Morphology And Molecular Motions Of Styrene-Isoprene Block Copolymers Upon Elongation As Probed By Solid-state High-resolution NMR Spectroscopy

In this work, we investigate into the morphology and the molecular motion of polystyrene-block-polyisoprene-block-polystyrene, in which the polystyrene weight concentration are 14% and 22% respectively, during elongation by means of the solid-state high-resolution NMR spectroscopy.In chapter 1, we describe the NMR techniques and thermoplastic elastomers, especially for development of solid-state NMR and the influence to the elastomers, i.e. the physical property, caused by stretching. Furthermore, we provide the concepts of NMR relaxation time and molecular motion of polymers, and then concretely show how to utilize them to characterize the molecular motion. Finally, we briefly introduce the home-made device which makes the in-situ stretching NMR experiments possible.In chapter 2, we make use of 13C CP/MAS, 13C DD/MAS and 13C CP/MAS/TOSS experiments to identify the structure of two SIS samples which contain polystyrene differently. Due to the assignment of 13C spectra, we find that there are two kinds of conformation in the SIS structure. One is cis, the other is trans. According to the 13C CP/MAS at various factors of stretching, it's significantly observable that there is no crystalline peak, whereas the crystalline phenomenon induced by the elongation in pure polyisoprene was reported by previous work. We consider that the rigid polystyrene prevent the crystal from being generated and the decrease of molecular motion resulted from stretching doesn't refer to the transformation from amorphous phase to crystalline phase, but really belongs to unoriented structure to oriented structure, which cannot be exhibited in the 13C CP/MAS.We take advantage of mKWW molecular motion model, Cole-Davidson distribution function and BPP model to calculate and transfer T1 data of each carbon atom of polyisoprene into correlation time Ï„seg, which is turned to average segmental correlation time. Subsequently, we obtain the information of molecular motion of polyisoprene in 2 SIS samples at the temperature of 293K, 303K and 313K with respect to different factor of elongation. The molecular motion of the isoprene units changes by only 20% for the low concentration sample (SIS-14%) at T = 293 K and T...