Catalyzed Crosslinking Research Articles

“Mending with silk” enhances aged silk with mechanical and antibacterial properties

The reinforcement and preservation of historical silk are crucial for its continued research, heritage, and display. Herein, silk fibroin (SF) and carboxymethyl chitosan (CMCS) were utilized as raw materials to reinforce aged silk via two reinforcement methods, with transglutaminase (TGase) serving as a catalytic cross-linking agent. The covalent and non-covalent bond network formed by TGase catalytic cross-linking significantly improved the mechanical properties of aging silk, and CMCS as an antibacterial material gave excellent antibacterial properties of the aged silk. Compared with aged silk, the breaking stress and elongation at break of the aged silk after reinforcement are increased by 257.9% and 293.7% respectively. The antibacterial rate of the reinforced aged silk against Escherichia coli (E. coli) and Streptococcus aureus (S. aureus) exceeded 90%. Under accelerated simulated aging conditions, the aging rate of the reinforced silk was significantly reduced, demonstrating notable aging resistance. Notably, the one-step enhanced aged silk outperformed the two-step enhanced aged silk in all performance evaluations, while the appearance of the aged silk was not affected. This work provides a green and efficient process for the reinforcement and protection of silk-based cultural relics and the application of silk cultural relics protection materials.

Efficient flame retardancy of polypropylene by cobalt ions doped phytate melamine synergized with expandable graphite

Maintaining a delicate balance between flame retardancy and amount of expandable graphite (EG) in flame retardant polypropylene (PP) is still a formidable challenge, primarily due to the lower flame-retardant efficiency of EG. In order to address this concern, a novel cobalt-doped nanosheet flame retardant (PAMA-Co) was fabricated by a hydrothermal method utilizing phytic acid (PA) and melamine (MA), exhibiting a promising potential in constructing synergistic EG flame retardant PP. Significantly, the incorporation of only 7 wt% PAMA-Co/23 wt% EG system raises the limiting oxygen index (LOI) of PP to 27.3% and UL-94 V0 level, which indicates the excellent synergistic flame-retardant efficiency of PAMA-Co. Furthermore, both the peak heat release rate (PHRR) and the peak smoke production rate (PSPR) of PP composites with 7 wt% PAMA-Co/23 wt% EG are substantially reduced, exhibiting an 81.6% lower PHRR and 87.8% PSPR compared to pure PP. The excellent flame-retardant efficiency is attributed to the following mechanisms: Gas-phase dilution, catalytic cross-linking charring effect, and the suppression of the EG “popcorn effect” of PAMA-Co. In summary, this work not only advances an understanding of flame-retardant mechanisms but also offers a practical, green strategy for enhancing the safety and utility of PP in various applications.

Preparation of Multifunctional Hydrogels with In Situ Dual Network Structure and Promotion of Wound Healing.

As an emerging biomedical material, wound dressings play an important therapeutic function in the process of wound healing. It can provide an ideal healing environment while protecting the wound from a complex external environment. A hydrogel wound dressing composed of tilapia skin gelatin (Tsg) and fucoidan (Fuc) was designed in this article to enhance the microenvironment of wound treatment and stimulate wound healing. By mixing horseradish peroxidase (HRP), hydrogen peroxide (H2O2), tilapia skin gelatin-tyramine (Tsg-Tyr), and carboxylated fucoidan-tyramine in agarose (Aga), using the catalytic cross-linking of HRP/H2O2 and the sol-gel transformation of Aga, a novel gelatin-fucoidan (TF) double network hydrogel wound dressing was constructed. The TF hydrogels have a fast and adjustable gelation time, and the addition of Aga further enhances the stability of the hydrogels. Moreover, Tsg and Fuc are coordinated with each other in terms of biological efficacy, and the TF hydrogel demonstrated excellent antioxidant properties and biocompatibility in vitro. Also, in vivo wound healing experiments showed that the TF hydrogel could effectively accelerate wound healing, reduce wound microbial colonization, alleviate inflammation, and promote collagen deposition and angiogenesis. In conclusion, TF hydrogel wound dressings have the potential to replace traditional dressings in wound healing.

