Based On Confined Polymerization: In Situ Synthesis of PANI/PEEK Composite Film in One‐Step

Abstract Confined polymerization is an effective method for precise synthesis, which can further control the micro‐nano structure inside the composite material. Polyaniline (PANI)‐based composites are usually prepared by blending and original growth methods. However, due to the strong rigidity and hydrogen bonding of PANI, the content of PANI composites is low and easy to agglomerate. Here, based on confined polymerization, it is reported that polyaniline /polyether ether ketone (PANI/PEEK) film with high PANI content is synthesized in situ by a one‐step method. The micro‐nano structure of the two polymers in the confined space is further explored and it is found that PANI grows in the free volume of the PEEK chain, making the arrangement of the PEEK chain more orderly. Under the best experimental conditions, the prepared 16 µm‐PANI/PEEK film has a dielectric constant of 205.4 (dielectric loss 0.401), the 75 µm‐PANI/PEEK film has a conductivity of 3.01×10−4 S m−1. The prepared PANI/PEEK composite film can be further used as electronic packaging materials, conductive materials, and other fields, which has potential application prospects in anti‐static, electromagnetic shielding materials, corrosion resistance, and other fields.

The lattice structure of the PANI/PEEK film was tested by HR-TEM, the instrument model was FEI Tecnai G2 F20, purchased from FEI Company in the United States. The film was sectioned by a cryostat before the test, the sectioning mode was frozen (-100 °C) section, and the thickness was 30 nm.

Selected area electron diffraction (SAED)
The structure of the PANI/PEEK film was tested by electron diffraction, and the instrument model was FEI Tecnai G2 F20, which was purchased from FEI Company in the United States.
The film was sectioned by a cryostat before the test, the sectioning mode was frozen (-100 °C) section, and the thickness was 30 nm.

Scanning electron microscope (SEM)
The surface morphology of the sample was observed by the scanning electron microscope (SEM/FEI company, USA, Model Nova nano 450). Before testing, the sample was sprayed with Platinum for 60 seconds. The cross section was that the films were quenched in liquid nitrogen.

Dielectric and conductivity testing
Dielectric and conductive properties were measured using an Agilent LCR meter (4294A) and the sample films (diameter 7.0 mm) were deposited on 500 Å thick copper metal. Each sample was tested 4 times in parallel.

Density test (ρ)
The density of the film was tested by a densitometer, the model is SD-200L-solid density meter, purchased from Japan's ALFA MIRAGE company. The density of the film was tested by buoyancy.

Tensile strength test
The rectangle sample of the 5 mm (width) *25 mm (length) was cut from the PANI/PEEK film to test the tensile strength using the electronic universal testing machine (TA company, sample was 8 mm, and the tensile speed was 2 mm/min at room temperature.

Frozen Ultrathin Microtome
The film was sliced to prepare a test sample. The film was wrapped in epoxy resin, and sliced with a Leica cryo-microtome, the instrument model was EM FC7, which was purchased from Leica Company.

Elemental analysis (CHN)
The elemental analysis (CHN) of the film was tested by the combustion method (Model Vario EL cube/ Elementar company). The O element is calculated from the total content.

N 2 Adsorption test
The 100mg sample was degassed at 150 o C for 12 hours, and then tested at 77K by N2 adsorption equipment which is the Autosorb-iQ3 (Quantachrome Instruments).

Synthesis of N-phenyl (4,4′-difluorodiphenyl) ketamine
According to previous research [S2] , N-phenyl (4,4′-difluorodiphenyl) ketamine was successfully synrhesis. For specific synthetic steps, the Scheme S1 could be found. 21.82 g (0.10 mol) of DFBP, 13.7 mL (0.15 mol) of aniline, 50.00 g of molecular sieves (4 Å), and 80 mL of toluene were added into a 250 mL three-neck round-bottomed flask fitted with an argon inlet/outlet, a Dean-Stark trap, a mechanical stirrer and a reflux condenser. Then the reaction temperature was heated at 160 °C for 24 h, and fell to room temperature (RT). After filtrating to remove the molecular sieves, the mixture was evaporated by rotary evaporation.
Then the crude product was recrystallized by methanol for three times. The yellow product was obtained by drying in vacuum oven at 60 °C for 12 h. (23.76 g, 0.08 mol). Yield: 81 %.
More details of synthesis steps could be found from the Scheme S2. [S3.S4] 2.2022 g (20 mmol) of the 1,4-benzenediol monomer, 5.2796 g (20 mmol) of N-Phenyl (4,4′-difluorodiphenyl) ketamine, 3.3168 g of K 2 CO 3 , 12.0 mL of toluene, and 19.8 mL of sulfolane were charged in a 100 ml three-necked flask equipped with mechanical stirring, a Dean-Stark trap and a reflux condenser. Under nitrogen atmosphere, the reaction was heated to 155 °C to carry water for 3 hours to ensure that the water in the reaction was completely removed. The reaction was warmed to 210 °C for 7-9 h, and waited until the reaction system became a dark brown viscous liquid. Finally, the solution in the reaction was poured into deionized water to obtain a pale green flocculent solid. The strip-shaped solid was pulverized, and then washed by deionized water 5 times at room temperature conditions for 60 minutes each time. The product was placed in a vacuum oven at 60 °C for 24 h to completely remove water. A yellowish solid was finally obtained. The polymerization yield was as high as 97 %.

Preparation of PEEKt films
The films preparation and oxidation process were shown in Figure 1 and Scheme S3. The film was prepared with solution casting method. PEEKt was dissolved in DMAC solution (15 mL) and stirred at room temperature until completely dissolved. The solution was allowed to stand at room temperature for 12 h to ensure that bubbles were completely released. The solution was poured on a clean glass plate (10 cm*10 cm) and placed in an oven at 80 ⁰C. The oven was maintained at 80 ⁰C for 12 h and 120 ⁰C for 24 h, and then cooled to room temperature. The film was placed in deionized water coagulation bath until it was detached naturally. Finally, film with the different thickness was obtained.

Preparation of PANI/PEEK films
The obtained PEEKt films were subjected to oxidation treatment to prepare PANI / PEEK composite films in one step. The weighed (NH 4 ) 2 S 2 O 8 solid was dissolved in HCl and stirred until the solid was completely dissolved. The PEEKt film obtained before was cut into a size of 2 cm*2 cm and placed in a 25 ml airtight glass bottle, and then 20 ml of the prepared solution was added to it. The closed sample bottle was left in the oven for a certain period of time, and then cooled to room temperature. A detailed description of films manufacturing conditions was shown in the Supporting Information (Table S4-S7). Under the ultrasonic cleaner, the obtained composite films were washed with water and ethanol 3-5 times, each time for 15 minutes. Finally, the films were dried in 80 ⁰C vacuum oven for later use.
3.5 Preparation of 220-PANI/PEEK films PANI/PEEK film was placed in a high temperature oven at 220 °C and treated with high temperature vacuum for 5 hours. After cooling slowly, 220-PANI/PEEK film was obtained.

Preparation of PEEKt(HCl) films
The previously prepared PEEKt film was cut into a size of 2 cm*2 cm, and placed in 20 ml, 2.5 M HCl solution, and reacted at 60 o C for 6 hours. Take it out and ultrasonically clean it with ethanol and water 3 times.

Statistics Analysis
Each experiment was tested three times in parallel. All experimental results requiring quantitative analysis were analyzed using statistical product and service solution 13.0 (SPSS 13.0) software. Data were expressed as mean ± standard error of the mean.