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The possibility to design composites with superior properties by incorporation of nanoscale reinforcing material still remains to be fulfilled. In the current study, bisphenol A diglycidyl ether-based epoxy resin has been successfully modified with polyhedral oligomeric silsesquioxane (POSS) nanoparticles to give epoxy/POSS nanocomposites. Carbon fiber reinforced composites with different fiber orientations are processed via vacuum bagging technique using this composite as the matrix. Scanning electron microscopy indicated that POSS nanofillers homogeneously distributed in the matrix. As proved by the tensile, flexural, and interlaminar shear strength tests, the inclusion of POSS nanofillers in the polymer matrix has promoted significant improvements in the mechanical properties of the carbon fiber reinforced POSS/epoxy hybrid composites compared to the analogues with neat epoxy matrix. Thus, hybrid composites with exceptional properties are obtained via a straightforward modification in the matrix and a novel paradigm without using any expensive compound has been added to the library of nanocomposite formulations.

Dimanganese decacarbonyl (Mn2(CO)10) and alkyl halide combination has unique visible light radical generating property which is useful in the fabrication of many complex macromolecular structures. Herein, we present a generic simple and rapid synthetic approach for the preparation amphiphilic hyperbranched macromolecular structures with controlled branching density and hydrophilicity. The method is based on the visible light induced self-condensing vinyl copolymerization of methyl methacrylate (MMA), 2-(2-bromoisobutryloxy)ethyl methacrylate (BIBEM) and poly(ethylene glycol) methyl ether methacrylate as monomer, inimer and hydrophilic comonomer, respectively, in the presence of Mn2(CO)10. The resulting polymers possess both hydrophobic and hydrophilic sequences offering many potential bio applications such as controlled drug delivery and release. Moreover, the resulting polymers contain also unreacted bromide groups in the final structure which allow postfunctionalization through copper(I)-catalyzed alkyne-azide cycloaddition “click” reactions.

In the present study, homogeneous mixtures of halloysite nanotubes (HNTs)-epoxy nanocomposites are prepared through chemical treatments. Naturally present halloysite nanotubes (HNT) are primarily modified by 3-(glycidyloxypropyl)trimethoxysilane and subsequently utilized as nanofillers in a mixture of bisphenol A diglycidyl ether and trimethylolpropane triglycidyl ether by varying weight % of modified HNT from 0 to 8%. Photoinitiated cationic crosslinking polymerization of this mixture facilitates the in-situ preparation of HNT/thermoset nanocomposites at room temperature. The covalent attachment of HNT in the thermoset matrix has been confirmed by monitoring the characteristic signals of the mixture, nanofiller, neat thermoset, and final nanocomposite using fourier transformed infrared (FT-IR) spectroscopy. Furthermore, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses proved the existence and distribution of HNT in the thermoset nanocomposites. Indeed, a combination of agglomerated/non-agglomerated HNTs in the thermoset matrix is also determined. On the other hand, mechanical properties of nanocomposites are significantly improved with increase in HNT loading up to 4% ratio. Adding 4% of modified HNT into epoxy increased its tensile strength and elasticity modulus by 6.9 times and 2.3 times than the corresponding neat epoxy thermoset, respectively, without scarifying thermal stability. Therefore, the HNT/epoxy thermoset nanocomposites are suitable candidates for various applications as an alternative of expensive carbon nanotube containing analogues.

A straightforward transformation protocol combining two distinct living polymerization methods for the controlled synthesis of block copolymers is described. In the first step, bromo-terminated poly(methyl methacrylate) is prepared by atom transfer radical polymerization (ATRP). Then, a bromide end group is substituted with a triphenylmethyl (trityl) functionality under visible light irradiation using dimanganese decacarbonyl (Mn2 (CO)10 ) photochemistry. The resulting polymers with trityl end groups are used as macroiniferter for the polymerization of styrene and tert-butyl acrylate (tBA) to yield desired block copolymers with narrow molecular weight distribution. Moreover, the amphiphilic copolymers with acrylic acid functionalities are obtained by the hydrolyzation of poly(tert-butyl acrylate) containing block copolymers with trifluoroacetic acid.

Linear poly(hydroxyethyl methacrylate-co-methyl methacrylate) P(HEMA-co-MMA) and poly(dimehylaminoethyl methacrylate-co-methyl methacrylate) P(DMAEMA-co-MMA) and their corresponding hyperbranched copolymers were synthesized by conventional photoinitiated free radical polymerization and self-condensing vinyl polymerization (SCVP) using Type I and Type II photoinitiators, respectively. Then, the polymers were processed by electrospraying in N, N-dimethylformamide. The surface of the resulting electrospray coatings was examined by SEM, XPS, and WCA then compared with those prepared by drop casting. Regardless of the structural nature of the polymers, electrospraying allows the preparation of rough surface that shows more hydrophobic behavior. Electrospray coatings with linear and hyperbranched copolymers exhibited WCA as ∼150° and ∼130°, respectively, indicating that branching reduces the WCA., Istanbul Technical University; Scientific and Technological Research Council of Turkey (TUBITAK)

