Abstract
A procedure to construct $K$-matrices from the generalized $q$-Onsager algebra $\cal{O}_{q}(\hat{g})$ is proposed. This procedure extends the intertwiner techniques used to obtain scalar (c-number) solutions of the reflection equation to dynamical (non-c-number) solutions. It shows the relation between soliton non-preserving reflection equations or twisted reflection equations and the generalized $q$-Onsager algebras. These dynamical $K$-matrices are important to quantum integrable models with extra degrees of freedom located at the boundaries: for instance, in the quantum affine Toda field theories on the half-line they yield the boundary amplitudes. As examples, the cases of $\cal{O}_{q}(a^{(2)}_{2})$ and $\cal{O}_{q}(a^{(1)}_{2})$ are treated in details.