The demand of stretchability for a semiconducting polymer has increased to realize wearable devices and sensors. However, studies involving intrinsically stretchable π‐conjugated polymers are still limited. Here, we develop a soft‐polythiophene derivative, P3SiHT, with a trisiloxane unit in the side chains via a hexylene spacer unit. In addition, diblock (P3HT‐b‐P3SiHT) and triblock (P3HT‐b‐P3SiHT‐b‐P3HT) copolymers could be synthesized based on Kumada catalyst‐transfer polycondensation. The results of atomic force microscopy and grazing incidence small‐angle X‐ray scattering indicate that the block copolymer thin films form a phase‐separated structure between the P3HT and P3SiHT domains. The organic thin film transistor devices were prepared to assess the electrical properties of the block polymers. As a result, the block copolymers showed comparable or even higher hole mobility than that of P3HT homopolymer, thus due to the enhanced phase‐separation and thereby charge transportation. The mechanical test of the bulk films indicates that P3HT‐b‐P3SiHT‐b‐P3HT shows lower tensile modulus and longer elongation at break than P3HT homopolymer and other diblock copolymers. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 1787–1794

Highly thermal-mechanical stable polymers have attracted extensive research interest as substrates for flexible or wearable electronic devices, such as polyimides (PIs). Here, we report a class of PIs as substrates for flexible organic field-effect transistors (OFETs), prepared by the polycondensation of pyromellitic dianhydride (PMDA) or 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) with three kinds of heterocyclic diamines, including 2,6-diaminothianthrene (SSDA), 2,6-diaminophenoxathiin (SODA), and 2,6-diaminodibenzo-p-dioxin (OODA). Flexible and tough PI films were obtained with a very low coefficient of thermal expansion (CTE) down to 7.3 ppm K −1 . Furthermore, the copolymers of PI(OODA−PmBn) prepared from PMDA and BPDA with OODA could exhibit an extremely low CTE of 5.5 ppm K −1 (PI(OODA−P5B5)) without an observed T g up to 400 °C, which was attributed to the suitable polymer chain rigidity and packing resulting in better in-plane orientation. Finally, this superheat-resistant PI(OODA−P5B5) was applied as the substrate in flexible OFETs, showing compatible and stable device performance even after being baked at 200 °C for 2 h or bended for 1000 cycles. These results indicate that the designed super-thermal-mechanically stable polyimides have potential applications as substrates for flexible electronics.

The new series of ABC-type miktoarm star polymer (ABC star, A = polyisoprene (PI), B = polystyrene (PS), and C = poly­(3-hexylthiophene) (P3HT)) and ABCD-type miktoarm star polymer (ABCD star, A = PI, B = PS, C = poly­(α-methylstyrene) (PαMS), and D = P3HT) could be synthesized by the combination of the controlled KCTP, anionic linking reaction, and Click chemistry. By the copper­(I)-catalyzed Huisgen 1,3-dipolar cycloaddition click reaction of the azido-chain-end-functional P3HT (P3HT-N 3 ) with the alkyne-in-chain-functional AB diblock copolymer (A = PI and B = PS) (AB-alkyne) or alkyne-core-functional ABC miktoarm star polymer (A = PI, B = PS, and C = PαMS) (ABC-alkyne), the target ABC star and ABCD star, respectively, were obtained, as confirmed by size exclusion chromatography (SEC) and proton nuclear magnetic resonance (1H NMR). The thermal and optical properties of these star polymers were examined by thermal gravimetric analysis (TGA) and UV–vis spectroscopy. The dynamic scattering calorimetry (DSC), atomic force micrograph (AFM) image, and grazing incidence small-angle X-ray scattering (GISAXS) results showed that the periodic P3HT fibril nanostructures rather than microphase separation occurred in the ABCD star film. In addition, it was found that highly crystalline P3HT domains aligned in the “edge-on” orientation, as supported by grazing incidence wide-angle X-ray scattering (GIWAXS).

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We developed highly thermally resistant and colorless polyimides (CPIs) with an ultralow coefficient of thermal expansion (CTE) and sufficient mechanical durability as a flexible substrate for organic field-effect transistors (OFETs). The CPIs were synthesized from trans-1,4-cyclohexyl diamine (t-CHDA) with different ratios of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (s-BPDA) and pyromellitic dianhydride (PMDA). The effects of the composition of s-BPDA and PMDA on the thermal, mechanical, electrical, and optical properties of CPIs were investigated. The optimized CPI, PI-3 with 90 mol % s-BPDA and 10 mol % PMDA, showed a relatively high elongation at break (8%) with a low CTE of 14 ppm K–1, a high glass transition temperature (T g) of 340 °C, and a large tensile modulus (E) of 4.1 GPa, respectively. Besides, PI-3 possessed a high transparency with a light transmittance at 400 nm (T 400) of 81% and a low cutoff wavelength (λcutoff) of 349 nm. Next, the dimer diamine of DDA (Priamine 1074) was introduced into the PI-3 structure to reduce the dielectric constant and enhance the stretchability. For example, PI-6C, with 85 mol % t-CHDA and 15 mol % DDA, showed a low dielectric constant (D k) of 2.8, a low dissipation factor (D f) of 0.004, and a high T 400 of 86% with maintained thermal and mechanical properties. Finally, a flexible OFET device using PI-3 as the substrate and dielectric was fabricated and characterized and exhibited an outstanding performance preservation after 1000 bending cycles or the high-temperature heating test, suggesting its excellent durability. The experimental results indicate that the CPIs studied have potential applications for transparent organic electronic devices.