A procedure is established to determine the molar fraction (f doubly) of doubly-maleated polyisobutylene (PIBSA2) in a PIBSA sample mainly constituted of mono-maleated polyisobutylene (PIBSA1), where the succinic anhydride (SA) groups are located at the end of the PIB chain. To this end, a PIBSA sample was labeled with 1-pyrenemethylamine (PyMA) to generate PIB-PySI, where the 1-pyrenemethyl group was linked to the PIB chain via a succinimide group. Depending on the procedure applied to purify the PIB-PySI samples, different regions of the molecular weight distribution (MWD) representing the PIBSA samples could be isolated and characterized by a combination of GPC, FTIR, and UV–vis absorption analysis to yield its MWD, number of isobutylene units per succinic anhydride (N IB/N SA), and pyrene content (λPy, in μmol of pyrene per gram of sample). These analyses were consistent with the expected size and chemical composition of the different PIB-PySI samples. f doubly was calculated from the molar fraction (f agg) of pyrene labels attached onto the PIBSA2 species. f agg was determined through the global model free analysis (MFA) of the fluorescence decays of the pyrene monomer and excimer acquired for solutions of the PIB-PySI samples in THF. The different fractions of the MWD of the PIBSA sample yielded similar f doubly values across the MWD, implying an even distribution of PIBSA2 species across a PIBSA MWD. The constancy of f doubly across the MWD enabled the determination of the number average molecular weight (M n ) of the PIB-PySI samples from λPy. An analysis combining the GPC traces obtained with a differential refractive index and UV–vis absorption detector yielded the MWD of the original PIBSA sample. These experiments demonstrated that the proposed PEF-based methodology can be applied to characterize the SA end groups of PIBSA samples and could be further extended to characterize the end groups of other end-functionalized polymers.

The nature of the end-groups of a PIBSA sample, namely a polyisobutylene (PIB) sample, where each chain is supposedly terminated at one end with a single succinic anhydride group, was characterized through a combination of pyrene excimer fluorescence (PEF), gel permeation chromatography, and simulations. The PIBSA sample was reacted with different molar ratios of hexamethylene diamine to generate PIBSI molecules with succinimide (SI) groups in the corresponding reaction mixtures. The molecular weight distribution (MWD) of the different reaction mixtures was determined by fitting the gel permeation chromatography traces with sums of Gaussians. Comparison of the experimental MWD of the reaction mixtures with those simulated by assuming that the reaction between succinic anhydride and amine occurs through stochastic encounters led to the conclusion that 36 wt% of the PIBSA sample constituted unmaleated PIB chains. Based on this analysis, the PIBSA sample was found to be constituted of 0.50, 0.38, and 0.12 molar fractions of PIB chains that were singly maleated, unmaleated, and doubly maleated, respectively.

A poly(octadecyl methacrylate) sample fluorescently labeled with 6.7 mol% of pyrene (Py(6.7)-PC18MA) was used as a mimic of a pour point depressant (PPD) to investigate how Py(6.7)-PC18MA interacts with wax found in engine oils and ethylene-propylene (EP) copolymers used as mimics of viscosity index improvers (VIIs). The fluorescence spectra of Py(6.7)-PC18MA solutions in octane were acquired in octane at low and high concentrations of Py(6.7)-PC18MA and analyzed to obtain the molar fraction (finter) of pyrene labels, that formed excimer intermolecularly, a measure of the level of intermolecular interactions between Py(6.7)-PC18MA molecules in the solution. The finter-versus-T profile obtained for Py(6.7)-PC18MA alone in octane confirmed that Py(6.7)-PC18MA formed microcrystals at solution temperatures below 0 oC. The effect induced by the addition of wax and an amorphous (EP(AM)) and semicrystalline (EP(SM)) EP copolymer on the interactions experienced by Py(6.7)-PC18MA were characterized by monitoring finter as a function of temperature and comparing the different finter-versus-T plots obtained after the addition of the different components with the finter-versus-T plot obtained for Py(6.7)-PC18MA alone. These studies demonstrated that wax and EP(AM) increased the level of intermolecular interactions between the Py(6.7)-PC18MA molecules at all temperatures in octane. EP(SM) increased the interactions between Py(6.7)-PC18MA molecules at high temperature, where it was soluble in octane, but finter reverted to its value in the absence of EP(SM) at low temperatures, where EP(SM) had crystallized. These experiments illustrate how pyrene excimer fluorescence can be applied to probe the complex interactions taking place between the different components found in engine oils.