Influence of Oxyranylmethanol as a Catalytic Cross-linking Agent over Physiochemical Properties and Pb (II) Adsorption Performance of Resorcinol Formaldehyde Aerogels: a Comparative Study

Influence of Oxyranylmethanol as a Catalytic Cross-linking Agent over Physiochemical Properties and Pb (II) Adsorption Performance of Resorcinol Formaldehyde Aerogels: a Comparative Study

Mechanistic insight into homogeneous catalytic crosslinking behavior between cellulose and epoxide by explicit solvent models

Inspired by recent advances on functional modification of cellulosic materials, the crosslinking behaviors of epoxide with cellulose under the catalysis of different homogeneous catalysts including H2O, Brønsted acid, Brønsted base, Lewis acid and neutral salt were systematically investigated using density functional theory (DFT) methods with hybrid micro-solvation-continuum approach. The results showed that catalytic activity, reaction mechanism and regioselectivity are determined by the combined effect of catalyst type, electronic effect and steric hindrance. All the homogeneous catalysts have catalytic activity for the crosslinking reaction, which decreases in the order of NaOH > HCl > NCl3 > MCl2 > CH3COOH > NaCl (N = Fe3+, Al3+; M = Zn2+, Ca2+). Upon the catalysis of NaOH, hydroxyl group of cellulose is firstly deprotonated to form a carbanion-like intermediate which will further attack the less sterically hindered C atom of epoxide showing excellent regioselectivity. Acidic catalysts readily cause epoxide protonated, which suffers from nucleophilic attack of cellulose and forms the carbocation-like intermediate. Brønsted acid exhibits poor regioselectivity, however, Lewis acid shows an interesting balance between catalytic activity and regioselectivity for the crosslinking reaction, which may be attributed to the unique catalysis and stabilization effects of its coordinated H2O on the transition state structure.

Thermal management ability and flame retardancy of silicone rubber foam filled with flame retardant phase change capsules

A novel phase change capsule with layered double hydroxide (LDH) modified SiO2 shell (named M-EPCM) was designed and prepared, which was used to improve the thermal regulation performance and flame retardancy of silicone rubber foam (SRF). The SRF-3 composite containing 18 wt% M-EPCM presented greatly improved thermoregulation ability, and excellent thermal reliability even after 100 cycles. Besides, SRF-3 also exhibited excellent flame retardancy, with the limiting oxygen index exceeding 31.0%, reduced peak heat release rate (36.4%) and low total smoke yield (13.8 m2). The flame retardant mechanism analysis revealed that barrier effect, catalytic crosslinking and polyaromatic reaction provided by LDH played an important role. Moreover, SRF composites have outstanding mechanical properties, especially SRF-3 which showed a 150% and 85% increase in tensile strength and compression strength compared with pure SRF, respectively. This article provides a new idea for further application of LDH in the field of thermal management.

Enhancing flame retardancy of polyphenylene sulfide nanocomposite fibers by the synergistic effect of catalytic crosslinking and physical barrier

AbstractProtective clothing with fascinating flame‐retardant features is urgently needed to reduce the large amount of smoke and heat released from combustion during fire protection. In this study, polyphenylene sulfide (PPS) nanocomposite resin with efficient flame retardancy is obtained by mixing a low content of graphene and Fe2O3via a twin screw extruder. Followed by, the PPS/G/Fe2O3fibers are fabricated via melting spinning. The PPS/G/Fe2O3nanocomposite resin with 0.3 wt% of graphene and 1.0 wt% of Fe2O3performs the best during the flame retardant tests, giving a shorter self‐extinguishing time, lower peak heat release rate (22.3 kW/m2), total heat release (11.3 MJ/m2) and total smoke production (1.32 m2) than others. The pyrolysis analysis indicates that a large number of products with fused rings are formed in the residual char layer, which effectively inhibit the release of heat and smoke and thus improve the flame retardancy of PPS nanocomposite resin. In addition, the flame retardant textile weaved with PPS/G/Fe2O3fibers gives a high‐limiting oxygen index (40.1%), zero after‐flame time, no droppings and small damaged length (114 mm in warp and 98 mm in weft direction) during the standard flame retardancy tests provided by a third‐party independent inspection organization. The fabrication of PPS fibers with effective and enhanced synergistic flame retardancy through melting spinning is facile and scalable, providing a promising strategy for advanced protective clothing.

