I'm going to chime in again - despite the fact I haven't cut poly with a chainsaw!
When cutting plastics in a lathe, I cut dry, and I have my tool sharpened with a concave on the top. This helps the "swarf" come away. The tool profile is actually quite similar to a file sharpened chain, I think as long as you are clearing your chips you will be ok. Sharp chain, and you may need to look at your depth gauge heights. If you need to hit the chains on the grinder, and bring your depth gauges back to 010 -020 just so you don't have as much chip to clear then that may help - again, I don't know, but it would be an idea in the back of my head if it were me. Id just balance how much it self feeds by how much hook is on the chain. I figure you need to find the balance between it pulling itself in too much and you having to push. Pushing would be bad with a dry bar and chain, pulling itself aggressively into the cut would cause the spikes to dig into the pipe, and that doesn't sound cool either.
Let us know how you get on please!