主链含环二硅氮烷硅橡胶的热稳定性

本文采用TGA、IGA、GC和 GC-MS比较了主链含环二硅氮烷硅橡胶与一般硅橡胶的热稳定性,发现硅氮橡胶在升温失重时,起始失重温度比甲基硅橡胶高150—200℃,在350℃氮气下恒温热失重要比甲基和苯基硅橡胶低十多倍。环二硅氮烷的存在是硅氮橡胶主链热稳定性好的原因。另外硅氮橡胶主链中的硅氧链节数目,对其热稳定性几乎无影响,硅氮橡胶主链热降解机理与甲基硅橡胶不同,它的降解是先经过链之间的重排。     

耐高温室温硫化氟硅橡胶

采用原硅酸乙酯和硅氮聚合物（ＫＨ ＣＬ） 为交联剂制备了两种室温硫化氟硅橡胶,通过ＴＧ、ＩＧＡ 以及测定溶胶量等方法研究了两种氟硅橡胶在氮气下的降解动力学,并分别求出了降解速率和活化能．通过对比两种氟硅橡胶的热稳定性,阐述了硅氮交联剂对于提高氟硅橡胶热稳定性的作用机理．     

硅氮烷添加剂的水解稳定性对硅橡胶热稳定性的影响

采用一种新的方法研究了硅氮烷水解反应的动力学规律 ,根据实验数据测出硅氮烷水解速率对硅氮烷的浓度符合一级动力学关系 .计算出了几种硅氮化合物与水蒸气反应的表观活化能 ,结果表明硅氮烷的结构与其水解反应的表观活化能有密切的关系 .硅原子或氮原子上带有较大空间位阻的基团后 ,其水解稳定性提高 .其中六苯基环三硅氮烷 4的水解表观活化能为 2 14kJ mol,而苯基硅氮聚合物 5的水解表观活化能更达到 2 91 3kJ mol.添加到硅橡胶中的硅氮化合物水解表观活化能越大 ,即水解稳定性越高 ,其改进硅橡胶热稳定性的效果越好 .将 4和 5添加到硅橡胶生胶中 ,35 0℃下老化 2 4h的热失重分别为 0 96 %和 0 6 % .     

硅橡胶热降解动力学的研究

用恒温热失重方法，研究了甲基硅橡胶（Ｓｉ—Ｏ—１），用氢氧化钾催化聚合的甲基硅橡胶（Ｓｉ—Ｏ—２），主链含环二硅氮烷的硅氮橡胶（Ｓｉ—Ｎ—１）以及它与Ｓｉ—Ｏ—１的共混物Ｓｉ—Ｏ—３和与Ｓｉ—Ｏ—２的共混物Ｓｉ—Ｏ—４的热降解反应动力学．结果表明Ｓｉ—Ｎ—１有最高的热稳定性，在氮气下，其降解反应活化能为３４４ｋＪ／ｍｏｌ．并且发现它分别与Ｓｉ—Ｏ—１和Ｓｉ—Ｏ—２的共混物的热稳定性大幅度提高．Ｓｉ—Ｏ—３在氮气下的降解活化能由未加入Ｓｉ—Ｎ—１前的１５２ｋＪ／ｍｏｌ提高到２３０ｋＪ／ｍｏｌ；Ｓｉ─Ｏ─４则由未混入Ｓｉ─Ｎ─１前的６１ｋＪ／ｍｏｌ提高到１４４ｋＪ／ｍｏｌ．我们认为这种作用机理是由于硅氮橡胶除去了微量吸附水和硅羟基并导致催化剂的离子对难于分离的结果．     

硅氮聚合物研究的进展

综述了硅氮聚合物近年来在作为硅氮陶瓷前体和硅橡胶改性加工剂以及其结构分析方面研究的进展。     

超支化聚碳硅氮烷的合成与表征

聚碳硅氮烷是一种新型含硅有机金属聚合物,其主链由硅氮碳连接而成,侧链为有机基团;与其它含硅聚合物(聚硅氮烷、聚碳硅烷等)类似,聚碳硅氮烷适于用做力学性能极佳且耐高温氧化的氮化硅(Si3N4)和氮化硅/碳化硅(Si3N4/SiC)复相陶瓷的前驱体.[1]超支化聚合物具有溶解性好、粘度低     

硅氮聚合物交联剂交联的室温硫化硅橡胶的热稳定性

利用硅氮聚合物作交联剂使双组分缩合型室温硫化硅橡胶在不需要催化剂存在下硫化，通过对硫化胶老化后的热失重、交联密度和力学性能的测定，表明这种硫化胶的耐温性能由２００℃提高到３５０℃．对硫化胶的降解动力学研究表明：降解反应活化能由７０ＫＪ／ｍｏｌ提高到３３０ＫＪ／ｍｏｌ，这是由于消除了端基引发的主链降解．     

