Dynamics of cyclic and linear poly(oxyethylene) and threading conformation in their blends

Understanding the role of chain architecture in dynamics of polymers is important for processing a tremendous number of commercial products. Chemically identical but topologically different cyclic and linear polymers not only result in marked differences in diffusion and flow behaviors, but also lead to unique and unusual transport properties of their blends, where cyclic polymer components have chances to be threaded onto the linear polymer chains. This dissertation addresses the effect of ring architecture on dynamics using different time/distance scale techniques: self-diffusion coefficients by pulsed-field-gradient NMR (PFG NMR), NMR spin-spin relaxation time (T2) and bulk viscosity. The phase transition behaviors of a cyclic polymer and its blend with a linear polymer were investigated by differential scanning calorimetry (DSC) and polarized light microscope as well.; The first part of the dissertation focuses on the preparation of highly pure low-molecular-weight cyclic poly(oxyethylene) (CPOE) of different sizes and their dynamics in solution and melts. In deuterated water, CPOE diffused faster for a given chain length than both linear POE (LPOE) and linear POE dimethyl ether (LPOEDE), and had lower T2 values than LPOE across the entire molecular weight range studied. However, the self-diffusion coefficients in the melt state were arranged in the following manner: LPOEDE > CPOE > LPOE, in excellent agreement with T2 and viscosity data, showing topology and chain end effects. Like LPOE, CPOE was found to obey the Rouse model. Compared to the activation energy of viscosity for LPOEDE, CPOE and LPOE exhibited higher values and exhibited less dependence on the molecular weight, which were attributed to the absence of chain-end free volume and the suppression of chain-end free volume by hydrogen bonds, respectively.; In the second part of the dissertation, topological threading effect on the dynamics and phase transitions of the blends of CPOE and LPOE having a same molecular weight is explored. The self-diffusion coefficient and viscosity of the blends became closer to those of the slow component, LPOE, as increasing molecular weight. For 900 and 1500 g/mol, the diffusion coefficients negatively deviated from a binary mixing rule over a full concentration range of CPOE, and the weight fraction of the threaded cyclic and linear chains for 1500 g/mol is estimated by a three-term mixing rule. The viscosity data showed stronger enhancement at higher concentrations of CPOE. The glass transition temperatures of the blends of 900 g/mol were slightly higher than the predicted values from the Fox equation. The spherulite growth rate of LPOE of 1500 g/mol did not increase on addition of a faster component, CPOE of 1500 g/mol, up to 20%.