Mehmet Atilla Tasdelen

Diels–Alder “click” reactions: recent applications in polymer and material science

The “click” chemistry concept is based on utilizing rapid reactions which are efficient, versatile, and selective. Indeed, Diels–Alder (DA) reactions fulfill most of the requirements for the “click” chemistry concept. In this review, we discuss the recent reports concerned with the use of DA “click” reactions in the synthesis of various macromolecular architectures, bioconjugates and hybrid materials.

Photoinduced Controlled Radical Polymerization

Well-controlled radical polymerization of methyl methacrylate can be achieved by in situ photochemical generation of copper (I) complex from air-stable copper (II) species without using any reducing agent at room temperature. The living character of this polymerization was confirmed by both the linear tendency of molecular weight evolution with conversion and a chain extension experiment.

Sunlight induced atom transfer radical polymerization by using dimanganese decacarbonyl

A new photoredox catalyst system for atom transfer radical polymerization is developed on the basis of visible light photocatalysis using dimanganese decacarbonyl (Mn2(CO)10) that initiates and controls the polymerization at ambient temperature. The polymerization was performed by a Mn2(CO)10–alkyl halide system with visible- or sunlight in the presence of parts per million (ppm) copper catalysts. The photogenerated ˙Mn(CO)5 radicals are not only able to abstract halogen atoms from alkyl halides to generate carbon centered radicals but also reduce the CuIIBr2 to CuIBr directly, which was used as an activator in the Atom Transfer Radical Polymerization (ATRP) of vinyl monomers such as methyl methacrylate, methyl acrylate and styrene. The method was also used to synthesize graft copolymers from commercially available poly(vinyl chloride) without additional modification.

Photoinduced Atom Transfer Radical Polymerization Using Semiconductor Nanoparticles

Photoinduced atom transfer radical polymerization of methyl methacrylate initiated by in situ generation of copper (I) complex from higher oxidation state species using neat zinc oxide and iron-doped zinc oxide nanoparticles is investigated. The polymerizations proceed in a well-controlled manner under UV light at room temperature as evidenced by kinetic and light on-off experiments. The evolution of molecular weight with conversion shows good correlations between experimental and theoretical molecular weights, which confirmed good control over polymerization along with a narrow molecular weight distribution.

Photochemical Methods for the Preparation of Complex Linear and Cross-linked Macromolecular Structures

In this contribution, the current state of the art is summarized and an overview of photoinitiating systems for both radical and cationic polymerizations and their potential application in the preparation of complex linear and cross-linked macromolecular structures are described. Recent relevant studies have been devoted to developing novel free radical and cationic photoinitiators having spectroscopic sensitivity in the near-UV or visible range. Photoinitiated controlled radical polymerization methods leading to tailor-made polymers with predetermined structure and architecture are briefly presented. Several synthetic methodologies for the preparation of epoxy and (meth)acrylate based formulations containing clay or metal nanoparticles are also summarized. The nanoparticles are homogenously distributed in the network without macroscopic agglomeration. Applicability to both free radical and cationic systems is demonstrated.

POSS-based hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry

Abstract An efficient approach for the preparation of inorganic/organic hybrid thermosets via photoinduced copper-catalyzed azide–alkyne cycloaddition click chemistry is established. Highly cross-linked thermoset polymers have been practically obtained by this technique using multifunctional compounds, tri-alkyne (1,1,1-tris[4-(2-propynyloxy) phenyl]-ethane) with octakis-azido-POSS or tri-azide (3,3′-((2-((3-azido-2-hydroxypropoxy)methyl)-2-ethylpropane-1,3-diyl)bis(oxy))bis(1-azidopropan-2-ol)) in the presence of Cu(II)Br2/N,N,N′,N″,N‴-pentamethyldiethylenetriamine/2-dimethoxy-2-phenyl acetophenone. The homogeneously distributed POSS nanoparticles are clearly detected in the TEM micrographs; whereas the TGA analysis shows that the obtained hybrid thermosets are thermally stable up to 360 °C and begin to lose weight at higher temperatures with a char yield of 23–50% at 800 °C.

Orthogonal Synthesis of Block Copolymer via Photoinduced CuAAC and Ketene Chemistries

A novel route for the synthesis of poly(ethylene glycol)-b-polystyrene copolymer, starting from commercially available poly(ethylene glycol) methyl ether and azido terminated polystyrene prepared by atom transfer radical polymerization and subsequent nucleophilic substitution, is applied with simplicity and high efficiency. The combination of photoinduced copper (I)-catalyzed alkyne-azide cycloaddition (CuAAC) and ketene chemistry reactions proceeds either simultaneously or sequentially in a one-pot procedure under near-visible light irradiation. In both cases, excellent block copolymer formations are achieved, with an average molecular weight of around 7000 g mo1(-1) and a polydispersity index of 1.20.

CHAPTER 3:Controlled/Living Radical Polymerization in the Presence of Iniferters

Conventional free radical polymerization is limited in its inability to control polymer properties such as average molecular weight, molecular weight distribution and end-group functionality. New processes are being developed, in which the free radical propagating chain is reversibly terminated, allowing the free radical polymerization to behave in a controlled fashion. The first step in the development of controlled/living radical polymerization (C/LRP) dates back to the early 1980s when it was found that the use of iniferter (namely, agents that initiate, transfer, and terminate) systems exhibited a degree of livingness. Iniferter methodology can be used to polymerize most vinyl monomers under mild reaction conditions via thermal, redox and photochemical activations. The present chapter reviews recent advances in the use of iniferters in the C/LRP, their benefits, and current limitations. Applications of iniferters for the synthesis of telechelic polymers, complex macromolecular architectures and modification of surfaces are also discussed.

Synthesis of self-curable polysulfone containing pendant benzoxazine units via CuAAC click chemistry

Abstract Synthesis, characterization, and properties of new thermally curable polysulfone containing benzoxazine moieties in the side chain were investigated. First, chloromethylation and subsequent azidation processes were performed to form polysulfone containing pendant clickable azide groups. Independently, antagonist 3,4-dihydro-3-(prop-2-ynyl)-2H-benzoxazine was prepared by using paraformaldehyde, phenol and propargylamine. The following copper(I) catalyzed azide-alkyne cycloaddition click reaction was applied to obtain self-curable polysulfone with pendant benzoxazine units. The polymer and intermediates at various stages were characterized by 1H-NMR, 13C-NMR and FT-IR spectroscopies. The thermal properties and curing behavior of final polymer were investigated by differential scanning calorimetry and thermal gravimetric analysis. Compared to the neat polysulfone, the obtained polymers exhibited thermally more stable polymers.

In situ preparation of thermoset/clay nanocomposites via thiol-epoxy click chemistry

A series of thermoset/clay nanocomposites are prepared by thiol-epoxy click reaction using commercially available starting compounds at ambient conditions in very good yields. The incorporation and exfoliation of clay nanolayers in the thermoset matrix are confirmed by FT-IR, XRD and TEM analyses. The influence of clay loadings on the thermal and mechanical analyses is investigated and all nanocomposites exhibit improved properties than that of the pristine thermoset. The nanocomposite containing 1% montmorillonite by weight has the most improved mechanical properties due to its highly exfoliated structure resulting in efficient interactions between clay and polymer matrix. A further increase of the clay loading results in the aggregation of clay plates to form intercalated structures leading to deteriorated thermal and mechanical properties of nanocomposites.