Unfortunately Polymer comes only as HTML source, so to properly Polymer you need to generate the polymer.js yourself. Instead of just exposing a global, this package gives you a CommonJS module!
Use your favorite JS dependency manager to install it
jspm i github:greenify/polymer-js
bower:
bower install polymer-js
npm install polymer-js
This is an unofficial fork, it might be not updates as regularly.
I would be very happy if the Polymer team includes a Polymer.js into their build toolchain.
Basically this small script concatenates polymer-micro, polymer-mini and polymer.
Afterwards it strips <script> tags, HTML comments and included <link> for HTML Imports.