Effect of temperature on the molecular vibrations of linear and branched polyethylene

Abstract

The mechanical, electrical and thermal properties of Polyethylene are highly dependent on the temperature. It is necessary to study the effect of temperature at the molecular level of the polymer in order to understand the changing physical properties. Micro-Raman Spectroscopy has been used to determine the temperature dependence of the molecular vibrations in branched and unbranched polyethylene (Low density and High-density Polyethylene). A small temperature quench at the rate of 20°C/min was applied upto 10°C and the time evolution of the Raman spectrum was studied. A substantial decrease in the peak area, height and FWHM was observed for all the Raman modes. The decrease in peak parameters indicate towards a change in the molecular structure of the polymer which is induced due to the small temperature quench. The effect of branching was also studied with temperature where a major change in peak area was observed with temperature for the branched polymer. This indicates that the branched polyethylene is highly prone to the molecular reorientations with temperature as compared to the linear polyethylene.