On the equilibrium of funicular polyhedral frames and convex polyhedral force diagrams

This paper presents a three-dimensional extension of graphic statics using polyhedral form and force diagrams for the design of compression-only and tension-only spatial structures with externally applied loads. It explains the concept of 3D structural reciprocity based on Rankine’s original proposition for the equilibrium of spatial frames. It provides a definition for polyhedral reciprocal form and force diagrams that allows including external forces and discusses their geometrical and topological characteristics. This paper furthermore provides a geometrical procedure for constructing a pair of reciprocal polyhedral diagrams from a given polyhedron representing either the form or force diagram of a structural system. Using this method, this paper furthermore suggests a design strategy for finding complex funicular spatial forms in pure compression (or tension), based on the construction of force diagrams through the aggregation of convex polyhedral cells. Finally, it discusses the effect of changes in the geometry of the force diagram on the geometry of the form diagram and the distribution of forces in it.     

Synthesis of 3,13-diglycidyloxypropyloctaphenyl double-decker polyhedral oligomeric silsesquioxane and the thermal reaction properties with thermosetting phenol-formaldehyde resin

3,13-Diglycidyloxypropyloctaphenyl double-decker silsesquioxane (EP-DDSQ) was synthesized by process of alkaline hydrolysis condensation of phenyltrimethoxysilane and corner capping reaction of methyldichlorosilane, followed by hydrosilylation with allyl glycidyl ether, and the resultant structure was confirmed by fourier transform infrared spectrometer (FTIR) and nuclear magnetic resonance (NMR), respectively. The thermosetting phenol-formaldehyde (PF) resin was then modified by EP-DDSQ, and the reactivity of PF resin with EP-DDSQ and thermal pyrolysis of modified cured resin were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The surface morphologies of modified resins at high temperature were characterized with field emission scanning electron microscope (FESEM), and chemical structure of modified resins was analyzed through X-ray photoelectron spectrometer (XPS). The results showed that the appropriate addition of EP-DDSQ did not affect the curing temperature of the PF resin itself, but could improve the heat resistance of the system. When the amount of EP-DDSQ added was 10%, the initial degradation temperature of PF resin was increased by 49.31°C, and when the amount of EP-DDSQ added was 16%, the char yield of which was reached up to 61.39%, compared with that of pure PF resin (TGA_1,000°C of 57.62%) at Ar atmosphere. More importantly, the modified resin formed a regular and dense layer of SiC and SiO_x ceramic on the surface after ablation in the muffle furnace at 800°C air atmosphere, which is very important for ablative resistant materials.     

多面体低聚倍半硅氧烷的合成研究进展

首先介绍了多面体低聚倍半硅氧烷(POSS)的结构、分类和性质,然后综述了三官能度硅烷或四官能度硅烷在酸、碱和有机盐催化下通过水解缩合反应合成POSS的研究进展,以及以POSS为母体、通过封端关笼法、闭环法和官能团转化法合成POSS的研究进展。     

笼型倍半硅氧烷（POSS）的功能化改性 及应用研究进展

有机/无机杂化材料的改性及应用是目前材料科学中最富有活力的研究领域之一。其中笼型倍半硅氧烷（Polyhedral oligomeric silsesquioxane，POSS）在分子水平上实现了有机组分与无机组分的结合，结构呈硅氧骨架连接的立体笼型，具有优异的反应活性、耐热阻燃性、多孔性和纳米尺寸效应等特性，通过化学改性可将其应用在多个领域。本文主要从官能团改性、聚合改性和配位改性三个方面阐述了POSS的改性方法，综述了POSS在耐热材料、阻燃材料、增强材料和多孔材料等领域的应用研究进展，并对POSS今后的研究方向提出了展望。可从POSS的构效关系、改性方法以及安全性等方面进行更加深入和系统的研究，以促进POSS材料更广泛的应用。     

Epoxy‐functionalized polyhedral oligomeric silsesquioxane/cyanate ester resin organic–inorganic hybrids with enhanced mechanical and thermal properties

A series of cyanate ester resin (CE) based organic–inorganic hybrids containing different contents (0, 5, 10, 15 and 20 wt%) of epoxy‐functionalized polyhedral oligomeric silsesquioxane (POSS‐Ep) were prepared by casting and curing. The hybrid resin systems were studied by the gel time test to evaluate the effect of POSS‐Ep on the curing reactivity of CE. The impact and flexural strengths of the hybrids were investigated. The micromorphological, dynamic mechanical and thermal properties of the hybrids were studied by SEM, dynamic mechanical analysis (DMA) and TGA, respectively. Results showed that POSS‐Ep prolonged the gel time of CE. CE10 containing 10 wt% POSS‐Ep displayed not only the optimum impact strength but the optimum flexural strength. SEM results revealed that the improvement of mechanical properties was attributed to the large amount of tough whirls and fiber‐like pull‐outs observed on the fracture surfaces of CE10. DMA results indicated that POSS‐CE tended to decrease E′ of the hybrids in the glassy state but to increase E′ of the hybrids in the rubbery state. TGA results showed that CE10 also possesses the best thermal stability. The initial temperature of decomposition (T_i) of CE10 is 426 °C, 44 °C higher than that of pristine CE. © 2013 Society of Chemical Industry     

PC/POSS复合材料的制备及热性能

合成及表征了八苯基倍半硅氧烷（PH-POSS）、γ-甲基丙烯酰氧丙基倍半硅氧烷（MA-POSS）,并利用差示扫描量热（DSC）和热重分析（TGA）分别研究其在聚碳酸酯（PC）体系中对体系热性能的影响。研究结果表明,复合材料Tg随着PH-POSS含量的增加而降低;而随着MA-POSS含量的增加基本不受影响。在氮气中,复合...     

接枝法制备聚苯乙烯/笼型倍半硅氧烷复合材料

以工业级的3-氯丙基三氯硅烷和七聚(苯基)倍半硅氧烷三硅醇钠为原料,通过顶端封角法合成了含有一个3-氯丙基、七个苯基的单官能团POSS(3-氯丙基POSS),并以其作为聚苯乙烯的添加剂,采用化学接枝的方法制备POSS/PS复合材料.利用傅立叶转变红外光谱(FT-IR)、核磁共振(1H-NMR、29Si-NMR)和X-射...     

多官能度氨基苯基笼形硅倍半氧烷的合成表征及在聚碳酸酯中的应用

从合成八苯基硅倍半氧烷(OPS)出发,通过控制硝化条件制备了不同多官能度硝基苯基硅倍半氧烷(NPS),然后对NPS催化还原得到相应的多官能度氨基苯基硅倍半氧烷(APS).利用红外、核磁、元素分析、热失重对多面体低聚硅倍半氧烷(POSS)化学结构和热性能进行了表征.元素分析发现OPS硝化时间越长,硝基越多,但是不是正比关...     

功能化POSS对硅橡胶力学性能的影响及机理研究

研究了八聚笼型倍半硅氧烷(POSS)功能化侧基的种类和用量对硅橡胶力学性能的影响。结果表明,POSS的加入使硅橡胶的拉伸强度和断裂伸长率均下降,硬度均提高。乙烯基POSS的加入显著延长了硅橡胶的正硫化时间。POSS的加入能显著降低硅橡胶的压缩永久变形,乙烯基POSS的效果比甲基POSS好;且乙烯基含量越高,压缩永久变形越小。分析了功能化POSS对硅橡胶力学性能的影响机理。