Synthesis and characterization of new organosoluble poly(ether imide)s derived from various novel bis(ether anhydride)s - Polyimides and Other High Temperature Polymers - page 64

The thermal properties of the poly(ether imide)s were determined using differ-
ential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The
thermogravimetric (TG) analysis revealed that these poly(ether imide)s had good
thermal stability. They were stable up to temperatures above 440 C. The tempera-

ture at 10% weight loss (Td 10 ) of these polymers reached 441-535

°

C in nitrogen
atmosphere. It was observed that polymers with 2,2'-dimethyl-4,4'-biphenylene
having biphenylene unit showed higher Td 10 value than the others. For example,
Td 10 value of m-tert was observed to be 518

°

° C in nitrogen, which is higher than

that of TP-tert (501 ° C, in nitrogen), Tcardo-tert (504 ° C, in nitrogen), TMA-tert

(474 C,

in nitrogen). This is because the polymers with biphenylene unit exhibit higher ri-
gidity than the others. It was observed that polymers with 2,2'-dimethyl-4,4'-
biphenylene unit showed higher Td 10 values than those with diphenylmethylene
linkage. On comparing the polymers derived from the diamines (a and b), it was
observed that the polymer containing 2,2'-dimethyl-4,4'-biphenylene unit (m-m)
exhibited a higher Td 10 value than that bearing asymmetric tert-butyl substitution
group (m-tert). That is, a noncoplanar conformation can impart a greater thermal
stability to the polymer than the tert-butyl substitution [7, 18]. The solubility of
polymer was enhanced by the noncoplanar conformation of 2,2'-dimethyl substi-
tuted biphenylene in the polymer backbone, which reduced the polymer chains in-
teraction and rigidity [17]. The incorporation of the methyl substituent on the 2,2'-
dimethyl-4,4'-biphenylene unit did not significantly decrease the thermal stability
of the polymer but enhanced its processability [18]. The result of the TGA meas-
urements on these polymers indicated that polymers with noncoplanar bi-
phenylene groups exhibited higher thermal stability than those with kink di-
phenylmethylene linkages [38, 39]. The isothermal gravimetric analysis (IGA)
results showed that these poly(ether imide)s had good thermo-oxidative stability.
In general, the IGA results were in agreement with the TGA data. Specifically,
following 20 hrs isothermal aging at 350

° C, in nitrogen), Cyclo-tert (441 ° C, in nitrogen) and Ph-cardo-tert (495 °

C in static air, the polymer showed
weight losses of 7.0-10.5% (namely 7.0% for m-tert polyimide and 7.9% for m-
m polyimide). Upon comparing the weight loss values, it is seen that polyimides
containing 2,2'-dimethyl-4,4'-biphenylene unit (namely 7.0% for m-tert polyim-
ide and 7.9% for m-m polyimide) were somewhat more thermally stable than
those containing diphenylmethylene unit (namely 8.8% for TP-tert polyimide
and 9.0% for TP-m polyimide) [38, 39].

°