I was able to find this about someone dropping a probe with a PVC handle into their boil:
"A study published in the Journal of Applied Polymer Science shows high rates of leaching of plasticizers in PVC at high temperatures. PVC powder alone appears to be fairly inert, according to Ullmann's Encyclopedia of Industrial Chemistry, but Vinyl chloride monomer (VCM) is highly carcinogenic and is an upstream product in the manufacturing of PVC.
Does your thermometer carry an NSF logo? NSF logos indicate the device has passed certain safety tests for use in a food service environment.
I know it is really difficult to throw out a batch of beer; it may be fine to drink, too. The way I would approach this issue is by considering the incremental impact of routinely being concerned about what you're ingesting (i.e. a few dozen cigarettes never killed anyone, but a lifetime of smoking does kill). If it were mine, I'd probably keep the beer and be as cautious as possible down the road."