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 increased upon decreasing the temperature and increasing the polymer concentration as would have been expected from such a polymer. This result suggests that pyrene excimer formation provides a reliable method to quantitatively determine finter for EP copolymers used as VIIs, an information which is otherwise difficult to extract from standard FRET experiments.2

A novel methodology based on fluorescence quenching measurements is introduced to determine quantitatively the amine content of polyisobutylene succinimide (PIBSI) dispersants used as engine oil-additives. To this end, a series of five PIBSI dispersants were prepared by reacting 2 mol equiv of polyisobutylene succinic anhydride (PIBSA) with 1 mol equiv of hexamethylenediamine (HMDA), diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine to yield the corresponding b-PIBSI dispersants. After having demonstrated that the presence of hydrogen bonds between the polyamine linker and the succinimide carbonyls of the dispersants prevents the quantitative analysis of the (1)H NMR and FTIR spectra of the dispersants to determine their chemical composition, alternative procedures based on gel permeation chromatography (GPC) and fluorescence quenching were implemented to estimate the amine content of the b-PIBSI dispersants. Taking advantage of the doubling in size that occurs when 2 mol of PIBSA are reacted with 1 mol of HMDA, a combination of GPC and FTIR was employed to follow how the chemical composition and molecular weight distribution of the polymers produced evolved with the reaction of PIBSA and HMDA mixed at different molar ratios. These experiments provided the PIBSA-to-HMDA molar ratio yielding the largest b-PIBSI dispersants and this molar ratio was then selected to prepare the four other dispersants. Having prepared five b-PIBSI dispersants with well-defined secondary amine content, the fluorescence of the succinimide groups was found to decrease with increasing number of secondary amines present in the polyamine linker. This result suggests that fluorescence quenching provides a valid method to determine the chemical composition of b-PIBSI dispersants which is otherwise difficult to characterize by standard (1)H NMR and FTIR spectroscopies.

Maleated polyolefins (MaPOs) such as maleated ethylene propylene copolymers or polyisobutylene terminated at one end with a succininic anhydride can be used as polymeric dispersants in engine oils after reaction with polyamines while unmodified EP copolymers improve the viscosity index of oils. MaPOs can also be labeled with pyrene derivatives to generate pyrene-labeled polyolefins (PyLPOs) as fluorescent mimics of oil additives and pyrene excimer fluorescence (PEF) can be applied to probe their behavior in solution. This review describes new methodology that was recently implemented to characterize the complex fluorescence signal emitted by PyLPOs by using steady-state and time-resolved fluorescence. This methodology enables one to gain quantitative information about the level of clustering of the succinic pendants along a maleated polyolefins and intra-and intermolecular aggregation of polyolefins in solution. Such information is relevant to scientists aiming to characterize polymeric oil additives used in engine oil.

The secondary amines found in b-PIBSI dispersants prepared by attaching two polyisobutylene chains to a polyamine core via two succinimide moieties were reacted with ethylene carbonate (EC). The reaction generated urethane bonds on the polyamine core to yield the modified b-PIBSI dispersants (Mb-PIBSI). Five dispersants were prepared by reacting two molar equivalents (meq) of polyisobutylene terminated at one end with a succinic anhydride moiety (PIBSA) with one meq of hexamethylenediamine (HMDA),

A new methodology based on pyrene excimer fluorescence (PEF) was applied to quantitatively measure the actual level of intermolecular association between ethylene-propylene (EP) copolymers in toluene in the presence of wax, an intrinsic component of engine oils. EP copolymers are commonly used as viscosity index improvers (VIIs) in engine oils. Unfortunately waxes in engine oils thicken the oil and are suspected of associating with VIIs at low temperature.In this study, four EP copolymers were maleated to yield EP−MA and then fluorescently labeled with 1-pyrenemethylamine to yield Py-EP. Successful maleation and pyrene labeling were confirmed by Fourier transform infrared (FTIR) and UV-Vis absorption spectroscopy. The solution behaviour of the EP copolymers in the presence of wax was characterized by PEF, which was used to quantitatively measure the molar fraction of intermolecular interactions (finter) between EP copolymers in the absence or presence of wax. The fraction finter was determined through the analysis of the fluorescence spectra of the Py-EP solutions acquired as a function of temperature.Upon excitation, the Py-EP solutions generated excimer upon encounter between an excited and a ground-state pyrene. The ratio of the excimer fluorescence intensity (IE) over that of the monomer (IM) yielded the IE/IM ratio which was employed to determine finter. Plots of finter as a function of temperature provided a description of the solution behaviour of a given VII with or without wax present in solution. The results of this study indicate that wax in solution binds onto EP copolymers dissolved in toluene, which increases macromolecular associations as reflected by an increase in finter. The formation of microcrystals between semicrystalline EP copolymers however induces strong polymer-polymer interactions that result in the dissociation of the wax from the polymers.