Doctoral Dissertations

Date of Award

8-2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Chemistry

Major Professor

Mark D. Dadmun

Committee Members

Jimmy W. Mays, Charles S. Feigerle, Thomas A. Zawodzinski

Abstract

Methods are presented for modifying polymeric material surfaces using: 1) selective surface segregation in binary branched/linear polymer blends, and 2) surface functionalization with polymer brushes. Using neutron reflectivity, elastic recoil detection, and other complementary techniques, the aim was to identify structure-property relationships and provide fundamental insight into the time evolution and formation of surfaces and interfaces in these materials.

In blends of poly(styrene) (PS) HyperMacs and DendriMacs in a linear deuterated PS (d-PS) matrix, smaller hyperbranched additives (<1E6 g/mol) move slower than their linear analogues. Larger (>1E6 g/mol) and less flexible hyperbranched additives with smaller fractal dimensions move faster than their linear analogues, suggesting that they are less entangled with the linear matrix. In blends of poly(methyl methacrylate)-random-poly(ethylene glycol) methacrylate (P(MMA-r-PEGMA)) comb copolymers in a linear d-PMMA matrix, it was observed that while increasing the branch density of the comb increases the amount of surface excess, these combs are an order of magnitude slower than a linear analog. This was attributed to an increased number of branch points which can dominate the friction in a Reptating backbone. Using the Kramer-Jones theory and the Slow Mode theory, mutual and tracer diffusion coefficients for each blend were extracted.

A 3-dimensional inimer-embedded cross-linked system from which d-PS was grown was investigated. d-PS growth is initiated both at the surface and within the bulk of these materials. Increasing the amount of inimer increased d-PS growth throughout the entire layer. The surface growth of d-PS is more efficient at low concentrations of inimer, while higher concentrations resulted in the growth of d-PS throughout the bulk of the layer (due to differences in the amount of swelling in the network). A second polymer brush system was investigated in which functionalized poly(cyclohexadiene) (PCHD) brushes were attached to a solid substrate using a grafting-to approach and were subsequently aromatized to poly(paraphenylene) (PPP) in-situ. PPP, a conducting polymer with high chemical and thermal stability, is insoluble at high molecular weight. The approach utilized in this study was designed to overcome this challenge by focusing on the synthesis, assembly, and aromatization of functionalized PCHD brushes attached to a solid substrate.

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