Question

Suppose that you start with a diisocyanate and a diol. Show how their reaction can lead to a polymer called a polyurethane (Section 29.5D).

Short answer

Answer: The reaction between a diisocyanate and a diol results in the formation of urethane linkages. As the reaction continues, multiple urethane linkages form long chains, connecting the R1 and R2 chains in the diisocyanate and diol molecules. This leads to the formation of a polyurethane polymer with the general structure ...-O=C=N-R1-O-R2-O-...

Step-by-step solution

Define diisocyanates and diols

Diisocyanates are compounds with two functional isocyanate groups (-N=C=O) in their structure, while diols are compounds with two hydroxyl groups (-OH) in their structure.

Display the general structure of a diisocyanate and a diol

Let's represent the diisocyanate and diol with general structures. A general diisocyanate can be represented by the following structure: O=C=N-R1-N=C=O and a general diol can be represented by the following structure: HO-R2-OH where R1 and R2 are the carbon chains or other groups connecting the functional groups in each molecule.

Show the reaction between the diisocyanate and the diol

When the diisocyanate and diol react, the hydroxyl group of the diol (-OH) reacts with the isocyanate group of the diisocyanate (-N=C=O), forming a urethane linkage. The reaction can be represented as follows: O=C=N-R1-N=C=O + HO-R2-OH -> O=C=N-R1-O-R2-OH + O=C=N-R1-N=C=O Here, one urethane linkage is formed, and the other isocyanate group is still available to react with another diol molecule.

Obtain the structure of the resulting polyurethane

As the reaction continues, the isocyanate groups keep reacting with more diol molecules, creating long chains of urethane linkages and connecting the R1 and R2 chains, which forms the polyurethane polymer. In general, the structure of the polyurethane polymer would look like this: ...-O=C=N-R1-O-R2-O-... This is the result of the reaction between a diisocyanate and a diol, leading to a polyurethane polymer.