Precise Synthesis of Side-Chain-Functionalized Linear Polysiloxanes by Organocatalytic Ring-Opening Polymerization of Monofunctional Cyclotrisiloxanes

The organocatalytic controlled/living ring-opening polymerization (ROP) of monofunctional cyclotrisiloxanes using water or silanols as initiators, guanidines as catalysts, and organochlorosilanes as end-capping agents produced side-chain-functionalized linear polysiloxanes with controlled number-average molar mass (Mn), narrow molar-mass dispersity (ĐM), the desired terminal structures, and good distribution of the side-chain functionalities, namely, vinyl, 3-chloropropyl, and allyl groups. The synthesis of monofunctional cyclotrisiloxanes, such as vinylpentamethylcyclotrisiloxane, (3-chloropropyl)pentamethylcyclotrisiloxane, and allylpentamethylcyclotrisiloxane was achieved by the reaction of 1,3-dihydroxy-1,1,3,3-tetramethyldisiloxane and diacetoxysilanes using simple synthetic procedures. Control over the composition and monomeric sequences of the resulting side-chain-functionalized polysiloxanes was conveniently achieved using either polymerization or copolymerization and varying the initial feed ratio of the two monomers and the timing of monomer addition, i.e., using either the premix or two-stage method, in the copolymerizations. Analysis of the monomeric sequence using 29Si{1H} NMR measurements revealed that the propagation reaction with VD2, ClPD2, and AD2 proceeded almost completely via a statistical manner. Plausible monomeric sequences and chain-length distributions of the resulting side-chain-functionalized polysiloxanes were visualized using two simulation methods.