Surface chemistry of poly(p-xylylene) and nylon
The interaction of a material with its surroundings occurs at the material-environment interface, therefore, the chemical and physical characteristics of the material's surface plays a fundamental role in determining its properties, such as its biocompatibility, adhesion, and wettability, and ultimately, its technological applicability. This dissertation discusses aspects of the chemical surface modification of two polymers, poly(p-xylylene) and nylon.
Chapter 2 focuses on the synthesis and wet-chemistry surface modification of poly(p-xylylene) (PPX) thin films. A series of electrophilic aromatic substitutions were studied including chlorosulfonation, chloroamidomethylation, and Friedel-Crafts catalyzed reactions. It was found that the yields and surface selectivity of the reactions studied were highly dependent on the interaction of the polymer with the reaction medium.
Chapter 3 describes the use of vapor deposition polymerization in template-assisted synthesis. Poly(p-xylylene) nanotubes were synthesized by template assisted methods using porous aluminum oxide membranes as the templating material. The pore diameter showed a linear dependence with respect to the deposition time. FESEM analysis showed that PPX was deposited along the pores of the membranes. Exposure of the membranes to a reactive solution resulted in chemical functionalization of the inner walls of the nanotubes, confirmed by XPS.
Chapter 4 discusses the chemical reduction of nylon film surfaces by reaction with a borane-tetrahydrofuran complex. It was observed that, while the reaction occurs in high yields, its surface-confinement is highly dependent on the segmental mobility of the polymer. The amine-rich surfaces were further used as templates for the synthesis of composite films by electrostatic adsorption of polyanions.
Chapter 5 deals with the synthesis of linear polyalkyleneimines of different hydrocarbon lengths by the surface-mediated reduction of nylons. These polyalkyleneimines were further used as compatibilizers for the melt intercalation of montmorillonite clays, modified and unmodified, with polypropylene. The polyamines were found to interact favorably with the clays, leading to intercalated and exfoliated systems. The determining factor in controlling the degree of dispersion of the clays, was the enthalpic interaction between the clay and the compatibilizer.