The relationships between the structure and the dielectric properties of polyimides (PIs) were extensively studied to construct universal correlations of dielectric constant (D k ) and dissipation factor (D f ) on the structural parameters. In this study, 36 kinds of PIs with a plethora of functional groups including ether, fluorine, amide, ester, ketone, sulfide, sulfone, and alkane groups were prepared by polyaddition and thermal imidization. Accordingly, their thermal, mechanical, and dielectric properties were systematically investigated. The experimental results showed highly correlated relationships between the D k values and two structural parameters of fluorine content (F%) and volume polarizability (P/V) with a correlation coefficient of 0.98 and 0.90, respectively. Likewise, the D f value was highly correlated to the imide group content (Imide%) with a correlation coefficient of 0.95. However, a multiple positive trend was found in the relationship between the D f values and the volume dipole moment (μ/V) for the PIs. The discrepancy might be resulted from the difficulty to elucidate local molecular motions in the unit structure of PIs. Nevertheless, the D f values still presented a nontrivial relation to the orientational polarization and dipole moment of the unit structures. Collectively, our experimental results revealed the structure−dielectric properties relationships of the PIs by rational definition on a series of structural parameters and warrant further investigation. Meanwhile, this work provides systematic guidelines for molecular structure design of PIs which are promising for high frequency applications on the fifth-generation (5G) mobile communications technology.

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A polymer blend consisting of poly(2‐allyl‐6‐methylphenol‐co‐2,6‐dimethylphenol) (APPE) and polystyrene (PS) with additives such as 1,2‐bis(4‐vinylphenyl)ethane, cyanate ester, and nitrile butadiene rubber was formulated as an insulating high‐frequency adhesive film. The polymer blend of APPE and PS showed very high compatibility to these additives, and the resulting thermally cured polymer blend exhibited an excellent mechanical strength, as shown by an ultimate tensile strength of 51 MPa and Young's modulus of 1.4 GPa. Moreover, the blend exhibited very good dielectric properties, with a dielectric constant of 2.3 and a dissipation factor of 0.0030 at 10 GHz. The glass‐transition temperature of the cured polymer blend was 141 °C, as determined by differential scanning calorimetry, and the 5% weight loss temperature was 372 °C, indicating relatively high thermal resistance characteristics. Furthermore, its peel strength to a copper foil reached 0.80 N/mm. The present study suggested that the thermally cured APPE/PS polymer blend with additives will have potential applications for the next‐generation high‐frequency adhesives in microelectronic circuits. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47828.

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An alkaline developable and negative‐type PSPI with a high sensitivity and excellent mechanical properties based on a poly(amic acid) (PAA) and a photo‐base generator has been developed. The PAA was prepared by the polycondensation of p‐phenylenediamine (PDA) with an equimolar of 3,3′,4,4′‐biphenyltetracarboxylic dianhydride (BPDA) and 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6‐FDA) and converted thermally to the corresponding polyimide, PI(PDA‐BPDA/6‐FDA). PI(PDA‐BPDA/6‐FDA) showed the high thermal and mechanical properties and the dimensional stability such as the thermal decomposition temperature of 530°C, glass transition temperature of 369°C, linear coefficient of thermal expansion of 28 ppm/K, ultimate tensile strength of 148 MPa, elongation at break of 25% and dielectric constant of 2.8. The PSPI was formulated directly from PAA(PDA‐BPDA/6‐FDA) with a photo‐base generator (PBG), (E)‐3‐(2‐hydroxy‐4‐methoxyphenyl)‐1‐(piperidin‐1‐yl)prop‐2‐en‐1‐one (HMPP) (10 wt% to PAA) and the optimized parameters for photolithographic process were investigated including the PBG content, post‐exposure bake (PEB) temperature, and PEB time. The PSPI based on PAA(PDA‐BPDA/6‐FDA) and HMPP (10 wt% to PAA) showed a sensitivity of 114 mJ/cm2 and contrast of 1.29 when exposed to 365‐nm light (i‐line), post‐exposure baked at 160°C for 5 min, and developed with an aqueous solution of 2.38 wt% tetramethylammonium hydroxide and iso‐propanol. A clear negative 8‐μm features pattern was obtained by contact‐printing and converted into the PI pattern upon heating at 250°C, confirming by scanning electron microscopy and infrared spectroscopy.

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