Green synthesis of end-capped polyurethane prepolymer with high storage stability and its effects on bitumen properties

To increase the storage stability of polyurethane prepolymer (PUP), environmentally friendly end-capped PUP modifier was prepared to modify asphalt, which can improve the performance of bitumen while protecting the environment. Physical, chemical and mechanical characterizations of the end-capped PUP and the modified bitumen were conducted to fundamentally understand its modification mechanism. The outcomes demonstrated that the storage stability of PUP can be significantly increased by end-capping technology. End-capped PUP can be successfully uncapped in bitumen and used to modify bitumen. As a result of the interaction between PUP and the active spots within asphaltene and bituminous resin, urethane, urea, and amide linkages were created, creating a cross-linked structure. The modification procedure encourages the transformation of resin into asphaltene and the reconstruction of asphaltene. With the reorganization of asphaltene molecules and the strengthening of cross-linking, PUP modified bitumen have greatly improved their high temperature resistance. However, as curing time increases, bitumen's chemical composition changes, resulting in decreased low-temperature performance, but it is still better than the base bitumen. This research prepared high storage stability PUP and explored the mechanism of PUP to modify bitumen, which has guiding significance for the usuage of PUP modified bitumen.