STUDIES OF MOLECULAR MOTIONS IN NOVEL SYNDIOTACTIC ALTERNATING ETHYLENE-PROPYLENE CRYSTALLINE COPOLYMER BY DYNAMIC-MECHANICAL ANALYSIS AND SOLID-STATE C-13 NMR

A syndiotactic alternating ethylene-propylene (SYN-ALT-EP) copolymer w as synthesized. Two molecular relaxation processes (alpha and beta rel axations) have been found below room temperature via dynamic mechanica l analysis (d.m.a.): the alpha relaxation at -60 degrees C and the bet a relaxation at -125 degrees C. The apparent activation energy of the alpha relaxation is 285 kJ mol(-1), and the activation energy of the b eta relaxation is 43 kJ mol(-1) based on the Arrhenius equation. Molec ular motion in SYN-ALT-EP copolymer was probed by solid-state C-13 n.m .r. experiments. At temperatures above the glass transition temperatur e (T-g) there are two major molecular motions in this copolymer: a bac kbone motion (the rotational motion about single bonds) and a methyl s ide group rotation. The backbone motion is frozen below T-g, but there is still a methyl rotation. As the temperature is further decreased t o about -175 degrees C, well below the beta-transition observed in d.m .a., the methyl side group rotation slows down, suggesting that the me thyl rotation may be associated with the observed beta relaxation proc ess.