Supercritical fluid infusion of silver into polyimide films of varying chemical composition
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Supercritical fluid infusion of silver into polyimide films of varying chemical composition J. Rosolovsky Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
R. K. Boggess Department of Chemistry and Physics, Radford University, Radford, Virginia 24142
A. F. Rubira Departamento de Quimica, Universidade Estadual de Maringa, Av. Colombo 5790, 87020-900, Maringa-PR, Brazil
L. T. Taylor Department of Chemistry, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061
D. M. Stoakley and A. K. St. Clair NASA Langley Research Center, Materials Division, Hampton, Viriginia 23665 (Received 16 August 1996; accepted 19 March 1997)
Polyimides can be infused with silver complexes by the use of supercritical fluids. Highly reflective polyimide films were formed by infusing (1,5-cyclooctadiene1,1,1,5,5,5-hexafluoroacetylacetonato)silver(I) [Ag(COD) (HFA)] into a number of polyimides and then thermally curing those films at 300 ±C for time intervals between 30 min and 3 h. Reflectivities of the films exhibited strong dependence on the infusion and cure conditions as well as on the type of polyimide used. The highest reflectivity of 67.1% was achieved with a silvered film prepared from 3,30 ,4,40 -benzophenonetetracarboxylic acid dianhydride (BTDA) and oxydianiline (ODA) infused at 5000 psi, 100 ±C, for 30 min and cured for 1 h at 300 ±C. Reflectivities of silvered surfaces of other polyimides investigated varied from 39% to 61%. A strong correlation between the presence of a ketonic group in the polyimide structure and the formation of mirror surfaces was detected.
I. INTRODUCTION
Supercritical carbon dioxide (SC–CO2 ) has tremendous potential for the modification and processing of polymers.1 A sampling of these studies includes (1) medium for polymer synthesis,2 (2) polymer controlled precipitation,3 (3) polymer fractionation,4 and (4) polymer plasticization.5 Many polymers are known to swell in supercritical CO2 which suggests a high permeation rate of CO2 . In this regard, it has been shown that polymers possessing electron donating functional groups (e.g., carbonyl groups) exhibit specific interactions with CO2 which may be of a Lewis acid-base nature.6 The high diffusivity of supercritical CO2 in many solid polymers has implications in polymer modification. Berens7 and Sand8 demonstrated in 1986 that polymer substrates could be infused (or impregnated) by swelling the polymer with a solution of an organic penetrant in CO2 followed by rapid venting of the supercritical solution. The penetrant, having lower diffusivity than J. Mater. Res., Vol. 12, No. 11, Nov 1997
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the gaseous CO2 , was retained by the polymer. Chemical reactions may be carried out in the swollen solid polymer substrate or the CO2 may function only as a processing aid whereby the physical properties of the polymer are regained after processing. This approach has obvious advantag
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