Diisocyanates reaction with oligo-polyols

Prepolymers are formed by the reaction of a diisocyanate with an oligo-polyol, at the molar ratio [diisocyanate]/[OH group] of 1/1, in fact only one group of diisocyanate reacts with one hydroxyl group of the polyol. A structure with free terminal -NCO groups called prepolymer is produced (see Equation 2.4) ... 

As mentioned previously, the synthesis of polyurethanes, by the reaction of a diisocyanate (or polyisocyanate) with oligo-diols (or oligo-polyols), is a polyaddition reaction (or step-addition polymerisation), a particular type of polycondensation reaction. There is a great difference between the polycondensation and the polyaddition reactions and the classical radical polymerisation or ionic (living) polymerisation reactions. In radical polymerisations (typical chain reactions), the high MW polymer is formed at the beginning of polymerisation. The reaction system is constituted from monomer and high... 

A reliable method to determine the oligo-polyol reactivity is the study of the kinetics of the oligo-polyol s reaction with phenyl isocyanate, a model for the -NCO groups of toluene diisocyanate (TDI) or diphenylmethane diisocyanate (MDI) ... 

The very low glass transition temperature (Tg) of polysiloxane chains (Tg = -123 °C) is a very attractive property for using these kinds of polymeric chains to build an oligo-polyol structure with terminal hydroxyl groups [1]. The resulting structure called a polysiloxane polyol gives, after reaction with diisocyanates, polyurethane (PU) elastomers which conserve their high elasticity at very low temperatures [1]. 

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