Process investigating and modelling for the self-polymerization of toluene diisocyanate (TDI)-based polyurethane prepolymer

Toluene diisocyanate (TDI)-based polyisocyanate prepolymer was prepared via TDI self-polymerization with different catalysts at various temperatures. The self-polymerization process was followed by gel permeation chromatography to investigate the formation of individual components. The contents of isocyanate group (–NCO) and free TDI monomer were monitored to confirm the transformation of individual components through back-titration and gas chromatography, respectively. A step-growth polymerization mechanism for TDI-based polyisocyanate reaction was proposed. Simultaneously, a mathematical model was established to simulate the contents of all components in the self-polymerization process, and the simulated data were in good agreement with the experimental results. Mass spectrometry, Fourier transform infrared spectroscopy and ¹³C nuclear magnetic resonance spectroscopy were employed to identify and confirm the chemical structures of the polyisocyanate prepolymer. The experimental results indicate that several oligomers containing trimer, pentamer, heptamer and higher-molecular-weight oligomers presented simultaneously and interacted with each other. The desired content of each component in TDI-based polyisocyanate prepolymer could be obtained by controlling the reaction conditions.