Preparation of MOF-Based Core-Shell Gel Particles with Catalytic Activity and Their Plugging Performance.

Drilling fluid systems for deep and ultra-deep wells are hampered by both high-temperature downhole environments and lengthy cycle periods. Suppose that the gel particle-plugging agent, the primary treatment agent in the system, fails to offer durable and stable plugging performance. In such a scenario, the borehole wall is susceptible to instability and landslide after prolonged immersion, leading to downhole accidents. In this study, novel core-shell gel particles (modified ZIF) with ZIF particles employed as the core material and organosilicon-modified polyethylene polyamine (PEPA) as the polymer shell were fabricated using PEPA, in-house synthesized (3-aminopropyl) triethoxysilane (APTS), and the ZIF-8 metal-organic framework (MOF) as the raw materials to enhance the long-term plugging performance of gel plugging agents. The modified ZIF particles are nanoscale polygonal crystals and differ from conventional core-shell gel particles in that they feature high molecular sieve catalytic activity due to the presence of numerous interior micropores and mesopores. As a result, modified ZIF exhibits the performance characteristics of both rigid and flexible plugging agents and has an excellent catalytic cross-linking effect on the sulfonated phenolic resin (SMP-3) and sulfonated lignite resin (SPNH) in drilling fluids. Consequently, a cross-linking reaction occurs when SMP-3 and SPNH flow through the spacings in the plugging layer formed by the modified ZIF particles. This increases the viscosity of the liquid phase and simultaneously generates an insoluble gel, forming a particle-gel composite plugging structure with the modified ZIF and significantly enhancing the long-term plugging performance of the drilling fluid.

Transformation of phosphorus species during phosphoric acid-assisted pyrolysis of lignocellulose

Phosphoric acid-assisted pyrolysis (PAAP) is a pyrolysis technique with potential for the engineered and environmental application. Nevertheless, the volatilisation, immobilisation, and dissolution of phosphorus (P) species have been neglected during PAAP of lignocellulose. Therefore, we compared the transformation of P species with direct-pyrolysis and PAAP system, using multiple techniques including gas chromatography tandem mass spectrometry (GCMS) and 31P nuclear magnetic resonance (NMR). It was also investigated that the properties of pyrogenic and modified carbons obtained from lignocellulose pyrolysis at 200–650 °C. As the temperature increased, volatile P species evolved into gas-phase during PAAP, inhibiting the formation of the macromolecular volatile components. Compared with pyrogenic carbons, modified carbons with more aromatic structures experienced a higher degree of dehydration and cyclisation via catalytic crosslinking reaction. PAAP system facilitated more generation of persistent free radical (PFR) below 500 °C and the attenuation of PFR signals was observed at 500–650 °C, which may be associated with the sequestration and elimination of P species between carbon matrix. Notably, three configurations of C3PO, CPO, and COP were the major combinations of P and C elements on modified carbons. Increased gaseous P and decreased soluble P were observed with elevated temperatures in PAAP system. The species proportion of immobilised P clearly demonstrated the transformation of partial P species from inorganic to organic through pyrolysis. The immobilised P could serve as a potential sustained-release source participating in P biogeochemical cycles. These findings are fundamental for the technical design of lignocellulose pyrolysis.

