Polymers, high-temperature capabilities

Ordered polymer films made from poly benzthiazole (PBZT) and poly benzoxazole (PBO) can be used as substrates for multilayer printed circuit boards and advanced interconnects to fill the current need for high speed, high density packaging. Foster-Miller, Inc. has made thin substrates (0.002 in.) using biaxially oriented liquid crystal polymer films processed from nematic solutions. PBZT films were processed and laminated to make a substrate with dielectric constant of 2.8 at 1 MHz, and a controllable CTE of 3 to 7 ppm/°C. The films were evaluated for use in multilayer boards (MLBs) which require thin interconnect substrates with uniform controllable coefficient of thermal expansion (CTE), excellent dielectric properties, low moisture absorption, high temperature capability, and simple reliable processing methods. We found that ordered polymer films surpass the limitations of fiber reinforced resins and meet the requirements of future chip-to-chip interconnection. 

In consideration of the types of adhesive able to exhibit high-temperature capabilities, it is convenient to divide the discussion into two main parts first, a consideration of what could be regarded as the traditional high-temperature adhesives, that is, those that have been available for many years, and second a mention of some of the more recent developments in the high-temperature polymer area- developments designed to minimize the disadvantageous characteristics exhibited by the former types. 

In PMC, the polymer matrix is expected to wet and bond to the second (reinforcing) constituent, and it is expected to flow easily for complete penetration and elimination of voids in the system. It must be elastic enough with low shrinkage and low thermal expansion coefficients (TEC) it must be easily processable, must have proper chemical resistance, in addition to low and high temperature capabilities, dimensional stability and so on. 

The commercially important properties of Et>-Nb copolymers include low density, high transparency and low color, high moisture barrier and low moisture absorption, low optical distortion, excellent feature replication, resistance to polar solvents, high purity, shatter resistance, good biocompatibiUty, extremely low dielectric loss, high temperature capability, and compatibility with polyethylenes. The resins also have the low shrinkage and warpage typical of amorphous polymers. 

The electrical properties of the polymer are also exceptional - in many respects comparable to those of typical high performance engineering materials at room temperature, but in addition, changing little over a wide range of elevated temperatures. This is an important property, and of considerable interest when combined with high temperature capability. All of which has led to rapid acceptance of this polyetherimide in both electrical and electronic applications. 

There are several commercial thermotropic polyesters that exhibit outstanding high-temperature capabilities. These include (14,15) an increasing number of fibers and high temperature plastics. Similar to the lyotropic liquid crystalline polymers, the thermotropics exhibit unusually low viscosities because of orientation and lack of entanglement. Of course, the orientation serves to improve their mechanical properties. The chemical structure can be varied significantly. 

The all-important difference between the friction properties of elastomers and hard solids is its strong dependence on temperature and speed, demonstrating that these materials are not only elastic, but also have a strong viscous component. Both these aspects are important to achieve a high friction capability. The most obvious effect is that temperature and speed are related through the so-called WLF transformation. For simple systems with a well-defined glass transition temperature the transform is obeyed very accurately. Even for complex polymer blends the transform dominates the behavior deviations are quite small. 

Reduction of polymer flammability is of broad interest for applications ranging from plastics to textiles. For polyesters, given their inherent instability towards water at elevated temperatures, and the high temperatures of manufacture, many classes of flame-retardant (FR) agents, including most halogen-containing materials, are impractical. Phosphate esters, capable of incorporation into the polymer backbone, were pioneered by Hoechst AG, and continue to be the materials of choice [84, 85],... 

Cyclic ketene acetals, which have utility as co-polymers with functional groups capable of cross-linking, etc., have been prepared by the elimination of HX from 2-halomethyl-l,3-dioxolanes. Milder conditions are used under phase-transfer conditions, compared with traditional procedures, which require a strong base and high temperatures. Solid liquid elimination reactions frequently use potassium f-butoxide [27], but acceptable yields have been achieved with potassium hydroxide and without loss of any chiral centres. The added dimension of sonication reduces reaction times and improves the yields [28, 29]. Microwave irradiation has also been used in the synthesis of methyleneacetals and dithioacetals [30] and yields are superior to those obtained with sonofication. 

Organic polymers are widely used in modified electrodes [220], but inorganic materials such as zeoHtes, clays or microporous solids are attractive as replacements since they have much better stability, tolerance to high temperatures and oxidizing conditions, and chemical inertness. Due to the capability of clays to exchange intercalated ions, clay modified electrodes have been extensively studied. 

CO2 Separation Using a Thermally Optimised Membrane. This project aims to manufacture a high-temperature polymer membrane with better separation capabilities than current polymer membranes. The project focuses on the separation of CO2, methane, and nitrogen gases in the range of 100 to 400°C. 

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