加成型交链聚硅氧烷玻璃毛细管柱（ACOT）的研制及评价

]本文介绍一种加成交链方法制备交链毛细管柱,此方法采用端基含乙烯基的低分子量的甲基乙烯基硅油和含氢硅油在微量铂催化剂作用下室温加成,交链同时伴有链增大,使低分子量硅油交链并聚合形成高热稳定性的硅弹性体。玻璃毛细管柱采用氟化氢铵蚀刻法进行表面粗糙化,玻璃表面钝化采用六甲基二氨硅烷（HDMS）和含氢硅油钝化方法并收到了较好的效果。采用此方法制备出的玻璃毛细管柱,非极性、中极性柱理论板数高达4000块／m,并可在320℃～340℃下程序升温使用,氰乙基硅橡胶柱程序升温可到260℃,经Grob混合物评价,吸附较小,是一种低流失,耐高温、液膜不可抽提的高效柱。     

环二硅氮烷-聚硅氧烷共聚物高温气相色谱固定相的研究

含苯基的环二硅氮烷聚硅氧烷共聚物(TMCDPS)主链上含有刚性结构,具有良好的耐热性能。将此材料用作毛细管气相色谱固定相,考察该固定相的柱效、极性、热稳定性,并对石蜡、聚乙烯裂解产物、原油等样品进行色谱分析。实验结果表明:该固定相有着良好的分离效果,属于中等极性固定相,其最为突出的特点就是在聚硅氧烷主链上引入大分子基团,使得其耐温性能大大提高,温度达到400℃时,柱流失量依然不高。     

可紫外光固化的聚乙烯基硅氮烷合成与表征

采用带丙烯酸酯基团的烯丙基溴化合物(4-溴丁烯酸乙酯)和聚乙烯基硅氮烷发生取代反应,实现了丙烯酸酯基团在聚乙烯基硅氮烷主链上的链接.采用质子核磁共振谱(1H-NMR)和二维质子核磁共振谱(2D-1H-1H-NMR)对分子结构进行了表征,采用光学差热分析仪(Photo-DSC)和傅立叶转换红外光谱仪(FT-IR)测试了改性高分子的光敏性能,用热重分析仪(TGA)分析了产物在高纯氮气氛围下的陶瓷收率.结果表明,通过分子改性,交联固化时间从改性前的20min减少到1min之内,功能化的聚乙烯基硅氮烷可以在光刻蚀工艺中作为负性光刻胶使用.     

Synthesis and properties of thermoplastic and dissolvable polysiloxanes containing polyhedral oligomeric silsesquioxane

There are many benefits associated with thermoplastic silicones, but very few examples exist: silicone resins or rubbers are normally thermosets. In this article, a facile and efficient approach was reported to prepare thermoplastic silicone by introducing a bulky side siloxane group. Monofunctional polyhedral oligomeric silsesquioxane (POSS), as the bulky siloxane group, was grafted onto the linear polysiloxane backbone via thiol–ene click reaction, endowing the liquid polysiloxane with thermoplastic nature. The POSS-grafted polysiloxane could be remolded by a hot-melting or solution casting process. It was worth noting that the novel thermoplastic silicone was composed of both linear siloxane main chains and siloxane side groups, which was distinctly different from previous researches on thermoplastic silicones consisted of siloxane main chains and organic side groups. Thermal analysis, rheological characterization and molecular dynamics simulation results revealed the thermoplastic properties of POSS-grafted polysiloxane depended on the bulky POSS's hindrance to the movement of the polymer backbone rather than the interaction between the organic side groups.     

Synergistic effect between POSS and fumed silica on thermal stabilities and mechanical properties of room temperature vulcanized (RTV) silicone rubbers

In this paper, both divinyl-hexa[(trimethoxysilyl)ethyl]-POSS (DVPS) and fumed silica were firstly introduced into polydimethylsiloxane (PDMS) system using as the cross-linker and the reinforcing filler respectively. And a series of novel RTV silicone rubbers synergistically enhanced by DVPS and fumed silica were prepared. The cross-linked networks in the novel RTV silicone rubbers have been studied by attenuated total reflection infrared spectroscopy, and the dispersions of POSS and fumed silica in these novel RTV silicone rubbers have been observed by means of scanning electron microscope (SEM). And thermal stabilities, thermo-oxidative stabilities and mechanical properties of these novel RTV silicone rubbers were studied by means of thermal gravimetric analysis and universal tensile testing machine, respectively. From the obtained results, it was found that synergistic effect between POSS-rich areas and fumed silica on thermal stability and mechanical property of RTV silicone rubber indeed existed. And the experimental results also exhibited that the thermal stabilities and mechanical properties of the novel RTV silicone rubbers were far better than those of the reference materials (DVPR and MTFR). The striking enhancements in thermal properties and improvements on mechanical properties of novel RTV silicone rubbers were likely attributed to the synergistic effect between POSS-rich domains and fumed silica. Meanwhile, it was found that the mechanical properties of RTV silicone rubbers prepared with a given amount of POSS cross-linker were enhanced with the increment of the loading amount of fumed silica.     

