Polyimides derived from 2,2-bis[4-(4-aminophenoxy)phenyl]-hexafluoropropane (BDAF) and pyromellitic dianhydride (PMDA) displayed a glass transition temperature (Tg) at 306°C and a melting point (Tm) near 470°C as measured by differential scanning calorimetry (DSC) with a heating rate of 10°C/min. The degree of crystallinity increased with decreasing molecular weight. The incorporation of 20 mole percent of the comonomer, hexafluoroisopropylidene-2,2-bisphthalic acid anhydride (6FDA), gave a Tm of 440°C that appeared to be stable 20°C above the melt.
A fluorinated diamine, 1,1-bis[4-(4-aminophenoxy) phenyl]-1-phenyl-2,2,2-trifluoroethane (SFEDAM), was synthesized in 80% yield from trifluoroacetophenone with a melting point of 169-170°C. The 3FEDAM-PMDA polyimide controlled to 30,000 g/mol with phthalic anhydride exhibited by DSC a Tg of 308°C and a Tm of 476°C. Similar to the BDAF based copolymer, the 3FEDAM-20%6FDA/80%PMDA-PA polyimide had a Tg of 286°C and a Tm of 440°C which appeared to show short term thermal stability above the Tm.
Three 1,4-bis(4-aminophenoxy)benzene (TPEQ) homopolyimides were synthesized with 3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA), 3,3',4,4'-biphenylcarboxylic dianhydride (BPDA), and 4,4'-oxydiphthalic anhydride (ODPA). The Tg values were 255°C, 251°C, and 239°C for the TPEQ-BPDA-PA, TPEQ-BTDA-PA, and TPEQ-ODPA-PA polyimides, respectively. The TPEQ-ODPA-PA polyimide displayed the lowest Tm of 411°C. A series of TPEQ-ODPA polyimides of different molecular weights were synthesized using the Carother's equation and the monofunctional reagent, phthalic anhydride. The Tg values ranged from 214°C to 239°C for the 7.5K to the 30K polyimides. All the TPEQ-ODPA polyimides displayed an endotherm on the first heat of the DSC analysis. However, the 7.5K, 10K, and 15K polyimide also recrystallized upon heating.
Polyimide powders were directly synthesized via preparation of the poly(amic acid) followed by cyclodehydration by solution imidization. One requirement is the polyimide must be crystalline so that as the polyimide is formed it will crystallize and precipitate from solution as small particles in the range of 2-16 pm. The particle size may be controlled by the concentration of the solution, temperature, and drying process. / Ph. D.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/38290 |
| Date | 06 June 2008 |
| Creators | Brink, M. Heather |
| Contributors | Chemistry, McGrath, James E., Kander, Ronald C., Riffle, Judy S., Marand, Hervé L., Tanko, James M. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation, Text |
| Format | xviii, 207 leaves, BTD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
| Relation | OCLC# 30909513, LD5655.V856_1994.B757.pdf |
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