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<p>To achieve higher cyclization and polymerization degrees (DP), oleum is the most commonly used medium for synthesizing aromatic polyoxadiazole (POD) with excellent thermal stability, chemical resistance, and unique electrochemical properties. However, the stringent dissolution conditions and complex polymerization system limited the effective characterization of POD and hindered stable control of the polymerization process. Consequently, the current understanding of its polymerization mechanism and kinetics remains superficial, with even the basic structure of POD being debated. This study employs anhydrous dioxane as a precipitating agent to obtain POD with a defined structure of alternating benzene and oxadiazole rings terminated with carboxyl groups. Furthermore, elemental analysis is used to calculate the DP of isothermal reaction products under varying conditions, yielding an apparent rate constant, the apparent activation energy (95&#xa0;kJ/mol), and reaction orders for various substrates (2nd order for hydrazine sulfate, 1st order for terephthalic acid, and 3.3rd order for SO₃). The relationship between system viscosity and polymerization degree (η ~ N) was established to address the impact of high conversion rates on mass transfer, and the intrinsic polymerization kinetics were explored through rheokinetics. This validated previous conclusions and yielded the chemical reaction activation energy (177&#xa0;kJ/mol), an overall reaction order of 3, and optimal ranges for various conditions. Transition state theory analysis attributes the activation energy gap to diffusive entropy penalties. Finally, based on experimental findings, a plausible polymerization mechanism is proposed to account for the system’s complete cyclization, supported by mathematical validation. This study offers significant insights into the polymerization kinetics of POD, advancing the controllable synthesis of high-performance polymers and providing a foundational framework for future mechanistic and material optimization studies.</p>

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Rheokinetic-driven polycondensation control of aromatic polyoxadiazole in oleum: from structural precision to kinetic parameterization

  • 期刊论文

  • 发表日期：

    2026年1月8日

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  • Yulin Zhou,
  • Yuanyuan Yu,
  • Weiwei Zhang,
  • Qian Mao,
  • Jiadeng Zhu,
  • Shuheng Liang,
  • Qibao Xie,
  • Mengjin Jiang

摘要

To achieve higher cyclization and polymerization degrees (DP), oleum is the most commonly used medium for synthesizing aromatic polyoxadiazole (POD) with excellent thermal stability, chemical resistance, and unique electrochemical properties. However, the stringent dissolution conditions and complex polymerization system limited the effective characterization of POD and hindered stable control of the polymerization process. Consequently, the current understanding of its polymerization mechanism and kinetics remains superficial, with even the basic structure of POD being debated. This study employs anhydrous dioxane as a precipitating agent to obtain POD with a defined structure of alternating benzene and oxadiazole rings terminated with carboxyl groups. Furthermore, elemental analysis is used to calculate the DP of isothermal reaction products under varying conditions, yielding an apparent rate constant, the apparent activation energy (95 kJ/mol), and reaction orders for various substrates (2nd order for hydrazine sulfate, 1st order for terephthalic acid, and 3.3rd order for SO₃). The relationship between system viscosity and polymerization degree (η ~ N) was established to address the impact of high conversion rates on mass transfer, and the intrinsic polymerization kinetics were explored through rheokinetics. This validated previous conclusions and yielded the chemical reaction activation energy (177 kJ/mol), an overall reaction order of 3, and optimal ranges for various conditions. Transition state theory analysis attributes the activation energy gap to diffusive entropy penalties. Finally, based on experimental findings, a plausible polymerization mechanism is proposed to account for the system’s complete cyclization, supported by mathematical validation. This study offers significant insights into the polymerization kinetics of POD, advancing the controllable synthesis of high-performance polymers and providing a foundational framework for future mechanistic and material optimization studies.