Polymer Institute of the Slovak Academy of Sciences

ADVERTISEMENT RETURN TO ISSUEPREVReviewNEXTStrategies to Reduce Oxygen Inhibition in Photoinduced PolymerizationSamuel Clark Ligon†, Branislav Husár†‡, Harald Wutzel†, Richard Holman§, and Robert Liska*†View Author Information† Institute of Applied Synthetic Chemistry, Vienna University of Technology, Getreidemarkt 9/163/MC, A-1060 Vienna, Austria‡ Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava 45, Slovakia§ The Paint Research Association, 14 Castle Mews, High Street, TW12 2NP Hampton, United Kingdom*E-mail: [email protected]Cite this: Chem. Rev. 2014, 114, 1, 557–589Publication Date (Web):October 1, 2013Publication History Received9 January 2013Published online1 October 2013Published inissue 8 January 2014https://pubs.acs.org/doi/10.1021/cr3005197https://doi.org/10.1021/cr3005197review-articleACS PublicationsCopyright © 2013 American Chemical SocietyRequest reuse permissionsArticle Views15316Altmetric-Citations523LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-AlertscloseSupporting Info (1)»Supporting Information Supporting Information SUBJECTS:Inhibition,Monomers,Organic compounds,Oxygen,Polymerization Get e-Alerts

Well-controlled polymerization of methyl methacrylate at 35 °C was achieved by photochemically mediated atom transfer radical polymerization using a copper catalyst concentration as low as 50–100 ppm. Irradiation at λ > 350 nm provided both a reduction of initially added copper(II) catalyst complexed with either PMDETA or TPMA ligand to a copper(I) activator and a sufficient rate of polymerization. Poly(methyl methacrylate) with a narrow dispersity and predictable molar mass was obtained when an initiator, such as 2-bromopropionitrile, was used. Successful chain-extension polymerization confirmed the living character of the photopolymerization system.

This chapter contains sections titled: Introduction Photorearrangement of Aryl Esters of Carboxylie Acids Photorearrangement of Aryl Esters of Sulfonic Acids. Photorearrangement of N-Aryl Amides of Carboxylic Acids Photorearrangement of N-Aryl Lactams Photorearrangement of N-Aryl Amides of Sulfonic Acids Photorearrangement of Enol Esters of Carboxylic Acids Reversible Photorearrangement of Enol Lactones and Nonenolizable b̃-Diketones Photorearrangement of Enamides of Carboxylic Acids

In this study, a simple and green strategy was reported to prepare bimetallic nanoparticles (NPs) by the combination of zinc oxide (ZnO) and copper oxide (CuO) using Sambucus nigra L. extract. The physicochemical properties of these NPs such as crystal structure, size, and morphology were studied by X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), and transmission electron microscopy (TEM). The results suggested that these NPs contained polygonal ZnO NPs with hexagonal phase and spherical CuO NPs with monoclinic phase. The anticancer activity of the prepared bimetallic NPs was evaluated against lung and human melanoma cell lines based on MTT assay. As a result, the bimetallic ZnO/CuO NPs exhibited high toxicity on melanoma cancer cells while their toxicity on lung cancer cells was low.

Bioprinting offers tremendous potential in the fabrication of functional tissue constructs for replacement of damaged or diseased tissues. Among other fabrication methods used in tissue engineering, bioprinting provides accurate control over the construct's geometric and compositional attributes using an automated approach. Bioinks are composed of the hydrogel material and living cells that are critical process variables in the fabrication of functional, mechanically robust constructs. Appropriate cells can be encapsulated in bioinks to create functional tissue structures. Ideal bioinks are required to undergo a sol–gel transition consuming minimal processing time, and a plethora of chemical and physical crosslinking mechanisms are generally exploited to achieve high shape fidelity and construct stability. In contrast, crosslinking of hydrogel material at rapid rates can cause nozzle clogging, and hence, optimization of the bioink is often necessary. Bioinks can be formulated using natural or synthetic biomaterials, alone or in combination of these biomaterials. Herein, the various bioprinting methods are discussed; the natural, synthetic, or hybrid materials used as bioinks are analyzed; and the challenges, limitations, and future directions concerning the bioprinting technique are appraised.

The effect of various inorganic fillers on the storage modulus of four elastomers was determined experimentally. Results are interpreted using the Kerner equation, modified to include a parameter, B, in the volume fraction terms. This factor combines particle size and specific interaction effects, and in theory can be evaluated from energy dissipation measurements.

Size exclusion chromatography, SEC is one of the most popular methods for the separation of different kinds of macromolecules. This critical review gives concise information about macromolecules and their behavior in solution, basic understanding about principles, instrumentation, and application possibilities of SEC, and more in detail discusses drawbacks and pitfalls of the method with the emphasis on synthetic polymers. Selected practical advices are included to help enhance the quality of SEC results.

