Polyimide solvent resistance

L.S. White, Transport properties of a polyimide solvent resistant nanofiltration membrane, J. Memhr. Sci. 205 (2002) 191-202. 

L. S. White, "Transport Properties of a Polyimide Solvent-resistant Nanofiltration Membrane , J. Memb. Sci. 205, 191 (2002). 

Acetylene terminated polyimide prepolymers have many advantages over conventional polyimides in the areas of processing and solvent resistance. In addition, the presence of the isoimide structure further extends the the utility of these systems by modification of the solubility properties and glass transition temperature. 

The first, and currently only, successful solvent-permeable hyperfiltration membrane is the Starmem series of solvent-resistant membranes developed by W.R. Grace [40]. These are asymmetric polyimide phase-inversion membranes prepared from Matrimid (Ciba-Geigy) and related materials. The Matrimid polyimide structure is extremely rigid with a Tg of 305 °C and the polymer remains glassy and unswollen even in aggressive solvents. These membranes found their first large-scale commercial use in Mobil Oil s processes to separate lube oil from methyl ethyl ketone-toluene solvent mixtures [41-43], Scarpello et al. [44] have also achieved rejections of >99 % when using these membranes to separate dissolved phase transfer catalysts (MW 600) from tetrahydrofuran and ethyl acetate solutions. 

Aromatic polyimides with dielectric constants < 3.0 and reduced levels of moisture absorption can be obtained by the incorporation of fluorine into the polymer backbone. However, this approach can also lead to a reduction in the thermal properties (Tg), and/or solvent resistance of the polymer. It has been found that the incorporation of paraphenylene diamine (PPD) into the 6FDA/BDAF polyimide affords copolymers having improved thermal performance and solvent resistance as compared with the parent homopolymer while maintaining a dielectric constant of 2.9 and moisture uptake < 2.0%. This approach can be considered as a possible alternative to the use of... 

Strathmann prepared an all-polyimide composite membrane-both bottom and top layers.97 A microporous asymmetric film of the polyamic acid intermediate was cast by quenching in acetone, then dried and thermally cyclized to the polyimide at 300°C. The microporous polyimide sheet was then overcoated with a dilute solution of the same polymer, which was allowed to evaporate to give a 300-angstrom-thick coating. This was also cyclized to the polyimide to generate a fully solvent resistant reverse osmosis membrane. 

Use of nanofiltration for non-aqueous separations is limited by membrane compatibility - a common material in composite nanofiltration membranes used for aqueous separations is polysulfone which possesses limited solvent resistance [134]. However, during the past two decades a number of materials have emerged with improved solvent resistance that have enabled a broad range of organic solvent nanofiltration (OSN) applications. These materials include polydimethylsiloxane, polyphenylene oxide, polyacrylic acid, polyimides, polyurethanes, and a limited number of ceramics. Commercial products are offered by Koch Membrane Systems, W.R. Grace, SolSep, and Hermsdorfer Institut fur Technische Keramik (HITK) [135]. 

A quaternary ammonium salt, tetraoctylammonium bromide (TOABr) and doco-sane were used as solutes and toluene was used as the solvent. The membrane used in this study was again the solvent-resistant polyimide membrane, STAR-MEM 122. A dual-cell crossflow filtration rig, similar to the one described in Section 4.3.1 was used in all the experiments with an effective membrane area of 78 cm. The stage cut was between 0.01 and 0.3% over the whole concentration and pressure range. Ideal mixing is assumed throughout the system. 

Introducing a thermoplastic resin [53,54] into the matrix such as a thermoplastic polyimide Matrimid 5218 [55,56], polyethersidfone [54-57], polyetherimide [55-56,58-61] and poly (arylene ether) [58-59,61-63]. All these polymers however, cause an attendant loss of processability coupled with poorer solvent resistance. 

Alkane-imide resin n. A thermoplastic introduced by Raychem Corp under the trade name Polyimidal. The polymer retains high strength up to 200°C and melts at 302°C. It has good electrical properties, low water absorption, and high solvent resistance. 

In 1908, aromatic polyimides were first reported by Bogert and Renstiaw [1]. Aromatic polyimides became well-known in 1950, after successful development of two-step polyimide synthesis by DuPont [2]. This class of polymers possesses a number of outstanding properties such as excellent thermal stability, mechanical strength, and electrical properties that have led to application in several fields from engineering thermoplastics to the aerospace and electronics industries, as well as for fibers and adhesives and in matrices for composite materials [3-5]. In addition, polyimides have high thermo-oxidative stability and chemical- and solvent-resistive properties, leading to many membrane-based applications... 

Aromatic polyimides are an important class of high-performance polymers with interesting properties such as good chemical and solvent resistance, high thermal and mechanical properties, and high optical transparency. These excellent properties make them suitable for engineering plastics to be used in... 

Aromatic polyimides are resistant to most organic solvents and dilute acids, however, long term exposure to caustic solution is not desirable. They are also soluble in highly polar solvents. 

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