An ester dianhydride bearing alicyclic cis-ethylenic double bond, bicyclo [2.2.1]hept-5-ene-2, 3-diylbis(methylene)bis(1, 3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylate) (BHEM) and its hydrogenated analogue bicyclo[2.2.1]heptane-2, 3-diylbis(methylene)bis(1, 3-dioxo-1, 3-dihydroisobenzofuran-5-carboxylate) (BHSM) were synthesized and polymerized with three aromatic diamines, respectively, to prepare two analogous series of polyimide (PI) films. Comparative studies were carried out to elucidate how the unsaturated bicylo[2.2.1]heptenyl structure and the saturated bicyclo[2.2.1]heptyl structure in polymer main chain influence the properties of the PI films. The structural characteristics of the two analogous alicyclic structures including reactivity, bulkiness, configuration, polarity were found to impact the solubility, hydrophobicity, surface morphology, and the thermal, optical and dynamic dielectric properties of PI films. The aggregation state of both series of PI films was analyzed by wide-angle X-ray scattering (WAXD) and computed tomography (CT) fluorescence, which reveals the structural characteristics differences between unsaturated alicyclic containing cis-ethylenic double bond with planar sp2 hybrid configuration and saturated alicyclic with wholly tetrahedral sp3 hybrid configuration. It indicates that the thermally crosslinkable alicyclic cis-ethylenic double bonds in BHEM incline to induce a closer polarized chain packing via inter-chain Π-Π complex, while the wholly tetrahedral sp3 configuration of the bulkier saturated alicyclic in BHSM inhibits the chain aggregation in the PI film and leads to greater chain mobility.
alicyclic cis-ethylenic double bond polyimide film aggregation state interchain CT interaction
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