Preparation and Characterization of Boron Nitride PMMA Composites by In Situ Polymerization

ABSTRACT As an excellent insulating yet thermally conductive material, hexagonal boron nitride (h‐BN) can dramatically improve the thermal conductivity of polymethyl methacrylate (PMMA) when incorporated into this typically low‐thermal‐conductivity polymer. In this study, to address key challenges in current research on h‐BN‐reinforced polymers, particularly poor filler dispersion and the difficulty in achieving simultaneous optimization of thermal conductivity and mechanical properties, h‐BN/PMMA thermoplastic composites were fabricated via in situ polymerization, by varying the types of initiators (BPO/DMA, DPO/DMA, DPO/DMT) and the particle size of filler materials (5 μm versus 20 μm). The coupling mechanism between interfacial chemistry and microstructure was also systematically investigated. Experimental results demonstrate that composites incorporating 20 μm h‐BN and the DPO/DMA initiator exhibit optimal thermal conductivity, achieving a 131% increase (from 0.24 W/(m K) for pure PMMA to 0.57 W/(m K)), while retaining excellent mechanical performance. Specifically, the tensile modulus reached 3432.7 MPa (20% higher than the matrix), and the flexural modulus was 4179.2 MPa (a 39% improvement). This study presents a novel design strategy and establishes a theoretical foundation for developing high‐performance polymer‐based functional materials with balanced thermal and mechanical properties, while providing new insights into the fabrication of multifunctional composites.