Eight amorphous polyethers and poly(ether ketones) were
synthesized and characterized
by gel permeation chromatography, thermogravimetric analysis,
differential scanning calorimetry, and
dynamic mechanical thermal analysis. Polymers containing bulky,
cyclic 2,2‘-biphenyl side groups were
found to have the highest glass transition temperatures, were more
thermally stable and exhibited the
highest intramolecular barriers to rotation. Incorporation of
perfluorophenylene groups resulted in
internal plasticisation and a relative lowering of
T
g. The steepness of cooperativity plots
determined
from Williams−Landel−Ferry shift factors correlated with the rigid
nature of the polymer chains, but
not with the broadness of the relaxation (characterized by the
Kohlrausch−Williams−Watts stretch
exponent β) as predicted by the coupling model. A β-process
observed in the polymers containing cyclic
biphenyl side groups was similar in appearance to a typical
“structural” relaxation. The position, intensity,
and breadth of the γ-process was sensitive to chemical structure and
absorbed moisture.
A series of aromatic polyimides and partially fluorinated aromatic polyimides were prepared and investigated to determine the structural features affecting their moisture absorption, dielectric constant, and dielectric constant as a function of relative humidity. The moisture absorption of polyimides is related to the total imide content of the polymer. Polyimides with a lower weight per cent of imide have a lower moisture absorption. Both dielectric constant and moisture absorption of polyimides can be reduced by incorporation of fluorine into the polymer. However, a minimum in moisture absorption (about 0.7 wt.%) and dielectric constant (about 2.7) is approached at about 20% fluorine by weight of the polymer.
A series of new, fluorinated poly(imide-amide-su1fone)s has been synthesized by solution polycondensation of aromatic diamines containing sulfone groups with diacid chlorides incorporating both imide and hexafluoroisopropylidene units. These polymers are soluble in polar amidic solvents, and their solutions can be cast into colorless, thin, flexible films having good electrical insulating properties and high thermal stability. The dielectric constant value is 3.49-3.68. The decomposition temperature in air is 464-479"C, and the glass transition temperature is in the range 279-359°C. All these characteristics have been discussed and compared with those of related fluorinated poly(imide-amide)s which do not contain sulfone groups and with other imide polymers without hexafluoroisopropylidene units.
A series of fluorinated polyinides and fluorinated polyimides containing heterocyclic moieties were prepared and investigated to determine their dielectric constants, dielectric constants as a function of relative humidity (RH) and thermal properties. Thle fluorinated polyimides containing heterocyclic moieties were prepared from diamines containing pyridine, pyridazine, oxadiazole or benzoxazole moieties. The properties of the fluorinated heterocyclic-containing polyimides were compared with those of fluorinated polyimides prepared from aromatic diamines. In most cases, the introduction of heterocyclic moieties caused an increase in dielectric constant, an increase in the dielectric constant as a function of relative humidity and a decrease in thermal stability compared with the polyimides prepared with aromatic diamines.
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