Polymer can only be crafted in the Fabricator and is created from 2 Obsidian and 2 Cementing Paste. If you need to produce this resource in bulk, remember that you can use more than 1 Fabricator at a time, although this may not be very efficient with Gasoline usage. Polymer is also used in the Rockwell Recipe for Soap.
The only tough part about producing this resource in larger quantities is the production of Cementing Paste and the acquisition of Obsidian. However, there are a few good techniques that can help take the sting out of both of these challenges.