Synthesis and chracterization of graft copolymers by photo "click" chemistry

A star polymer consists of several linear polymer chains connected at one central core is one of the simplest form of branched topologies. The presence of a central core in these macromolecules has lead to new, often improved characteristics, compared with their linear polymer analogs. The main feature of star polymers differing them from the linear analogues of identical molar masses, is their compact structure (smaller hydrodynamic volume and radius of gyration, and therefore lower viscosity) and the multiple functionality. This generates several potential applications for star polymers, including drug delivery, cosmetics, coatings, membrane, or lithography.Synthetic strategies for the construction of star polymers can be divided into three main categories according to their formation sequence of core and arms; (i) "core-first"; (ii) "arm-first"; and (iii) "coupling onto". Each of these approaches has associated advantages and disadvantages. 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, "strainpromoted" cycloaddition reaction of the photochemically generated cycloalkynes azides photoinduced ester formation reaction of benzodioxinones with alcohols and photoinduced Diels-Alder reactions have been developed. Although thiolene/ thiol-yne reactions can proceed extremely rapidly yielding products quantitatively under facile conditions (i.e., at ambient temperature and humidity under an air atmosphere), the simultaneous reactions of the photochemically formed primary radicals with enes reduce the click efficiency. In the other methods such as photoinduced acylation reactions using benzodioxinones, the preparation and purification of click reagents cumbersome and result in low product yields. In this thesis, synthesis and characterization of star copolymers through the combination of light-induced CuAAC "Click" chemistry and atom transfer radical polymerization (ATRP) has been investigated. For this purpose, the linear arms of the star polymers are synthesized by ATRP and nucleophilic substitution reactions first followed by the light-induced click reactions between arms containing a reactive chain end group and a multifunctional coupling agent. Spectroscopic and chromatographic investigations revealed that successful star polymers have been achieved by this technique.