聚钽碳硅烷陶瓷先驱体的制备与表征

为了提高SiC陶瓷纤维的综合性能,利用聚二甲基硅烷热解制得的产物液态聚硅烷(LPS)与五氯化钽(TaCl5)反应,制得含钽SiC陶瓷纤维的先驱体聚钽碳硅烷(PTCS).研究表明,反应过程中存在LPS的裂解重排反应,Si-H键在反应中显示出很高的活性,PTCS摩尔质量的增加是LPS形成的Si-H键与TaCl5发生交联反应的结果,用LPS与TaCl5为原料不但能够使钽元素成功地引入到先驱体中并分布均匀,而且由于其成本比其它原料相对低廉,便于大批量合成.     

聚铝碳硅烷的制备及应用进展

介绍了碳化硅（SiC）陶瓷纤维、含铝SiC陶瓷纤维的特点,综述了用聚碳硅烷、聚硅碳硅烷、聚二甲基硅烷与乙酰丙酮铝反应制备聚铝碳硅烷先驱体的合成方法,聚铝碳硅烷的化学结构及在制备耐超高温陶瓷纤维和发光陶瓷薄膜中的应用,评述了各种制备工艺的优缺点,提出了当前工作中需要解决的问题,并展望了今后的发展趋势。     

聚碳硅烷纤维的不熔化工艺研究

以聚二甲基硅烷(PDMS)为原料,在高压釜内高温高压反应合成了聚碳硅烷(PCS)先驱体,经多孔熔融纺丝制备lrPcs纤维。研究了不熔化温度、时间对PCS纤维质量、Si-H键反应程度、凝胶含量及氧含量的影响。研究表明：在不熔化过程中,PCS结构中的Si-H键与氧反应,在PCS分子间形成Si-O-Si交联结构;随着不熔化温度的提高,时间的延长,PCS纤维的质量、Si-H键反应程度、凝胶含量、氧含量均逐渐增加,并逐渐趋于稳定。高压合成的PCS不溶化反应活性较高,引入少量的氧(4％～7％)即可实现不熔化。     

由聚碳硅烷纤维通过化学气相交联法制备低氧含量碳化硅纤维

以环己烯和1-己炔作为反应气氛,对聚碳硅烷(polycarbosilane,PCS)纤维进行化学气相交联不熔化处理,研究不熔化过程中PCS纤维的反应程度,凝胶含量变化以及烧成纤维的组成结构和性能.结果表明:在不饱和烃不熔化过程中,PCS分子结构中的Si-H键参与反应,Si-H键反应程度和PCS纤维的凝胶含量均随不熔化温度的提高逐渐增加且逐渐趋于稳定.制得的SiC纤维中氧的质量分数降低到5%～6%,纤维的拉伸强度达到2.60 GPa.X射线衍射谱显示:与空气不熔化相比,化学气相交联法制备的SiC纤维具有更好的β-SiC微晶结构.     

先驱体转化法原位制备TiO_2膜层SiO_2纤维

用聚碳硅烷与钛酸四正丁酯(titanium tetrabutoxide,TBT)在200℃氮气气氛中反应5h得到含过量TBT的聚钛碳硅烷(polytitanocarbosilane,TPTC)先驱体。将先驱体TPTC于160℃熔融纺丝制得原纤维后,经空气中100℃熟化处理20h,200℃交联处理20h及1200℃烧结可原位制得TiO2/SiO2纤维。利用红外光谱、核磁共振(13C,29Si)、X射线衍射、扫描电镜和能量散射X射线光谱分析表征发现:随着TBT量的增加,TPTC中的Si—H键含量减少,Si—O键增多;纤维由无定形SiO2和锐钛矿TiO2组成,表面光滑致密无明显缺陷,纤维表面为TiO2富集。     

γ射线辐照聚碳硅烷先驱丝协同热交联制备高强度碳化硅纤维

采用γ射线在空气中辐照聚碳硅烷(polycarbosilane,PCS)先驱丝,将吸收剂量低于凝胶点剂量的PCS先驱丝在选定条件下作特殊的热交联处理,然后在惰性气氛保护下热解转化为SiC陶瓷纤维.通过红外光谱、热重分析、拉伸强度和氧含量测试研究了聚碳硅烷先驱丝的化学结构、热分解特性的变化以及烧成SiC纤维的结构与性能.结果表明:经热处理PCS的先驱丝形成了三维网络不熔不溶结构,其陶瓷产率高于未经热处理的先驱丝的陶瓷产率;经热交联处理的先驱丝所烧成的SiC纤维抗拉强度达2.3 GPa,较未经热交联处理的先驱丝所制得的SiC纤维的拉伸强度大幅提高;辐照协同热交联法制备的SiC纤维的氧含量低于直接辐照不熔化法制备的SiC纤维的氧含量.     

