(57i) Unraveling the Impact of Aging on Diels Alder Polyphenylene (DAPP) for Applications below Tg

Aging, a process occurring below the glass transition temperature (Tg), significantly influences the mechanical viscoelastic behavior of polymers. Extensive research has focused on characterizing the relaxation mechanisms during aging. While numerous studies have investigated bulk thermodynamic properties and microstructural patterns, disparities persist. The implications of these aging phenomena span multiple industries. Notably, high Tg polymers remain inadequately examined. This study centers on Diels Alder Polyphenylene (DAPP), characterized by its high strength and molecular weight, with the objective of bridging the knowledge gap regarding aging's impact on Polyphenylene (PP) and its suitability for industrial applications below Tg. A novel research approach explores how cooling rate and temperature affect PP's aging properties, specifically targeting the temperature range up to 350°C, where PP materials retain their processability. Our investigation employs a diverse range of characterization techniques. We utilize gas permeation measurements to assess transport properties, density measurements to gain insights into chain relaxation analysis, and modulated differential scanning calorimetry (DSC) to link cooling rate effects with observed Tg changes and enthalpic recovery. Additionally, birefringence measurements track alterations in stress patterns. We anticipate that our study will offer valuable insights into the evolution of gas transport properties over time during aging, encompassing reduced permeability and increased selectivity rates. Intriguingly, preliminary findings indicate a decrease in density rather than an increase. These results will contribute to a deeper understanding of DAPP's aging behavior, providing essential data for optimizing its industrial applications below the glass transition temperature. Future studies will expand our knowledge base by obtaining additional microstructural evidence through techniques such as transmission electron microscopy and investigating the mechanical properties within the linear viscoelastic region, encompassing creep compliance, stress-relaxation modulus, and other dynamic mechanical properties like stress-strain.