Other than glass transition Tg...

I don't believe it undergoes another phase change as the temp decreases, it just gets more brittle.

There's more where this came from:Failue Analysis of PVC Pipe

Agreed, however is there some known temperature where this occurs drastically more than anywhere else? And of this point exists for PVC, does it exist for other materials as well and how is it calculated? Thanks

pardon my previous post, I'm embarassed that I did not read the link posted immediately, my appologies, and thanks very much for the information provided.