2,2-Bis(3,4-dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA)-derived polyimides containing polar functional groups have been extensively studied for membrane-based gas separations and used as precursors for various solid-state thermal modifications such as thermal crosslinking of carboxyl-groups or thermal rearrangement of hydroxyl groups to form polybenzoxazoles. In this work, we studied four 6FDA-derived polyimides without polar functional groups to investigate in-situ thermal crosslinking involving partial decomposition of the hexafluoroisopropylidene (–C(CF₃)₂–) mainchain group. A thorough examination of the 6FDA-based polyimides via thermal gravimetric analysis coupled with mass spectroscopy (TGA-MS) and energy dispersive X-ray spectroscopy (EDX) under isothermal treatment at 450 °C for up to 3 h revealed that thermal treatment triggered continuous evolution of fluorine from (–C(CF₃)₂–) groups. The 6FDA-based polyimides were insoluble after thermal treatment for only 30 min and maintained good mechanical strength with favorable changes in gas separation properties. For example, after 3 h isothermal heat treatment, the CO₂ permeability of crosslinked 6FDA-pPDA noticeably increased threefold from 39 to 115 barrer coupled with only a small drop in CO₂/CH₄ selectivity from 54 to 46. The crosslinked polyimides demonstrated excellent plasticization resistance when tested under high-pressure binary CO₂/CH₄ mixed-gas conditions.

2,2-双（3,4-二羧基苯基）-六氟丙烷二酐（6FDA）衍生的含有极性官能团的聚酰亚胺已被广泛研究用于基于膜的气体分离，并用作各种固态热改性（如热交联）的前体羧基或羟基热重排形成聚苯并恶唑。在这项工作中，我们研究了四种不含极性官能团的 6FDA 衍生聚酰亚胺，以研究涉及六氟异亚丙基（–C(CF ₃ ) ₂部分分解）的原位热交联–) 主链组。通过热重分析结合质谱 (TGA-MS) 和能量色散 X 射线光谱 (EDX) 在 450 °C 下等温处理长达 3 小时，对基于 6FDA 的聚酰亚胺进行了彻底检查，结果表明热处理触发了连续氟从 (-C(CF ₃ ) ₂ -) 基团的演化。基于 6FDA 的聚酰亚胺在热处理仅 30 分钟后不溶，并保持良好的机械强度，气体分离性能发生有利变化。例如，等温热处理 3 小时后，交联的 6FDA-pPDA的 CO ₂渗透率显着增加了三倍，从 39 barrer 增加到 115 barrer，而 CO ₂ /CH ₄仅略有下降选择性从 54 到 46。在高压二元 CO ₂ /CH ₄混合气体条件下测试时，交联聚酰亚胺表现出优异的抗塑化性。