含氧气氛下电子束辐照聚碳硅烷制备碳化硅纤维

以聚碳硅烷(polycarbosilane,PCS)为原料,在含氧气(1%)的气氛下用电子束低剂量辐照PCS原丝,然后在惰性气氛下退火实现不熔化处理并烧成制得碳化硅(SiC)纤维.分析了退火温度对辐照后PCS的氧含量、凝胶含量及化学结构的影响,研究了PCS在含氧气氛下辐照及在惰性气氛下退火所发生的化学反应.结果表明:在辐照过程中,主要是Si-H与O2反应生成Si-OH;在退火过程中,主要是Si-OH缩合脱水生成Si-O-Si交联结构.在1250℃烧成制得的SiC纤维呈芯-壳结构,表壳富氧,而芯部氧含量较低.纤维的平均拉伸强度为2.4GPa,平均弹性模量为170.1 GPa.     

聚碳硅烷应用的研究进展

聚碳硅烷(PCS)作为碳化硅(SiC)陶瓷的先驱体,具有陶瓷产率高、制备连续纤维可改性加工性优异以及自交联性良好等特点,被广泛用于航空航天等高科技领域.本文就聚碳硅烷的性能以及它在SiC陶瓷和其他方面的应用进行了阐述.     

聚碳硅烷—沥青共聚物的合成和应用

聚碳硅烷一沥青共聚物是制备SiC—C材料的先驱体,具有很广阔的应用前景。这里介绍了聚碳硅烷一沥青共聚物的合成、性能及应用。     

可固化高陶瓷产率聚碳硅烷的合成与性能研究

以聚碳硅烷(PCS)和四甲基四乙烯基环四硅氧烷(DVi4)为原料,合成了新型含乙烯基聚碳硅烷(PVCS).利用FT- IR、GPC、DSC、TG、XRD等分析手段对PVCS的结构、固化特性及裂解特性进行表征.结果表明:PVCS中含有Si-H及C＝C基,可在200～ 350℃固化,350℃固化质量保留率为96.6％,1 000℃陶瓷产率为80.0％,1 200℃陶瓷产物出现β- SiC微晶.     

Insect antifeedant properties of anthranoids from the genusVismia

Vismiones and ferruginins, representatives of a new class of lypophilic anthranoids from the genusVismia were found to inhibit feeding in larvae of species ofSpodoptera, Heliothis, and inLocusta migratoria.     

Direct observation of freeze-thaw instability of latex coatings via high pressure freezing and cryogenic SEM

Despite its industrial importance, the subject of freeze-thaw (F/T) stability of latex coatings has not been studied extensively. There is also a lack of fundamental understanding about the process and the mechanisms through which a coating becomes destabilized. High pressure (2100 bar) freezing fixes the state of water-suspended particles of polymer binder and inorganic pigments without the growth of ice crystals during freezing that produce artifacts in direct imaging scanning electron microscopy (SEM) of fracture surfaces of frozen coatings. We show that by incorporating copolymerizable functional monomers, it is possible to achieve F/T stability in polymer latexes and in low-VOC paints, as judged by the microstructures revealed by the cryogenic SEM technique. Particle coalescence as well as pigment segregation in F/T unstable systems are visualized. In order to achieve F/T stability in paints, latex particles must not flocculate and should provide protection to inorganic pigment and extender particles. Because of the unique capabilities of the cryogenic SEM, we are able to separate the effects of freezing and thawing, and study the influence of the rate of freezing and thawing on F/T stability. Destabilization can be caused by either freezing or thawing. A slow freezing process is more detrimental to F/T stability than a fast freezing process; the latter actually preserves suspension stability during freezing. Presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27–29, 2004 in Chicago, IL. Tied for first place in The John A. Gordon Best Paper Competition.     

Ethanol and (−)-α-Pinene: Attractant Kairomones for Bark and Ambrosia Beetles in the Southeastern US

