Degradation modelling oligomer diffusion

Model formulation usually implies mass balances where the interplay between chemical reactions and transport phenomena (i.e., monomer and oligomer diffusion) is considered. The literature offers a wide variety of models with different degrees of complexity. An autocatalytic effect is not always explicitly included or a diffusivity increase because of hydrolysis onset. Degradation is usually described with pseudo-first order kinetics (where it is assumed that water concentration is constant) or second order kinetics, where the hydrolysis rate depends on the ester bond and water concentration, or on the ester bond and acid concentration when autocatalysis in considered. Also 1.5th and 2.5th order kinetics have been proposed (Siparsky et al., 1998 Lyu et al., 2007). 

Han, X., Pan, J., 2011. Polymer chain scission, oligomer production and diffusion a two-scale model for degradation of bioresorbable polyesters. Acta Biomaterialia 538—547. 

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