The synthesis of polyethylene-graft-polystyrene copolymers by a multistep “grafting from” approach is described. In the first step, a bromo-functional polyethylene (PE-Br) was synthesized via ring-opening metathesis polymerization (ROMP) of cis-cyclooctene (COE) and quantitative hydrobromination. Subsequent irradiation of PE-Br under visible light in the presence of dimanganese decacarbonyl (Mn2(CO)10) and 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) resulted in the formation of TEMPO-substituted polyethylene (PE-TEMPO). Polystyrene (PS) chains were then grown via nitroxide mediated radical polymerization (NMRP) from the PE-TEMPO precursor to give desired PE-g-PS copolymers in a controlled manner. The intermediates at each step and final graft copolymers were characterized by 1H NMR, FT-IR, GPC, and DSC analyses.

A facile strategy for synthesizing block copolymers by the combination of two different living polymerization techniques, namely, photoinduced radical oxidation/addition/deactivation (PROAD) and iniferter processes is described. In the first step, PROAD polymerization of isobutyl vinyl ether using bromotriphenylmethane, dimanganese decacarbonyl (Mn2 (CO)10 ), and diphenyliodonium bromide (Ph2 I+ Br- ) is carried out to yield polymers with triphenylmethyl (trityl) end groups. These prepolymers are used as macroiniferters in thermally induced free radical polymerization of vinyl monomers such as methyl methacrylate, tert-butyl acrylate, and styrene, resulting in the formation of corresponding block copolymers free from homopolymers. The precursor polymer and final block copolymers are characterized by 1 H NMR, FT-IR, GPC, and DSC analyses.

Hyperbranched polymers (HBPs), a unique class of dendritic macromolecules, have received continuous interest from macromolecular scientists due to their inherent properties such as high level of functional terminal units, high solubility, and low viscosity. Despite enormous efforts devoted to the synthesis of HBPs by traditional methods such as single and double monomer strategies involving step-growth polymerization and self-condensing vinyl polymerization (SCVP) processes, there have been limited attempts to employ light-induced processes. Photochemical methods, however, exhibit distinct advantages not characteristically disclosed by traditional ones, such as spatial and temporal control, low energy, and site-specific activation. This review, after a brief summary of the conventional methods, presents the unique features and the key functionalities of the inimers for photoinduced SCVP and strategies for preparing HBPs.

A novel polymerization mechanism transformation strategy, combining ring-opening metathesis polymerization (ROMP) and visible light induced cationic polymerization, is successfully applied for the synthesis of polyethylene-graft-poly(cyclohexene oxide) (PE-g-PCHO). First, cis-cyclooctene (COE) was polymerized via ROMP in the presence of a chain transfer agent and quantitatively hydrobrominated to give bromo functional polyethylene (PE-Br). Subsequent irradiation of PE-Br in the visible range using dimanganese decacarbonyl (Mn-2(CO)(10)) and diphenyl iodonium hexafluorophosphate (Ph2I+PF6) as radical generator and oxidant, respectively, initiated cationic polymerization of cyclohexene oxide (CHO) resulting in the formation of PE-g-PCHO. The effect of irradiation time and Mn-2(CO)(10) concentration on the grafting density and efficiency was evaluated. Both the precursor polymers and the corresponding graft copolymers were characterized by H-1 NMR and Fourier transform infrared (FT-IR) spectroscopy, gel-permeation chromatography (GPC), and differential scanning calorimetric (DSC) analyses.

A simple approach for the preparation of a clickable poly(ethylene glycol)-based hydrogel as a polymeric support for protein immobilization via photoinitiated free radical polymerization of poly(ethylene glycol) diacrylate and propargyl acrylate is established. Bioconjugation to the obtained gels was achieved by azide–alkyne click reaction with azido-functionalized anti-immunoglobulin G (anti-IgG) and anti-His tag antibodies. Evaluation of the affinities of the PEG hydrogels to the corresponding substrates (IgG and His-tagged YFP, respectively) indicates their specific binding capability.

A facile synthesis method for the preparation of clickable hydrogels and linear polymers is described. The strategy pertains to the photochemical generation of initiating radicals by hydrogen abstraction of excited camphorquinone from acetylenic alcohol followed by free radical polymerization. For hydrogels, poly(ethylene glycol) methyl ether methacrylate and poly(ethylene glycol) diacrylate were used in the system as monomer and crosslinker, respectively. Fluorescent pyrene groups were anchored onto the hydrogels through copper-catalyzed Huisgen 1,3-dipolar azide/alkyne click reaction by using 2-azidomethyl pyrene as evidenced by Fourier transform infrared and fluorescence spectroscopy. The applicability of the method for macromolecular synthesis is also demonstrated. For this purpose, poly(methyl methacrylate) with alkyne terminal groups was prepared by photoinitiated free radical polymerization of methyl methacrylate using camphorquinone and 3-(trimethylsilyl)propargyl alcohol as sensitizer and hydrogen donor, respectively. After deprotection, the click reaction with azido polystyrene obtained by atom transfer radical polymerization followed by azidation resulted in the formation of polystyrene-b-poly(methyl methacrylate). The intermediates at various stages and the final block copolymer were characterized by spectral analysis and gel permeation chromatography. © 2014 Society of Chemical Industry