In order to increase chromatographic selectivity and to extend the analytical capability of reversed phase liquid chromatography (RP HPLC) many investigators have concentrated on the preparation of silica based column packings with chemically bonded phases (CBP). These phases have also been successfully used in sample preparation techniques, mainly in solid phase extraction (SPE). Although alkyl bonded phases (e.g., C2, C8, and C18) are the most widely used packings in RP HPLC and SPE, various specific applications require CBPs with polar functional groups (e.g., -NH2, -NO2, -CN, and/or -OH). The solution of problems with separation of complicated chiral compounds was attempted by applying stationary phases with chiral selectors (e.g., cyclodextrins, Pirkle phases, crown ethers, etc.). On the other hand, packings with pseudo-membrane or liquid crystal properties have been utilized for the separation of various substances of natural origin. Porous silica is commonly used as a support in the preparation of CBPs. Its physico-chemical characteristics, such as: type and structure of siliceous matrix, porosity, type and concentration of silanol groups, as well as surface purity, strongly influence the density and structure of chemically bonded phases. Recognition of these properties is helpful in optimizing separation processes based on RP HPLC elution and/or extraction of substances with polar character.

Porous organic polymers represent an unexplored field of materials for organic photovoltaic applications with great potential.

Development of new types of antibacterial coatings or nanocomposites is of great importance due to widespread multidrug-resistant infections including bacterial infections. Herein, we investigated biocompatibility as well as structural, photocatalytic, and antibacterial properties of photoactive hydrophobic carbon quantum dots/polyurethane nanocomposite. The swell-encapsulation-shrink method was applied for production of these nanocomposites. Hydrophobic carbon quantum dots/polyurethane nanocomposites were found to be highly effective generator of singlet oxygen upon irradiation by low-power blue light. Analysis of conducted antibacterial tests on Staphyloccocus aureus and Escherichia coli showed 5-log bactericidal effect of these nanocomposites within 60 min of irradiation. Very powerful degradation of dye (rose bengal) was observed within 180 min of blue light irradiation of the nanocomposites. Biocompatibility studies revealed that nanocomposites were not cytotoxic against mouse embryonic fibroblast cell line, whereas they showed moderate cytotoxicity toward adenocarcinomic human epithelial cell line. Minor hemolytic effect of these nanocomposites toward red blood cells was revealed.

Pulsed laser polymerization (PLP) in conjunction with size-exclusion chromatography (SEC), both being carried out in the aqueous phase, was used to determine propagation rate coefficients, k(p), of nonionized acrylic acid (AA) at temperatures between 2 and 25 degreesC and monomer concentrations, c(AA), from 1 to 10 wt %. The product k(p)c(AA,local) is the primary experimental quantity deduced via the PLP-SEC technique. Assuming c(AA,local) to be identical to overall monomer concentration, c(AA), yields apparent kp values, which, upon enhancing c(AA), first increase and, after passing through a maximum at around 3 wt % AA, significantly decrease. A kp value as high as 180 000 L.mol(-1).s(-1) was determined for 3 wt % AA at 25 degreesC. The decrease observed toward higher AA concentration is fully consistent with what has been found in a preceding study into k(p) of nonionized AA at monomer concentrations of 20 and 40 wt %. At constant temperature, variations in apparent kp by about a factor of 3 are seen in the range up to 40 wt % AA. Discussion of the measured rate data suggests that it is primarily c(AA,local) that changes as a function of monomer concentration rather than kp. As a consequence of strong hydrogen bonds between polymer segments, between polymer segments and AA monomer, and between both these species and water, the AA concentration at the radical site may significantly differ from overall c(AA). The assignment of the observed changes in apparent kp to c(AA,local) is supported by PLP-SEC experiments in which appreciable amounts of propionic acid (PA) have been added to aqueous AA solutions. The addition of PA significantly reduces apparent k(p). Addition of NaCl to an aqueous solution of AA in its nonionized form, on the other hand, does not affect apparent k(p). Whether the observed changes in k(p)c(AA,local) are entirely due to c(AA,local) differing from c(AA) or whether also the "true" propagation rate coefficient varies cannot be safely decided on the basis of the presently available data.

Synthetic polypeptides derived from the ring-opening polymerization of N-carboxyanhydrides can spontaneously fold into stable secondary structures under specific environmental conditions. These secondary structures and their dynamic transitions play an important role in regulating the properties of polypeptides in self-assembly, catalysis, polymerization, and biomedical applications. Here, we review the current strategies to modulate the secondary structures, and highlight the conformation-specific dynamic properties of synthetic polypeptides and the corresponding materials. A number of mechanistic studies elucidating the role of secondary structures are discussed, aiming to provide insights into the new designs and applications of synthetic polypeptides. We aim for this article to bring to people's attention synthetic polymers with ordered conformations, which may exhibit association behaviors and material properties that are otherwise not found in polymers without stable secondary structures.

