Some of the nutrients in the popcorn will be cooked/denatured by the heat of popping, so you would expect some difference in the nutritional value.

Of course, if you boil your cob of corn, some of the nutrients will end up in the water. If you grill it, you're also going to denature it.

There are free online calculators of nutritional information that will contain a database of these differences - http://www.foodstandards.gov.au/industry/npc/Pages/Nutrition-Panel-Calculator-introduction.aspx

You can actually check the difference between corn still on the cob and popcorn on that database.

Of course, popcorn without the added butter, salt, etc.

Does popcorn have the same nutritional value as regular corn on the cob?