聚硅氧烷热稳定性研究进展

综述了聚硅氧烷的热老化机理、影响其热稳定性的因素和提高其热稳定性的途径。聚硅氧烷的热老化反应主要包括热解聚和热氧化两个反应。氧气、水或醇、酸、碱或残留催化剂、硅油、机械外力、填料、聚硅氧烷的链端基等都会影响聚硅氧烷的热稳定性。提高聚硅氧烷热稳定性的途径主要有改变聚硅氧烷的分子结构以及在体系中添加热稳定剂。     

空间质子与电子综合辐照作用下甲基硅橡胶破坏模型

利用空间辐照环境模拟设备对甲基硅橡胶进行了质子、电子综合辐照试验.质子、电子的辐照能量均为150 keV,辐照剂量均为10¹⁶ cm^-2.质谱测试发现,综合辐照过程中有CH₃Si(O)CH₃气体生成.量子化学计算表明,H⁺直接进攻硅橡胶高分子链中的氧而导致高分子链断裂的过程要放热655.34 kJ/mol,是唯一的放热反应通道.这一过程不会形成稳定的过渡态和中间体,而是直接形成断键产物.计算分析结果与综合辐照形成的气体产物CH₃Si(O)CH₃相吻合.     

Synthesis,characterization, and cure kinetics analysis of high refractive index copolysiloxanes

Two kinds of high refractive index of polysiloxane compounds containing both pendent and terminal vinyl groups were successfully synthesized through a cohydrolysis-condensation method based on alkoxy silanes in the presence of acids and anionic ring-opening copolymerization of methylphenycyclosiloxane (D_n) and octamethylcyclotetrasiloxane (D₄), respectively. Their structures were confirmed by Fourier-transformed infrared and nuclear magnetic resonance spectra (¹H NMR and ²⁹Si NMR). The curing kinetics of the silicone resin (MPSR) in the presence of phenylvinyl silicone oil (MPSO) as reactive diluent and T-shaped hydrosiloxane (TPHS) as crosslinking agent was studied by non-isothermal differential scanning calorimeter at different heating rates. The kinetic parameters of the curing process were determined by Friedman and ?esták–Berggren method. A comparison of the results calculated with the experimental data showed that ?esták–Berggren equation was found to be the most adequately selected to describe the cure kinetics of the studied silicone resin, and the experimental data had a great coherence with that theoretically calculated. It would give a valuable guide for the curing process of silicone resin. In addition, TG curves showed that the cured MPSR/MPSO/TPHS system exhibited much higher heat resistance and thermal stability compared to MQ resin/PMVS/PHVS blends.     

Preparation and characterization of silicone rubber through the reaction between γ‐chloropropyl and amino groups with siloxane polyamidoamine dendrimers as cross‐linkers

A novel heat‐curable silicone rubber (MCSR/Si‐PAMAM) was prepared by using siloxane polyamidoamine (Si‐PAMAM) dendrimers as cross‐linkers and polysiloxane containing γ‐chloropropyl groups as gums. The chemical cross‐linking occurs through the reaction between Si‐PAMAM dendrimers and polysiloxane containing γ‐chloropropyl groups. The effect of various amounts of cross‐linkers on mechanical properties of MCSR/Si‐PAMAM was discussed in this paper. MCSR/Si‐PAMAM exhibits favorable mechanical properties with a tensile strength of 10.06 MPa and a tear strength of 47.9 kN/m when the molar ratio r of [N‐H]/[CH₂CH₂CH₂Cl] is 1:1. These excellent mechanical properties can be attributed to the formation of concentrative cross‐linking from Si‐PAMAM dendrimers in the cross‐linking networks, along with the introduction of Si–O–Si units in the internal structure of dendrimers. The introduction of Si–O–Si units reduces the steric hindrance of molecular structure, which facilitates the N–H bonds in the interior layers of dendrimers to react with γ‐chloropropyl groups. In addition, thermogravimetric analysis results indicate that MCSR/Si‐PAMAM is thermally stable even at high temperatures in a nitrogen atmosphere. Differential scanning calorimetry analysis reveals that the glass transition peak of MCSR/Si‐PAMAM is not identified in the temperature range −150 to −30°C, only a melting endothermic peak at −40°C.     