Abstract Polypropylene (PP) nanocomposites with multi‐walled carbon nanotubes (CNT) were produced by a small‐scale masterbatch melt dilution technique using five PP differing in melt flow index (MFI) and degree of maleination. PP used in a masterbatch has MFI = 12 (PP 12 ), the others used PP which have MFI = 2 or MFI = 8. The state of CNT dispersion as assessed by melt rheological and morphological investigations indicated a better dispersion when using unmodified PP with MFI = 8 (PP 8 ) and the masterbatch's PP 12 . Electrical conductivity results showed nanotube percolation at contents between 1.1 and 2.0 vol %, whereas lower values were obtained for the matrices with the best dispersion, i.e., PP 8 and PP 12 . The dependencies of the relative Young's modulus on the CNT content showed that the maleinization improved the interfacial interactions between the components, especially in the case of maleated PP with MFI = 8 (PP‐MA 8 ), but the better dispersion was prevented by the incompatibility between polar groups of PP‐MA and the nonpolar origin masterbatch PP 12 . © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Inimitable properties of carbon quantum dots as well as a cheap production contribute to their possible application in biomedicine especially as antibacterial and antibiofouling coatings. Fluorescent hydrophobic carbon quantum dots are synthesized by bottom-up condensation method and used for deposition of uniform and homogeneous Langmuir–Blodgett thin films on different substrates. It is found that this kind of quantum dots generates singlet oxygen under blue light irradiation. Antibacterial and antibiofouling testing on four different bacteria strains (Escherichia coli, Staphylococcus aureus, Bacillus cereus, and Pseudomonas aeruginosa) reveals enhanced antibacterial and antibiofouling activity of hydrophobic carbon dots thin films under blue light irradiation. Moreover, hydrophobic quantum dots show noncytotoxic effect on mouse fibroblast cell line. These properties enable potential usage of hydrophobic carbon quantum dots thin films as excellent antibacterial and antibiofouling coatings for different biomedical applications.

Abstract Propagation rate coefficients, k p , which have been previously reported by several groups for free‐radical bulk polymerizations of cyclohexyl methacrylate (CHMA), glycidyl methacrylate (GMA), benzyl methacrylate (BzMA), and isobornyl methacrylate (iBoMA) are critically evaluated. All data were determined by the combination of pulsed‐laser polymerization (PLP) and subsequent polymer analysis by size‐exclusion chromatography (SEC). This so‐called PLP‐SEC technique has been recommended as the method of choice for the determination of k p by the IUPAC Working Party on Modeling of Polymerisation Kinetics and Processes . The present data fulfill consistency criteria and the agreement among the data from different laboratories is remarkable. The values for CHMA, GMA, and BzMA are therefore recommended as constituting benchmark data sets for each monomer. The data for iBoMA are also considered reliable, but since SEC calibration was established only by a single group, the data are not considered as a benchmark data set. All k p data for each monomer are best fitted by the following Arrhenius relations: CHMA: $k_{\rm p} = 10^{6.80} \;{\rm L} \cdot {\rm mol}^{ - 1} \cdot {\rm s}^{ - 1} \exp \left( {{{ - 23.0\;{\rm kJ} \cdot {\rm mol}^{ - 1} } \over {{\rm R} \cdot T}}} \right)$ , GMA: $k_{\rm p} = 10^{6.79} \;{\rm L} \cdot {\rm mol}^{ - 1} \cdot {\rm s}^{ - 1} \exp \left( {{{ - 22.9\;{\rm kJ} \cdot {\rm mol}^{ - 1} } \over {{\rm R} \cdot T}}} \right)$ , BzMA: $k_{\rm p} = 10^{6.83} \;{\rm L} \cdot {\rm mol}^{ - 1} \cdot {\rm s}^{ - 1} \exp \left( {{{ - 22.9\;{\rm kJ} \cdot {\rm mol}^{ - 1} } \over {{\rm R} \cdot T}}} \right)$ , iBoMA: $k_{\rm p} = 10^{6.79} \;{\rm L} \cdot {\rm mol}^{ - 1} \cdot {\rm s}^{ - 1} \exp \left( {{{ - 23.1\;{\rm kJ} \cdot {\rm mol}^{ - 1} } \over {{\rm R} \cdot T}}} \right)$ . Rather remarkably, for the methacrylates under investigation, the k p values are all very similar. Thus, all data can be fitted well by a single Arrhenius relation resulting in a pre‐exponential factor of 4.24 × 10 6 L · mol −1 · s −1 and an activation energy of 21.9 kJ · mol −1 . All activation parameters refer to bulk polymerizations at ambient pressure and temperatures below 100 °C. Joint confidence intervals are also provided, enabling values and uncertainties for k p to be estimated at any temperature. 95% joint confidence intervals for Arrhenius parameters A and E A for cyclohexyl (CHMA), glycidyl (GMA), benzyl (BzMA), and isobornyl (iBoMA) methacrylate; for details see text. magnified image 95% joint confidence intervals for Arrhenius parameters A and E A for cyclohexyl (CHMA), glycidyl (GMA), benzyl (BzMA), and isobornyl (iBoMA) methacrylate; for details see text.

