Iran Polymer and Petrochemical Institute Polyolefins Journal 2322-2212 10 4 2023 11 01 Effect of hydroxyl terminated polybutadiene number-averaged molecular weight on chemorheological behavior of polyurethane networking 191 204 1956 10.22063/poj.2023.3256.1241 EN Abolfazl Deylami Chemical Engineering Department, Imam Hossein Comprehensive University, Tehran, Iran 0009-0002-6749-4546 Abbas Kebritchi Chemical Engineering Department, Imam Hossein Comprehensive University, Tehran, Iran 0000-0001-6129-9323 Journal Article 2022 10 31 The time available for proper casting of the polyurethane (PU) system after isocyanate addition (called pot life) affects the macrodiol microstructure. In this research, the effect of molecular weight ( M<sub>n</sub> ) of hydroxyl terminated polybutadiene (HTPB) as an important macrodiol on the pot life of polyurethane system was rheologically investigated. The chemorheological behavior of polyurethane systems based on five different HTPBs with M<sub>n</sub> ranging from 2810 to 4450 g/mol and two common diisocyantes (TDI and IPDI) were studied in situ. The results showed that by increasing M<sub>n</sub> , the rotational viscosity as well as the constant reaction rate of urethane formation increases; whereas the pot life of the polyurethane system decreases. The pseudoplastic behavior of the samples showed the minimum rate constant/longest pot life at a critical molecular weight (M<sub>c</sub>) of about 3100 g/mol, which may be due to physical chain entanglements. Rheomechanical spectrometry interestingly depicted that tan δ originated-gel point occurs before the intersection of stored modulus (G') and loss modulus (G") (t<sub>gel</sub>< t<sub>G'=G"</sub>). The kinetic model developed by Hsich showed excellent agreement with the cross-linking data of three polyurethane systems. HTPB, number-averaged molecular weight pot life Gel Time Dynamic Rheological polyurethane system http://poj.ippi.ac.ir/article_1956_ae8964dbe2a52c17e96457e21ef4ccea.pdf