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.