I would recommend to start with DSC and XRD. Both these techniques can determine crystallinity of semi-crystalline polymers. You would need a relative heat of fusion value of a 100% crystalline reference sample. I'm not sure if there are literature values available for PVDF-TrFE? I have not worked on this polymer myself.
I would also recommend looking at the work done by Prof Bruno Ameduri. He might have done some work on this.