AEROSPACE MATERIALS

LINEAR, POLYDIMETHYLSILOXANE-POLYIMIDE BLOCK COPOLYMERS MAY PROVE TO BE USEFUL AS HIGH PERFORMANCE COATINGS IN APPLICATIONS WHERE EXTREME ENVIRONMENTAL CONDITIONS WILL BE ENCOUNTERED. THE OBJECTIVE OF THE RESEARCH DISCUSSED HEREIN IS TO DEVELOP A COATING MATERIAL WHICH WOULD PROTECT THE UNDERLYING SUBSTRATE AGAINST DEGRADATION DUE TO ATOMIC OXYGEN BOMBARDMENT. IN ADDITION, THIS COATING MATERIAL SHOULD ALSO BE HYDROLYTICALLY, ODIDATIVELY, AND THERMALLY STABLE OVER A WIDE TEMPERATURE RANGE. THERE IS EVIDENCE THAT POLYSILOXANE SURFACES REACT WITH ATOMIC OXYGEN TO FORM PROTECTIVE SILICON DIOXIDE COATINGS. POLYIMIDE HOMOPOLYMERSARE KNOWN TO BE THERMALLY AND HYDROLYTICALLY STABLE AND TO POSSESS EXCELLENT MECHANICAL PROPERTIES. THEREFORE, CHEMICALLY, IT IS BELIEVED THAT A POLYSILOXANE-POLYIMIDE COPOLYMER WOULD MAKE AN EXCELLENT COATING. UNFORTUNATELY, POLYIMIDES ARE NORMALLY INTRACTIBLE, INFUSIBLE POLYMERS. POLYSILOXANE-POLYMIDES MADE TO DATE ARE EITHER INSOLUBLE MATERIALS OR HAVE VERY LOW UPPER USE TEMPERATURES DUE TO EXTREMELY SHORT BLOCK LENGTHS OF THE RIGID COMPONENT. THE FEASIBILITY OF DEVELOPMENT OF A SOLUBLE COATING MATERIAL HAVING THE POLYSILOXANE-POLYIMIDE BLOCK COPOLYMER STRUCTURE WILL BE EVALUATED USING THREE BASIC SCHEMES: 1. COPOLYMER SYNTHESIS VIA THE REACTION OF DIISOCYANATES, 2. POLYAMIDE-IMIDE-SILOXANE COPOLYMER SYNTHESIS, AND FINALLY, 3. COPOLYMER SYNTHESIS EMPLOYING A MICHAEL REACTIONFOR CHAIN EXTENSION.