Improved thermal conductivity and excellent electrical insulation properties of polysiloxane nanocomposite-incorporated functional boron nitride sheets via in situ polymerization.

Benefiting from its high thermal conductivity (κ) and superior insulation, the boron nitride nanosheet (BNNS) is widely investigated as a promising filler for thermal nanocomposites. However, poor dispersibility and weak interaction with polymer matrix hinder the further improvement of BNNS-based thermal composites. Here, inspired by side-chain liquid crystal polysiloxane (SCLCP) with good mesomorphic structures, highly thermoconductive nanocomposites prepared via in situ polymerization using SCLCP with 2D BNNS are reported. The surface of BNNS is silanized with γ-(methacryloxy)propyltrimethoxysilane (KH-570) to introduce double bonds (defined as f-BNNS), and it is directly linked with SCLCP chains during polymerization. Therefore, the alternating stacking of f-BNNS and microscopic ordered structure of SCLCP yielded a high κ of 2.463 W m-1 K-1 at only 30 wt% f-BNNS content, improving dramatically the κ of pure SCLCP by ∼9 times. Further, the volume electrical resistivity reached 2.11 × 1014 Ω cm, which is five orders of magnitude higher than the critical resistance for electrical insulation (109 Ω cm). Also, the f-BNNS/SCLCP composites as thermal management materials decreased the temperature of the LED chip by 17.5 °C, exhibiting superior thermal management performance. Along with high κ and excellent electrical resistance, this type of nanocomposites displays great advantages in thermal properties for electronic packaging and thermal management of electronics.

Synthesis and Properties of a Novel Thermally Conductive Pressure-Sensitive Adhesive with UV-Responsive Peelability.

Thermally conductive pressure-sensitive adhesive (PSA) has received a great amount of attention in recent years, but the traditional PSA hardly loses adhesion properties after UV irradiation or heating. Therefore, endowing thermally conductive adhesive with UV-responsive peelability becomes a design strategy. Herein, vinyl-functionalized graphene (AA-GMA-G) is prepared by modifying graphene with acrylic acid and subsequently reacting with glycidyl methacrylate. Then, the UV-curable acrylate copolymer is synthesized by grafting glycidyl methacrylate. Finally, the novel thermally conductivity PSA with UV-responsive peelability is obtained by blending the copolymer with AA-GMA-G and photoinitiator. The results show that the PSA at 2 wt% AA-GMA-G loading exhibits an excellent thermal conductivity (0.74 W m-1 K-1 ) and a relatively strong peel strength, increasing by 15% compared with pristine graphene/PSA. Interestingly, the peel strength of AA-GMA-G/PSA can achieve a dramatic drop after UV treatment, and the decrease rate is 96.7%. Therefore, the novel thermally conductive PSA with UV-responsive peelability has potential applications in certain electronic devices.

Antibacterial and Alkali-responsive Cationic Waterborne Polyurethane Based on Modification of Aloe Emodin.

Cationic water-based polyurethane(CWPU) was synthesized to explore aloe-emodin modifies to obtain CWPU materials with better comprehensive performance. It provides a simple way to synthesize antibacterial waterborne polyurethane, which is to introduce the end-blocking group of herbal extracts into the structure. It contains synergistic antibacterial effect of herbal antibacterial and quaternary ammonium ion on Escherichia coli. It makes the material resist the erosion of bacterial, and increase the service life of materials. When the pH value of the environment changes, the UV absorbance of the aloe-emodin modified cationic water-based polyurethane(AE-CWPU) also changes. Therefore, within a certain detection range, AE-CWPU has great applications in the field of smart response materials. The modified thermodynamic properties have been improved, and the mechanical properties basically maintained the maximum stress, and the elongation at break was reduced.

Self-assembled supramolecule for synthesizing highly thermally conductive Cellulose/Carbon nitride nanocomposites with improved flame retardancy.

