Polyethylene terephthalate (PET) is one of the most widely used plastics worldwide and is applied, i.a., as packaging material in the food industry. Like many polymers, PET is susceptible to photochemical degradation and absorbs in the ultraviolet (UV) range.
As already known, UV irradiation of PET leads to shorter molecular chains and thus to a higher number of carboxyl end groups,[3,4] which was confirmed here with attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR). To clarify whether this pretreatment method also affects the chain dynamics of PET, we used centerband-only detection of exchange (CODEX) and rotating-frame spin-lattice relaxation times for protons (T1ρ(1H)) to investigate PET chain dynamics on various timescales at ambient temperature (30 °C) as well as close to its glass transition temperature (70 °C) before and after UV illumination. CODEX is a one-dimensional exchange experiment which allows for characterization of slow segmental reorientations on the millisecond to second timescale, whereas T1ρ(1H) times provide information about molecular dynamics on the microsecond to millisecond timescale.
Both MAS NMR experiments revealed an increased mobility of the PET chains at 70 °C compared to 30 °C. Furthermore, T1ρ(1H) experiments showed slower motions after UV treatment at both temperatures and CODEX experiments indicated lower mobility for the UV illuminated sample at 70 °C.
 World Economic Forum, Ellen MacArthur Foundation, McKinsey & Company. The New Plastics Economy – Rethinking the future of plastics. 2016.
 M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:175–189, 1972.
 M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:203–215, 1972.
 M. Day, D. M. Wiles. J. Appl. Polym. Sci., 16:191–202, 1972.
 E. R. deAzevedo, W.-G. Hu, T. J. Bonagamba, K. Schmidt-Rohr. J. Am. Chem. Soc., 121:8411–8412, 1999.
 K. Schmidt-Rohr, H. W. Spiess. Multidimensional Solid-State NMR and Polymers. Academic Press, London, 1994.