Ok- I know this is really easy. PBW (parts by weight): can you have 100 pbw of one polymer and 5-100pbw of another to formulate a composition? Isn't that incorrect usage of the parameters? I thought pbw was essentially parts of the whole product- such as weight %.
HELP!!
Thanks... feeling stupid. Can't find a citation...

I think parts by weight usually is meant to be a concentration. I guess it could also be weight ratios as opposed to volume ratios. If you mix water and methanol, you would get slightly different solutions using equal weight, and equal volumes.