How to find the best solution ?

[Johny]

I have a text and would like  to split the text into smaller parts,
say into 100 characters each. But if  the 100th character is not a
blank ( but word) this must be less than 100 character.That means the
word itself can not be split.
These smaller parts must contains only whole( not split) words.
I was thinking  about  RegEx but do not know how to find the correct
Regular Expression.
Can anyone help?
Thanks
L.