Toluene Diisocyanate

High Quality Content by WIKIPEDIA articles! Each of the isocyanate functional groups in TDI can react with a hydroxyl group to form a urethane linkage. 2,4-TDI is an asymmetrical molecule and thus has two isocyanate groups of different reactivity. The 4-position is approximately four times more reactive than the 2-position. 2,6-TDI is a symmetrical molecule and thus has two isocyanate groups of similar reactivity, similar to the 2-position on 2,4-TDI. However, since both isocyanate groups are attached to the same aromatic ring, reaction of one isocyanate group will cause a change in the reactivity of the second isocyanate group.