The functionalization methods of polymeric materials using various types of cross-links, such as supramolecular cross-links, photo cross-links, and associative dynamic covalent bonded cross-links, were described. First, the enhancement and precise tuning of the thermal and mechanical properties are demonstrated in the supramolecular cross-link-based and photo cross-link-based designs. In the latter section, the design and physical property tuning of functional materials based on a special type of cross-linked materials with associative dynamic covalent bonded cross-links, known as vitrimers, are demonstrated.