Everything works fine without polymere. Adding it causes a crash even before the Minecraft Window pops up.
Logs:
https://mclo.gs/PN11LR3

No Mods except Polymer

You're running an outdated version of the loader beta, this issue no longer appears on 0.18.1-beta.65.

Issue with quilt beta loader version, not polymers

Well... It appears they've just rolled out an update that fixed the issue a few minutes ago.