The fabrication of polymer composites with excellent thermal conductivity typically involves complex matrix or fillers modifications. This study proposed a simple technique based on precursor selection for obtaining highly thermally conductive cellulose nanofiber (CNF)/supramolecule-synthesized carbon nitride (SCN) composites. Fourier-transform infrared tests demonstrated the construction of hydrogen bonds between CNF and SCN; a highly ordered structure and relatively compact in-plane stacking were confirmed via scanning electron microscopy and X-ray diffraction characterizations. Consequently, the resultant CNF/SCN composites exhibited remarkable in-plane thermal conductivity of 11.83 ± 0.41 W m-1 K-1 at 30 wt% SCN content, which was attributed to the significantly reduced interfacial phonon scattering. It also showed evident improvements in electrical insulation and flame retardancy compared with the pure CNF film, where the volume resistivity, peak heat release rate, and total heat release were remarkably enhanced by 1242% and reduced by 59.9% and 15.8%, respectively. Further analysis of char residuals revealed a relatively dense surface, high concentration of carbon materials, and a high degree of graphitization, indicating that the char residual functioned as a robust physical barrier to effectively inhibit combustion. This study provides a facile approach to achieving high-efficiency improvements in thermal conductivity and flame retardancy, and simultaneously facilitating broader applications of carbon nitride in thermal management.

Effect of modified bamboo lignin replacing part of C5 petroleum resin on properties of polyurethane/polysiloxane pressure-sensitive adhesive and its application on the wood substrate.

This paper reports a fresh and robust strategy to develop polyurethane/polysiloxane pressure-sensitive adhesives (PSAs) with excellent properties by replacing part of C5 petroleum resin with modified lignin. A unique aspect of this work is the use of renewable lignin to obtain modified monomers. The phenolic hydroxyl group of lignin is increased by 21.4% after demethylation, which will help to introduce 6-bromo-1-hexene into the lignin structure through Williamson method. The L3 lignin and C5 petroleum resin are mixed with polyurethane/polysiloxane prepolymer, and furthermore a series of PSAs are obtained under ultraviolet light. It turns out that L3 lignin can not only replace part of C5 petroleum resin, but also obtain attractive and controllable features. Especially when the mass ratio of C5 petroleum resin to L3 lignin is 6:4, compared with pure C5 petroleum resin, the 180° peel strength and the shear strength of PU46 are increased by 24.1% and 91.5% respectively. Additionally, the shear strength on the wood substrate is increased by 320.6%. This study provides an effective method for the preparation of high value-added lignin PSA, and expands the application fields of PSA.

Alkynyl-functionalization of hydroxypropyl cellulose and thermoresponsive hydrogel thereof prepared with P(NIPAAm-co-HEMAPCL).

A ternary system thermoresponsive hydrogel, poly(N-isopropylacrylamide-co-hydroxyethyl methylacrylate polycaprolactone)/hydroxypropyl cellulose (or P(NIPAAm-co-HEMAPCL)/HPC), was prepared via "alkynyl/azide" click chemistry between the azide modified graft copolymer P(NIPAAm-co-HEMAPCL-N3) and the alkynyl modified HPC (or alkynyl-HPC). The structures of P(NIPAAm-co-HEMAPCL-N3) and alkynyl-HPC were characterized by (1)H NMR, SEC and FT-IR, and the results demonstrated that the mole ratio of the alkynyl and azide functional groups, and the feed ratios of HPC, PCL, and PNIPAAm could be easily adjusted. The incorporation of PCL and HPC dramatically enhanced the compression modulus of the P(NIPAAm-co-HEMAPCL)/HPC hydrogel, which ranged from 500 to 1000 g/cm(2). Due to the immiscibility of HPC and PCL, a heterogeneous and semicontinuous structure was observed via SEM. The incorporation of HPC accelerated the water absorption rate and enhanced the hydrogel's ability to shed water. The swelling-deswelling and compressive properties could also be adjusted by changing the feeding ratio. The hydrogel exhibited reversible swelling-deswelling behavior after three "swelling-deswelling" cycles.