Preparation of Mn2+ Doped Piperazine Phosphate as a Char-Forming Agent for Improving the Fire Safety of Polypropylene/Ammonium Polyphosphate Composites.

A piperazine phosphate doped with Mn2+ (HP-Mn), as a new char-forming agent for intumescent flame retardant systems (IFR), was designed and synthesized using 1-hydroxy ethylidene-1,1-diphosphonic acid, piperazine, and manganese acetate tetrahydrate as raw materials. The effect of HP-Mn and ammonium polyphosphate (APP) on the fire safety and thermal stability of polypropylene (PP) was investigated. The results showed that the combined incorporation of 25 wt.% APP/HP-Mn at a ratio of 1:1 endowed the flame retardant PP (PP6) composite with the limiting oxygen index (LOI) of 30.7% and UL-94 V-0 rating. In comparison with the pure PP, the peak heat release rate (PHRR), the total heat release (THR), and the smoke production rate (PSPR) of the PP6 were reduced by 74%, 30%, and 70%, respectively. SEM and Raman analysis of the char residues demonstrated that the Mn2+ displayed a catalytic cross-linking charring ability to form a continuous and compact carbon layer with a high degree of graphitization, which can effectively improve the flame retardancy of PP/APP composites. A possible flame-retardant mechanism was proposed to reveal the synergistic effect between APP and HP-Mn.

Coal tar pitch-based hierarchical porous carbons prepared in molten salt for supercapacitors

As electrode materials for supercapacitors (SCs), hierarchical porous carbons (HPCs) have attracted tremendous attention due to their high specific surface area (SSA) and hierarchical pore structure. However, the complex template preparation process for HCPs usually brings high cost. Here, by combining the pre-carbonizing process of coal tar pitch (CTP) in eutectic salt (ZnCl2–NaCl, denoted as MZS, Sm260 °C) with the KOH activating process, HPCs with high capacitive performance have been prepared. The pre-carbonizing process is carried out under atmosphere to obtain the primitive carbon (PC), during which the MZS will not only provide a liquid environment for catalytic cross-linking of CTP but also act as the porogen agent. The effects of temperatures, heating rates, the mass ratio of KOH to PC (mKOH/mC) and the activating temperatures on the structure and capacitive properties of HPCs are explored. The results show that the HPCs prepared by activating the optimal PC (prepared at 560 °C in the MZS with a heating rate of 2.5 °C min−1) at temperature of 800 °C (heating rate of 10.0 °C min−1 and mKOH/mC ratio of 5) exhibit high specific surface area (2984 m2 g−1), large total pore volume (2.2 cm3 g−1) and wide pore size distribution. Based on the two-electrode test system, the optimal HCP shows a specific capacitance of 320 F g−1, the symmetric cells exhibit an energy density of 10.6 Wh kg−1 at power density of 50.1 W kg−1. Furthermore, the cell displays a good cyclic stability (the capacitance retention of 94.0% after 10,000 cycles). This strategy may be developed as a promising method for preparing high-performance HPC from CTP.

Controlled Cryogelation and Catalytic Cross-Linking Yields Highly Elastic and Robust Silk Fibroin Scaffolds.

Silk biomaterials with tunable mechanical properties and biological properties are of special importance for tissue engineering. Here, we fabricated silk fibroin (SF, from Bombyx mori silk) scaffolds from cryogelation under controlled temperature and catalytic cross-linking conditions. Structurally, the cryogelled scaffolds demonstrated a greater β-sheet content but significantly smaller β-sheet domains compared to that without chemical cross-linking and catalyst. Mechanically, the cryogelled scaffolds were softer and highly elastic under tension and compression. The 120% tensile elongation and >85% recoverable compressive strain were among the best properties reported for SF scaffolds. Cyclic compression tests proved the robustness of such scaffolds to resist fatigue. The mechanical properties, as well as the degradation rate of the scaffolds, can be fine-tuned by varying the concentrations of the catalyst and the cross-linker. For biological responses, in vitro rat bone mesenchymal stem cell (rBMSC) culture studies demonstrated that cryogelled SF scaffolds supported better cell attachment and proliferation than the routine freeze-thawed scaffolds. The in vivo subcutaneous implantation results showed excellent histocompatibility and tissue ingrowth for the cryogelled SF scaffolds. This straightforward approach of enhanced elasticity of SF scaffolds and fine-tunability in mechanical performances, suggests a promising strategy to develop novel SF biomaterials for soft tissue engineering and regenerative medicine.

