The most common polyurethane prepolymers are TDI type and MDI type. When the polyurethane elastomer is prepared by the casting process, the TDI prepolymer is generally cured with an amine chain extender, and the MDI prepolymer is generally cured with an alcohol chain extender.
Oligomer diols commonly used in the synthesis of polyurethane prepolymers are: adipate polyester diol, polycaprolactone diol (PCL), polycarbonate diol (PCDL, PPCL), PTMEG, PPG. TDI-type prepolymers are generally synthesized using oligomer diols (partial prepolymers use oligomer triols) and TDI as raw materials. When the casting process is used to prepare polyurethane elastomers with TDI prepolymers as raw materials, commonly used amine chain extenders (curing agents) include MOCA, ML-200, E-100, E-300, 740M, M-CDEA, etc. MDI prepolymers are generally synthesized from oligomer diols (or triols) and MDI-50, modified MDI or pure MDI. Its available chain extenders (curing agents) include 1,4-butanediol, HQEE, HER, HQEE-L, HER-L, E-100, E-300 and M-CDEA, etc.
TDI is highly volatile and has a strong pungent odor especially after heating. The free TDI in the TDI type prepolymer with high NCO content is high. It needs to pay attention to labor protection when it is used, and try to use low free prepolymer. The validity period of the prepolymer at 25°C is 12 to 24 months. The polyurethane prepolymers needs to be tested for NCO% before use, and it can be used only after passing the test.
Prepolymer storage temperature and validity period
|
Temperature（℃） |
Validity Period |
|
60 |
7 days |
|
70 |
3 days |
|
80 |
36 hours |
|
90 |
12 hours |
|
100 |
8 hours |
