Restriction of Spin Probe Motions in Polymer Composites Due to Chemical Factors

Abstract

Hyperfine splitting constants of the nitroxyl radical, with and without hydrogen bonds to the surrounding molecules, have been calculated using the UHF method on a 6-31G* base. In polyethylene filled with silica, hydrogen bonds are formed between nitroxyl radicals and —OH groups of the filler. The formation of hydrogen bonds leads to a change in the A _zz value from 3.33 mT for an isolated nitroxyl radical to 3.83 mT for a radical with a hydrogen bond. The relevant values as measured experimentally are 3.4 and 4.0 mT, respectively. The same procedure was used to calculate the theoretical A _zz value for a nitroxyl radical interacting with polyamide via a hydrogen bond. The value was found to be 3.63 mT (experimental value = 3.6 mT). Hydrogen bond formation results in a restricted motion of the nitroxyl radical in a polymeric medium.