Surface Modification and Characterization of Polymeric Materials for Targeted Functionality

We have investigated the surface modification of polymeric materials as a viable means by which to create novel functional surfaces for use in a wide range of (nano)technologies, including the development of nanocomposites.;Improvement of the barrier properties of rPET is the overarching theme of this project. It is known that inorganic fillers introduced into a polymer matrix tend to decrease gas permeation by increasing the diffusive path length of penetrant species through the material. Nanoclays as filler materials are ideal for this purpose because of the high aspect ratio of the clay platelets. Therefore, we have sought to generate rPET/clay nanocomposites by two different protocols in this study: attachment of natural clay platelets on functionalized rPET surface, and mechanical alloying of rPET flakes with natural clay platelets.;We have shown that PET surfaces can be chemically modified while avoiding chemical degradation. Specifically, we find that brief exposure of PET substrates to ultraviolet/ozone (UVO) generates a large surface concentration of hydrophilic moieties.;Chemical surface modification routes have also been explored due to the irregular and 3D nature of rough rPET flakes. Polyethyleneimine (PEI), as "molecular glue", increases the adsorption of clay platelets on modified rPET surface. Subsequent characterization reveals that the presence of PEI molecules permits adsorption of 1-2 clay platelets/layer on the modified rPET surface. Extrusion of these surface-modified materials yields polymer/clay nanocomposites, but the high melting point of PET causes considerable degradation under non-optimized conditions. Hence, we have substituted rPET with a low melting poly(ethylene- co-octene) to perform PEI and clay adsorption multiple times and thus adjust the concentration of clay platelets in the polymer matrix. The presence of clay platelets results in a decrease in O2 and CO 2 permeabilities, which compares favorably with calculations from the Neilsen model. In addition, the thermal stability of the nanocomposites increases with increasing clay loading due to the presence of the inorganic platelets.;Electrospun PET fiber surfaces have also been chemically functionalized with polymer brushes composed of poly(N-isopropyl acrylamide) (PNIPAAm), poly(dimethylaminoethyl methacrylate) (PDMAEMA) and poly(hydroxyethyl methacrylate) (PHEMA) via surface-initiated polymerization. These fibers can be used as functional filters to 1) capture metal salts or cyanide ions from water, 2) prepare antibacterial or antifouling fibers, and 3) produce fibers responsive to temperature or pH.;We have also investigated the formation of rPET/clay nanocomposites via mechanical alloying by using high-energy ball milling as an alternative route to melt processing. Solid-state mechanical alloying was conducted using natural clay and rPET at ambient temperature. Specifically, polymer and clay powders were mixed in a steel vial in the presence of steel balls designed to induce considerable and repeated shear, fracture and welding and thus exfoliate the clay platelets in the rPET matrix. The molecular weight of mechanically milled rPET and virgin-PET is found to decrease with increasing milling time, reaching ≈45% of their original values after 16 h of milling. Characterization of the resulting nanocomposites by x-ray diffractometry and transmission electron microscopy confirm exfoliation of clay platelets irregardless of milling time.;The development of a universal polymer coating has been achieved by chemically coupling trichlorosilane (TCS) to the vinyl groups of poly(vinylmethyl siloxane) (PVMS) via hydrosilylation. The resultant PVMS-TCS coating can be deposited as a functional organic layer on a variety of substrates ranging from hydrophobic to hydrophilic. Spin-coating PVMS-TCS onto a substrate yields a uniform coating layer and exposing the coating to minute amounts of moisture generates a large density of surface-bound hydroxyl groups. Moreover, treating the PVMS-TCS substrates with UVO further increases the density of hydroxyl groups on the surface. The elastic modulus of the coating can be regulated by adjusting the TCS concentration. Several case studies demonstrating the remarkable properties of these PVMS-TCS functional coatings are presented.;Decreasing supplies of fresh water and increasing population necessitate the development of water cleaning technologies that would expedite the removal of pollutants. To assist water purification processes, we have synthesized functionalized macromolecules that contribute to decontamination by scavenging detrimental chemicals. Epitomizing this role, the thioimide unit enables chemical flexibility that facilitates reversible catch-release of the ions on the basis of subtle reduction-oxidation environmental changes. Chemical tunability of the thioimide moiety enables synthesis of thioimide-based monomers and post-polymerization modification agents. Two distinct synthetic pathways, polymerization and post-polymerization modification, have been explored, leading to functional thioimide-based macromolecules. The presence of thioimide units on macromolecular chains decreases the concentration of cyanide ions in water from 24 to 3 ppm in less than 1 h.