İkili "Click" reaksiyonları ile poliüretan modifikasyonu

Polyurethanes (PU) discovered by Otto Bayer in 1937 and has gained grate importance since the discovery. PUs are employed in a broad range of uses and applications, including machinery, transport, furnishing, textiles, paper-making, packaging, adhesives, sealants and medicine. In addition, the outstanding mechanical properties and biocompatibility of the polyurethanes makes them some of the most promising synthetic biomaterials. PUs comprise three monomers: a diisocyanate, a macroglycol (which is an oligomeric monomer), which possess more complex chemical structures than other available polymers. By selecting the type of isocyanate and polyols, or combination of these groups, one can design the structure to obtain desired physical and chemical properties. Many different modification methods are used for modification of polyurethanes but among them click chemistry is the most versatile pathway for synthesis of polymeric structures. In 2001, Sharpless and coworkers introduced "click" chemistry, a new approach in organic synthesis that involves a collection of almost perfect chemical reactions. Nowadays there are several processes have been identified under this term in order to meet Sharpless's criteria. Among those selected reactions, copper(I)-catalyzed azidealkyne (CuAAC), active ester substitution reactions and Diels-Alder (DA) cycloaddition reactions have gained much interest among the chemists not only the synthetic ones but also the polymer chemists. CuAAC reaction is a virtually quantitative, very robust, insensitive, general, and orthogonal ligation reaction between organic azides and alkynes. When compared with Huisgen 1,3-dipolar cycloaddition reaction, the copper catalyzed reaction allows to proceed much faster under much milder conditions and produces only one isomer which is 1,4-regiosomer triazole. In fact, the discovery of Cu (I) as catalyst has a great importance which efficiently and regiospecifically combines terminal alkynes and azides under mild conditions. Diels-Alder (DA) reaction is one of the most common reactions used in organic chemistry, and invented by Otto Diels and Kurt Alder who received the Nobel Prize in 1950 for their discovery. The Diels-Alder reaction is a concerted [4π+2π] cycloaddition reaction of a conjugated diene and a dienophile to yield a 6-membered ring. This reaction is one of the most powerful tools used in the synthesis of important organic molecules in high yields. In addition to CuAAC and DA reactions, active esters are famous in the field of peptide synthesis in organic chemistry. This methodology has been much applied mainly to form peptide bonds under mild conditions in both liquid and solid phase synthesis. Many different active esters have been presented but among them perfluorophenyl esters gained great interest in polymer chemistry. These reactive groups can be transformed into amide groups by polymer analogous reaction with primary or secondary amines in a quantitative and simple way. In this study, different PUs were prepared with pendant functional groups suitable for click chemistry to modify PUs with highly efficient click reactions. After polymerization of hexamethylene diisocyanate with three different functional diols consisting alkyne, anthracene and perfluorophenyl ester functional groups PU- (anthracene-co-alkyne) and PU-(Anthracene-co-Alkyne-co-Perfluorophenyl) were obtained. PU-(Anthracene-co-Alkyne-co-Perfluorophenyl) was reacted with azide, maleimide and amine functional compounds using CuAAC, active ester substitution reaction and DA reaction respectively. PU-(anthracene-co-alkyne) first studied as model reactions with small molecules to determine CuAAC and DA reaction efficiency. Next, CuAAC and DA reaction were employed to obtain PU-g-(PEGPMMA) by reacting azide end functional polyethylene glycol and maleimide end functional poly(methyl methacrylate) respectively. The UV, NMR and GPC measurements revealed that CuAAC, Diels-Alder and active ester substitution reactions displayed an efficient and an alternative pathway for modification of PUs.