I had arm problems with poly in the past. I considered giving it up, but I've found a way to use it that works well for me.
First off, I use a copoly (SPPP), which is supposedly a bit less harsh than some other polys.
Next, string low. I started with poly in the low 60s. That sounds nuts, but the original recommendation was to string poly 10% lower, and I was using syn gut at 67lbs. So I went down to 61. That's way too high for poly. I now string it at 45. It took a little adjusting, but I actually think this is how you get the benefits of poly - amazing spin generation at low tensions.
Lastly, restring before the strings go dead. Poly was initially marketed to rec players (and still is) as a durable string for string breakers. I don't think that's a good way to think about poly. You're generally safe playing with nat gut until it breaks because it's a soft string with good resiliency. Poly is the opposite. To me, the "durability" of poly is more of a liability than an asset, because it means it won't break until long after it goes dead (with predictable effects on your arm). One thing - I have found that SPPP, which supposedly has better tension maintenance along with low tension does greatly extend the life of the strings, so I'm pretty sure I use my string job for more than 10 hours. Not totally sure, because my test is to pull the strings back and see if they snap back into place. If they don't, or they're sluggish about moving back into place, that's a pretty good sign that I need to restring.
Now that I use a a copoly, low tension, and restring before it goes dead, I haven't had any trouble at all with arm soreness from poly.