Selective Deuteration along a Polyethylene Chain: Differentiating Conformation Segment by Segment

To improve the circularity and performance of polyolefin materials, recent innovations have enabled the synthesis of polyolefins with new structural features, such as cleavable breakpoints, functional chain ends, and unique comonomers. As new polyolefin structures become synthetically accessible, a fundamental understanding of the effects of structural features on polymer (re)processing and mechanical performance is increasingly important. While bulk material properties are readily measured through conventional thermal or mechanical techniques, selective measurement of local material properties near structural defects is a major characterization challenge. Here, we synthesized a series of polyethylenes with selectively deuterated segments using a polyhomologation approach and employed vibrational spectroscopy to evaluate the crystallization and melting of chain segments near features of interest (e.g., end groups, chain centers, and midchain structural defects). Chain-end functionality and defects were observed to strongly influence the crystallinity of adjacent deuterated chain segments. Additionally, chain-end crystallinity was observed to have different molar mass dependence than midchain crystallinity. The synthesis and spectroscopy techniques demonstrated here can be applied to a range of previously inaccessible deuterated polyethylene structures to provide direct insight into local crystallization behavior.