Molecular dynamics in complex polymeric systems as studied by dielectric relaxation spectroscopy (DRS) and dynamic mechanical spectroscopy (DMS).

摘要

All polymer chains exhibit global and segmental dynamics in the mechanical field of dynamic mechanical spectroscopy (DMS) measurements. But only a few polymer chains exhibit both normal and segmental processes in the electrical field of dielectric relaxation spectroscopy (DRS) measurements. For such polymers, data generated by DRS and DMS could be compared. Normal process is present in polymers that contain a persistent cumulative dipole moment along the chain contour, and segmental process is present in polymers that contain transverse dipole moment perpendicular to the chain. The comparison between DRS and DMS provides fundamental understanding of molecular dynamics and the interplay between chain and segmental dynamics.; This thesis research consists of four parts: (1) A study of chain and segmental dynamics in poly(propylene oxide) (PPO) homopolymers, presented in chapter 3. This study is performed by DRS and DMS on a series of PPOs with different molecular weight, molecular architecture, and functional end groups. (2) A DRS and DMS study of the changes of molecular dynamics in polymer networks undergoing chemical cross-linking, described in chapter 4. Two kinds of polymer networks containing linear and star-shaped functionalized poly(propylene oxide) (PPO) chains are studied, and the changes in dynamic are recorded as a function of the advancement of cure. (3) A study of the relaxation phenomena in multi-graft (MG) copolymers is discussed in chapter 5, including the effect on molecular dynamics of different molecular architecture, i.e. a polyisoprene with one, two and four polystyrene emanating from each branch point, designated as combs, centipedes, and barbwires respectively. (4) A comprehensive study of deoxyribose nucleic acid (DNA) aqueous solutions by DRS and DMS in chapter 6. The hierarchy of DNA molecular motions and the difference in dynamic properties between double-stranded and single-stranded DNAs are described.