Q34E - Organic Chemistry (Mcmurry)

Question

The smoking salons of the Hindenburg and other hydrogen-filled dirigibles of the 1930s were insulated with urea–formaldehyde polymer foams. The structure of this polymer is highly cross-linked, like that of Bakelite (Section 31-6). Propose a structure.

Step-by-Step Solution

Answer

The proposed structure of thermosetting resin is:

Step 1: Thermosetting resins

Thermosetting resins refers to a petrochemical material that is irreversibly cures, because they retain their form and stay solid under heat once they are cured. Thermosetting resin becomes highly cross-linked and solidify into a hard, insoluble mass when heated.

For example, Bakelite, a thermosetting resin first produced in 1907, has been in commercial use longer than any other synthetic polymer. It is widely used for molded parts, adhesives, coatings, and even high-temperature applications such as missile nose cones. 

Chemically, Bakelite is a phenolic resin, produced by reaction of phenol and formaldehyde.

Step 2: Propose a structure

As the mentioned structure of the polymer is highly crossed link like a Bakelite, so it is also a phenolic resin, produced by the reaction of urea and formaldehyde. 

On heating, water is eliminated, many cross-links form and the polymer sets into a rocklike mass. The cross-linking in these thermosetting resins is three-dimensional and is so extensive that we can’t really speak of polymer “chains.

Step 3: Result

The proposed structure of thermosetting resin is: