Experimental and theoretical investigations of natural rubber (cis-1,4-polyisoprene) using Coloumb attenuating and Hartree–Fock theoretical methods

Abstract

A systematic analysis of natural rubber (NR) has been carried out in the present investigation. The Fourier transform infrared (FTIR) spectrum of NR has been recorded in the range of 4000–400cm−1 and the vibrational frequencies of the fundamental modes have been precisely assigned. Density functional CAM-B3LYP/6-311++G(d,p) and Hartree–Fock HF/6-311++G(d,p) calculations were performed to obtain the optimized molecular structures, vibrational frequencies, natural bonding orbital (NBO) analysis and thermodynamic parameters. The computed static dipole moment (μtot) and first hyperpolarizability (β0) of the present molecule has been determined using the CAM/HF levels of theory. The optimized geometric parameters (bond lengths, bond angles and bond dihedrals) are found to be almost same at the B3LYP/6-311++G(d,p) and HF/6-311++G(d,p) levels of theory. The vibrational frequencies obtained by CAM-B3LYP/6-311++G(d,p) method are much better than HF/6-311++G(d,p) when compared with the experimental FTIR values. From the NBO analysis, it was observed that C5 is more electronegative compared with other carbon atoms. The dielectric constant being an important parameter in deciding the insulation characteristic of the material was determined for NR in the X-band and K-band microwave frequency region by employing Roberts and Von Hippel's method. From Thermogravimetric analysis (TGA), the thermal stability of natural rubber has been discussed and important thermal transitions have been detected using Differential thermal analysis (DTA). In addition the hardness of the natural rubber was determined using shore ‘A’ durometer.