In 2002–2004, we examined the flight responses of 49 species of native and exotic bark and ambrosia beetles (Coleoptera: Scolytidae and Platypodidae) to traps baited with ethanol and/or (−)-α-pinene in the southeastern US. Eight field trials were conducted in mature pine stands in Alabama, Florida, Georgia, North Carolina, and South Carolina. Funnel traps baited with ethanol lures (release rate, about 0.6 g/day at 25–28°C) were attractive to ten species of ambrosia beetles (Ambrosiodmus tachygraphus, Anisandrus sayi, Dryoxylon onoharaensum, Monarthrum mali, Xyleborinus saxesenii, Xyleborus affinis, Xyleborus ferrugineus, Xylosandrus compactus, Xylosandrus crassiusculus, and Xylosandrus germanus) and two species of bark beetles (Cryptocarenus heveae and Hypothenemus sp.). Traps baited with (−)-α-pinene lures (release rate, 2–6 g/day at 25–28°C) were attractive to five bark beetle species (Dendroctonus terebrans, Hylastes porculus, Hylastes salebrosus, Hylastes tenuis, and Ips grandicollis) and one platypodid ambrosia beetle species (Myoplatypus flavicornis). Ethanol enhanced responses of some species (Xyleborus pubescens, H. porculus, H. salebrosus, H. tenuis, and Pityophthorus cariniceps) to traps baited with (−)-α-pinene in some locations. (−)-α-Pinene interrupted the response of some ambrosia beetle species to traps baited with ethanol, but only the response of D. onoharaensum was interrupted consistently at most locations. Of 23 species of ambrosia beetles captured in our field trials, nine were exotic and accounted for 70–97% of total catches of ambrosia beetles. Our results provide support for the continued use of separate traps baited with ethanol alone and ethanol with (−)-α-pinene to detect and monitor common bark and ambrosia beetles from the southeastern region of the US.     

Methyl 2,4,6-decatrienoates Attract Stink Bugs and Tachinid Parasitoids

Halyomorpha halys (Stål) (Pentatomidae), called the brown marmorated stink bug (BMSB), is a newly invasive species in the eastern USA that is rapidly spreading from the original point of establishment in Allentown, PA. In its native range, the BMSB is reportedly attracted to methyl (E,E,Z)-2,4,6-decatrienoate, the male-produced pheromone of another pentatomid common in eastern Asia, Plautia stali Scott. In North America, Thyanta spp. are the only pentatomids known to produce methyl 2,4,6-decatrienoate [the (E,Z,Z)-isomer] as part of their pheromones. Methyl 2,4,6-decatrienoates were field-tested in Maryland to monitor the spread of the BMSB and to explore the possibility that Thyanta spp. are an alternate host for parasitic tachinid flies that use stink bug pheromones as host-finding kairomones. Here we report the first captures of adult and nymph BMSBs in traps baited with methyl (E,E,Z)-2,4,6-decatrienoate in central Maryland and present data verifying that the tachinid, Euclytia flava (Townsend), exploits methyl (E,Z,Z)-2,4,6-decatrienoate as a kairomone. We also report the unexpected finding that various isomers of methyl 2,4,6-decatrienoate attract Acrosternum hilare (Say), although this bug apparently does not produce methyl decatrienoates. Other stink bugs and tachinids native to North America were also attracted to methyl 2,4,6-decatrienoates. These data indicate there are Heteroptera in North America in addition to Thyanta spp. that probably use methyl 2,4,6-decatrienoates as pheromones. The evidence that some pentatomids exploit the pheromones of other true bugs as kairomones to find food or to congregate as a passive defense against tachinid parasitism is discussed.     

2007～2008年世界塑料工业进展

收集了2007年7月～2008年6月世界塑料工业的相关资料,介绍了2007～2008年国外塑料工业的发展情况,提供了世界塑料产量、消费量及全球各类树脂的需求量及产能情况.按通用热塑性树脂(聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂)、工程塑料(尼龙、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚)、特种工程塑料(聚苯·硫醚、液晶聚合物、聚醚醚酮)、通用热固性树脂(酚醛、聚氨酯、不饱和聚酯树脂、环氧树脂)不同品种的顺序,对树脂的产量、消费量、供需状况及合成工艺、产品应用开发、树脂品种的延伸及应用的进一步扩展等技术作了详细介绍.     

2005～2006年国外塑料工业进展

收集了2005年7月～2006年6月国外塑料工业的相关资料,介绍了2005—2006年国外塑料工业的发展情况。提供了世界塑料产量、消费量及全球各类树脂生产量以及各国塑料制品的进出口情况。作为对比,介绍了中国塑料的生产情况。按通用热塑性树脂（聚乙烯、聚丙烯、聚苯乙烯、聚氯乙烯、ABS树脂）、工程塑料（聚酰胺、聚碳酸酯、聚甲醛、热塑性聚酯、聚苯醚）、通用热固性树脂（酚醛、聚氨酯、不饱和树脂、环氧树脂）、特种工程塑料（聚苯硫醚、液晶聚合物、聚醚醚酮）的品种顺序,对树脂的产量、消费量、供需状况及合成工艺、产品开发、树脂品种的延伸及应用的扩展作了详细的介绍。