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<p>Rigid polyurethane foams (RPUFs), owing to excellent physical and chemical qualities, play an indispensable role in various fields of industry and defense applications. The polyurethane prepolymer (PUP) method is a significant strategy for controlling the performance of RPUFs. However, systematic investigations on how PUP synthesis parameters influence the properties of RPUFs remain limited. In this study, a “process parameters-structure-properties” correlation for RPUFs synthesized by toluene diisocyanate (TDI)—diethylene glycol (DEG) PUP was established. By systematically changing PUP synthesis temperature (40–120&#xa0;°C) and the NCO/OH molar ratio R (defined as <i>n[NCO]/n[OH]</i>, varied from 3 to 5), it was revealed that these parameters critically influence molecular composition, cellular morphology, and mechanical performance. High-performance liquid chromatography/mass spectrometry analysis revealed that increasing synthesis temperature reduces the free TDI content (from 41.70% to 21.93%) but promotes side reactions leading to crosslinking, thereby increasing viscosity and inhibiting cell growth during foaming. In contrast, a higher R increases the free TDI content (up to 46.90% at <i>R</i> = 5), reduces viscosity, and enhances the exothermic reaction, which drives cell formation, strut solidification, and even thermal degradation. Optical microscopy and mechanical testing of density-controlled RPUFs (0.102 ± 0.003&#xa0;g/cm3) indicated that foams formed from PUPs synthesized at 100&#xa0;°C display homogenous cellular structures, minimal stress concentration, and better comprehensive performance. PUPs synthesized at 40&#xa0;°C and 120&#xa0;°C boost mechanical strength via thicker supporting struts and hard segment enrichment, however, this is coupled with higher brittleness. This cascade mechanism, linking synthesis settings, PUP molecular structure, foaming kinetics, microstructural morphology, and macroscopic mechanical properties, lays a scientific foundation for the precision manufacture of tunable RPUFs and their composites.</p> Graphical abstract <p></p>

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Influence of toluene diisocyanate-diethylene glycol prepolymer synthesis parameters on the structure–property relationships of rigid polyurethane foams

  • 期刊论文

  • 发表日期：

    2025年12月11日

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  • Yan Guo,
  • Fei Duan,
  • Cheng Zhang,
  • Jiangtao Hao,
  • Lei Liu,
  • Sai Ma,
  • Danyang Zhao

摘要

Rigid polyurethane foams (RPUFs), owing to excellent physical and chemical qualities, play an indispensable role in various fields of industry and defense applications. The polyurethane prepolymer (PUP) method is a significant strategy for controlling the performance of RPUFs. However, systematic investigations on how PUP synthesis parameters influence the properties of RPUFs remain limited. In this study, a “process parameters-structure-properties” correlation for RPUFs synthesized by toluene diisocyanate (TDI)—diethylene glycol (DEG) PUP was established. By systematically changing PUP synthesis temperature (40–120 °C) and the NCO/OH molar ratio R (defined as n[NCO]/n[OH], varied from 3 to 5), it was revealed that these parameters critically influence molecular composition, cellular morphology, and mechanical performance. High-performance liquid chromatography/mass spectrometry analysis revealed that increasing synthesis temperature reduces the free TDI content (from 41.70% to 21.93%) but promotes side reactions leading to crosslinking, thereby increasing viscosity and inhibiting cell growth during foaming. In contrast, a higher R increases the free TDI content (up to 46.90% at R = 5), reduces viscosity, and enhances the exothermic reaction, which drives cell formation, strut solidification, and even thermal degradation. Optical microscopy and mechanical testing of density-controlled RPUFs (0.102 ± 0.003 g/cm3) indicated that foams formed from PUPs synthesized at 100 °C display homogenous cellular structures, minimal stress concentration, and better comprehensive performance. PUPs synthesized at 40 °C and 120 °C boost mechanical strength via thicker supporting struts and hard segment enrichment, however, this is coupled with higher brittleness. This cascade mechanism, linking synthesis settings, PUP molecular structure, foaming kinetics, microstructural morphology, and macroscopic mechanical properties, lays a scientific foundation for the precision manufacture of tunable RPUFs and their composites.

Graphical abstract