Isocyanate, addition reactions capped

A number of issues related to this reaction should be discussed. First, a polymer is rarely isolated in this form. In the early 1950s a technology was developed that has since come to be known as the one-shot process. While the technique certainly produces a capped polyol, it immediately reacts further to achieve its ultimate form (Figure 2.6, bottom). You will notice that the capped polyol still has isocyanate functionalities as end groups. Regardless of the process, these end groups must continue to react (by the addition of water and/or a catalyst) to complete the process. While this reaction produces one of the most commonly constructed polyurethanes, it is rarely isolated as an end product. 

The SMMs were synthesized using a two-step solution polymerization method (Carman 1956 Fang et al. 1994 Khayet et al. 2005a,b Suk et al. 2006 Qtaishat et al. 2009a,b). The solvent DMAc was distilled at about 25°C under a pressure of 133.3 Pa. Methylene bis(j)-phsay isocyanate) (diphenylmethane diisocyanate MDI) was also distilled at 150°C under 66.7 Pa (0.5 Torr). PPG, a,a)-aminopropyl PDMS, and 2-(perfluoroalkyl)ethanol (FAE) were degassed for 24 h under 66.7 Pa. The first polymerization step was conducted in a solution with a predetermined composition to form polyurethane from the reaction of MDI with PPG or to form polyurea from the reaction of MDI with PDMS as a prepolymer. In the second polymerization step, the prepolymer was end-capped by the addition of FAE, resulting in a solution of SMM. 

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