Benchmark propagation rate coefficient (<italic>k</italic>_p) data for the radical polymerization of methyl acrylate are provided.

The absorption and fluorescence spectra of substituted coumarins (2-oxo-2H-chromenes) were investigated in solvents and in polymer matrices. The substitutions involved were: (1) by groups with varying electron donating ability such as CH₃, OCH₃ and N(CH₃)₂, mainly, but not exclusively, in positions 7 and (2), by either CHO or 4-PhNHCONHN=CH- in position 3. While the spectra of non-substituted coumarin-3-carbaldehyde has absorptions at approximately 305 and 350 nm, substitution at position 7 leads to remarkable changes in the shape of the absorption spectrum and shifts the absorption to a longer wavelength. Similarly, the replacement of the formyl group with a semicarbazide group substantially influences the shape of the absorption spectrum, and coumarins which have only N(CH₃)₂ in position 7 experience small changes. These changes are associated with the increasing intramolecular charge transfer (ICT) character and increasing conjugation length of the chromophoric system, respectively, in the studied molecules. The fluorescence is almost negligible for derivatives which have H in this position. With increasing electron donating ability, and the possibility of a positive mesomeric (+M) effect of the substituent in position 7 of the coumarin moiety, the fluorescence increases, and this increase is most intense when N(CH₃)₂ substitutes in this position, for both 3-substituted derivatives. Spectral measurements of the studied coumarins in polymer matrices revealed that the absorption and fluorescence maxima lay within the maxima for solvents, and that coumarins yield more intense fluorescence in polymer matrices than when they are in solution. The quantum yield of derivatives which have a dimethylamino group in position 7 in polymer matrices approaches 1, and the fluorescence lifetime is within the range of 0.5-4 ns. The high quantum yield of 7-dimethylamino derivatives qualifies them as laser dyes which have k(F) higher than k(nr) in the given medium. This is caused by stiffening of the coumarin structure in polar polymer matrices, such as PMMA and PVC, due to higher micro-viscosity than in solution and intermolecular dipole-dipole interaction between chromophore (dopant) and matrix.

Abstract Polyamide 6 (PA6)/multi‐walled carbon nanotubes (MWCNT) nanocomposites were produced by diluting a masterbach containing 20 wt % nanotubes using melt mixing. The influence of the addition of well dispersed MWCNT (as indicated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM)) on the thermal transitions, and crystallization behavior of the PA6 matrix is investigated. Differential scanning calorimetry (DSC) results show a reduction in heat capacity jump at the glass transition which is interpreted by an immobilized interfacial layer near the nanotubes. Furthermore, both DSC and X‐ray diffraction (XRD) measurements indicate that nanotubes favor the formation of the α crystalline form of PA6. These findings are correlated with the observed improvement of the storage modulus as revealed by dynamic mechanical thermal analysis (DMTA). Additionally, a new crystallization peak appears when MWCNT are added, and is attributed to the formation of a different morphology of the same type crystallite around the nanotubes walls ( trans ‐crystallinity). Finally, water sorption measurements show an increase of water content, normalized to the amorphous polymer fraction, in the nanocomposites. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 764–774, 2009

The addition of heteroatoms to pristine carbon quantum dots (CQDs) change their structure and optical properties. In this study, fluorine (F)- and chlorine (Cl)-doped CQDs are prepared by the one-step green hydrothermal route from sodium fluoride, sodium chloride, urea, and citric acid as the starting precursors. Microscopy analysis reveals that the average size of these quantum dots is 5 ± 2 nm, whereas the chemical study shows the existence of C–F and C–Cl bonds. The produced F- and Cl-doped CQDs have fluorescence quantum yields of 0.151 and 0.284, respectively, at an excitation wavelength of 450 nm. Charge transfer resistance of F- and Cl-doped CQDs films is 2 orders of magnitude higher than in the pristine CQD films. Transport band gap of the doped CQDs is 2 eV bigger than that of pristine CQDs. Radical scavenging activity shows very good antioxidant activity of doped CQDs. Antibacterial testing reveals poor antibacterial activity against Staphylococcus aureus and Escherichia coli. The F- and Cl-doped CQDs are successfully used as fluorescent probes for cell imaging as shown by confocal microscopy.

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