Synthesis and chracterization of graft copolymers by photo-"click" (CuAAC) chemistry

Graft copolymers belong to the general class of segmented copolymers and generally consist of a linear backbone of one composition and randomly distributed branches of a different composition. Well-defined graft copolymers are most frequently prepared by either i) a "grafting through" or ii) a "grafting from" and ii) macromonomer techniques. Traditionally, graft copolymers have been prepared by ionic polymerizations. However, these techniques suffer from rigorous synthetic conditions and incompability wide range of monomer units. The combination of controlled radical polymerization and "Click" chemistry reactions overcomes these problems and allows the synthesis of well-defined graft block copolymers under mild conditions. "Click" chemistry describes a class of chemical reactions that are easy to perform, give rise to their intended products in very high yields with little or no byproducts, work well under many conditions, and are unaffected by the nature of the groups being connected to each other. The most prominent example of click chemistry reaction is based on the well-established copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition (CuAAC) reaction between azides and terminal alkynes, discovered by the groups of Sharpless and Meldal. The CuAAC click reaction has received considerable attention as powerful modular synthesis approach, which has found numerous applications in organic chemistry, supramolecular chemistry, drug discovery, bioconjugation and materials science.Light-induced reactions offer the possibility of both spatial and temporal control over the reaction, which are not available in thermal conjugation-reactions. In recent years, photoinduced thiol-ene/thiol-yne coupling, photoinduced 1,3-dipolar cycloaddition reaction of alkenes and nitrile imines, "strain promoted" cycloaddition reaction of the photochemically generated cycloalkynes and azides photoinduced ester formation reaction of benzodioxinones with alcohols and photoinduced Diels-Alder reactions have been developed. In this thesis, firstly, chlorine groups of commercially available poly(vinyl chloride) or polystyrene-random-poly(chloromethyl styrene), which was obtained by nitroxide mediated radical polymerization, were converted to azide groups by substitution reactions with sodium azide. On the other hand, alkyne end-functional poly(epsilon caprolactone) was synthesized by ring-opening polymerization using propargyl alcohol/tin(II) 2-ethylhexanoate as initiator. After, the photo CuAAC "Click" reaction of azide and alkyne functional polymers were conducted under UV light irradiation to give corresponding graft copolymers. The structures of obtained graft copolymers were characterized by spectroscopic (FT-IR and NMR), chromatographic (GPC) and thermal (DSC) analyses.