Fig. 2: Performance of the RCPI films.

a A photograph of an RCPI film (10 cm × 10 cm × 20 μm) on the top of a tree branch for demonstrating the high optical transmittance of the RCPI. b Optical transmittance of the PI-COOH and RCPI films (with a thickness of about 20 μm). c Residue weight of the dried PI-COOH and RCPI films after soaking in different solvents for 24 h. d The histogram containing values of Tg, CTE, Young’s modulus and tensile strength for the PI-COOH and RCPI films.