Core-shell Inverse Amphiphilic Molecular Terpolymer Bottlebrushes Towards Lubrication and Microelectronic Applications

Abstract

Understanding of structure-function relationships is of vital importance to produce optimum materials for progression in the microelectronics and tribological fields. This dissertation focuses on the fundamental studies to develop core-shell amphiphilic bottlebrush polymers towards their potentials as lubricant and surface neutralizing additives. Well-defined core-shell amphiphilic bottlebrush nanostructures were produced through the synthetic methodologies of controlled radical reversible addition-fragmentation chain-transfer polymerization, ring-opening metathesis polymerization, and simple and facile chemical modification. The impact of the chemical composition of the shell on the intramolecular conformations and morphologies of core-shell amphiphilic bottlebrush polymers was explored through the comparison of two bottlebrush polymers having the same hydrophilic poly(acrylic acid) core with differing shell chemistries. Poly(norbornenyl-graft-[[poly(acrylic acid)]-block-[polystyrene]]) (PNB-g-[[PAA]-b-[PS]]) and poly(norbornenyl-graft-[[poly(acrylic acid)]-block-[poly(n-hexyl acrylate)]]) (PNB-g-[[PAA]-b-[PHA]]) were synthesized. The unimolecular structures resulted in either spherical/collapsed or an extended cylindrical/worm-like morphologies visualized by atomic force microscopy (AFM) and transmission electron microscopy (TEM). Coarse-grain simulations provided further details, demonstrating qualitative agreement with the experimental data, and corroborated the bottlebrush morphological structures and conformations were dependent upon combinations of intra- and intermolecular polymer-polymer and polymer-solvent interactions. The insights to the molecular conformations and resulting elongated morphologies of the core-shell inverse amphiphilic molecular bottlebrush terpolymers were applied to investigate the macromolecules as potential lubricant additives. The lowest average in-situ coefficient of friction (COF) (0.2) and frictional force (10 mN) was achieved by the core-shell amphiphilic bottlebrush polymer additive with an alkylated-based shell at a 0.5-1.0 wt.% in dodecanes and an applied normal force of 50 mN. A 75% decrease in the in-situ COF compared to the bare substrate was observed. Overall, core-shell amphiphilic bottlebrush terpolymers outperformed their linear block copolymers counterparts as at lowering the COF. Finally, linear block copolymers with high Flory-Huggins parameter, Ⲭ, between the chemical compositions of the polymeric blocks, potential smectic physicochemical properties, or unique properties from fluorine-containing polymers were explored as materials towards lithographic molds. The difference in intermolecular and interfacial interactions provided varying domain microphase segregation and helped identify potential block copolymers as polymer matrices. Formation of lamellar domains with random orientation could benefit from core-shell bottlebrush terpolymer additives for formation of clear lamellar domains with controlled and organized anisotropic orientations for lithographic applications. This work provided vital information for the rational design of core-shell amphiphilic bottlebrush terpolymers with varying chemistries and their resulting extended or collapsed structures through the combination of experimental and computational studies and their potential as additives in the microelectronic and tribological fields.