Polyimide, surface modification

Polyimide surface modification by a wet chemical process is described. Poly(pyromellitic dianhydride-oxydianiline) (PMDA-ODA) and poly(bisphenyl dianhydride-para-phenylenediamine) (BPDA-PDA) polyimide film surfaces are initially modified with KOH aqueous solution. These modified surfaces are further treated with aqueous HC1 solution to protonate the ionic molecules. Modified surfaces are identified with X-ray photoelectron spectroscopy (XPS), external reflectance infrared (ER IR) spectroscopy, gravimetric analysis, contact angle and thickness measurement. Initial reaction with KOH transforms the polyimide surface to a potassium polyamate surface. The reaction of the polyamate surface with HC1 yields a polyamic acid surface. Upon curing the modified surface, the starting polyimide surface is produced. The depth of modification, which is measured by a method using an absorbance-thickness relationship established with ellipsometry and ER IR, is controlled by the KOH reaction temperature and the reaction time. Surface topography and film thickness can be maintained while a strong polyimide-polyimide adhesion is achieved. Relationship between surface structure and adhesion is discussed. 

Polyimide surface modification with KOH or NaOH aqueous solution is well defined. The reaction initially gives potassium or sodium polyamate which is then protonated with acid to yield polyamic acid. The outermost layer (5 A) of PMDA-ODA can be completely modified within a minute of reaction in KOH solution. The depth of modification can be measured by a method using an absorbance-thickness relationship established with ellipsometry and external reflectance IR. The modification depth of PMDA-ODA treated with 1 M KOH aqueous solution at 22 °C for 10 min is approximately 230 A. Surface topography and film thickness can be maintained while a strong... 

Distortions of the bond and out-of-plan rotation of polyimides have been suggested to explain the surface modification by rubbing.33... 

Surface modification (texturing) of polyimide through a metal clustering and migration process is reported. This process involves heat treatment of polyimide coated with a thin copper layer. Subsequent metallization of the textured surface leads to improved adhesion due to mechanical anchoring. Adhesion values of 7-10 lbs/in (ambient) and 4-6 lbs/in (after solder float) have been obtained. 

The surface chemical structure of several thin polyimide films formed by curing of polyamic acid resins was studied using X-ray photoelectron spectroscopy (ESCA or XPS). The surface modifications of one of the polymer systems after exposure to KOH, after exposure to temperature and humidity, after exposure to boiling water, and after exposure to O2 and 02/CF plasmas were also evaluated. The results showed imide bond formation for all cured polyimide systems. It was found that (a) K on the surface of the polyamic acid alters the "normal" imidization process, (b) cured polyimide surfaces are not invarient after T H and boiling water exposures, and (c) extensive modifications of cured polyimide surfaces occur after exposures to plasma environments. Very complex surfaces for these polymer films were illustrated by the C Is, 0 Is, N Is and F Is line characteristics. 

The second method of surface modification permits the formation of a composite particle, the core of which is composed of polymer (UHMWPE or polyimide) and the surface of which is coated with titanium carbide which is hard and abrasion resistant. The composite particles can be incorporated into any suitable matrix resulting in improved abrasion resistance, lowered fiiction, higher compressive strength, improved creep resistance, etc. This new product is a unique form of raw material which has the potential to improve the properties of many products. 

K. Meier, M. Langsam, H. C. Klotz, Selectivity enhancement via photooxidative surface modification of polyimide air separation membranes, J. Membr. Sci., 94, 195-212 (1994). 

Alterations in polyamic acid-polyimide surfaces produced by the use of different methods of curing (oven vs. hot plate), the application of a silane adhesion promotor (y-aminopropyltriethoxysilane), and the deposition of copper have been studied using ESCA. Our objective was to develop chemical state information (elemental composition, chemical bonding features) about the modifications occurring in the outermost few tens of angstroms of polyimide films. The results show different C Is spectral features for hot plate vs. oven cured films but identical stoichiometries. The silane treated amic acid surface... 

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