Synergistic role of in-situ crosslinkable electrospun nanofiber/epoxy nanocomposite interlayers for superior laminated composites

Adopting a multi-scaled/hierarchical toughening approach, we have produced nanofiber-reinforced epoxy laminate composites with superior toughness as a consequence of built-in, thermally catalyzed cross-linking between the nanofiber and the epoxy matrix, in addition to the usual curing within the epoxy itself. The nanofiber composition of P(St-co-GMA)/TBA-PA is designed such that the cross-linking agent PA groups are catalyzed by the thermally stimulated TBA initiators and inherent epoxy-nanofiber interfacial quality is promoted for toughening purposes. These nanofibers are electrospun onto two forms of the same base epoxy—neat resin films and pre-preg plies containing unidirectional carbon fibers. The nanofiber/epoxy nanocomposite specimens are manufactured via an in-house hot-press film molding method. DSC analysis reveal an increase in exothermic curing enthalpy, consistent with cross-linking between the epoxide groups of the fiber and epoxy matrix occurring in-situ, i.e., triggered and advanced during the epoxy curing cycle. Analysis of the curing kinetics, following Ozawa-Flynn-Wall method, shows that the P(St-co-GMA)/TBA-PA nanofibers have a significant autocatalytic effect on the epoxy matrix curing. Increases in tensile strength (30%) and elastic modulus (8%) are measured compared to the un-reinforced epoxy specimens. Furthermore, end-notched flexure tests reveal a 95% increase in GIIC, due to the incorporation of a single P(St-co-GMA)/TBA-PA nanofiber interlayer into laminated carbon fiber-reinforced composite of (0)48 lay-up configuration. These results suggest that the self-initiated cross-linking between the nanofibers and surrounding epoxy matrix synergistically forms interlayer zones that contribute to toughening. Analysis of the fracture surfaces is presented to elaborate on the significant role of the proposed in-situ cross-linked nanofibers on the remarkable improvements in mechanical behavior of these nanocomposites and interlayered laminates.

Increasing the Room-Temperature Electric Double Layer Retention Time in Two-Dimensional Crystal FETs.

Poly(vinyl alcohol) (PVA) and LiClO4, a solid polymer electrolyte with a glass transition temperature (Tg) of 80 °C, is used to electrostatically gate graphene field-effect transistors. The ions in PVA:LiClO4 are drifted into place by field-effect at T > Tg, providing n- or p-type doping, and when the device is cooled to room temperature, the polymer mobility and, hence ion mobility are arrested and the electric double layer (EDL) is "locked" into place in the absence of a gate bias. Unlike other electrolytes used to gate two-dimensional devices for which the Tg, and therefore the "locking" temperature, is well below room temperature, the electrolyte demonstrated in this work provides a route to achieve room-temperature EDL stability. Specifically, a 6 orders of magnitude increase in the room temperature EDL retention time is demonstrated over the commonly used electrolyte, poly(ethylene oxide) (PEO) and LiClO4. Hall measurements confirm that large sheet carrier densities can be achieved with PVA:LiClO4 at top gate programming voltages of ±2 V (-6.3 ± 0.03 × 1013 cm-2 for electrons and 1.6 ± 0.3 × 1014 cm-2 for holes). Transient drain current measurements show that at least 75% of the EDL is retained after more than 4 h at room temperature. Unlike PEO-based electrolytes, PVA:LiClO4 is compatible with the chemicals used in standard photolithographic processes enabling the direct deposition of patterned, metal contacts on the surface of the electrolyte. A thermal instability in the electrolyte is detected by both I-V measurements and differential scanning calorimetry, and FTIR measurements suggest that thermally catalyzed cross-linking may be driving phase separation between the polymer and the salt. Nevertheless, this work highlights how the relationship between polymer and ion mobility can be exploited to tune the state retention time and the charge carrier density of a 2D crystal transistor.

