In chain-growth polymerization, the polymerization behaviors are governed by the nature of monomer depending on the side-chain structure (e.g. conjugated/non-conjugated, electron-rich/deficient), leading to limitations in (co)polymers we can synthesize. This highlight review summarizes recent development in polymer reactions to overcome such limitations. The key is the design of transformable monomers as well as the utilization of novel organic transformations.