Application of Polysiloxane–Polyphosphate–Pyrophosphate Ternary Block Copolymer in Thermoplastic Vulcanizates: Effect of Polysiloxane Molecular Weight on Flame Retardancy and Mechanical Properties

ABSTRACT This study employed a molecular organization approach based on flame‐retardant group block copolymerization, using different phosphorus–nitrogen flame‐retardant groups and polydimethylsiloxane (PDMSi x ) groups with varying molecular weights. These ternary block copolymers P‐M‐ n MSi x were successfully synthesized with distinct molecular weights and PDMSi x ratios, then applied to prepare TPV composites. The study investigated the influence of PDMSi molecular weight and ratio on the comprehensive properties of TPV. Compared to pure TPV, TPV composites incorporating the ternary block copolymers exhibited superior flame retardancy with higher limiting oxygen index (LOI) values. The P‐M‐8MSi 10000 /TPV composite achieved the highest LOI of 28.2% at a PAPP/MPP/PDMSi x ratio of 70/30/8. Additionally, both P‐M‐8MSi 5000 /TPV and P‐M‐8MSi 10000 /TPV passed the UL 94 V‐0 (1.6 mm) rating. In cone calorimeter testing, compared to P‐M‐8MSi 2000 /TPV, P‐M‐8MSi 10000 /TPV exhibited a 32.6% reduction in PHRR and a 44.6% increase in FPI. Residual carbon analysis was used to compare the influence of different PDMSi x molecular weights on the flame retardancy of the condensed phase in the terpolymer block copolymer. Tensile testing of P‐M‐8MSi x /TPV composites revealed that P‐M‐8MSi x caused a decrease in TPV mechanical properties. The reasons for this decrease were investigated by observing the microstructure of the tensile fracture surface.