Why are you implementing your own linked list? Why don't you just let your Polynomial class consist of a List<Term>, which if you wanted to, you could sort with a Comparator<Term> that ranks terms by their exponents? Or you could even use a TreeMap.
This will get rid of a lot of ugly C-like code (for(Monomial tmp = head; tmp != null; tmp = tmp.next); eww) and you can focus on your problem.
As for your input problem, you could give the Polynomial class a load(InputStream) method, which will scan the stream for pairs of integers until it hits end-of-line, or maybe some other delimiter.
subject: Polynomial LinkedList from Text File (Modification)