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3 Structural Characterization of Sulfonic Acids Resins PSPAs, PSTMAs, PSTHPAs and PSPMDAs

3 Structural Characterization of Sulfonic Acids Resins PSPAs, PSTMAs, PSTHPAs and PSPMDAs

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SYNTHESES, CHARACTERIZATION



277



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



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GANGULY



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.



SYNTHESES, CHARACTERIZATION



279



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



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GANGULY



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

PSNTDA

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.



SYNTHESES, CHARACTERIZATION



281



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-



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