I was painting & got green paint on my white north face jacket. I used bleach (plenty of it) & the stain is still there.
The problem you have is similar to cleaning dried latex paint off a brush with synthetic (nylong or polyester) bristles. With brushes, you can easily soak them in a solvent for an extended period of time; unfortunately, you cannot safely adapt this technique to clean your jacket. The solvents used by painters for this purpose are flammable, and fabrics (i.e. rags) that are used for applying or wiping up paint solvents should NEVER go into a clothes washer or dryer due to the risk of spontaneous combustion. Appliance manufacturers include warnings to this effect in the user’s guide and on the machines themselves because this is such a big safety issue.
However, I did find one website that mentions a method for using a liquid fabric softener + water solution for cleaning paintbrushes, and you can read about it here: http://nwrenovation.com/painting-articles/paint-brushes-101/ . Scroll down to the section on cleaning brushes, and hopefully this will work for you.
Paint stains can certainly be pesky! Do any of my readers have any tricks or tips for removing paint from clothing?