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<p>Polyimide (PI) constitutes an indispensable class of materials for advanced optoelectronic devices. However, the simultaneous realization of high optical transparency, superior thermal stability, and thermoplastic processability remains a formidable challenge owing to intrinsic conflicts in conventional molecular design. To decouple these competing attributes, a semi-rigid methyl substitution strategy is introduced. A series of plasticized colorless polyimides (PCPI) is synthesized via copolymerization of 4,4’-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4’-oxydianiline (ODA) with two methyl-substituted diamines. As methyl unit content increases, optical transmittance rises, with the optimal composition (semi-rigid unit/6FDA = 1:1) achieving an average transparency (T<sub>avg</sub>) of 90% along with excellent solubility. All PCPIs maintain high thermal stability, exhibiting decomposition temperatures (the 10% weight temperature, <i>T</i><sub>d10</sub>) exceeding 530&#xa0;°C, a low coefficient of thermal expansion (CTE), and glass transition temperatures (<i>T</i><sub>g</sub>) around 300 °C. The toughness of these PI films was further supported by their high tensile strength. Theoretical modeling and <i>Density Functional Theory</i> (DFT) calculations reveal that the methyl groups and the semi-rigid backbone collectively balance chain packing and charge transfer interactions, leading to synergistic property enhancement. This work offers a practical and effective structural design route to high-performance PCPIs through controlled rigidity modulation.</p>

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Semi-rigid methyl substitution strategy for decoupling conflicting properties in transparent and thermally robust polyimide

  • 期刊论文

  • 发表日期：

    2026年5月12日

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  • Zhenqi Xu,
  • Rui Zhao,
  • Zhen Lu,
  • Linxi Hou

摘要

Polyimide (PI) constitutes an indispensable class of materials for advanced optoelectronic devices. However, the simultaneous realization of high optical transparency, superior thermal stability, and thermoplastic processability remains a formidable challenge owing to intrinsic conflicts in conventional molecular design. To decouple these competing attributes, a semi-rigid methyl substitution strategy is introduced. A series of plasticized colorless polyimides (PCPI) is synthesized via copolymerization of 4,4’-(Hexafluoroisopropylidene) diphthalic anhydride (6FDA) and 4,4’-oxydianiline (ODA) with two methyl-substituted diamines. As methyl unit content increases, optical transmittance rises, with the optimal composition (semi-rigid unit/6FDA = 1:1) achieving an average transparency (Tavg) of 90% along with excellent solubility. All PCPIs maintain high thermal stability, exhibiting decomposition temperatures (the 10% weight temperature, Td10) exceeding 530 °C, a low coefficient of thermal expansion (CTE), and glass transition temperatures (Tg) around 300 °C. The toughness of these PI films was further supported by their high tensile strength. Theoretical modeling and Density Functional Theory (DFT) calculations reveal that the methyl groups and the semi-rigid backbone collectively balance chain packing and charge transfer interactions, leading to synergistic property enhancement. This work offers a practical and effective structural design route to high-performance PCPIs through controlled rigidity modulation.