  We analyze the dynamics of desorption of a polymer molecule which is pulled
at one of its ends with force $f$, trying to desorb it. We assume a monomer to
desorb when the pulling force on it exceeds a critical value $f_{c}$. We
formulate an equation for the average position of the $n^{th}$ monomer, which
takes into account excluded volume interaction through the blob-picture of a
polymer under external constraints. The approach leads to a diffusion equation
with a $p$-Laplacian for the propagation of the stretching along the chain.
This has to be solved subject to a moving boundary condition. Interestingly,
within this approach, the problem can be solved exactly in the trumpet,
stem-flower and stem regimes. In the trumpet regime, we get
$\tau=\tau_{0}n_d^{2}$ where $n_d$ is the number of monomers that have desorbed
at the time $\tau$. $\tau_{0}$ is known only numerically, but for $f$ close to
$f_{c}$, it is found to be $\tau_{0}\sim f_c/(f^{2/3}-f_{c}^{2/3})$. If one
used simple Rouse dynamics, this result changes to {\normalsize $\tau\sim f_c
n_d^2/(f-f_{c})$.} In the other regimes too, one can find exact solution, and
interestingly, in all regimes $\tau \sim n_d^2$.
