Doctor of Philosophy, University of Akron, 2013, Polymer Science

The development of polymeric drug delivery devices began five decades ago, starting with hydrogels in 1960. After that, nano-sized drug carriers were developed to increase the efficiency of the drug uptake. This has been accomplished by encapsulating the drug in polymer carriers that increase the circulation time of the drug in the blood, preventing early adsorption, elimination and targeting the drug where it needs to be delivered. One of the most important strategies to increase the circulation time of nanocarriers is PEGylation, in which poly(ethylene glycol) coats the device to prevent premature elimination from the bloodstream due to protein attachment. The goal of this project is to compare the protein adsorption onto polymeric micelles that have either a cyclic or a linear architecture on the hydrophilic coating. We synthesized PEG-b-PCL amphiphilic diblock copolymers in which the poly(ethylene glycol) block is hydrophilic and the PCL block is hydrophobic. First, PEG macroinitiators were synthesized with either cyclic or linear architectures. The macroinitiators were then used for ring-opening polymerization of e-caprolactone. These diblock copolymers were self-assembled into micelles suspended in water by a co-solvent evaporation method. These two types of polymers (no end groups and end groups) allowed us to study the role of polymer architecture on protein adsorption and circulation time.

Committee: Coleen Pugh Dr. (Advisor); Matthew Becker Dr. (Committee Member); George Newkome Dr. (Committee Member); William Landis Dr. (Committee Member); Chrys Wesdemiotis Dr. (Committee Member) Subjects: Polymer Chemistry; Polymers

Doctor of Philosophy, University of Akron, 2007, Polymer Science

The main objective of the work presented in this thesis is to understand the surface and interface structure and dynamics of diblock copolymer brushes (DCBs). DCBs are stimuli-responsive materials and the surface properties of a DCB can be changed from those characteristic of one polymer block to those characteristic of the other one by treating the DCB with a solvent selective for one of its blocks. For this purpose, polystyrene-block-polyacrylate or polyacrylate-block-polystyrene brushes were synthesized using the “grafting from” technique in combination with atom transfer radical polymerization (ATRP). In the first part of this project the internal structure of DCBs after the synthesis and surface rearrangement were investigated using neutron reflectivity (NR) and grazing incidence small angle X-ray scattering (GISAXS). It was found that the internal brush structure depends strongly on the synthesis sequence of polymer blocks and the value of xN. For small values of xN (xN is smaller than 11), a model of two layers with an interfacial region of finite width provides a good description of the data. The interface width is found to be larger for DCBs which have the polymer block with the lower surface energy synthesized next to the substrate. A three layer model must be used to describe the structure of DCBs of larger xN values (xN is greater than 23) and of sufficiently asymmetric composition. The necessity of including a third layer is consistent with the presence of a lateral ordering of some type in the center of the brush, as evidenced by correlation peaks in the GISAXS data. The spacing of the in-plane ordering varies with the thickness of the poly(methyl acrylate) (PMA) block. After a DCB is treated with a selective solvent, Bragg rods appear in the GISAXS pattern. The appearance of Bragg rods indicates the formation of a new 2D structure which has a lateral spacing on the order of the total thickness of the brush. The Bragg rods disappear upon heating to 80 (open full item for complete abstract)

Committee: Mark Foster (Advisor) Subjects:

Doctor of Philosophy, University of Akron, 2006, Polymer Science

Single crystals of poly(methyl methacrylate)-b-polystyrene-b-poly(L-lactic acid) (PMMA-b-PS-b-PLLA) triblock copolymers with different compositions have been grown in dilute solution and utilized as ideal models for the study of structures and morphologies of tethered PS-PMMA diblock copolymer chains. With control of tethering density and tethering density distribution, the diblock copolymers are found to form switchable characteristic morphologies in selective solvent treatments. A novel “onion”-like structure has been observed for the first time due to the controllable and uniform tethering density. This switching behavior has been confirmed by surface enhanced Raman spectroscopic experiments. Two series of triblock copolymers with a crystalline block in the middle, polystyrene-b-poly(ethylene oxide)-b-poly(butene oxide) (PS-b-PEO-b-PBO) and polystyrene-b-poly(ethylene oxide)-b-poly(dimethyl siloxane) (PS-b-PEO-b-PDMS) have been synthesized. Scrolled single crystals have been found which were favored with increased tethering density. The scrolling direction was found to be along the (120) plane of the PEO single lamellar crystal. Based on the curvature of scrolling, strain energy can be calculated which corresponds to the unbalanced near surface stresses caused by tethered chains on opposite folding surfaces under a mechanic equilibrium.

Committee: Stephen Cheng (Advisor) Subjects: