Preparation and Properties of Reprocessable Phenolic Resin Based on Modification of Long‐Chain Isocyanate

ABSTRACT Phenolic resin has high heat resistance and excellent mechanical properties, and its cross‐linked network structure shows excellent mechanical properties after curing. However, it is difficult to recycle the cross‐linked phenolic resin because of its insoluble and infusible features. In order to make the phenolic resin recyclable and reprocessable, we introduced polymethylene polyphenyl polyisocyanate (PAPI) into the phenolic resin, made the phenol hydroxyl group react with the isocyanate group to form reversible dynamic covalent bond, and prepared the modified phenolic resin (PANR). The structure, thermal stability, mechanical properties, fracture morphology and reprocessable of PANR were characterized. The results showed that when PAPI was introduced into NR, the successfully cross‐linked to form dynamic covalent bonds. DSC showed that the glass transition temperature of PANR was as high as 175°C, and TGA showed that the mass retention rate of PANR was still about 40% at 800°C. The tensile strength of PANR is 14.7 MPa, and its tensile strength and chemical properties remain more than 95% of the original mechanical properties after five cycles, which successfully realizes the recovery and reprocessing of cured phenolic resin. PANR is expected to be used in the reprocessing of phenolic resin.