I have a Lifeproof case for an iPhone4 that I am trying to repair. I did some research and concluded that the screen cover may be made of PET (Polyethylene terephthalate). This polymer has a glass transition temperature of 67 to 81 *C. Remembering the concept of glass transition temperature led me to theorize that placing the screen cover in hot water would relax a bend that had developed following degradation of the rubber, possibly due to fry oil , that surrounded its perimeter.
The theory of using hot water proved correct and the bend flattened out, leading to a flat sheet again.
I had previously tried to glue the cover to the body of the case with rubber cement. This anchored the screen in place, but I was dissatisfied with the sticky gummy rubber that was left behind after the solvent dried. Shown below is the components of the case along with a pen that I plan to use to reconstruct a plastic toggle switch lever.
At the moment, I may try another form of rubber to replace the degraded rubber that crumbled from the case. I may try dissolving a damaged bicycle inner tube in gasoline, then paint the solvated rubber on the case. I am not sure it will work, but butyl rubber, which may be the material used for the inner tube, is incompatible with gasoline according to Moss Rubber (http://www.mossrubber.com/pdfs/Chem_Res.pdf). This leads me to guess that gasoline is a solvent for butyl rubber. If I am lucky, I may have my own "rubber cement" that does not dry as a sticky mess.