Synthesis of Zirconium-Containing Polyhedral Oligometallasilsesquioxane as an Efficient Thermal Stabilizer for Silicone Rubber

Abstract

Abstract:Free radicals play a negative role during the thermal degradation of silicone rubber (SR). Quenching free radicals is proposed to be an efficient way to improve the thermal-oxidative stability of SR. In this work, a novel zirconium-containing polyhedral oligometallasilsesquioxane (Zr-POSS) with free-radical quenching capability was synthesized and characterized. The incorporation of Zr-POSS effectively improved the thermal-oxidative stability of SR. The T 5 (temperature at 5% weight loss) of SR/Zr-POSS significantly increased by 31.7 • C when compared to the unmodified SR. Notably, after aging 12 h at 280 • C, SR/Zr-POSS was still retaining about 65%, 60%, 75%, and 100% of the tensile strength, tear strength, elongation at break, and hardness before aging, respectively, while the mechanical properties of the unmodified SR were significantly decreased. The possible mechanism of Zr-POSS for improving the thermal-oxidative stability of SR was intensively studied and it was revealed that the POSS structure could act as a limiting point to suppress the random scission reaction of backbone. Furthermore, Zr could quench the free radicals by its empty orbital and transformation of valence states. Therefore, it effectively suppressed the thermal-oxidative degradation and crosslinking reaction of the side chains.

Effects of Thermal Reflowing Stress on Mechanical Properties of Novel SMT-SREKs

“…5 presents the average T r of SMT-SREKs that experience different reflowing profiles. The mechanical properties of silicone rubber materials are highly sensitive to the increase of subjected temperature [11], and the hardness and compression set of silicone rubber materials increase with increasing temperature [9], [13]. A similar decay phenomenon was found in SMT-SREKs subjected to the reflowing process.…”

“…8 (b)); a similar decline is also observed in the absorption peak at 793 cm −1 from the coupling of stretching vibration of Si-C and rocking vibration of −CH 3 (Fig. 8 (c) reflowing temperature, mainly including de-crosslinking reaction at cross-linked sites of silicone rubbers and combination reaction on the rubber backbone [1], [9], [11]. Furthermore, the increasing T p , acting as a thermal shock stress to silicone rubbers, slightly aggravates the degradation of most absorption peaks on the FTIR spectra, which results in the mechanical performance decay law of SMT-SREKs in various reflowing processes.…”

“…12 and 13). The yield phenomenon for the impact of repeated reflowing process on the decay rate should be attributed to the mentioned increase in the hardness and compression set of silicone rubber materials [9], [13]. The change of T r with increasing pressing number can further illustrate the degradation of the mechanical properties of SMT-SREKs (Fig.…”

“…However, investigations on the temperature influence on mechanical performance and reliability assessment for SMT-SREK applications are limited. Some scholars have studied the mechanical, thermal, and aging properties of silicone rubbers for various applications [8], [9]. For example, Chandrasekar et al [10] investigated the aging of silicone rubber insulation material in a high-temperature environment and found that thermal aging affects the tensile strength and storage modulus characteristics of silicone rubber materials.…”

“…Some researchers found that after long usage in different environments, the silicone rubber surface may crack and its tensile strength may decline [16], [17]. Furthermore, the specimen hardness, tensile strength, and elongation at break may also increase [9], [18], [19]. Zhu et al [20] studied the surface degradation of unfilled high-temperature vulcanized silicone rubber resulting from creeping corona discharges under atmospheric pressure.…”