Polybenzoxazine/organosilicon composites with low dielectric constant and dielectric loss

The evolution of electronic communication technology raises higher requirements for low dielectric constant(low-k)materials.For this,a benzoxazine functional organosilicon(HP-aptes)with dense Si—O—Si crosslinking networks and large sterically hindered tert-butyl groups was prepared by the sol–gel method.Then,a series of polybenzoxazine composites(PPHP)were prepared from intrinsically low dielectric constant bis-functional benzoxazine monomer(P-aptmds)and HP-aptes.The double crosslinking networks of polybenzoxazine and organosilicon further increased the crosslinking density and decreased the dipole density of composites,which endowed the composites with enhanced low-k properties.When the content of HP-aptes is 30%(mass),the crosslinking density was 2.05×10^(-3)mol·cm^(-3),while that of PP-aptmds was 3.31×10^(-3)mol·cm^(-3).In addition,the dielectric constant and dielectric loss of PPHP composite at 1 MHz could reach 2.61 and 0.0056,respectively.

PULTRUSION OF POLYBENZOXAZINE RESIN MATRIX Z-PIN

The pultrusion of the polybenzoxazine resin matrix Z-pin is studied, because the Z-pin technology is an efficient reinforcement method for composites. Based on the curing characteristics acquired by differential scanning calorimeter（DSC） analysis, the suitable mould temperature for pultrusion is researched with the visual inspection and the Z-pin short beam shear test. The pull-out test is designed to evaluate the post oven temperature that can affect the combination between Z-pins and laminates. And then, the appropriate temperature for the post oven is obtained. Finally, micro photos are used to inspect the defects in Z-pins. The results show that when the resin is heated to 70°C, Z-pin pultrusion demands for viscosity are satisfied, and the shelf-life is about 4 h. With the mould temperature increasing to 140°C, the Z-pin short beam shear strength rises correspondingly and the cross section profile is the best. When the post oven temperature declines, the combination between Z-pins and laminates becomes stronger. However, pores appear in Z-pins unless the oven temperature increases to 200°C. Therefore, the optimum post oven temperature should be set at 200°C.

Molecular Modeling of the Chain Structures of Polybenzoxazines

The structures and properties of benzoxazines were investigated by virtue of molecular modeling at a molecular level. By means of Cerius software(version 4.0) supplied by Molecular Simulations Inc., the molecular mechanics and the molecular dynamics were performed under a PCFF force field. Five kinds of the polymeric chains of benzoxazines were created by using polymer builder and energy minimization. The relaxation process was conducted with both energy minimization and molecular dynamics.

Kevlar fabric reinforced polybenzoxazine composites filled with silane treated microcrystalline cellulose in the interlayers:The next generation of multi-layered armor panels

The design of astonishing combinations of benzoxazine resins with various fillers is nowadays of great interest for high quality products,especially in ballistic armors.The objective of this study is to investigate a new hybrid material prepared as multi-layered composite plate by hand lay-up technique.Different composites were manufactured from Kevlar fabrics reinforced polybenzoxazine,which was filled with silane treated microcrystalline cellulose(MCC Si)at various amounts in the interlayers.The developed materials were tested for their flexural,dynamic mechanical and ballistic performance.The aim was to highlight the effect of adding different amounts of MCC Si on the behavior of the different plates.Compared to the baseline,the dynamic mechanical and bending tests revealed an obvious decrease of the glass transition of 21℃and a notable increase in storage modulus and flexural strength of about 180%and17%,respectively,upon adding 1%MMC Si as filler.Similarly,the ballistic test exhibited an enhancement in kinetic energy absorption for which the composite supplemented with 1%MCC Si had the maximal energy absorption of 166.60 J.These results indicated that the developed panels,with interesting mechanical and ballistic features,are suitable to be employed as raw materials to produce body armor.

Facile preparation of low shrinkage polybenzoxazine aerogels for high efficiency thermal insulation

High performance thermal insulation materials are urgently demanded for energy saving and thermal protection applications.Organic aerogels are considered as promising and highly efficient thermal insulation materials,but high shrinkage has been a major obstacle to limit their development and application.Herein,by a co-polymerization of formaldehyde(F)and benzoxazine prepolymers,polybenzoxazine with increased crosslink density and thus enhanced gel strength was formed,leading to low shrinkage polybenzoxazine(PBOF)aerogels with hierarchical micro/nanostructures.The hierarchical porous nanoskeleton of PBOF aerogels,composed of stacked thick-united spherical nanoparticles,was formed due to the different solubility of the reactants in N,N-dimethylformamide and F aqueous solution.Benefitting from the low shrinkage(13.22%,exceeding 60%reduction),the PBOF aerogels exhibit a low thermal conductivity of 0.0397 W m^(−1)K^(−1)at room temperature and outstanding thermal protection ability at high temperature.A 13 mm thick sample could resist a butane flame of 1300°C for 90 s,and the hand was not burn when touching the back.This strategy enables PBOF aerogels with a new perspective for their applications in civil and military fields.

