I would like to ask if there is a difference between finnish polytechnics and vocational schools.

Different types of vocational training can be attended after completing the basic education (comprehensive school) whereas the polytechnic schools belong to the upper secondary education options which are attended after the higher school. There is a good diagram about the finnish school system at the following address:
http://www.cop.fi/eng/welcometocop/edusystem_large.html

You can read more about the finnish education system in English at various Internet sites. Use Google and the search terms “finnish school system” or “finnish education system”.