Poly(amic acid)s and their ionic salt solutions: Synthesis, characterization and stability study - Polyimides and Other High Temperature Polymers - page 15

Figure 13. Acid number of BPDA based co-poly(amic acid) (Co-PAA) after 1 month storage at RT.
Figure 14. Acid number of BTDA based Co-PDPAA [ionic salt formulation of co-poly(amic acid)
(Co-PAA) with DEEM] after 1 month storage at RT.
Even though bulk viscosity, inherent viscosity and molecular weight decreased
over a period of time in our study, the acid number was also shown to decrease
rather than increase (Figures 13-17). We used BTDA with an E a (electron affinity)
value of 1.57 eV, BPDA with an E a value of 1.38 eV and a very weak diamine,
SiDA, as co-diamine in the synthesis of Co-PAA. It has been reported that most
reactive dianhydrides with high E a values are most susceptible to premature hy-
drolysis during storage with an increase in acid number and are most likely to un-
dergo side reactions with an amide solvent [21, 22].