Fast synthesis of high molecular weights polydiethylsiloxanes and random poly(dimethylsiloxane-co-diethylsiloxane) copolysiloxanes via cyclic trimeric phosphazene base catalyzed ring-opening (co)polymerization

Abstract

Listen

Translate article

High molecular weights polydiethylsiloxanes and random poly(dimethylsiloxane-co-diethylsiloxane) copolysiloxanes were synthesized via cyclic trimeric phosphazene base catalyzed ring-opening (co)polymerization at room temperature. • PDES homopolymers, with molecular weight up to 404.0 kg/mol, were conveniently synthesized at room temperature within 4 hrs using CTPB as catalyst. • High molecular weight random copolymers of diethylsiloxane with different dimethylsiloxane contents were successfully prepared within 5 min at room temperature in high yields. • Reactivity ratio determination experiments suggested that the ROCP of D 3 Et with D 4 mediated by CTPB proceeded in a fully random manner, demonstrating the high catalytic activity of CTPB. Polysiloxanes containing diethylsiloxane units with unique low temperature flexibility have been widely applied under extreme conditions in many fields. However, the synthesis of polydiethylsiloxane (PDES) and its copolymers was challenging due to the easy accessible polymerization-depolymerization equilibrium between linear propagating chains and cyclosiloxane byproducts in the ring-opening polymerization (ROP) of hexaethylcyclotrisiloxane (D 3 Et ) and the large reactivity gaps among different cyclosiloxanes in the copolymerization. In this work, PDESs were successfully prepared via cyclic trimeric phosphazene base (CTPB) catalyzed ROP at room temperature in high yields. The ROP of D 3 Et proceeded efficiently with low CTPB loading (low to 0.01 mol%) and the resulting PDES homopolymers had high molecular weights (up to 404.0 kg/mol). Moreover, poly(dimethylsiloxane- co -diethylsiloxane) (PMES) random copolymers with tunable diethylsiloxane contents (20 ∼ 87 mol%) can be directly prepared via ring-opening copolymerization (ROCP) of D 3 Et and octamethylcyclotetrasiloxane (D 4 ) using CTPB as catalyst within 5 min at ambient temperature. The reactivity ratio of D 3 Et ( r = 1.04) and D 4 ( r = 0.89) suggested the comparable reactivity between D 3 Et and D 4 to ensure their random copolymerization characteristics, thus proving the unique high efficiency of CTPB catalyst applied here. Microstructure characterizations of the PMES copolymers by 1 H and 29 Si NMR verified the controlled copolymer composition and the random distribution of diethylsiloxane and dimethylsiloxane units. The thermal property investigations by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) indicated the good low-temperature flexibility and thermal stability of PMES copolymers, displaying great potential in extreme environmental applications.