STUDIES ON POLYSILOXANE-POLYSTYRENE COMPOSITE LATEXES

Polysiloxane-polystyrene composite latexes were prepared by two-stage emulsionpolymerization. Polymerization of styrene in swollen polysiloxane latex particles were studied.Formation of simple polystyrene particle in the 2nd-stage polymerization depends on the particlesize of the lst-stage latex and the polymerization temperature. Polystyrene domains in thevulcanizates reinforce the silicone rubbers effectively.     

Thermal behaviour and mechanical properties of novel RTV silicone rubbers using divinyl-hexa[(trimethoxysilyl)ethyl]-POSS as cross-linker

Divinyl-hexa[(trimethoxysilyl)ethyl]-POSS (DVPS) as an octavinyl-POSS derivative was first prepared. A series of novel polydimethylsiloxane (PDMS)/DVPS hybrid materials as room temperature vulcanized (RTV) silicone rubber were prepared. The chemical incorporation of novel POSS into hydroxyl-terminated PDMS system by hydrolytic condensation reaction was verified by attenuated total reflection (ATR) infrared spectroscopy. Thermal degradation, thermo-oxidative stability and mechanical properties of these novel RTV silicone rubbers were studied by means of thermogravimetric analysis and tensile testing. The results exhibited significantly enhanced effects on the thermal stabilities and mechanical properties as compared to the PDMS polymer prepared with tetraethoxysilane (TEOS). The observed improvements in thermal properties could be attributed to the effective three-dimensional network structures resulting from the structure of DVPS. The thermal decomposition of the RTV silicone rubbers in nitrogen was also monitored by TGA coupled with real-time FTIR, and the degradation residues were also characterized by FTIR. It was found that the POSS cross-linker facilitated the formation of cross-links in the degradation residues. The striking improvement in mechanical properties could be attributed to the synergistic action of the structure of three-dimensional multi-arm cross-linker (vinyl-POSS derivative), the plasticization of self-cross-linking Vinyl-POSS derivative and perfect distribution of vinyl-POSS derivative.     

Alkoxysilane functionalized polycaprolactone/polysiloxane modified epoxy resin through sol-gel process

Incorporating elastic polysiloxane and/or an inorganic silica network in epoxy resin could result in the enhancement of physico-chemical properties due to the existence of Si-O bonds. To improve the compatibility between polysiloxane and epoxy matrices and intensively strengthen the properties of the modified system, here polysiloxane was introduced into epoxy resin through compatibilizing epoxy-immiscible polysiloxane with epoxy-miscible polycaprolactone segments via a sol-gel process. To fulfill the process, a blend containing alkoxysilane-functionalized polycaprolactone/polydimethylsiloxane (PCS-2Si) was firstly synthesized using direct nucleophilic addition between -OH groups of polydiol and -NCO of a silane. And then a series of modified epoxy resins were prepared in different epoxy/PCS-2Si weight ratios. All the modified composites were characterized by conventional methods, and their morphological, thermal degradation and surface properties were studied. The results showed that increasing the PCS-2Si content caused the changes of miscibility between epoxy and polysiloxane. Also, the thermal stability of the modified composites was greatly improved. As for the temperature value at 5% weight loss, it reached to 308.5 °C for the composite containing 50-60% (wt%) PCS-2Si, over 150 °C higher than that for neat amine-cured epoxy resin. Similarly, the modified composites showed good hydrophobicity. The improvement of these properties came from the improved interaction between PCS-2Si and epoxy, the forming of Si-O-Si network and the enrichment of siloxane chains on the surface of films. Therefore, it is believed that this modified epoxy appears promising as new high performance and highly functional materials.     

Synthesis of an adhesion‐enhancing polysiloxane containing epoxy groups for addition‐cure silicone light emitting diodes encapsulant

Addition‐cure silicone resin is considered as a good choice for light emitting diodes (LEDs); however, it has very poor adhesion to the substrate, which limits its practical application. A novel polysiloxane with self‐adhesion ability and higher refractive index for the encapsulating of high‐power LEDs is prepared and characterized. This polysiloxane containing vinyl groups, phenyl groups, and epoxy groups was synthesized by a sol‐gel condensation process from methacryloxy propyl trimethoxyl silane, γ‐(2,3‐epoxypropoxy)propytrimethoxysilane, and diphenylsilanediol under the catalysis of an anion exchange resin. Then, the resin‐type encapsulation material was prepared by hydrosilylation of methylphenyl hydrogen‐containing silicone resin and the newly synthesized polysiloxane material. The novel polysiloxane was characterized by ¹H‐NMR and Fourier transform infrared spectroscopy. On the basis of higher refractive index, higher transparency, excellent thermal stability, and appropriate hardness, as well as good adhesive strength between the encapsulating material and the LED lead frame (polyphthalamide), the curable silicone resin‐type encapsulation material can be used as an encapsulant for LEDs. Copyright © 2014 John Wiley & Sons, Ltd.