TGA– FTi.r. investigation of the thermal degradation of Nafion® and Nafion®/[silicon oxide]-based nanocomposites

• Published in: Polymer (Guilford) Vol. 39; no. 24; pp. 5961 - 5972
• Main Authors: Deng, Q., Wilkie, C.A., Moore, R.B., Mauritz, K.A.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-11-1998; Elsevier
• Subjects: Applied sciences; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Nafion®/[silicon oxide]; Polymer industry, paints, wood; Technology of polymers; TGA– FTi.r; thermal degradation; Nafion®/[silicon oxide]; TGA– FTi.r; thermal degradation; Hydrophobization; Dispersion reinforced material; Experimental study; Silica; Composite material; Thermal stability; Sulfonate copolymer; Tetrafluoroethylene copolymer; Cation exchange membrane; Reaction mechanism; Nanostructured materials; Thermal degradation; Modified material
• ISSN: 0032-3861; 1873-2291
• DOI: 10.1016/S0032-3861(98)00055-X

The integrated TGA–
FTi.r. technique probed the thermal degradation of: (1) a Nafion®–H
+ membrane; (2) this membrane as modified by incorporation of a SiO
2
[1-
x/4]
(OH)
x
phase via
in situ sol–gel reactions for tetraethoxysilane; and (3) this modified membrane as further modified, organically, via post-reaction with diethoxydimethylsilane. Gravimetric loss is multistep for (1) and (2), but occurs in a single step for (3) which has the greatest thermal degradative stability. The considerable inhibition of SO
2 evolution for (2) and (3) is rationalized in terms of side-chains that are immobilized within silicon oxide cages that block reactions involving SO
3 groups. Degradation of SiO
2
[1-
x/4]
(OH)
x
`cores' by generated HF is retarded by their organic `shells' in (3). Substituted carbonyl fluorides and CF
2-containing fragments appear. Si-CH
3 and CH
3 groups and/or –CHCH
2 vinyl compounds are degradation products for (3). It is unlikely that intact R-SO
2-OH groups, or perfluoroalkylether groups issuing from the side-chains of Nafion®, exist as gas phase products. The origins of some peaks are in question owing to spectral complexity. Altogether, the hybrid (3) is superior with respect to degradation onset temperature, subsequent mass loss over a range of about 100°C, and low quantity of evolved products.