Thermally stable polyimide block and graft copolymers with labile con1ponents (especially polypropylene oxide), have been prepared and investigated as low dielectric materials that afford desirable thermal, mechanical and electrical properties. Polyimide nanofoams based upon the controlled pyrolysis of the labile component were prepared. The methodology for producing the nanofoams was to first spin cast well-designed microphase separated graft or block copolymer solutions comprised of the thermally stable 1,1-Bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3FDA)/pyromellitic dianhydride (PMDA) based polyimide main chain and polypropylene oxide based thermally labile graft of block copolymers. The thermally stable material was designed to be the continuous phase, and the unstable moiety served as the dispersed phase so that closed cell structures could be obtained. Upon thermal treatment under inert atmosphere, the materials can be spun cast and cured in place, if so desired. However, if the polymers are exposed to the oxygen atmosphere, the unstable component can be selectively degraded, generating micropores that are related to the size of the initial microphase separated copolymer morphology.
The copolymer synthesis was conducted through the poly(amic acid) precursor and subsequent cyclodehydration to the polyimide, usually by chemical imidization. Dynamic mechanical analysis (DMTA) confirmed microphase separated morphology for all the copolymers. Upon degradation of poly(propylene oxide), a 13-18% reduction in the density was observed, which is consistent with foam generation. These features have been confirmed using small angle X-ray analysis (SAXS) and transmission electron microscopy (TEM). The pores ranged from 100-250°A in size from TEM, and were stable up to nearly the polyimide Tg (~400°C),
Related efforts demonstrated that it was possible to introduce ethynyl containing terminal groups, in order to develop crosslinked polyimide foams with better chemical resistance. In addition to the propylene oxide labile components, poly(methyl methacrylate) and polyethylene oxide were also investigated. Macromonomers were synthesized via group transfer polymerization, followed by a derivatization to produce appropriately reactive diamino aryl terminal oligomer. Surprisingly, the poly(methyl methacrylate) component was found to be miscible with 3FDA/PMDA based polyimide. Indeed, even physical blends of the two homopolymers appear to be miscible. Polyethylene oxide has also been tried as a labile block for the generation of polyimide nanofoams, with only limited success.
The optimum resulting materials are of considerable further interest for electronic packaging applications where air is utilized as a component to reduce the dielectric constant. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/37901 |
| Date | 22 May 2007 |
| Creators | Jayaraman, Saikumar |
| Contributors | Chemistry, McGrath, James E., Gibson, Harry W., Marand, Hervé L., Riffle, Judy S., Goldfarb, Ivan J. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xxviii, 334 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 32912233, LD5655.V856_1995.J393.pdf |
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