Now, Carothers reasoned, if two molecules could join, why not more? Look at the molecules pictured above. Each one can join with another molecule only at one end. What if, Carothers thought, each molecule could react at both ends? Then, it should be possible to make them join into long chains, like you see below. Click here to see a movie of how this happens.

One could say Carothers was inquisitive like a little kid. In addition to playing with building blocks (although tiny molecular ones), he never stopped asking questions. He wanted to know more. As is often the case in science, each answer that he found raised new questions for him to explore. Could long chain-like molecules be made by linking together smaller molecules in a chain? How long a chain could be made? These were some of the questions that Carothers had been asking, and now he planned to find some answers.

Building Macromolecules

Carothers set out to see if he could build macromolecules by joining small molecules in long chains. He tried a lot of different small molecule combinations. For example, he knew that a carboxylic acid and an amine can combine in the presence of hydrochloric acid (HCl) to form a larger molecule called an amide:

But what if one were to use an amine that could react twice, and an acid that could react twice? Shouldn't they join into long chains like you see below?

Carothers and his team of scientists tried many reactions similar to this one, and in the early 1930s they got his idea to work.

When Carothers tried this and similar reactions, he knew he had made macromolecules because when the products were titrated, the products were found to contain very little acid. If the molecules had not joined, there would be a great deal of acid present, since half the original molecules going into the reaction were acidic.

How long were the chains that Carothers made? Some of the chains he and his team made had molecular masses of 20,000. Of course, that is small potatoes as polymers go, because natural polymers were thought to have molecular masses in the millions. Remember for comparison, a water molecule has a molecular mass of only 18.

Carothers had shown that macromolecules could exist. What's more, a lot of the macromolecules Carothers created had properties similar to silk, a natural polymer. This suggested that natural polymers like silk were made of macromolecules, but it didn't strictly rule out any other theories.

The final piece of the puzzle was put into place when an Austrian scientist named Herman Mark found evidence, using a technique called x-ray crystallography, that natural polymers were macromolecules. Thanks to Herman Mark and Wallace Carothers, most scientists became convinced that polymer molecules were made of thousands of atoms, all held together by the same covalent bonds that joined atoms in small molecules. Hermann Staudinger had been vindicated at last.

Next: Nylon

Prove It! — a look at what it really means to prove something from the viewpoint of a scientist, created by David Dice, Carlton Comprehensive High School.