Most coating's sensitivity goes quite a bit into the visible part of light,
dichromate sensitized gelatin for instance is sensitive even to green light. So
it won't be impossible to print with Mylar-negs. But you may expect longer
exposure times. Last semester two of my students took xeroxed (mylar?) foils as
negs and it worked quite well. The problem was that the images are not dense
enough but very contrasty.
Klaus Pollmeier