Ab initio molecular dynamics simulations (AIMD) are used to investigate the influence of the vacancy and divacancy (5-8-5) defects on the surface of single-walled carbon nanotube (SWCNT)(10,0) on the structural properties of covalently attached aromatic diisocyanate molecules, namely 4,4'-methylene diphenyl diisocyanate (MDI) and toluene-2,4-diisocyanate (TDI). The structural rearrangements and flexibility of MDI and TDI attached to the defective SWCNTs are analysed and compared with the defect -free SWCNT(10,0). The results obtained indicate more than 4 times higher reactivity of vacancy defective SWCNT(10,0) comparing with the defect -free system. Due to weak C-H center dot center dot center dot O and C-H center dot center dot center dot pi hydrogen bonds, formed during the covalent functionalisation, the flexibility of the attached diisocyanates is suppressed. Detailed analysis of the time evolution of the structural parameters during AIMD simulations suggests cyclically repeated mechanism of the structural rearrangements of aromatic diisocyanates on the surface of SWCNTs(10,0). (C) 2015 Elsevier B.V. All rights reserved.