Preparation of hyperbranched polycarbosilazane via ultraviolet initiated hydrosilylation

Hyperbranched polycarbosilazane P1 was successfully prepared from AB₄ type monomer bis(N, N-diallylamino) methylsilane via fast hydrosilylation initiated by ultraviolet (UV) irradiation, with bis(acetylacet-onato) platinum (II) as the catalyst. For comparison, hyperbranched polycarbosilazane P2 was also prepared with the same monomer via heating-initiated polymerization at 80°C with Karstedt's catalyst. The structures of the resulting polymers were well characterized by FTIR, ¹H NMR, ¹³C NMR, ²⁹Si NMR and size exclusion chromatography/multi-angle laser light scattering (SEC/MALLS) technology. By IR monitoring, it was found that polyhydrosilylation initiated by UV irradiation was much faster than that initiated by heating. NMR analyses confirmed that the resulting polymer possessed a hyperbranched architecture, indicating that a-hydrosilylation may mainly occur during UV-initiated polymerization. Degree of branching (DB) and average number of branches (ANB) of P1 were determined via Si NMR and were found to be 0.46 and 0.53, which were close to the theoretical values, respectively. And the weight average molecular weight, polydispersity index and exponent for Mark-Houwink equation of P1 were determined to be 12500 g/mol, 2.1 and 0.44, respectively, which were similar to those of P2.