Molecular Motions of Crystalline Polymers by Solid-State MAS NMR
Chain dynamics in the crystalline region of semicrystalline polymers play an important role for bulk material properties such as mechanical strength, creep, drawability, crystallization process, and crystal transformation. Therefore, it is important to characterize chain dynamics in detail. 2D exchange NMR is a reliable tool for polymer dynamics analysis, because this method provides motional geometry and time-kinetic parameters quantitively. However, it is difficult to apply this sophisticated method for polymers with chemically complicated polymers in natural abundance. ID-MAS exchange NMR method is possible to give the same information, and has a great advantage of characterizing molecular dynamics for multi-functional groups of molecules without isotope labeling. In this contribution, we briefly explain ID-MAS exchange NMR, and their applications to slow dynamics of crystalline polymers with chemically complicated structures in natural abundance. We will show which part of polymer in the crystalline region contributes to mechanical property and what type of motions occur in the unstable crystalline form prior to crystal-crystal transformation.