Terpolymer poly(α‐methylstyrene‐co‐glycidyl methacrylate‐co‐4‐acryloyl tetraphenylethylene) (PAGT) was synthesized by radical copolymerization using α‐methylstyrene, glycidyl methacrylate, and trace fluorescent monomer 4‐acryloyl tetraphenylethylene. Thermal decomposition of α‐methylstyrene constitutional units in copolymer chains is known to produce macromolecular radicals at temperatures exceeding 90 °C, which may be melt‐grafted to polypropylene (PP) without other initiators by means of extrusion. In this study, the PP‐g‐PAGT microporous material was prepared by casting and stretching. The structure and properties of the PAGT were characterized by Fourier transform infrared spectroscopy, 1H‐nuclear magnetic resonance, and thermogravimetic analysis. The grafting degree and rheological properties proved that the PAGT chains were successfully grafted onto the PP. The uniformity of the PAGT in the PP‐g‐PAGT was observed using a spectrofluorophotometer. The polarity of the cast membrane was characterized by the water contact angle. The results showed that the PAGT evenly grafted onto the PP, and the polarity and hydrophilicity of the cast membranes were improved. The microporous structure of the separator was observed via scanning electron microscopy. Testing of the performance of the lithium battery showed that the impedance decreased and the ionic conductivity increased with the introduction of PAGT onto PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46020.