Synthesis and characterization of hyperbranched polycarbosilazanes with controllable degradation behavior

Two novel degradable hyperbranched polycarbosilazanes were synthesized via hydrosilylation reaction and well characterized by FT-IR, ¹H-NMR, ¹³C-NMR, ²⁹Si-NMR and size exclusion chromatogram-multi- angle laser light scattering (SEC-MALLS) technology. First, two monomers, bis(N,N-bis(dimethylvinylsilyl)amino)-methylsilane (AB₄M) as well as (N,N-bis(dimethylvinylsilyl)amino)-dimethylsilane (AB₂M), were prepared by nucleophilic substitution of MeHSiCl₂ and Me ₂HSiCl with lithium teramethyldivinyldisilazane, respectively. Then the two monomers were polymerized for obtaining hyperbranched polycarbosilazanes via hydrosilylation reaction using a Karstedt catalyst. The structure analyses indicate that α-addition mainly occurs during the polymerization, and the polymers synthesized consist of N(=Si-C≡)₃ linkages with hyperbranched architecture and a large amount of functional vinyl bonds as end groups. The molecular weight (M_w) and its polydispersity index (M_w/M_n) were determined to be 7800 and 2.54 for PAB ₄M, and 5860 and 2.31 for PAB₂M, respectively. Preliminary studies on the chemical stability of polymers shows that the hyperbranched polymer synthesized is stable to chlorosilane as well as water. However, it can be hydrolyzed with hydrochloric acid solution, and the degradation rate can be controlled by changing the concentration of HCl. The results suggest that controlled degradation of these hyperbranched polymers is attainable.