Progress in Anionic Ring-opening Homo/Co-polymerization of Cyclosiloxanes

As a class of typical organic/inorganic polymers, polysiloxanes are widely used in numerous areas owing to their remarkable properties, such as excellent environmental adaptability and endurance of wide temperature range. A broad spectrum of applications has been exploited for polysiloxanes, including surfactants, lubricants, adhesives, and insulating or coating materials. The overall properties of polysiloxanes are dependent primarily on its backbone. For example, poly(dimethylsiloxane) (PDMS), as a typical representative for polysiloxanes, shows special characteristics such as a low glass transition temperature, thermal stability, antioxidant stability, and physiological inertness. Anionic ring-opening polymerization of cyclosiloxanes is a prevalent approach to preparing polysiloxanes with various chain structures and functionalities and one of the most important areas for organosilicone research. Generally, the reaction processes of anionic ring-opening polymerizations are controllable in terms of a specific molecular weight, narrow molecular weight distributions, and well-defined structures. Besides, anionic ring-opening polymerization of cyclosiloxanes can be very useful in the preparation of new polymers with novel structures, particularly the microstructure-controlled copolymers that are difficult to be achieved by homopolymerization and conventional methods otherwise. Thus, anionic ringopening polymerizations of cyclosiloxanes have received wide attention in the past decades. Focusing on cyclosiloxanes with different chemical structures used in anionic ring-opening polymerizations, this review elucidates the corresponding initiating agents, polymerization conditions, and final products involved in both homopolymerization and copolymerization processes. The covered topics regarding various monomers and initiating agents toward anionic ring-opening polymerizations of cyclosiloxanes will be of particular interest to organosilicon chemists as well as polymer and catalytic scientists who concern the precise control of the linear, branched, and cross-linked structure of polysiloxanes. These would be essential for preparing the next generation of organosilicon materials with much superior properties. A great number of research groups both domestic and overseas have polymerized various cyclic compounds by using different formulas, and the representative polymerization systems have been set out for convenient retrieval and comparison.