  We develop a theoretical model to explain the long induction interval of
water intake that precedes the onset of erosion due to degradation caused by
hydrolysis in the recently synthesized and studied cross-linked polyanhydrides.
Various kinetic mechanisms are incorporated in the model in an attempt to
explain the experimental data for the mass loss profile. Our key finding is
that the observed long induction interval is attributable to the nonlinear
dependence of the degradation rate constants on the local water concentration,
which essentially amounts to the breakdown of the standard rate-equation
approach, potential causes for which are then discussed. Our theoretical
results offer physical insights into which microscopic studies will be required
to supplement the presently available macroscopic mass-loss data in order to
fully understand the origin of the observed behavior.
