| Aggregated ionic groups in ionomers act as temporary crosslinks, influencing ionomer melt flow behavior by limiting motion of chain segments to an ion-hopping mechanism. To understand the dynamics of chain and cation motion in ionomers, a series of ethylene-methacrylic acid (E/MAA) ionomers and a complementary model ionomer system were investigated via rheological and spectroscopic techniques. The objective of this dissertation is to test the ion-hopping model and theories of ionomer dynamics by measuring the terminal relaxation time of the polymer chain, td, and the ion-hopping time, τ, and elucidating their dependence upon molecular structure.; All ionomers exhibit terminal flow at sufficiently low shear rates, thus indicating that while the presence of ionic groups slows reptation of polymer chains, terminal relaxation does indeed occur at long times. Td has a strong dependence on ion content or neutralization level, but the type of neutralizing cation plays only a secondary role in the observed flow behavior.; In a detailed examination of cation diffusion, hence τ, in E/MAA ionomer melts, we observe that the type of neutralizing cation does not greatly affect cation diffusion coefficients, as with the macroscopic relaxation time. Secondly, we find that τ and td have a similar dependence upon temperature, in agreement with theories of ionomer dynamics. Comparing the two relaxation times, τ is four orders of magnitude faster than t d for highly neutralized E/MAA ionomers. In addition, the unneutralized acid groups present in E/MAA ionomers significantly influence the observed flow behavior by plasticizing associations between ionic groups, thus contributing to the strong dependence of td on neutralization level.; Model sulfonated or carboxylated styrene-ethylene-butene (SEB) random ionomers were synthesized to directly compare with theories of ionomer dynamics. Measurements were limited to lightly entangled polymers due to the strong ionic associations, resulting in large viscosities at low molecular weights and numbers of ionic groups per chain. For lightly entangled sulfonated ionomer melts, a mechanism is proposed whereby ionic associations between sulfonate groups dominate the resulting flow behavior. In addition, the type of bound ionic group does not greatly affect the resulting flow behavior, as carboxylated and sulfonated SEB ionomers behave similarly. |
