Chemical Modification of Polyisobutylene Succinimide Dispersants and Characterization of Their Associative Properties

This document is the Accepted Manuscript version of a Published Work that appeared in final form in Journal Of Physical Chemistry B, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.jpcb.5b04515The 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 2 molar equivalent (m(eq)) of polyisobutylene terminated at one end with a succinic anhydride moiety (PIBSA) with 1 m(eq) of hexamethylenediamine (HMDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA) to yield the corresponding b-PIBSI dispersants. Characterization of the level of secondary amine modification for the Mb-PIBSI dispersants with traditional techniques such as FTIR and H-1 NMR spectroscopies was greatly complicated by interactions between the carbonyls of the succinimide groups and unreacted secondary amines of the Mb-PIBSI dispersants. Therefore, an alternative procedure was developed based on fluorescence quenching of the succinimides by secondary amines and urethane groups. The procedure took advantage of the fact that the succinimide fluorescence of the Mb-PIBSI dispersants was quenched much more efficiently by secondary amines than by the urethane groups that resulted from the EC modification of the amines. While EC modification did not proceed for b-PIBSI-DETA and b-PIBSI-TETA certainly due to steric hindrance, 60 and 70% of the secondary amines found in the longer polyamine core of b-PLBSI-TEPA and b-PIBSI-PEHA had reacted with EC as determined by the fluorescence quenching analysis. Furthermore, the ability of the Mb-PIBSI dispersants to adsorb at the surface of carbon black particles used as mimic of the carbonaceous particles typically found in engine oils was compared to that of their unmodified analogues.Imperial OilNSER

Adsorption of Polyisobutylene-Based Dispersants onto Carbon Black

The formation of carbonaceous by-products (e.g. soot) during the operation of an internal combustion engine is unavoidable and the aggregation of this soot leads to deleterious effects including abrasive wear of the engine, increased oil viscosities, and sludge deposition. Dispersants, which are composed of a hydrophobic tail and a polar headgroup, are used as oil additives to aid in the suspension and stabilization of the soot particles. Polyisobutylene succinimide (PIBSI) is the most well-studied class of dispersants and is characterized by a linear architecture and polyamine headgroup that interacts with soot by acid-base and dipole-dipole interactions. As such, there remains a lack in understanding on the effect of dispersant architecture and alternative dispersant-soot interactions and the governing characteristics of these interactions. In the first project, we synthesized a library of polyisobutylene (PIB)-based dispersants with varying architecture. Linear dispersants were prepared via living cationic polymerization and grafted dispersants by the acid-catalyzed cleavage/alkylation of butyl rubber. Comb dispersants were prepared from the alternating copolymerization of vinyl-ether PIB (VE-PIB) macromers with maleic anhydride where the rate of copolymerization was found to be heavily influenced by molecular weight of the VE-PIB macromer. The affinity and degree to which comb and grafted dispersants adsorbed to carbon black was found to be similar whereas a linear dispersant exhibited reduced affinity yet increased adsorption capacity. In the second project, we investigated the effect of PIB-based dispersants containing exclusively non-nucleophilic nitrogen in addition to how π-π interactions can be leveraged for the adsorption of dispersants. Linear PIB was functionalized with 1-(2-aminoethylpiperazine) and was subsequently functionalized with cyclic anhydrides of varying degrees of aromaticity. Metal corrosion and fluoroelastomer compatibility indicated that dispersants with non-nucleophilic nitrogen were less aggressive while providing a greater degree of total base number in comparison to PIBSI dispersants. A critical size of at least two terminal aromatic rings was found to be able to leverage advantageous π-π interactions between dispersants and carbon black for increased adsorption. In the third project, we investigated cation-π interactions between carbon black and ionic-liquid terminated PIB (PIB-IL) dispersants. Interaction of the nitrogenous cation with the quadrupole moment of the aromatic surface provided for strong non-covalent interactions which can be used as an alternative mechanism for adsorption. A library of PIB-IL dispersants was prepared through the quaternization of aromatic amines and metathesis of counterions. The characteristics of PIB-IL micellization (Nagg, CMC, Mmicelle, Rh) were heavily influenced by anion hydrophobicity whereas PIB-IL adsorption to carbon black was dictated by the molar volume of the cation. The fourth project, which was of an alternative focus, investigated Diels-Alder crosslinked PIB networks which were prepared from multifunctional PIB-Furan and PIB-Maleimide macromers utilizing the acid catalyzed cleavage/alkylation of butyl rubber. Thermal stability, including decomposition temperature and retro Diels-Alder temperatures (TRDA) were independent of macromer choice however the viscoelastic properties were heavily influenced. Recyclability was demonstrated by remolding and recasting of destroyed networks at elevated temperatures and a slight hysteresis in mechanical properties was observed as compared to original networks