SYNTHESIS AND CHARACTERIZATION OF POLYBENZOXAZINE CONTAINING PHOSPHORUS

The novel benzoxazine monomer containing phosphorus has been synthesized based on multifianctional amine route from bis（4-aminophenyl）phenylphosphate, p-cresol and formaldehyde. Subsequently, the benzoxazine monomer was thermo-cured into polybenzoxazine containing phosphorus. The chemical structures were identified by nuclear magnetic resonance （NMR）, Fourier transform infrared spectroscopy （FT-IR）. The curing reaction was monitored by differential scanning calorimetry （DSC） and FT-IR. The thermal and flame-retardant properties of obtained polybenzoxazine were evaluated by dynamic mechanical thermal analysis （DMA）, thermal gravimetric analysis （TGA） and oxygen index meter, respectively. The results show that the novel polybenzoxazine has high limiting oxygen index （38.1） and glass transition temperature （232℃）.

Smart synthesis of silver nanoparticles supported in porous polybenzoxazine nanocomposites via a main-chain type benzoxazine resin

In this article, novel silver nanoparticles immobilized on macroporous polybenzoxazine nanocomposites （Ag-poly（BA-ddm）^x main） were prepared as catalysts for catalytic reduction reaction. For this purpose, a main-chain type benzoxazine was cured in dimethyl sulfoxide by thermally activated ring-opening polymerization at 180℃ for 2days followed by the reduction of silver nitrate in homogeneous polybenzoxazine solution. The porous structure of the resin was confirmed by scanning electron microscope （SEM） analysis and N2 adsorption]desorption studies. Besides, transmission electron microscopy images showed that spherical particles （around 3-10 nm in sized） are dispersed in Ag-poly （BA-ddm）^x main network. The catalytic activity of the as-prepared nanocomposite has been investigated by photometrically monitoring the reduction of methylene blue by an excess of NaBH4. The kinetic data of the reduction reaction was explained by the assumption of a pseudo-first-order reaction with regard to methylene blue （MB）. As evidence by Ultraviolet （UV） spectral analysis, the Ag-poly（BA-ddm）^x main catalyst possesses excellent catalytic reduction of MB, and no deactivation or poisoning of the catalyst was observed. The results demonstrate that porous polybenzoxazine supported silver nanoparticles can be applied as reusable catalysts with satisfied catalytic activity.

Surface Properties and Hydrogen Bonds of Mono-functional Polybenzoxazines with Different N-substituents

A series of mono-functional benzoxazine monomers with different N-substituents were synthesized from phenol, formaldehyde, and various amines （ammonia, methylamine, n-butylamine, dodecylamine）, named P-am, P-m, P-b, and P-da, respectively. The surface properties of these polybenzoxazine films were proven by contact angle measurements. The hydrogen bond network of the polybenzoxazine systems was studied using the FTIR spectra. And the results showed that the surface free energy increased with increasing the fraction of intermolecular hydrogen bonding when the N-substituent was an alkyl chain. However, the rule was not suitable when the N-substituent was H. That was because there was one more kind of intramolecular hydrogen bond in the poly（P-am）. Based on these findings, we proposed that both the N-substituent alkyl group and the fraction of intermolecular hydrogen bonding had effects on the surface free energy.

Cyclotriphosphazene Fibre Reinforced Poly(benzoxazine-co-ε-caprolactam) Nanocomposites for Flame Retardant Applications

Cyclophosphazene nanotube （PZT） incorporated poly（benzoxazine-co-g-caprolactam） （P（BZ-co-CPL）） nano- composites were developed for improving flame retardant properties. The effects of PZT on the flammability properties of P（BZ-co-CPL） matrix were evaluated through UL-94 flammability test and limiting oxygen index （LOI）. The UL-94 results of P（BZ-co-CPL）/PZT hybrid nanocomposites showed V-1 rating, whereas neat P（BZ-co-CPL） showed burning rating. The LOI values are increased from 25.4 to 31.4 for 1.5 wt% PZT incorporated P（BZ-co-CPL） nanocomposite systems. SEM was used to study the char morphology of P（BZ-co-CPL）/PZT after being exposed to UL-94 flammability test. Data from thermal studies indicate that the PZT incorporated P（BZ-co-CPL） systems possess better Tg and thermal degradation behavior when compared to the neat P（BZ-co-CPL）. The values of dielectric constant are decreased with increasing temperature. From the values, it is ascertained that the P（BZ-co-CPL）/PZT systems exhibit stable dielectric behavior with regard to variation in temperature. The TEM images ascertain the uniform dispersion of PZT in the P（BZ-co-CPL） matrix.