Graphene nanosheets are prepared by solution‐phase exfoliation of graphite and successfully incorporated with polyimide to obtain polyimide/graphene (DABPI/G) nanocomposites via in situ polymerization. Compared with those of pure DABPI, the DABPI/G nanocomposites exhibit better barrier and thermal properties. The oxygen and water vapor transmission rates of the DABPI/G (0.5 wt%) nanocomposite are 0.69 cm3 m−2 d−1 and 0.44 g m−2 d−1, respectively, which are 92 and 85% lower than those of pure DABPI. Meanwhile, the DABPI/G (0.5 wt%) nanocomposite exhibits excellent thermal stability with a Td5% of 578 °C and a coefficient of thermal expansion of −0.19 ppm K−1. The excellent barrier and thermal properties of DABPI/G nanocomposites are mainly attributed to the fine dispersion and orientation of the graphene nanosheets, increased crystallinity, and low free volume of the DABPI matrix. These are the result of the “dual‐plane” structure effect, which is the synergistic orientation effect between the rigid planar molecular chains of DABPI and the nanosheets of graphene.
A high-barrier polyimide (2,7-CPI) was synthesized through the polymerization of pyromellitic dianhydride (PMDA) and a novel diamine (2,7-CDA) containing carbazole moiety. The synthesized diamine and polyimide were fully characterized by elemental analyses, FTIR and NMR. The 2,7-CPI displays very attractive barrier performances, with oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) low to 0.14 cm3·m−2·day−1 and 0.05 g·m−2·day−1, respectively. Meanwhile, 2,7-CPI also exhibits exceptional thermal stability with a glass transition temperature (Tg) of 467 °C, 5% weight-loss temperature (Td5%) of 550 °C under N2 and coefficient of thermal expansion (CTE) of 3.4 ppm/K. The barrier performances of 2,7-CPI are compared with those of a structural analogue (2,7-CPPI) and a typical polyimide (Kapton). Their barrier performances with respect to microstructure were investigated by molecular simulations, wide angle X-ray diffraction (WAXD), and positron annihilation lifetime spectroscopy (PALS). The results show that 2,7-CPI possesses better coplanar structure and more number of intermolecular hydrogen bonds among the three PIs, which result in tight chain packing and thereby high crystallinity, low free volume, and decreased chains mobility. That is, the high crystallinity and low free volume of 2,7-CPI reduce the diffusion and solubility of gases. Meanwhile, the poor chains mobility further decreases the gases diffusion. The reduced diffusion and solubility of gases consequently promote the improvement of barrier properties for 2,7-CPI. The polyimide has a wide application prospect in the field of flexible electronic packaging industries.
A novel diamine (FAPDA) bearing rigid planar fluorene and amide groups was successfully synthesized. Using such diamine and pyromellitic dianhydride (PMDA), a highbarrier polyimide (FAPPI) was obtained. FAPPI exhibits an outstanding gas barrier. Its water vapor transmission rate (WVTR) and oxygen transmission rate (OTR) are as low as 0.51 g•m −2 • day −1 and 0.43 cm 3 •m −2 •day −1 , respectively. Additionally, FAPPI shows excellent thermal stability with a coefficient of thermal expansion (CTE) of 5.8 ppm•K −1 and a glass transition temperature (T g ) of 416 °C. Molecular simulations, positron annihilation, and X-ray diffraction were utilized to gain insight on the microstructures for the enhanced barrier properties. Introducing fluorene moieties and amide groups improves the regularity and rigidity of molecular chains and increases interchain interaction of PI, resulting in low free volumes and decreased movement capacity of the chain. The low free volumes of FAPPI restrain the gas diffusivity and solubility. Meanwhile, the decreased chain movement reduces the diffusivity of gases. Consequently, barrier performances of FAPPI are improved. The polyimide possesses widespread application in the microelectronics packaging fields.
Back Cover: In article https://doi.org/10.1002/mame.201800053 by Jinhua Tan and co‐workers, polyimide/graphene (DABPI/G) nanocomposites are prepared via in situ polymerization, with DABPI possessing a rigid planar molecular structure as a matrix, and a layered‐structure of graphene as a filler. The nanocomposites show high gas barrier properties due to the “dual‐plane” structure effect and have potential applications in flexible electronics encapsulation.
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