Date of Award

Fall 2019

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Polymer Science and Engineering

Committee Chair

Robson F. Storey

Committee Chair School

Polymer Science and Engineering

Committee Member 2

Sarah E. Morgan

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Yoan C. Simon

Committee Member 3 School

Polymer Science and Engineering

Committee Member 4

William L. Jarrett

Committee Member 4 School

Polymer Science and Engineering

Committee Member 5

Jeffrey S. Wiggins

Committee Member 5 School

Polymer Science and Engineering

Abstract

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.

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