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3 Structural Characterization of Sulfonic Acids Resins PSPAs, PSTMAs, PSTHPAs and PSPMDAs
polyethylene chain which posses the most rigid cross-links, hence a highly limited
conformational mobility. The sodium salt of the resins are brittle and brownish
black in color and exhibit the same solubility characteristics of H-form of resins.
Reproduced Author’s work from J. of Appl. Polym.(9).
Table 5. summarizes the pertinent IR absorptions in PSPAS, PSTMAS,
PSTHPAS and PSPMDAS, and their assignments. Significantly, no stretching
band due to –COOH group appears in the IR spectra.
Incorporation of sulfonic acid group is also endorsed by the results of sulfur
analysis. For sulfonation reaction of four resins, effect of variation of sulfuric acid
amount, effect of variation of temperature was studied in detail. Table 6 and 7
summarize ion exchange capacities.
pK values for PSPAS, PSTMAS, PSTHPAS and PSPMDAS are 1.64, 1.31,
1.74 and 1.98 respectively which falls in the range of sulfonic acid resins. The pK
values follow the trend: PSPMDAS>PSTHPAS>PSPAS>PSTMAS which implies
that the dissociation of the resins is somewhat suppressed along the series.
The DTA and TGA (Table 8) studies of the modified polystyrene
based resins have a better thermal stability compared to sulfonated
polystyrene as well as commercial polystyrene divinyl benzene resins like
Zeo-carb 225 and Indion 225 (available in India). Isothermal degradation
of the commercial resins was studied at 250 °C +/-10 °C for 72h in air and
the analysis of the degraded product has also been carried out.
Isothermal degradation studies of PSPAS, PSTMAS, PSTHPAS and
PSPMDAS at 150 °C+/-10 °C for 72 h in air and nitrogen reveal significant
change in IR, decrease in sulfur content, and increase in ion-exchange capacity
values. The pH-metric titration characteristics of PSPMDAS after isothermal
heating under the above conditions indicate weak acid behavior, in contrast to the
strong acid nature of the original resin. The isothermal decomposition of the resin
in water reveals a maximum capacity loss of ~ 15% in all the resins except for the
PSPMDAS for which the corresponding loss is ~3.5%. The sodium salts of the
resins exhibit, in general, better thermal stabilities.
3.4 Structural Characterization of PSPTDA, PS6FDA and
Comparison of DTA (Figure 16) TGA (Figure 17) analyses of PS with that of
PSPTDA, PSNTDA and PS6FDA confirms the incorporation of dianhydride
moieties into PS . The very high thermal stability of PSPTDA, PSNTDA and
PS6FDA compared to that of PS are apparently consistent with a more rigid
network due to polycyclic aromatic system and presence of fluoro derivatives
combining with interchain crosslinking involving dianhydride moieties.
PS shows traditional endothermic peak at 400 °C whereas PSPTDA, PSNTDA
and PS6FDA show exotherms. The
spectra of hypercrosslinked
PSNTDA(Figurel8), PSPTDA(Figure l9) and PS6FDA(Figure 20) show peaks at
129ppm sharp peak for proton bearing aromatic carbons and small peak at 146-