Although various PEGs have large scale applications, with many very useful, one can guess just from its name PEG= polyethylene glycol, about its manufacturing.
Polyethylene = plastic and that's exactly what PEGs are, a mixture of different petroleum based compounds.
I already mentioned well known options in the Aconitum thread and will add more.
Seeds treatments are useful only when applied in correlation with the type of seedcoat and dormancy.
For seeds with underdeveloped embryos, trying to soften the seed coat has no purpose, because until the embryo grows, no germination can occur anyway.