I had same problems when mold PDMS on another cured PDMS. It cured
everywhere except where it was in contact with the bottom PDMS.

On Mon, Jul 13, 2009 at 11:19 PM, Mikael Evander wrote:
> Hi.
>
> I've just run into a strange problem. I've previously used several different
materials as master for PDMS molding and never ever had any problems. The other
day I tried using a laser ablated polyester film as a master and the PDMS cured
everywhere except where it was in contact with the polyester. Others in the lab
seem to have seen the same problem when using acrylic masters.
>
> I haven't been able to find anything about it and e-mailed dow corning without
a response. Has anyone else seen this and know why it happens? Evaporating
solvents? Materials that aren't compatible with PDMS for some reason?
>
> thanks in advance!
>
> /Mikael