Mechanical, thermal, and degradation behavior of addition-cure liquid silicone rubber modified with vinyl-functionalized oleanolic acid

A vinyl-silylated derivative of oleanolic acid (Vi-OAAP), derived from its natural pentacyclic triterpenoid backbone, was developed to enhance the thermal stability and mechanical properties of addition-cure liquid silicone rubber. Vi-OAAP was synthesized via a facile two-step route involving amidation with 3-aminopropanol followed by vinyl silylation with dimethylvinylchlorosilane, yielding a bio-based molecule with a single vinyl group. The molecular structure of Vi-OAAP was confirmed by FTIR, 1H NMR, and 13C NMR. Using a platinum catalyst, Vi-OAAP was covalently incorporated into the silicone rubber network via hydrosilylation between its vinyl group and the Si-H bond, affording Vi-OAAP/SR composites. Their morphology, mechanical behavior, and thermal properties were systematically investigated using SEM, universal mechanical testing, TGA, and TG-FTIR. The rigid triterpenoid framework and the intermolecular hydrogen bonding from the amide and hydroxyl groups restricted polymer chain mobility, leading to markedly improved composite performance. At an optimal loading of 1.0 phr Vi-OAAP, the composite’s tensile strength increased by 49.8% (from 0.261 to 0.391 MPa), elongation at break nearly doubled (from 49.4% to 89.2%), and the maximum weight-loss temperature increased by 60.9 °C (from 568.2 to 629.1 °C). This work demonstrates a simple and effective strategy for incorporating oleanolic acid-derived bio-based functional molecules into high-performance silicone rubber systems.