The introduction of functionalities to synthetic biomaterials represents a major direction and a significant challenge in biomedical engineering. A synthetic platform using novel acid-induced epoxide ring-opening polymerization promoted by a newly designed catalyst to produce a variety of biodegradable and functionalized biomaterials is reported. The polymerization proceeds smoothly in the presence of functional groups including alkenyl, aromatic, ether, ester, and free hydroxyl groups. The functionalities of the resultant biomaterials can be further enriched using many post-functionalization methods. This platform yields biomaterials with a wide range of hydrophilicity, crystallinity, charge, mechanical properties, and cell interactions. This platform for functionalized biomaterials is simple, versatile, and can be easily adapted to specific cell types and tissues of interest.