E.p.r. spectroscopy of spin-labelled macromolecules as a tool for determining chain conformations in amorphous solid polymers

Abstract

The feasibility of using e.p.r. spectrscopy in studying conformations of spin-labelled macromolecules in the amorphous solid state is examined. The algorithm for e.p.r. spectra computation is developed. It was assumed that molecular weights of labelled linear chains are high and their solid solution is diluted. It is shown that the scaling exponent which determines the dependence of mean-square end-to-end distance on molecular weight and stiffness parameter (mean-square length of monomer unit) may be extracted from the spectra. Computed spectra are compared with experimental ones, measured at 77 K, of diluted solutions of spin-labelled poly(4-vinyl pyridine) [P(4-VP)] of different molecular weights in methanol and non-labelled P(4-VP). The conformational state (Gaussian coil), parameter of stiffness, and radius of gyration of spin-labelled P(4-VP) macromolecule in frozen solutions are determined. A conclusion is drawn that e.p.r. spectroscopy may become a new tool for studying chain conformatin in solid polymers.