Many applications of polymeric materials desire and in certain instances require various functions in one family of polymeric architectures. In this work, synthetic routes and methods to obtain novel oxasilacycles and their use in polymer chemistry as both monomer and cross-linking agents are presented. Photoacid generators are used for the acid-catalyzed ring-opening polymerization of the synthesized oxasilacycles allowing photoinitiated and controlled polymerizations. The polymerization behavior and influence of different photoacids as well as the influence of catalyst loading are examined using in situ IR spectroscopy. The synthesized cyclic structures offer a broad variety in polymer chemistry. Oxasilaspirocycles can either homopolymerize or function as a cross-linking reactant in organic polymers. A polystyrenehydroxyethyl methacrylate copolymer is cross-linked via polycondensation reactions of the oxasilaspirocycle. An isopropoxy-substituted oxasilamonocycle is synthesized for the modification of hydroxyl-terminated polydimethylsiloxanes for photoacid-initiated polymerizable telechelic structures. Additionally, the synthesis of multifunctional oligomers containing the photoacid generator unit and the cross-linking agent leads to highly cross-linked polydimethylsiloxane-based structures. In this system it is possible to predefine the gel content as well as the viscosity of the cross-linked polydimethylsiloxane after irradiation by the ratio of oxasilacycle to polydimethylsiloxane.