Anisotropic polyimide (PI)/graphene composite aerogels were fabricated by unidirectional freezing. A poly­(amic acid) (PAA) ammonium salt/graphene dispersion was first synthesized by mixing together PAA, H2O, triethylamine (TEA), and graphene and then was successively subjected to one-way freezing, freeze-drying, and thermal imidization. The one-way growth of ice crystals endowed the composite aerogels with highly arranged tubular pores. The PI/graphene composite aerogels possessed anisotropic conductivity, electromagnetic interference (EMI) shielding, heat transfer, and compression performance. Moreover, the composite aerogels with low density (0.076 g·cm–3) exhibited high EMI shielding effectiveness (SE) of 26.1–28.8 dB, and its specific EMI SE value achieved 1373–1518 dB·cm2·g–1 when the graphene content was 13 wt %. The main electromagnetic interference shielding mechanism of these composite aerogels was microwave absorption. The composite aerogels had excellent thermal stability, and their 5% weight loss temperature was higher than 546 °C in nitrogen. This research provided an easy and environmentally friendly approach to prepare lightweight and anisotropic PI-based composite aerogels.

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Epoxy adhesives that combine flexibility, high-temperature adhesion property, and medium–low-temperature curing ability are an urgent need in the microelectronic device era. Unfortunately, it is still a challenge so far. In this context, two kinds of curing agents are combined to construct homogeneous rigid–flexible crosslinking networks via the stepwise curing method for preparing an epoxy adhesive with prominent deformation ability and high-temperature adhesive strength. Detailed analysis showed that the crosslinking network constructed by the stepwise curing method was higher and more homogenous than that of the one-step curing method. Benefitting from the homogeneous rigid–flexible crosslinking network, the elongation at break and high-temperature adhesion strength (200 °C) of the epoxy adhesive prepared by the stepwise method were up to about 100% and 1.60 MPa, respectively, which were about 1677.7 and 112.5% higher than those of the epoxy adhesive cured by the one-step curing method. The epoxy adhesive with medium–low-temperature curing ability, excellent flexibility, and high-temperature adhesion was first reported. It is expected that this work could provide some inspiration to design the special epoxy adhesives.

A kind of four‐functional epoxy resin containing tertiary ester groups (FETE) was designed and synthesized by two‐step reaction: first, the nucleophilic substitution reaction between linalool and isophthaloyl chloride, and then epoxidation. The chemical structure of obtained product was determined by infrared (IR) spectroscopy and nuclear magnetic resonance spectroscopy. Unlike traditional thermosetting epoxy resins, the cured FETE could degrade rapidly at low temperature (200–300°C). Dynamic mechanical analysis analysis showed that through copolymerization of FETE with (4,5‐epoxycyclohexane‐1,2‐dicarboxylic acid diglycidyl ester) epoxy resin (TDE‐85), the glass transition temperature (Tg) of copolymer system could be adjusted in the range of 136–179°C; FETE had good miscibility with TDE‐85. The thermal degradation behavior of the copolymer system was studied by theoretical calculation, thermogravimetric (TG), and TG coupled with FTIR analysis, the results showed the thermal decomposition performance of the copolymer system could be adjusted in the range of 200–400°C. The tertiary ester groups in FETE were easy to thermally degrade and caused the network skeleton of the copolymer system to collapse. The FETE would have good prospects in reworkable electronic packaging, recycling or degradable epoxy resin area.

In this work, gradient polyimide (PI)/graphene composite aerogels were prepared with poly(amic acid) ammonium salt/graphene aqueous solution through layer-bylayer assembly, unidirectional freezing, freezing drying, and thermal imidization process. Each layer of gradient PI aerogels was consisted of oriented channel-like pores along the freezing direction. The gradient PI/graphene composite aerogels exhibited anisotropic conductivity and heat transfer property. The conductivity of composite aerogels in the perpendicular direction of oriented channel-like pores was higher than that along the direction of oriented pores. The heat transfer from the high-density end to the low-density end of gradient density composite aerogels was faster. Compared with those of homogeneous composite aerogel with same density, the compression yield stress of gradient density composite aerogels obviously decreased, and their compression platform region also obviously shortened. Moreover, when the compressive strain exceeded 35%, the compressive strength of gradient composite aerogel with more layers was much higher. K E Y W O R D S mechanical properties, microscopy, polyimides, porous materials, thermal properties 1 | INTRODUCTION Functional gradient materials (FGMs) are a new type of nonhomogeneous materials, their structure or composition varies gradually in spatial gradient. Although the term of FGM originates from Japan in 1980's, the gradient structure is not uncommon in nature, for example, bamboo and straw, animal skin, bones, teeth, and spider webs have gradient structure. 1-4 Because the structure or composition of FGMs varies gradually along one direction, the problems such as weak interfacial bonding or sudden change of properties, are effectively solved, which are caused by great physical or chemical differences between two type of different compositions. With the development of technology and the demand for high performance materials, gradient porous materials, whose