Chain Dynamics in Antiplasticized and Annealed Poly(ethylene terephthalate) Determined by Solid-State NMR and Correlated with Enhanced Barrier Properties

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• 作者：Rudra Prosad Choudhury ; Jong Suk Lee ; Robert M. Kriegel ; William J. Koros ; Haskell W. Beckham
• 刊名：Macromolecules
• 出版年：2012
• 出版时间：January 24, 2012
• 年：2012
• 卷：45
• 期：2
• 页码：879-887
• 全文大小：435K
• 年卷期：v.45,no.2(January 24, 2012)
• ISSN：1520-5835

文摘

Using solid-state NMR, site-specific chain dynamics from the hertz to mid-kilohertz regime were examined in compression-molded films of poly(ethylene terephthalate) (PET), PET filled with 2 wt % acetanilide or phenacetin, and PET annealed below and above the glass transition temperature (T_g). More specifically, ¹³C relaxation time in the rotating frame, ¹H鈥?sup>13C cross-polarization times, and ¹³C chemical-shift anisotropy exchange were measured at natural abundance. ¹³C CP/MAS spectra revealed that PET annealed above T_g was 28% crystalline, and all other PET samples were completely amorphous. Relaxation times in these polymers were analyzed using stretched exponentials which yielded characteristic time constants. The filled PET and PET annealed above T_g exhibited suppressed chain dynamics across the entire hertz to mid-kilohertz regime that were correlated with reduced CO₂ and O₂ permeabilities. Using the centerband-only detection of exchange (CODEX) sequence, the fraction of flipping phenylene rings was observed to decrease in these polymers, with the decrease in the semicrystalline sample consistent with the crystalline fraction.