Yusuf Yagci

Externally stimulated initiator systems for cationic polymerization

Abstract At present, there is growing interest in polymerizations initiated by external stimulation, such as photoirradiation, heating or high energy irradiation. Since many industrially important monomers can only be polymerized by a cationic mechanism, much effort has been made to develop systems that produce initiating cations upon external stimulation. In this article, the latest developments in externally stimulated systems for cationic polymerization are reviewed. The goal is, furthermore, to show differences as well as parallels between systems for different modes of external stimulation.

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.

Self-Curable Benzoxazine Functional Polybutadienes Synthesized by Click Chemistry

Novel side-chain benzoxazine functional polybutadiene (PB-benzoxazine) was synthesized by using click chemistry strategy. First, some of double bonds were brominated with Br2 in CCl4 and subsequently converted to azido groups by using NaN3 in DMF. Propargyl benzoxazine was prepared independently by a ring-closure reaction between p-propargyloxy aniline, paraformaldehyde and phenol. Finally, azidofunctionalized polybutadiene was coupled to propargyl benzoxazine with high efficiency by click chemistry. The spectral and thermal analysis confirmed the presence of benzoxazine functionality in the resulting polymer. It is shown that PB-benzoxazine undergoes thermally activated curing in the absence of any catalyst forming polybutadiene thermoset with high char yield.

Thioxanthone - ethylcarbazole as a soluble visible light photoinitiator for free radical and free radical promoted cationic polymerizations

Thioxanthone-ethylcarbazole (TX-EC), 7-ethylthiochromeno[2,3-b]carbazol-13(7H)-one, as a novel visible light absorbing one-component Type II photoinitiator with high solubility, was synthesized and characterized. Its ability to initiate free radical photopolymerization of methyl methacrylate (MMA) was demonstrated and compared with that of the parent thioxanthone-carbazole (TX-C) both in the presence and absence of a co-initiator. It is found that TX-EC is a more effective photoinitiator in all cases. The mechanism of initiating radical formation for free radical polymerization in the absence of an added co-initiator involves photoexcitation of TX-EC and hydrogen abstraction of triplet states of TX-EC from the ethyl group attached to the carbazole moiety. In the presence of triethyl amine, the corresponding hydrogen abstraction reaction occurs between a triplet photoinitiator and the amine compound. The possibility of visible light photoinitiation of free radical promoted cationic polymerization of several monomers, namely cyclohexene oxide (CHO), n-butyl vinylether (BVE), N-vinyl carbazole (NVC) and 3,4-epoxycyclohexyl-3′,4′-epoxycyclohexene carboxylate (EEC) using TX-EC and Ph2I+PF6− combination was also demonstrated.

Block copolymers of thiophene-capped Poly(methyl methacrylate) with pyrrole

Poly(methyl methacrylate) with a thiophene end group having narrow polydispersity was prepared by the Atom Transfer Radical Polymerization (ATRP) technique. Subsequently, electrically conducting block copolymers of thiophene-capped poly(methyl methacrylate) with pyrrole were synthesized by using p-toluene sulfonic acid and sodium dodecyl sulfate as the supporting electrolytes via constant potential electrolysis. Characterization of the block copolymers were performed by CV, FTIR, SEM, TGA, and DSC analyses. Electrical conductivities were evaluated by the four-probe technique.

Shining a light on an adaptable photoinitiator: advances in photopolymerizations initiated by thioxanthones

Photochemistry plays a central role in synthetic polymer research. Aromatic ketones, examples of which include benzophenone, thioxanthone, camphorquinone, among others, are renowned for their excellent optical characteristics and have been extensively utilized for photochemical induction of polymerization processes. Of particular interest is thioxanthone due to its adaptability for bearing different functionalities and its applications in various modes of photopolymerization, in which it accomplishes photoinitiation in conjunction with other co-initiator compounds; a behavior that is referred to as bi-molecular photoinitiation. In this paper, we review the photochemistry of thioxanthone-based systems and their use in different modes of photoinitiated polymerizations. Citing examples from the literature, the development of various photoinitiating systems based on thioxanthones along with an understanding of their mechanistic behavior has been elucidated previously.

Synthesis of ABC type miktoarm star copolymers by triple click chemistry

An ABC type miktoarm star copolymer possessing polystyrene (PS), poly(e-caprolactone) (PCL) and poly(ethylene glycol) (PEG) arms was synthesized by combining existing triple click chemistries, namely thiol–ene, copper catalyzed azide–alkyne cycloaddition (CuAAC) and Diels–Alder (DA) reactions. For this purpose, a core (1-(allyloxy)-3-azidopropan-2-yl (anthracen-9-ylmethyl) succinate) with allyl, azide and anthracene functionalities was synthesized in two steps with high yields. Then, polymers with corresponding clickable sites, namely ω-thiol polystyrene (PS-SH), α-alkyne poly(e-caprolactone) (alkyne-PCL) and ω-maleimide poly(ethylene glycol) (Me-PEG-MI), were independently prepared. As the first step of the grafting onto process, PS-SH was thiol–ene clicked onto the core to yield PS-N3-Ant. Finally, alkyne-PCL and Me-PEG-MI were bonded to PS-N3-Ant either in a sequential or a one-pot in situ manner using CuAAC and DA click reactions. All intermediates, related polymers at different stages and final PS-PCL-PEG miktoarm star copolymer were characterized by 1H NMR, FT-IR, and GPC analyses.

Immobilization of polyphenol oxidase in conducting copolymers and determination of phenolic compounds in wines with enzyme electrodes

Polyphenol oxidase (PPO) was immobilized in copolymers of thiophene functionalized menthyl monomer (MM) with pyrrole. Immobilization of enzyme was performed via entrapment in conducting copolymers during electrochemical polymerization of pyrrole. Maximum reaction rates, Michaelis-Menten constants and temperature, pH and operational stabilities of enzyme electrodes were investigated. Total amount of phenolic compounds in red wines of Turkey were analyzed by using these electrodes.