  We find strictly ascending HNN extensions of finite rank free groups
possessing a presentation 2-complex which is a non positively curved square
complex. On showing these groups are word hyperbolic, we have by results of
Wise and Agol that they are linear over the integers. An example is the
endomorphism of the free group on a,b with inverses A,B that sends a to aBaab
and b to bAbba.
