Understanding even-odd effects in linear semi-crystalline polymers: Polyethers, polycarbonates, polyesters, and polyamides

Abstract

The intricate relationship between the chemical structure of polymers, their thermal history, and various influencing variables has been systematically explored over the last several decades. A significant finding in this area is the impact of the alkyl chain length in the polymer backbone separating functional groups within the repeating unit on thermal properties such as melting and crystallization. Research has revealed an alternating pattern in solid-state properties linked to the number of methylene (–CH₂–) units in the main chain, demonstrating a remarkable distinction based on whether this number is even or odd. This intriguing phenomenon is termed the “even-odd effect."

In this review contribution, we delve into recent advancements in understanding the even-odd effect from the crystallization point of view, showcasing specific examples across key polymer families, including polyethers, polycarbonates, polyesters, and polyamides. We meticulously review the methodologies applied to study these cases, introducing innovative techniques for investigating the even-odd effect, such as crystallization kinetics determination and Successive Self-nucleation and annealing thermal fractionation. Our analysis reveals that the saturation of the even-odd effect is heavily contingent upon the intermolecular interactions within each polymer family, with some families showing no reported saturation thus far.

Moreover, we dedicate a comprehensive section to examining how polymer structure's even or odd characteristics influence crystallization behavior, emphasizing the emergence of novel behaviors within random copolymers. In conclusion, while significant progress has been made, it is crucial to recognize that numerous facets of this topic remain unexplored. Our findings underscore the importance of continued research, which is vital not only for the synthesis of innovative homopolymers but also for advancing copolymer development.