The best way to do research is to think things out before you start typing away in the search engines. First, as advanced design stated, visit some paint manufacturer websites and even contact them about this question. Doing some basic searching you will probably find the progression of paint technology. Armed with that information I would then begin searching the specifics. Armed with that knowledge now you could expand your project to cover topics such as:
-chemical differences and improvement
-safety and health
-single stage/ clear coat
-changes in the painting process (tools, machines, etc.)
Hope that helps.