.44 W·m^–1·K^–1 and 65 dB (3.00 mm), increased by 1223.1% and 2066.7%, respectively, compared with λ_|| (0.26 W·m^–1·K^–1 ) and EMI SE_|| (3 dB) of neat PLA matrix. This work offers a novel and easily route for designing and manufacturing highly thermally conductive polymer composites with superior EMI SE for broader application.

The polymorphic transition of trans-1,4-polyisoprene (TPI) during stretching was investigated by in situ wide-angle X-ray diffraction and Fourier transform infrared spectroscopy. The influences of the initial structure, stretching temperature, and strain rate on the contents of different crystal modifications (α, β) were explored. The results confirm that the α-β transition occurs during stretching of TPI that only contains α crystal (α-TPI). When the stress is relaxed, the β crystal formed during stretching remains, which indicates that the transition is irreversible. On the other hand, stretching of TPI that only contains β crystal (β-TPI) results in orientated β crystal. No β-α transition occurs during stretching. The different structures of stretched α-TPI and β-TPI exclude the previously proposed “melting-recrystallization mechanism”. The α-β transition depends significantly on temperature and strain rate, indicating the transition is governed both by thermodynamics and kinetics. Our results support a solid-solid transition mechanism rather than a melting-recrystallization mechanism. The irreversible nature of the transition is attributed to the metastability of the β phase in the unstretched state. Different from the “β phases” that appear in polymers with stress-induced reversible transitions, e.g. poly(butylene terephthalate) and poly(butylene succinate), the stability of β phase in TPI is high that can be long-lived. The strain rate dependence of α-β transition hinders the determination of critical stress for the transition. It further indicates that the local stress within the sample is more heterogeneous at higher strain rates.

A group of five bis(arylimino)pyridine-cobalt(II) chloride complexes, [2-{(2,6-(Ph₂CH)₂-4-MeOC₆H₂)N＝CMe}-6-(ArN＝CMe)C₅H₃N]CoCl₂ (Ar = 2,6-Me₂C₆H₃ Co1, 2,6-Et₂C₆H₃ Co2, 2,6-iPr₂C₆H₃ Co3, 2,4,6-Me₃C₆H₂ Co4, 2,6-Et₂-4-MeC₆H₂ Co5), each containing one N-4-methoxy-2,6-dibenzhydrylphenyl group and one smaller sterically/electronically variable N-aryl group, have been synthesized in good yield (>71%) from the corresponding neutral terdentate nitrogen-donor precursor,L1–L5. All complexes have been characterized by ¹H-NMR and FTIR spectroscopy with the former highlighting the paramagnetic nature of these cobaltous species and the unsymmetrical nature of the chelating ligand. The molecular structures of Co3 and Co4 emphasize the steric differences of the two inequivalent N-aryl groups and the distorted square pyramidal geometry about the metal centers. In the presence of MAO or MMAO, Co1–Co5 collectively displayed high activities for ethylene polymerization producing high molecular weight polyethylenes that, in general, exhibited narrow dispersities (M_w/M_n values: 2.12–4.07). Notably, the least sterically hindered Co1 when activated with MAO was the most productive (6.92×10⁶ g_PE·mol⁻¹_(Co)·h⁻¹) at an operating temperature of 60 ºC. Conversely, the most sterically hindered Co3/MMAO produced the highest molecular weight polyethylene (M_w=6.29×10⁵ g·mol⁻¹). All the polymers displayed high linearity as demonstrated by their melting temperatures (>130 °C) and their¹H- and ¹³C-NMR spectra. By comparison of Co1 with its para-methyl, -chloro and -nitro counterparts, the presence of the para-methoxy substituent showed the most noticeable effect of enhancing the thermal stability of the catalyst.

In this work, a fully rigid coplanar symmetric heterocyclic unit was introduced into the rigid polyimide macromolecular backbone structure to prepare high-performance polyimide fibers. The novel co-polyimide (co-PI) fibers based on 3,3’,4,4’-biphenyltetracarboxylic anhydride (BPDA), p-phenylenediamine (PDA) and 2,6-(4,4’-diaminodiphenyl) benzo[1,2-d:5,4-d'] bisoxazole (PBOA) were fabricated via a two-step wet-spinning method. The effects of benzobisoxazole moiety on spinnability, aggregation structure, and mechanical properties of fibers were systematically discussed. The detailed structural analysis revealed that the well-defined aggregation structures of co-PI fibers were obtained from initial amorphous structure when post hot-drawing temperature was higher than 460 °C under proper drawing ratio, and the incorporation PBOA into BPDA-PDA structures produced more compact structural co-PI fiber than homo BPDA-PDA fiber. The BPDA-PDA/PBOA co-PI fibers exhibited optimum tensile strength and modulus of 2.65 and 103 GPa, which increased by 182% and 84% compared to the homo BPDA-PDA fiber, respectively.

