  We investigate a two-dimensional problem of an isolated self-interacting
end-grafted polymer, pulled by one end. In the thermodynamic limit, we find
that the model has only two different phases, namely a collapsed phase and a
stretched phase. We show that the phase diagram obtained by Kumar {\it at al.\}
[Phys. Rev. Lett. {\bf 98}, 128101 (2007)] for small systems, where differences
between various statistical ensembles play an important role, differ from the
phase diagram obtained here in the thermodynamic limit.
