It's fine to use poly blend for a quilt, but I would advise not mixing poly blends with cotton in the same quilt. This is because cotton fades over time, with exposure to light, while cotton poly blends do not. Years down the line the quilt can look quite "spotty" with brilliant colors in some pieces and faded colors in others.
Poly blend is a little more difficult to work with than cotton. It frays more easily and is more slippery (harder to make seams meet exactly). You might want to choose a pattern that does not have a lot of exacting seam matching. Depending on how much it frays, you also might want to make your seam allowances 3/8" or even 1/2".