Synthesis and characterization of acrylic hexagonal boron nitride nanosheets for thermally stable polymethylmethacrylate composites

In this work, hexagonal boron nitride (h-BN) was modified with the covalent attachment of polymer chains using the “grafting to” strategy. The main objective is to incorporate pMMA into the h-BN structure by introducing a functional group to the h-BN capable of forming a copolymer and enhance thermal stability of pMMA. Amino silane was initially grafted to h-BN and then methacrylic functionality was introduced to h-BN via a Michael Addition reaction. The synthesized monomer (BNACOM) was polymerized with methyl methacrylate (MMA) using the atom transfer radical polymerization method (ATRP). The monomer of h-BN with methacrylic functionality and hexagonal boron nitride with amino silane functionality (BN-APTES) were characterized by FT-IR spectroscopy. The appearance of carbonyl peak C[dbnd]O at 1720 cm⁻¹, acyl group C[sbnd]O at 1166, 1064 cm⁻¹, and the hydroxyl group at 3475 cm⁻¹ evidenced the addition of 3-(acryloyloxy)-2-hydroxypropyl methacrylate to the structure. The disappearance of double-bond carbon atom peaks in the SSNMR ¹³C spectrum proved that the copolymers were synthesized successfully. The h-BN is a thermally stable compound and according to the TGA results, it was seen that the increase in the amount of BNACOM in copolymerizations enhanced thermal stability of copolymers from residue at 700 °C 84.9 % to 87.2 %. The decrease in the conversion percentage from 40.6 % to 5.4 % of polymethyl methacrylate (pMMA), removed by the washing procedure, showed that adding MMA to the copolymer structure increased with the increasing amount of BNACOM. The growth of the carbonyl peak at 1720 cm⁻¹ in the FT-IR spectrum also supports this. Looking at the DSC results, it can be seen that the glass transition temperature of the copolymer approaches the glass transition temperature of pMMA.