ISSN:
1089-7550
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Several high temperature polyimides, as model polymers with various chain rigidities and chain orders, were synthesized through the polycondensation of p-phenylene diamine (PDA) with five different aromatic dianhydrides [i.e., pyromellitic dianhydride (PMDA), biphenyltetracarboxylic dianhydride (BPDA), 4,4′-oxydiphthalic anhydride (ODPA), benzophenonetetracarboxylic dianhydride (BTDA), and 4,4′-hexafluoroisopropylidenediphthalic anhydride (6F)], and investigated in terms of structure and properties. Both fully rodlike PMDA-PDA and ether-linked ODPA-PDA polyimides showed excellent orientation and poor ordering of chain in x-ray diffraction patterns, whereas both biphenyl-linked (BPDA-PDA) and carbonyl-linked (BTDA-PDA) polyimides exhibited excellent orientation and high ordering of chain. However, hexafluoroisopropylidene-linked 6F-PDA polyimide is structureless. The coherence length along the chain axis, which is a measure of chain rigidity and ordering, was estimated from (00l) peaks of x-ray diffraction patters: 6F-PDA (could not be measured) 〈ODPA-PDA (95 Å)〈BTDA-PDA (98 Å)〈BPDA-PDA (104 Å)〈PMDA-PDA (130 Å). In films prepared on substrates, all polyimides were preferentially oriented in the film plane. However, the degree of molecular in-plane orientation strongly depended on the coherence length. Higher coherence length, i.e., higher chain rigidity and ordering, caused higher in-plane orientation of chains. However, the chain rigidity is more critically responsible for molecular in-plane orientation, in comparison to the chain ordering. Higher in-plane orientation of chains led to larger anisotropies of refractive indices and dielectric constants, higher in-plane modulus, lower in-plane thermal expansion coefficient, and lower residual stress. © 1997 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.364210
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