MOLECULAR-DYNAMICS OF HAIRY ROD MOLECULES IN THE SOLID-STATE - POLY(GAMMA-METHYL L-GLUTAMATE)-CO-(GAMMA-N-OCTADECYL L-GLUTAMATE) IN SOLUTION-CAST FILMS

We present the thermal, structural, and dynamic properties of poly(gam ma-methyl L-glutamate)-co-(gamma-octadecyl L-glutamate) with 30% octad ecyl chains in solution-cast films. This substance is an example of a so-called ''hairy rod'' molecule. The peptide backbones form stiff rod s which are surrounded by the side chains. The structure of the soluti on-cast film was measured by WAXS and SAXS. We found amorphous and cry stalline side chain parts. The melting point of the crystalline side c hains is ca. 293 K. The thermal properties of these ''hairy rods'' are investigated with differential scanning calorimetry, and the dynamic properties are measured between 110 and 370 K with broad-band dielectr ic spectroscopy (10(-2)-10(9) Hz) and variable-temperature C-13-CP/MAS solid-state NMR. Three dielectric-active relaxation processes are obs erved: Two processes have a temperature dependence according to the Wi lliams-Landel-Ferry (WLF) equation. They approach each other with decr easing temperature and merge at about 238 K, i.e., the calorimetric gl ass transition temperature. These two processes are discussed as fluct uations of the main chain and the surrounding side chain groups. The t hird relaxation process has an Arrhenius-type temperature dependence w ith an activation energy of 43 kJ/mol. It is assigned to fluctuations of the carboxyl groups in the side chains. The variable-temperature NM R results confirm that one of the WLF-type relaxations is caused by th e side chains. These NMR, experiments also show that the main chains u ndergo no local relaxation in the investigated temperature and frequen cy region and stay in the or-helix conformation.