聚苯醚热固性改性及其性能研究

通过溴化聚苯醚和格利雅试剂反应，将不饱和基团烯丙基引入聚苯醚中实现其热固性改性，由^1H-NMR和FTIR进行结构表征。确定了烯丙化聚苯醚的固化工艺，并对其固化产物性能进行测试。结果表明：按合成新工艺制备的热固性聚苯醚，其固化产物具有优异的介电性能(低介电常数、低介电损耗因子)，良好的耐溶剂性能和低吸湿性。     

Rehabilitation of a Spark Erosion Prosthesis: A Clinical Report

When complex prostheses are fabricated, it is expected that at some point maintenance will be necessary. This clinical report documents a 10-year-old maxillary spark erosion prosthesis that had been repaired many times, was discolored, and exhibited significant signs of wear. The metal superstructure was intact; therefore, only the acrylic resin base and teeth needed to be replaced. To reduce both cost and time without the prosthesis for the patient, the rehabilitation was completed within 24 hours.     

Novel Semi‐Fluorinated Poly(ether imide)s Derived From 4‐(p‐Aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl

An unsymmetrical diamine monomer 4‐(p‐aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl has been synthesized successfully. This monomer leads to the synthesis of different novel poly(ether imide)s when reacted with different dianhydrides like pyromellatic dianhydride (PMDA), benzophenone tetracarboxylic acid dianhydride (BTDA), 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane (6FDA), and oxy diphthalic anhydride (ODA). The poly(ether imide) prepared from this monomer on reaction with 6FDA is soluble in several organic solvents such as N‐methylpyrolidinone (NMP), dimethylformamide (DMF), N,N‐dimethylacetamide (DMAc), tetrahydrofuran (THF), and CHCl₃. The poly(ether imide)s prepared from BTDA and ODA are soluble in NMP, DMF, and DMAc but not in THF or CHCl₃, whereas the polymer prepared from PMDA is soluble only in NMP. The water uptake value for these poly(ether imide) films is very low (0.2–0.5%), and exhibited low dielectric constants (2.81 at 1 MHz). The polymers exhibited high thermal stability up to 532 °C in air for 5% weight loss, and high glass transition temperatures up to 288 °C. The polymer exhibited high tensile strength up to 135 MPa, modulus 3.2 GPa, and elongation at break up to 25%, depending on the exact polymer structure.

The structure of the poly(ether imide) synthesised from 4‐(p‐aminophenoxy)‐3‐trifluoromethyl‐4′‐aminobiphenyl and 2,2‐bis(3,4‐dicarboxyphenyl) hexafluoropropane. This polymer was soluble in many organic solvents.     

Development and Optimization of Broadband Acoustic Metamaterial Absorber Based on Parallel–Connection Square Helmholtz Resonators

An acoustic metamaterial absorber of parallel–connection square Helmholtz resonators is proposed in this study, and its sound absorption coefficients are optimized to reduce the noise for the given conditions in the factory. A two–dimensional equivalent simulation model is built to obtain the initial value of parameters and a three–dimensional finite element model is constructed to simulate the sound absorption performance of the metamaterial cell, which aims to improve the research efficiency. The optimal parameters of metamaterial cells are obtained through the particle swarm optimization algorithm, and its effectiveness and accuracy are validated through preparing the experimental sample using 3D printing and measuring the sound absorption coefficient by the standing wave tube detection. The consistency between the experimental data and simulation data verifies feasibility of the proposed optimization method and usefulness of the developed acoustic metamaterial absorber, and the desired sound absorption performances for given conditions are achieved. The experimental results prove that parallel–connection square Helmholtz resonators can achieve an adjustable frequency spectrum for the low frequency noise control by parameter optimization, which is propitious to promote its application in reducing the noise in the factory.     

抗肿瘤有效成分20(R)-25-OCH3-原人参二醇的结晶法分离

目的 从25-OCH₃-原人参二醇（25-OCH₃-PPD）非消旋体混合物中分离得到抗肿瘤有效成分20(R)-25-OCH₃-PPD （AD-1）。方法 采用结晶法拆分25-OCH₃-PPD非消旋体混合物中的AD-1,并对所用溶剂的种类、用量及结晶温度等分离条件进行了优化,探讨溶剂的介电常数和25-OCH₃-PPD非消旋体混合物的S/R比例间的关系。结果 25-OCH₃-PPD非消旋体混合物（R：59.34%;S：38.35%）,在最优条件下,丙酮26 mL、4 ℃时,可以获得AD-1的产率与纯度分别为38.76%、97.83%。结论 溶剂的电解质范围在20.7左右,低饱和度的溶剂以及低温有利于AD-1的分离。     

A Procedure to Measure the in-Situ Hygrothermal Behavior of Earth Walls

Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount of water contained in wall pores and its evolution. Thus the aim of this paper is to present a procedure to measure this key parameter in rammed earth or cob walls by using two types of probes operating on the Time Domain Reflectometry (TDR) principle. A calibration procedure for the probes requiring solely four parameters is described. This calibration procedure is then used to monitor the hygrothermal behavior of a rammed earth wall (1.5 m × 1 m × 0.5 m), instrumented by six probes during its manufacture, and submitted to insulated, natural convection and forced convection conditions. These measurements underline the robustness of the calibration procedure over a large range of water content, even if the wall is submitted to quite important temperature variations. They also emphasize the importance of gravity on water content heterogeneity when the saturation is high, as well as the role of liquid-to-vapor phase change on the thermal behavior.     

New Fluoropolymers Having Both Low Water Uptake and a Low Dielectric Constant

Polymers with both low water uptake and a low dielectric constant have seen interest from both the electronic and microelectronic industries for several years. They play a crucial role in maintaining the good operating situation of devices, whereas most other materials are unsatisfactory. In this contribution, two new fluoropolymers are reported, which are derived from the thermo‐crosslinking reaction of functional monomers containing perfluorocyclobutane and benzocyclobutene moieties. These polymers show water uptake ranging from 0.11 to 0.31% after immersion in boiling water (near 98 °C) for 96 h, and exhibit dielectric constants (k) of below 2.4 at a range of frequencies from 0.1 MHz to 30 MHz. In contrast, a comparative polymer without perfluorocyclobutane units has a k value of more than 2.70 and water uptake of 0.67%, respectively, suggesting that the low water absorption and dielectric constants of the fluoropolymers can be attributed to the existence of perfluorocyclobutane groups in the molecular backbone. These results also indicate that the properties of the fluoropolymers are superior to these of the most commercial polymeric low‐k materials, implying that these fluoropolymers could be used as the varnish for enameled wire in the electrical industry and as encapsulation resins in the microelectronics industry.

     

Broadband Dielectric Relaxation Spectroscopy of Functionalized Biobased Castor Oil Copolymer Thermosets

Novel biorenewable copolymer thermosets are successfully synthesized by the ring‐opening metathesis polymerization (ROMP) of norbornenyl‐functionalized castor oil (NCO) and norbornenyl‐functionalized castor oil alcohol (NCA) with controlled amounts of 0.8 and 1.8 norbornene rings per fatty acid chain, respectively. The NCO and NCA monomers are mixed in different concentrations and simultaneously polymerized via ROMP using Grubbs catalyst. Broadband dielectric relaxation spectroscopy (BDRS) is used to investigate the molecular dynamics of the fully cured copolymer thermosets over a wide range of frequencies (5 × 10^?2 to 0.5 × 10⁷ Hz) at different constant temperatures (?70 to 125 °C). Four phenomena, namely α‐, β‐, and γ‐relaxation processes and ionic conductivity are observed for all the measured samples.