Synthesis of copolymers with cyclodextrin as pendants and its end group effect as superplasticizer.

In this paper, the efficient approach for the synthesis of ß-cyclodextrin (CD) based functional monomers was described. Based on the monovinyl ß-CD monomer (GMA-EDA-CD), a new type poly(AA-co-GMA-EDA-CD) (PCDs) copolymer bearing pendent CD groups was synthesized and used as superplasticizer. Their chemical compositions were characterized by FT-IR, NMR, MALDI-TOF and GPC. The effects of PCDs on dispersion and adsorption in cement mortars were detailed discussed. The results indicated that PCD copolymers behaved excellent dispersion ability and strong retarding effect. PCD2 with molar ratio (%) for monomer (AA:GMA-EDA-CD=80:20) had the best dispersion and dispersion maintaining abilities, which were mainly attributed to the synergistic effects of steric hindrance and electrostatic repulsive force, and the retarding effect of PCD copolymers resulted from steric hindrance repulsion of CD pendants and the large number of hydroxyl groups, which affected the hydration reaction of cement.

The effects of different solvents and excitation wavelength on the photophysical properties of two novel Ir(III) complexes based on phenylcinnoline ligand.

Two novel cyclometalated iridium(III) complexes, Ir(pcl)2(pic) and Ir(pcl)2(fpic) (pcl: 3-phenylcinnoline, pic: picolinic acid, fpic: 5-fluoro-2-picolinic acid) were synthesized and characterized by FTIR, (1)H NMR spectroscopy, UV-vis, PL, and MALDI-TOF. These two Ir-complexes geometry were predicted using the Sparkle/PM6 model and suggested to a chemical environment of very low symmetry around the Ir ions (C 1). The PL spectrum of Ir(pcl)2(pic) and Ir(pcl)2(fpic) indicated that these complex belonged to red light emission, and maximum emission wavelength located at 647 and 641 nm, respectively. Most importantly, the effects of different solvents on their photoluminescent properties were detailed investigated. The results indicated that the polarity of solvent played an important role for their emission spectra. With introducing fluoro group to the pyridyl ring, the maximum emission wavelength of Ir(pcl)2(fpic) was blue shifted about 6 nm, and the quantum yield was slightly higher than that of Ir(pcl)2(pic). In addition, the thermal properties of these two Ir-complexes were measured by TGA, and results indicated that they had relative good thermal properties.

The effect of two additional Eu3+ lumophors in two novel trinuclear europium complexes on their photoluminescent properties.

Two novel trinuclear europium complexes based on trisphen(1,3,5-tris{4-((1,10-phenanthroline-[5,6-d]imidazol-2yl)phenoxy)methyl}-2,4,6-trimethyl-benzene) as a second ligand were designed, synthesized, and characterized by FT-IR, (1)H NMR, UV-visible, photoluminescence (PL) spectroscopy, elemental analysis (EA) and ESI-MS. The geometries of these two trinuclear europium complexes were predicted using the Sparkle/PM3 model and suggested a chemical environment of very low symmetry around the lanthanide ions (C(1)), which is in agreement with the luminescent spectra. CV analysis demonstrated that the trinuclear complexes possessed excellent electro-injection abilities. The effects of two additional Eu(3+) lumophors in these trinuclear europium complexes on their photoluminescent properties were investigated in detail. The results indicated that these trinuclear europium complexes exhibited highly luminescent quantum efficiencies and experimental intensity parameters in the solid state. Especially, due to the contribution of the two additional Eu(3+) lumophors in the trinuclear europium complexes, the quantum efficiency of the trinuclear complex Eu(3)(TTA)(9)trisphen was higher (ca. 34%) than the mononuclear europium complex Eu(TTA)(3)imidazophen.