The recently developed photoinitiated atom transfer radical polymerization has been implemented in the inverse microemulsion polymerization of oligo(ethylene glycol) monomethyl ether methacrylate. Two different mechanisms including a simultaneous reverse and normal initiated ATRP and a combination of activators generated by electron transfer and initiators for continuous activator regeneration ATRP are investigated under UV light. The effects of various reaction parameters on the resulting particles have been systematically investigated, and it has been demonstrated that the particle size can be tuned based on UV light, initial stoichiometry, and aqueous phase fraction. The formed particles contained well-defined water-soluble polymers with relatively narrow molecular weight distribution (M-w/M-n < 1.4).

Visible light induced self-condensing vinyl polymerization is explored using 2-bromoethyl methacrylate (2-BEMA) and methyl methacrylate (MMA) as inimer and comonomer, respectively, in the presence of dimanganese decacarbonyl (Mn2(CO)10) for the preparation of hyperbranched polymers. Upon photoexcitation in the visible range, Mn2(CO)10 undergoes irreversible decomposition leading to the formation of initiating radicals through bromine abstraction from 2-BEMA. Depending on the concentrations of 2-BEMA and Mn2(CO)10 and irradiation time, hyperbranched polymers with different branching density and cross-linked polymers were formed. The resulting polymers possess unreacted bromide groups in the structure which allow postfunctionalization through visible light photopolymerization and Cu(I)-catalyzed click reactions.

Polyethylene-graft-poly(tert-butylacrylate) (PE-g-PtBA) copolymers were prepared by using a combination of ring-opening metathesis polymerization (ROMP), hydrobromination, and visible light-induced free radical polymerization. First, cis-cyclooctene was polymerized via ROMP in the presence of a chain transfer agent and quantitatively hydrobrominated. Poly(tert-butyl acrylate) (PtBA) chains were then grown via a grafting from approach from the Br-substituted linear poly(ethylene) (PE) backbone using dimanganese decacarbonyl (Mn2(CO)10) under visible light. The effect of Mn2(CO)10 concentration and irradiation time on the grafting density and efficiency was evaluated. The tert-butyl acrylate (tBA) esters of the graft copolymers were hydrolyzed into acrylic acid functionalities by acidolysis to obtain hydrophilic polyolefins. The precursor polymer, graft copolymer, and hydrolyzed polymer were characterized by 1H and 13C NMR, Fourier transform infrared, atomic force microscopy, and contact angle measurements.

Visible light-induced reverse and simultaneous reverse and normal initiation (SR&NI) atom transfer radical polymerizations of vinyl monomers are examined using various dyes and type I photoinitiators. The effect of photoinitiator types on the control of molecular weight and distribution is described. In both dye and type I photoinitiator sensitized SR&NI ATRP systems, the molecular weights increase linearly with conversion. However, the experimental molecular weights are considerably higher than the theoretical values and the polymers show broad-molecular-weight distributions ranging from 1.28 to 1.60 in the dye-sensitized SR&NI ATRP. However, the polymers obtained by SR&NI ATRP using type I photoinitiator system had molecular weight values close to the theoretical ones and very narrow-molecular-weight distributions ranging from 1.11–1.18.

Type II photoinitiated self-condensing vinyl polymerization for the preparation of hyperbranched polymers is explored using 2-hydroxyethyl methacrylate (HEMA) or 2-(dimethylamino) ethyl methacrylate (DMAEMA), and methyl methacrylate as hydrogen donating inimers and comonomer, respectively, in the presence of benzophenone and camphorquinone under UV and visible light. Upon irradiation at the corresponding wavelength, the excited photoinitiator abstracts hydrogen from HEMA or DMAEMA leading to the formation of initiating radicals. Depending on the concentration of inimers, type of the photoinitiator, and irradiation time, hyperbranched polymers with different branching densities and cross-linked polymers are formed.

Side chain modification of polyolefins applying a copper-mediated “click chemistry” strategy is described. First, a bromo-functionalized polyethylene (PE-Br) are synthesized via ring-opening metathesis polymerization of cis-cyclooctene followed by quantitative hydrobromination. Subsequently, the bromide moieties of the functional PE-based polymer are converted into azide groups via simple nucleophilic substitution. Success of the click reaction is demonstrated by using low molar mass and polymeric alkyne functional click components, namely pyrene alkyne and polystyrene alkyne, respectively. The intermediates at various stages and final polymers are characterized by 1H NMR, Fourier transform infrared, Gel permeation chromatography, and differential scanning calorimetry analysis.

Lightly branched, hyperbranched and cross-linked polymers with clickable sites were synthesized via a modified version of self-condensing photoinitiated copolymerization of methyl acrylate (MA) with propargyl acrylate (PA). The method is based on the use of a PA monomer containing two polymerizable groups, namely acrylate and propargyl groups with different reactivities in photoinitiated free radical copolymerization with MA.