Functionalized carbon nanotube (CNT)/polymer composites have received significant interest as promising structural materials with applications in the most demanding areas of industry such as aerospace and ballistic protection. In order to optimise the properties of this class of materials, it is imperative to understand how load is transferred through the interface, between the functionalized CNT and polymer matrix with the aim to identify the key factors determining the interfacial shear strength and dominant failure mechanisms. Computational investigation of the interface requires simulations of tens of thousands of atoms in order to accurately describe the movement of polymer chains; however, critical interfacial failure involves changes in local chemistry such as bond-forming and breaking effects, necessitating a quantum-mechanical (QM) treatment. These issues are addressed by employing a quantum/classical hybrid simulation technique; in this approach, molecular dynamics based on a classical forcefield is used to simulate the majority of the system under strain, while regions of particular interest, such as the functional groups where changes in electronic structure are likely to occur, are investigated using QM methods resulting in an accurate description of bond-breaking processes.