Comparative Study of Silicone Resin Cured with a Linear and a Branched Cross-Linking Agent

The molecular structure of hydropolysiloxane curing agents is expected to greatly affect the curing reaction and properties of the cured species, but the exact influence still remains somewhat misunderstood. Herein, we choose two representative cross-linking agents: a linear polysiloxane with the Si–H group (LPHS for short) and a branched polysiloxane with the Si–H group (TPHS for short) and a kind of high refractive index of polysiloxane resin with the vinyl-end group (short for MPSR) which was successfully synthesized in laboratories. The curing behaviors, dynamic mechanical properties, optical and electrical properties, and thermal stability of two kinds of curing systems (MPSR/TPHS and MPSR/LPHS) were systematically investigated and compared. The effect of molecular architecture of two different cross-linking agents on the curing activation energy, reactivity, and reaction rate has been studied by DSC and online FT-IR spectroscopy. The results confirm that the MPSR/TPHS system shows lower effective activation energy, higher reaction rate, and higher the degree of cure (α) than MPSR/LPHS under the same cure conditions. Furthermore, the MPSR/TPHS system shows excellent optical transparency in the UV–visible region, low dielectric constant, and stable dielectric loss over the whole frequency compared to MPSR/LPHS. At last, DMA exhibits cured MPSR/TPHS which has much higher glass transition temperature, storage modulus, and cross-link density than MPSR/LPHS, and thermogravimetric analysis (TGA) reveals the LPHS-cured silicone resin has excellent thermal stability with high char yield.