Polyimide performance enhancement

Polyimide. Polyimide is a biaxiaHy oriented high performance film that is tough, flexible, and temperature- and combustion-resistant. Its room temperature properties compare to poly(ethylene terephthalate), but it retains these good characteristics at temperatures above 400°C. Its electrical resistance is good and it is dimensionally stable. The principal detriment is fairly high moisture absorbance. The main uses are for electrical insulation, particularly where high temperatures are prevalent or ionizing radiation is a problem. The films may be coated to reduce water absorption and enhance... 

As mentioned earlier, siloxanes impart a number of beneficial properties to polymeric systems into which they are incorporated, including enhanced solubility, resistance to degradation in aggressive oxygen environments, impact resistance and modified surface properties. These particular advantages render polysiloxane-modified polyimides attractive for aerospace, microelectronic and other high performance applications (40-43). 

Materials. Biaxially oriented polypropylene (PP) films of 50 um thickness were obtained from 3M and have been described (2). PMDA-ODA (PI) was Kapton H polyimide from Dupont. Copper-plated PTFE films were obtained from Spire Corporation (Bedford, MA). They were prepared using the Ion Beam Enhanced Deposition (IBED) process in which a 100 nm thick Cu film was vapor-deposited onto a PTFE substrate in the presence of a beam of 400 eV Ar+ ions of 25 uA/cm2 (IQ). Shortly before SIMS analysis, the Cu film was removed slowly by peeling at 90° in ambient conditions. Metal-coated PI films were prepared by sputtering 50 nm Cr and 1 um Cu onto a 50 um thick Kapton film on both sides. Thermal annealing was performed in a vacuum chamber at 2xl0 6 torr using a quartz lamp as the heating source. The samples were held for 15 min at the desired temperature and then cooled down to ambient temperature inside the chamber for about 2 hours. Just prior to SIMS analysis, the metal films were peeled slowly at 90° and then immediately introduced into the vacuum chamber of the instrument. 

Polyimides (PI) were introduced in 1962 as thermally non-processable Kapton . To improve processability, the main-chain flexibility was enhanced by incorporating segments with higher mobility, viz. polyamide-imide (PAl), polyether-imide (PEI), polyimide-sulfone (PISO), etc. These polymers are characterized by high T = 150-420°C and thermal resistance. They are blended with PPS to enhance its moldability, thermal stability and mechanical performance. 

Shao, L., Chung, T.-S., Goh, S.H. and Pramoda, K.P. 2005a. Polyimide modification by a linear aliphatic diamine to enhance transport performance and plasticization resistance. J. Memb. Sci. 256 46-56. 

Commercial membranes for CO2 removal are polymer based, and the materials of choice are cellulose acetate, polyimides, polyamides, polysulfone, polycarbonates, and polyeth-erimide [12]. The most tested and used material is cellulose acetate, although polyimide has also some potential in certain CO2 removal applications. The properties of polyimides and other polymers can be modified to enhance the performance of the membrane. For instance, polyimide membranes were initially used for hydrogen recovery, but they were then modified for CO2 removal [13]. Cellulose acetate membranes were initially developed for reverse osmosis [14], and now they are the most popular CO2 removal membrane. To overcome state-of-the-art membranes for CO2 separation, new polymers, copolymers, block copolymers, blends and nanocomposites (mixed matrix membranes) have been developed [15-22]. However, many of them have failed during application because of different reasons (expensive materials, weak mechanical and chemical stability, etc.). 

Polyimides are probably the most appropriate dass of polymers for the production of bicontinuous nanocomposites, in so far as they represent types of polymers that have been widely used in applications requiring stringent performance at high temperatures. The incorporation of continuous silica domains, therefore, is expected to enhance the high-temperature properties to bridge the gap between polymers and... 

There are two main areas where polyimide nanocomposites have been investigated by the author as a means of enhancing the performance of composites ... 

The incorporation of a polysiloxane component in poly(imide)s imparts a number of useful properties to the polymeric system, including enhanced solubility good thermal, oxidative, and ultraviolet stability reduced water uptake and modified surface properties. Because of these advantages, polysilox-ane-modified polyimides draw attention in the fields of aerospace, microelectronics, gas separation, and other high-performance applications. 

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