“One‐pot” synthesis of crosslinked silicone‐containing macromolecular charring agent and its synergistic flame retardant poly(l‐lactic acid) with ammonium polyphosphate

A crosslinked silicone‐containing macromolecular charring agent (CSi‐MCA) was synthesized via “one‐pot” process, and it was combined with ammonium polyphosphate (APP) to synergistically improve the flame retardancy of poly(l‐lactic acid) (PLA). The chemical structure of synthesized CSi‐MCA was characterized by Fourier transform infrared spectroscopy and solid‐state 13C nuclear magnetic resonance. The thermal gravimetric analyzer indicated that the CSi‐MCA displayed good thermal stability and high residue via the catalytic crosslinking. Furthermore, the flame retardant effect of CSi‐MCA and APP as intumescent flame retardants in PLA system was investigated by limited oxygen index, UL94, and cone calorimeter test. When the content of CSi‐MCA was 5 wt% and APP was 10 wt% (CSi‐MCA/APP = 1/2), the limited oxygen index value of composites was 33.6 and UL94 classed a V‐0 rating. The peak heat release rate and total heat release of PLA composites containing both APP and CSi‐MCA decreased significantly in comparison with those with APP or CSi‐MCA alone. The flame retardancy mechanism was investigated via analyzing residual chars by scanning electron microscopy and X‐ray photoelectron spectroscopy as well as the possible chemical reaction between APP and CSi‐MCA by thermal gravimetric analyzer and Fourier transform infrared spectroscopy. The results showed that the enhanced flame retardancy was attributed mainly to synergistic effect of CSi‐MCA and APP, which could form a compact, continuous, and protective layer during combustion. Copyright © 2017 John Wiley & Sons, Ltd.

Catalytic crosslinking of a regenerated hydrophobic benzylated cellulose and nano TiO2 composite for enhanced oil absorbency

AbstractHydrophobic cellulosic composites with the nano form of metal oxides possess good absorptive and adsorptive potentials. Native cellulose was regenerated, benzylated, crosslinked and blended with TiO2 nanoparticles to absorb toluene, xylene, chloroform, kerosene and petrol. The composite was fully characterized by scanning electron microscopy (SEM), transmission emission microscopy (TEM), Fourier transform infrared (FTIR) and X-ray diffraction (XRD). The effect of crosslinker, catalyst and time of absorption was investigated. The FTIR shows stretch and bend vibrations of hydroxyl (-OH), alkyl (-CH), aromatic double bond (C=C) for benzyl cellulose while the appearance of new peaks at 816, 769 and 726 cm−1 for Ti-O stretching vibrations confirms the successful synthesis of the composite. The SEM images revealed the transformation of foam-like appearance of benzyl cellulose to a solidified mass after TiO2 compositing. Enhanced oil absorption was seen as the amount of the aluminum sulfate catalyst was doubled as a high Qmax of 24.16, 25.81, 27.22, 24.03 and 24.43 was obtained when the amount of catalyst used was doubled.

Electrochemical Detection and Distribution Analysis of β-Catenin for the Evaluation of Invasion and Metastasis in Hepatocellular Carcinoma.

