Free volume manipulation of a 6FDA-HAB polyimide using a solid-state protection/deprotection strategy

Tert-butoxycarbonyl (t-BOC) is a thermally labile moiety that can be used to protect hydroxyl groups on polymers. In this study, t-BOC was appended onto a polyimide consisting of 2,2'-bis-(3,4-dicarboxyphenyl) hexafluompropane dianhydride (6FDA) and 3,3'-dihydroxy-4,4'-diamino-biphenyl (HAB), after which the polymer was formed into self-standing films. Solid-state thermal treatments were performed to systematically remove t-BOC moieties to alter the physical packing structure and concomitant gas transport properties of the polymer. Despite performing deprotection reactions well below the glass transition temperature of 6FDA-HAB (similar to 300 degrees C), this free volume manipulation (FVM) approach produced only subtle differences in polymer density, fractional free volume, average free volume element size, and gas transport properties relative to the unprotected polymer. While these findings suggest that thermally removing covalently bound functional groups from polymer films can be used to manipulate free volume and gas transport performance for glassy polymers, more robust polymer systems than linear polyimides are required to preserve the nascent free volume architecture generated from this approach.

Automated summary

This study investigated the use of thermally labile moiety t-BOC to protect hydroxyl groups on polymers, and the subsequent removal of t-BOC moieties through thermal treatment to alter the physical packing structure and gas transport properties of the polymer. While this approach can manipulate free volume and gas transport performance in glassy polymers, more robust polymer systems are needed to maintain the nascent free volume architecture generated by this method in linear polyimides.