  We study families of smooth immersed regular planar curves $ \alpha : \left
[-1,1 \right ]\times \left [0,T \right )\to \mathbb{R}^{2}$ satisfying the
fourth order nonlinear curve diffusion flow with generalised Neumann boundary
conditions inside cones. We show that if the initial curve has sufficiently
small oscillation of curvature then this remains so under the flow. Such
families of evolving curves either exist for a finite time, when an end of the
curve has reached the tip of the cone or the curvature has become unbounded in
$L^2$, or they exist for all time and converge exponentially in the
$C^{\infty}$- topology to a circular arc that, together with the cone boundary
encloses the same area as that of the initial curve and cone boundary. The same
kind of result is possible for the higher order polyharmonic curve diffusion
flows with appropriate boundary conditions; in particular in the sixth order
case the smallness condition on the oscillation of curvature is exactly the
same as for curve diffusion.
