I've been doing this to find the best seals for my project but then figured it might be usefully for others as well so here she goes:

R - 290,
HydroCarbon: PolyAmide (PA) Nylon; Nitrile Rubber; ChloroFluoroCarbons (FKM) (Viton-tm).

R - 600-a,
HydroCarbon: PolyAmide (PA) Nylon; Nitrile Rubber; ChloroPrene (CR); ChloroFluoroCarbons (FKM) (Viton-tm).

R - 152-a
PolyAmide (PA) Nylon; ChloroPrene (CR); EthylenePropylene (EPDM)

R - 022--
PolyAmide (PA) Nylon; EthylenePropylene (EPDM)

All thees synthetics are the supposed Ideal materials that will not overly swell or be permeable to the refrigerant.

Please add to this list.