Quantitative Characterization of Polymeric Engine Oil Additives in Solution by Fluorescene

The solution behavior of several polymeric oil additives has been characterized by using fluorescence. First, the chemical composition of the polyisobutylene-based dispersants was determined by using the inherent fluorescence of the succinimide moiety of the polyisobutylene succinimide (PIBSI) dispersants and its efficient quenching by secondary amines. A series of PIBSI dispersants were synthesized by reacting one molar equivalent (meq) of polyisobutylene succinic anhydride (PIBSA) with two meqs of hexamethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, and pentaethylenehexamine to yield the corresponding bis-PIBSI (b-PIBSI) dispersants. Intermolecular association of the dispersants in the solid state or in solution prevented the determination of the chemical composition of the b-PIBSI dispersants with traditional methods such as 1H NMR and FTIR. Therefore, two procedures were developed to estimate the amine content of the b-PIBSI dispersants based on gel permeation chromatography (GPC) and fluorescence quenching. The fluorescence study showed a decrease in the fluorescence of the succinimide groups with increasing number of secondary amines present in the polyamine linker. A similar method was then applied to determine the level of modification of the b-PIBSI dispersants after they were reacted with ethylene carbonate (EC) to generate modified b-PIBSI dispersants (Mb-PIBSI). The fact that the succinimide fluorescence of the Mb-PIBSI dispersants was quenched much more efficiently by secondary amines than by the urethane groups that resulted from the EC modification of the amines was employed to quantify the level of EC modification of the Mb-PIBSI dispersants. Moreover fluorescence was used to determine and compare the binding isotherms of a series of b-PIBSI and Mb-PIBSI dispersants as they adsorbed onto the surface of carbon black particles. Second, the molar fraction of intermolecular associations (finter) between ethylene-propylene (EP) copolymers was quantitatively determined by using pyrene excimer formation. In these experiments, a series of EP copolymers was maleated to yield EP-MA and then fluorescently labeled with 1-pyrenemethylamine and 2-(2-naphthyl)ethylamine to yield Py-EP and Np-EP, respectively. Fluorescence resonance energy transfer (FRET) experiments between Np-EP and Py-EP provided qualitative evidence of the existence of intermolecular association. A quantitative measure of finter was obtained by measuring the fluorescence intensity ratio of excimer-to-monomer (IE/IM) of the Py-EP solutions. The results showed that finter remained constant for amorphous Py-EP samples and increased for semicrystalline Py-EP samples upon decreasing the temperature as would have been expected from their chemical composition. This method was then applied to quantitatively measure finter between EP copolymers in solution in the presence of wax typically found in engine oils. The solution behaviour of four Py-EP copolymers in the presence of wax was characterized. The results showed that the interaction of wax with ethylene sequences in the EP copolymers increased macromolecular associations in solution as reflected by an increase in finter. In the case of the semicrystalline samples at lower temperatures, however, the formation of microcrystals induced strong polymer-polymer interactions that resulted in the formation of microcrystals and the dissociation of the wax from the polymers. Together the results presented in this thesis suggest that fluorescence provides reliable information on the chemical composition and behaviour of polymeric oil additives, an information that was otherwise difficult to extract from traditional characterization methods.1 yea