Quantifying the Level of Intermacromolecular Interactions in Ethylene–Propylene Copolymers by Using Pyrene Excimer Formation

Abstract

A unique methodology based on fluorescence measurements is introduced to quantitatively measure the actual level of interpolymeric association between ethylene–propylene (EP) copolymers used as viscosity index improvers (VIIs) in engine oils. To this end, two EP copolymers, one amorphous (EP(AM)) and the other semicrystalline (EP(SM)), were maleated and then fluorescently labeled with 1-pyrenemethylamine and 2-(2-naphthyl)ethylamine to yield Py-EP and Np-EP, respectively. Successful maleation and fluorescence labeling were confirmed by Fourier transform infrared (FTIR) spectroscopy. The level of crystallinity of the EP copolymers was inferred from FTIR, carbon nuclear magnetic resonance (13C NMR), and differential scanning calorimetry (DSC) experiments. The solution behavior of the EP copolymers was characterized by conducting intrinsic viscosity measurements as a function of temperature to define the temperature range where fluorescence studies should be conducted. Fluorescence resonance energy transfer ...