Evaluation of dipole moment of polyhedral oligomeric silsesquioxane compounds

The aggregation state of polyhedral oligomeric silsesquioxane (POSS) within a polymer matrix plays a crucial role. Molecular interactions are key driving forces for aggregation, and one of the key physical parameters is the dipole moment (DPM). Quantum calculations such as density functional theory (DFT) calculations can be used to estimate the DPM. However, concerns exist regarding the accuracy of DPM estimates for complex structures. There have been no reports of electrochemical measurement of DPMs of POSS compounds. In this study, we developed a method to measure the DPM using a readily available inductance-capacitance-resistance (LCR) meter and a coaxial cylindrical sample cell, and we successfully measured the DPMs of POSS compounds for the first time. The DPM values obtained by our measuring method using the concentration constant method and the Halverstadt-Kumler method were in close agreement with the values reported in the literature for the known compounds limonene, methyl benzoate, and nitro benzene, indicating that the DPMs of POSS compounds can be measured accurately. It was found that heptaisobutyl-monosubstituted POSS with n-propyl (7B1Pr-POSS) had a DPM of 0 D, with allyl (7B1AL-POSS) it had a DPM of 2.82 D, with 3-aminopropyl (7B1NH2-POSS) it had a DPM of 2.83 D, and with 3-chloropropyl (7B1Cl-POSS) it had a DPM of 3.58 D. The results indicate that the DPM is affected by the organic substituents on the POSS. The DPM values in different solutions were measured. Our method can be used to measure the DPM of POSS compounds with various substituents.