Preparation of Heat-Resistant Methyl Vinyl Phenyl Silicone Rubber and Study on Its Flexible Strain-Sensing Performance

Conventional flexible substrates for strain sensors generally exhibit good flexibility and processability; however, their limited heat resistance restricts their long-term application in high-temperature environments. Aiming at the problem of insufficient heat resistance of high-temperature flexible strain sensing matrix, triphenyltetramethylcyclotrisiloxane (P3), trimethyltrivinylcyclotrisiloxane (V3) and octamethylcyclotetrasiloxane (D4) were used as raw materials in this paper. Methyl vinyl phenyl silica gel (MVMPS) with high phenyl and vinyl content was prepared by anionic ring-opening polymerization, and condensed with KH-570 (3-Methacryloxypropyltrimethoxysilane) to obtain a condensed modified gel (C-MVMPS). Subsequently, a methyl vinyl phenyl silicone rubber composite was fabricated using fumed silica as the reinforcing filler and Si69 as the coupling agent and vulcanization assistant. In addition, flake silver powder was incorporated to prepare an Ag/MVMPS conductive adhesive, and a sandwich-structured strain sensor with a silicone rubber/Ag-MVMPS conductive adhesive/silicone rubber configuration was fabricated. The synthesized methyl vinyl monophenyl silicone gum exhibited a number-average molecular weight of 170,449, a phenyl content of 25.19%, and a vinyl content of 24.44%. The composite showed the best overall performance at 3 phr (parts per hundred of rubber) Si69 (Bis(gamma-triethoxysilylpropyl) tetrasulfide) and 30 phr SiO2 (Fumed silica), with a 5% weight-loss temperature (T5%) of 367.14 °C and a 10% weight-loss temperature (T10%) of 529.6 °C. The prepared sandwich-structured sensor exhibited clear and stable resistance responses within the strain range of 10–80%. The sensitivity increased with increasing strain, and good reproducibility was maintained under different loading rates. Moreover, the sensor still exhibited continuous and distinguishable cyclic responses after 1000 cycles at 20% strain. These results provide an experimental basis and a feasible design strategy for the application of methyl vinyl phenyl silicone rubber in high-temperature flexible strain sensors.