A new precursor of liquid and curable polysiloxane for highly cost-efficient SiOC-based composites

Polymer-derived SiOC matrix composites are very promising structure ceramics in moderate temperature (<?1200?°C) application, in view of their outstanding comprehensive performance and satisfying costs. Herein, we developed a new precursor of liquid and curable polysiloxane (LC-PSO) with Si-H and vinyl side groups to meet the requirements of precursor infiltration and pyrolysis (PIP) route for preparing highly cost-efficient composites. It was found that the crosslink structure was completely built below 150?°C through hydrosilylation reaction, thus converting the liquid precursor into solid state and rendering the cured product with a high ceramic yield of 81.1%. The addition reaction was also greatly inhibited under 5?°C in order that the LC-PSO was able to store for long time. We revealed that although the SiOC ceramic underwent structural rearrangement and slow crystallization during pyrolysis, no mass loss was observed below 1400?°C before the carbothermal reaction was initiated. The prepared carbon fiber-reinforced SiOC (2D-Cf/SiOC) composite verified the feasibility of directly using LC-PSO as precursor for PIP process, and the mean flexure strength and modulus of the composite were 253.3?MPa and 33.3?GPa, respectively. Our work presents the great potential of LC-PSO in fabricating highly cost-efficient CMCs for moderate temperature application.     

聚酰亚胺／烷基改性聚硅氧烷复合微粒子的制备与性质

在含有烷基改性聚硅氧烷的丙酮与甲苯的混合溶媒中，使用均苯四甲酸酐（PMDA）和4，4’-二氨基二苯醚（ODA）合成聚酰胺酸／烷基改性聚硅氧烷高分子共混物，该高分子共混物与溶媒分离后再在250℃经高温热环化得到聚酰亚胺／烷基改性聚硅氧烷复合微粒子。该复合微粒子的粒径主要分布在2-6μm的狭窄范围内，其热分解温度为384．6℃，并直具有极好的疏水化度。     

Preparation of polysiloxane/perfluorosulfonic acid nanocomposite membranes in supercritical carbon dioxide system for direct methanol fuel cell

In this work, polysiloxane-modified perfluorosulfonic acid (PFSA) membranes were prepared by a directed sol–gel synthesis method with (3-mercaptopropyl) methyldimethoxysilane (MPMDMS) as the precursor of silicon alkoxide in the supercritical carbon dioxide (Sc-CO₂) system. Contents of polysiloxane in the modified PFSA membranes were varied according to the added amount of precursor MPMDMS. The chemical and physical properties of these modified PFSA membranes were characterized by using attenuated total reflection-infrared spectra, X-ray diffraction, thermogravimetric analysis, universal testing machine, scanning electron microscopy and transmission electron microscope. The measurement results indicated that the polysiloxane particles were not restricted in the ion clusters and well dispersed in the PFSA membrane with ordered size of about 80–100 nm. In the meanwhile, the polysiloxanes have been incorporated into the hydrophobic fluorocarbon backbone regions and interacted with C–F backbones of PFSA polymers. Dimensional stability of the modified PFSA membrane was improved after the impregnation by using Sc-CO₂. The modified membranes almost can remain the same high tensile strength as the pristine membrane. Performance of these modified membranes was evaluated in terms of proton conductivity and methanol permeability. The highest selectivity value (ratio of proton conductivity to methanol permeability) of the modified membrane was about 75.6% higher than that of pristine PFSA membrane because of its higher proton conductivity and lower methanol permeability. All the results indicated that this novel synthesis method in Sc-CO₂ system is a promising method to improve the properties of PFSA membrane for direct methanol fuel cell application.     

Joining SiC ceramics with silicon resin YR3184

Joints between reaction-bonded silicon carbide (RBSiC) and joints between pressureless sintered silicon carbide (SSiC) were produced respectively using a polysiloxane silicon resin (YR3184, GE Toshiba Silicones) as joining material. Samples were heat treated in a nitrogen flux at temperatures around 1200 °C. The maximum three point bending strength of the joints between reaction-bonded silicon carbide is 197 MPa. The maximum three point bending strength of the joints between sintered silicon carbide is 163 MPa. The join layers are continuous, homogeneous and densified and have thickness of 2–5 μm. The joining mechanism is that the amorphous silicon oxycarbide ceramic pyrolyzed from YR3184 acts as an inorganic adhesive.     

聚氨酯改性有机硅的合成与性能

用含氧硅油、单烯丙基封端的聚醚和甲苯二异氰酸酯制备了聚氨酯改性有机硅乳液。并用高分辨电镜观察了乳液的粒径及其分布。研究了不同n（NCO/n（OH）值对乳液性能、成膜力学性能及热稳定性的影响.     

Mass patterning of polysiloxane layers using spin coating and photolithography techniques

Polysiloxane (PSX) containing 2,2-dimethoxy-2-phenylacetophenone (DMPA) photoinitiator has been used as a photosensitive polymer. Thus, thin PSX films have been deposited by spin coating and patterned thanks to standard ultraviolet (UV) photolithography. The influences of the different technological parameters (PSX dilution, spin speed, UV exposure time) have been studied in so as to understand the polysiloxane deposition and cross-linking phenomena. Finally, the whole process has been optimised. Results evidence the realisation of high quality PSX patterns for the development of mass-fabricated ion sensitive layers in the field of chemical microsensors.     

Polysiloxane based flexible electrical-optical-circuits-board

In the paper, a packaging technique of polysiloxane based flexible electrical-optical-circuits-board (EOCB) with Kapton (Dupont) foils was developed and introduced. The main mechanism of forming a good bonding between polysiloxane and Kapton foil was identified and verified. The optical and mechanical properties of the polysiloxane waveguide layer remained unchanged before and after packaging. According to the defined procedures, the environmental stability of packaged EOCBs has been tested with the result that they exhibited excellent mechanical, optical, and thermal stabilities. The mechanical stability limit of the tested EOCBs is determined only by the intrinsic mechanical stability of the used polysiloxane materials. The optical waveguide propagation loss at 850 nm is less than 0.1 dB/cm after surviving from the defined environmental test procedures.     

汽车内饰件用低气味耐刮擦聚丙烯的研制

分析了不同耐刮擦剂、不同聚丙烯基料、不同的滑石粉、不同相容剂对低气味耐刮擦聚丙烯材料的影响。结果表明,采用高结晶聚丙烯,高目数的滑石粉、使用低气味的相容剂、添加低气味改性型高聚硅氧烷制备的聚丙烯材料具有优异耐刮擦性及低气味性,可以满足汽车内饰件用聚丙烯材料的新要求。     

有机硅改性酚醛──丁腈胶粘剂的研制

］本文介绍了一种有机硅改性酚醛——丁腈胶粘剂，该胶具有优异的耐热老化性能，预热处固化温度低，时间短，高温强度高，可广泛用于各种耐热老化部件的粘接。