3 years ago

Thickness dependence of structural relaxation in spin-cast polynorbornene films with high glass transition temperatures (>613 K)

Thickness dependence of structural relaxation in spin-cast polynorbornene films with high glass transition temperatures (>613 K)
Bryan D. Vogt, Elizabeth A. Lewis
The isothermal structural relaxation (densification) of a family of glassy polynorbornene films with high glass transition temperatures (Tg > 613 K) is assessed via spectroscopic ellipsometry. Three polymers were examined: poly(butylnorbornene) (BuNB), poly(hydroxyhexafluoroisopropyl norbornene) (HFANB), and their random copolymer, BuNB-r-HFANB. The effective aging rate, β(T), of thick (∼1.2 μm) spun cast films of BuNB-r-HFANB is approximately 10−3 over a wide temperature window (0.49 < T/Tg < 0.68). At higher temperatures, these polymers undergo reactions that more dramatically decrease the film thickness, which prohibits erasing the process history by annealing above Tg. The aging rate for thick BuNB-r-HFANB films is independent of the casting solvent, which infers that rapid aging is not associated with residual solvent. β (at 373 K) decreases for films thinner than ∼500 nm. However, the isothermal structural relaxation of thin films of BuNB-r-HFANB exhibits nonmonotonic temporal evolution in thickness for films thinner than 115 nm film. The thickness after 18 h of aging at 373 K can be greater than the initial thickness. The rapid aging of these polynorbornene films is attributed to the unusual rapid local dynamics of this class of polymers and demonstrates the potential for unexpected structural relaxations in membranes and thin films of high-Tg polymers that could impact their performance. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 Polynorbornene films with high Tg's exhibit rapid aging (∼10−3) even at temperatures 300 K below their bulk Tg. For thin films, the thickness change was nonmonotonic during isothermal aging at lower temperatures. This phenomenon was attributed to the chain conformations that develop in the thin films on casting.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/polb.24434

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