In another thread, someone who apparently understands the chemistry of cold patching wrote the following. If this is all true, and you do it correctly, the end result is a permanently bonded patch. Unfortunately, I have found that I can always peel off my patches (which are properly applied and use the correct cement) by applying heat.
"It's a two part system, with a vulcanizing accelerant in the cement, plus finely ground unvulcanized rubber, and a solvent to make it all spreadable. The patch has a thin layer of specially prepared rubber on the surface that touches the tube; it's got an extremely fast acting vulcanization accelerant that requires external activation (by the accelerant in the cement). There's enough unbound sulphur on surface of the tube that the system produces a cross-linked connection from the tube surface through the rubber in the cement, and including the rubber of the patch. It's a very clever bit of applied chemistry. Details vary a bit from patch brand to patch brand (and is one of the reasons that some patches are very specific about what cement to use.)"