Date of Award

Fall 12-2015

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Polymers and High Performance Materials

Committee Chair

Sergei Nazarenko

Committee Chair Department

Polymers and High Performance Materials

Committee Member 2

Robert Lochhead

Committee Member 2 Department

Polymers and High Performance Materials

Committee Member 3

Robson Storey

Committee Member 3 Department

Polymers and High Performance Materials

Committee Member 4

James Rawlins

Committee Member 4 Department

Polymers and High Performance Materials

Committee Member 5

Derek Patton

Committee Member 5 Department

Polymers and High Performance Materials

Abstract

Dendritic architectures are echoed throughout nature. While the significance of these pervasive patterns is not entirely clear, connections between their structures and physical properties are fascinating to contemplate. Particular interest has been paid to a family of synthetically manufactured and commercially available dendritic polymers based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) as a monomer. Composed of two hydroxyls and a carboxyl group, bis-MPA based structures hydrogen bond (H-bond) profusely. Given the high concentration and unique spatial orientation of end-groups, as well as the multitude of carbonyl, ester, and ether interior H-bond acceptors, a set of distinct H-bond organizations may be observed for these dendritic systems. The purpose of this dissertation was to elucidate the H-bond organizations in relation to bulk thermal and free volume properties of bis-MPA based dendritic polymers, with an emphasis on developing a fundamental understanding of the extent to which randomly branched hyperbranched polymers (HBPs) of this type compare to perfectly branched dendrimers.

Chapter I of this dissertation provided a background of dendritic architectures, specifically those based on bis-MPA, relevant structure-property relationships, including those related to H-bonding, and a brief synopsis of molecular dynamics (MD) type computer simulations. In Chapter II, atomistic simulations of bis-MPA dendrimers and

HBPs allowed the visualization of the globular molecular shape and end-group distribution of these complicated architectures. Through synergistic efforts of experiments and computer simulations “chain-like clusters” of O-H∙∙∙O groups were found to pervade the bulk structure of both dendrimers and HBPs. Because these clusters bore remarkable similarity to analogous H-bond organizations in structural fluids such as water and hydrogen fluoride, it was speculated that the chain-like clusters may be responsible for specific favorable bulk physical properties of bis-MPA dendrimers. In Chapter III, the imperfect branching of the HBP was found to lead to a H-bond organization which was not prevalent in the perfectly branched analogous dendrimers, highlighting a fundamental structure-property difference between the two systems. The linear unit imperfections in the HBP were instrumental in forming a H-bond driven mesophase, which was composed of pseudo-hexagonally packed, parallel and straight, laterally H-bonded linear chain segments with cylindrical symmetry. The dynamics of mesophase ordering upon annealing were also revealed. In Chapter IV, the effect of H-bond ordering and generation number on the volumetric and thermodynamic parameters of bis-MPA based HBPs was addressed. Pressure-volume-temperature (PVT) properties were simulated and experimentally probed. The simulated bulk volumetric and thermodynamic properties were approximately similar to analogous experimental parameters, supporting that MD simulations can predict bulk properties of dendritic polymers. Thus, as the significance of dendritic architectures continues to be a mystery, the current understanding of the structure-property relationships of these fractal macromolecules has been improved through this dissertation work.

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