Achieving low friction and wear of poly(phenylene sulfide) (PPS) without using fillers or blending is a challenging task, but one of considerable practical importance. Here we describe how neat PPS with high tribological performance is achieved by manipulating processing parameters (pressure, flow and temperature). The key to achieving high tribological performance is comparatively high molecular chain orientation, realized in neat PPS, at high shear rates and low pressure. The friction coefficient and wear rate are as low as ~0.3 and ~10^‒6 mm³·N^‒1·m^‒1, respectively, which break the record for neat PPS. These values are even better than those for PPS-based blends and comparable to PPS composites. Further studies show, for the first time, that wear rate decreases exponentially with increasing molecular chain orientation, prompting us to revise the classical Archard’s law by including the effect of molecular chain orientation. These findings open the possibility of using neat PPS in highly demanding tribological applications.

Incorporation of nanoparticles into polymer blend to obtain finely dispersed morphology has been considered as an effective strategy to prepare nanocomposites. Owing to the renewable and degradable characters, cellulose nanocrystals (CNCs) have been proposed to tailor the phase morphology of poly(L-lactic acid) (PLLA) blend for producing high-performance fused deposition modeling (FDM) consumables. However, the main challenge associated with the ternary systems is the dispersion of the highly hydrophilic CNCs in non-polar PLLA blend by industrial melt blending without involving solution. Herein, with poly(vinyl acetate) (PVAc) modified CNCs powder (a mixture of PVAc grafted from CNCs and PVAc homopolymer latex), the selective dispersion of CNCs in PLLA has been achieved by simple melt processing of PLLA/TPU (polyether polyurethane)/CNCs blend. This results in the ultra-fine TPU droplets at nanoscale in PLLA and improves the melt processibility of composites in FDM due to the decreased viscosity ratio of the dispersed/matrix and the enhanced melt elasticity of PLLA. Combined with the intensive shear and continuous stretch effect during FDM, aligned TPU nanofibers (TNFs) were in situ formed along the elongational flow direction during deposition, which in turn contributed to the improvement of PLLA/TPU/CNCs with 5 wt% filler loading in tensile ductility by 418%, inter-layer adhesion strength and notched impact toughness by 261% and 210%, respectively, as well as achieved good dimensional accuracy and very fine surface quality.

Microporous organic polymers with high surface area are widely used in many applications. Among them, hypercrosslinked polymers have been extensively concerned because of their simple processes and low-cost reagents. However, due to most state-of-the-art strategies for HCPs based on condensation reactions, the release of small molecules such as hydrochloric acid and methanol involved in such strategies brings about new hazards to environment. Herein, we propose a method of fabrication of hypercrosslinked polymers via self-addition polymerization of divinyl benzene and its crosslinking with polar aromatic molecules. The hypercrosslinked polyDVB-based products are demonstrated by Friedel-Crafts addition reaction of double bonds on DVB that can connect adjacent phenyl rings of aromatic molecules to form the crosslinked networks. The HCPDVB-CB obtained in 1-chlorobutane as solvent has a high micropore content and displays high surface area up to 931 m²/g. Following this finding, DVB is used as a novel external crosslinker for knitting polar aromatic molecules. When L-phenylalanine and bisphenol A are used as the aromatic units, the obtained HCP(Phe-DVB) and HCP(BPA-DVB) could reach surface area of 612 and 471 m²/g, and have hydrogen uptake of 0.62 wt% and 0.58 wt% at 77 K and 1.13 bar by comparison with HCPDVB-CB having hydrogen uptake of 0.30 wt%, respectively.

Thermoset plastics have become one of the most important chemical products in the world. The consequent problem is that although the thermosets possess excellent performance in mechanical strength, they cannot be reprocessed because of the internal permanent network structures. Optimizing the molecular design of thermosets is one of the most feasible ways to improve their recyclability. Here we present a facile and robust strategy to engineer the reprocessability of thermoset polyurethanes without compromising their mechanical toughness and chemical resistance via adding supramolecular additives during the polymer synthesis process. By using a multiple hydrogen bonding moiety as the model supramolecular additive, we demonstrate that the mechanical properties, recyclability, and chemical resistance of the crosslinked polyurethanes can be precisely controlled by adjusting the contents of the supramolecular additive. Systematic studies on the relations between molecular design and material properties are performed, and the optimized polyurethane network with a moderate amount of the supramolecular additive achieves the right balance between the robustness and recyclability. This work provides a cost-effective and practical way to chemically engineer thermoset plastics, aiming to enable the recycling of mechanically tough and chemically stable polymer materials.