Pro-metastatic cell signaling controls the switch to distant metastasis and the final cancer death. In hepatocellular carcinoma (HCC), this death switch is turned on by the multiprotein interactions of β-catenin with many transcription factors, so a method to assay the bioactivity of β-catenin to participate in these pro-metastatic protein/protein interactions has been proposed in this work. This method employs cost-effective peptide-based protein targeting ligands, while the electrochemical catalytic cross-linking in this method also "finalize" the noncovalent molecular recognition, so that the robustness can be improved to enable detection of relatively more complex biosamples. In studying clinical samples with the proposed method, the cellular distribution and overall expression of β-catenin show a parallel with the pathological grade of the sample, particularly, nuclear translocation. The pro-metastatic activation of β-catenin can also be observed as evidently correlated with higher-grade cases, suggesting the active role of β-catenin in promoting metastasis. According to these results, the proposed method may have the prospective use as a prognostic tool for evaluating the potential of invasion and metastasis in cancer.

Acidic ionic liquid catalyzed crosslinking of oxycellulose with chitosan for advanced biocomposites

This paper presents a novel environmentally friendly production of chitosan-crosslinked oxycellulose films by using ionic liquids (AmimCl and SmimHSO4). The effect of reaction parameters on chitosan contents and mechanical properties of chitosan-crosslinked oxycellulose films was also investigated. The results revealed that appropriate SmimHSO4 dosage and reaction time were 5% and 2h respectively. FTIR analysis of chitosan-crosslinked oxycellulose film suggested that the chitosan was crosslinked with oxycellulose through the reaction between the amino groups in chitosan and the aldehyde groups in oxycellulose, and the results of XPS analysis further confirmed the reaction between both polysaccharides. SEM images suggested that the developed chitosan-crosslinked oxycellulose films had a smooth and compact structure, and a highly inhibitory effect against the bacteria of Escherichia coli and Staphylococcus aureus. The developed materials and technologies could be further formulated for the production of various antimicrobial and biomedical products or water treatment membranes.

Effects of transglutaminase catalyzed crosslinking on physicochemical characteristics of arachin and conarachin-rich peanut protein fractions

Arachin and conarachin-rich fractions of peanut protein were extracted by using cryoprecipitation followed by centrifugation. These two fractions were individually crosslinked using transglutaminase (TG). The physicochemical characteristics including aggregation due to crosslinking, solubility, thermal denaturation temperature (Td) and denaturation enthalpy (△H), morphology of microstructure and surface hydrophobicity (H0) of TG-treated and untreated arachin and conarachin-rich fractions were determined. The relative contents of arachin and conarachin in arachin and conarachin-rich fractions were 75% and 65%, respectively. Conarachin-rich fractions were found to more conveniently aggregate than arachin-rich from the results of SDS-PAGE. The solubility of treated arachin and conarachin-rich fractions was decreased by 66.13% and 36.91%, respectively. Only marginal increase in Td was observed in the case of crosslinked arachin-rich fraction while significant increase in Td (of the order of 10°C) was observed in crosslinked conarachin-rich fraction. The H0 values of both crosslinked arachin and conarachin-rich fractions decreased significantly. The treated arachin and conarachin-rich fractions had more compact microstructure compared to their untreated samples. Hence, the comparison of arachin and conarachin-rich in crosslinking and the mechanism of properties enhancement by TG is the aim of the research.

Convenient Pd‐Catalyzed Synthesis of Large Unimolecular Star Polyethylene Nanoparticles

A simplistic convenient "arm-first" catalytic synthesis method is demonstrated to render soft unimolecular star polyethylene nanoparticles. Low-dispersity polyethylene arms of controllable length and topology are first synthesized via Pd-catalyzed "living" ethylene poly-merization. The subsequent addition of norbornadiene as a unique cross-linker renders the block polymer containing a short polynorbornadiene (PNBD) sequence. Efficient and rapid catalytic cross-linking of the PNBD sequences occurs in the polymer precipitation and drying steps to give rise to star polyethylene nanoparticles. The star polymers are featured with tunable arm length and topology, high molecular weight (as high as 1770 kg mol⁻¹), high arm numbers (as high as 88), and desirable average nano-particle size (29-72 nm).