Dynamic mechanical study of molecular dynamics in ethylene–norbornene copolymers

Abstract

Dynamic mechanical studies of molecular dynamics have been performed for two ethylene–norbornene copolymers. The analysis of data indicates the existence of three relaxation processes: a primary (α) and two secondary (β and γ) ones. It was found that the secondary processes β and γ are connected with the local motions of ethylene and norbornene groups, respectively and that their rates follow the Arrhenius relation. Moreover, the β process was recognized as the Johari–Goldstein process acting as the precursor of the cooperative structural α-relaxation. Contrary to γ and β processes, the motional rate of α-one follows the Vogel–Fulcher–Tammann equation indicating the cooperative nature of motions involved in this process. An increase in norbornene content in copolymer slows down the molecular dynamics of both norbornene fragments and whole chains, and in consequence shifts these relaxation processes into higher temperatures. Using the Havriliak–Negami formalism the motional parameters for the processes mentioned above were estimated.