Visible laser lights in photoinduced polymerization. VI. Thioxanthones and ketocoumarins as photoinitiators

The efficiency of thioxanthones and ketocoumarins as photoinitiators has been checked in visible laser light-induced polymerization reactions and discussed in terms of excited-state reactivity (as revealed by time-resolved laser spectroscopy). These compounds undergo fast electron transfer reaction in the presence of amines and onium salts. Transient absorption spectra and rate constants of the processes involved have been determined. The combination photoinitiator-amine-onium salt appears as very promising for the design of efficient photosensitive systems.     

Synthesis and properties of triblock copolymers containing PDMS via AGET ATRP

The bromo-terminated macroinitiator was prepared by direct addition reaction of difunctional poly(dimethylsiloxane) (PDMS) containing methyl methacrylate end groups with hydrobromic acid in acetic acid under mild conditions, and well-defined triblock copolymers of poly(methyl methacrylate-b-dimethylsiloxane-b-methyl methacrylate) (MMA-b-DMS-b-MMA) were synthesized via activators generated by election transfer atom transfer radical polymerization (AGET ATRP). The gel permeation chromatography data obtained verified the polymerization and showed the well controlling of the reaction. FTIR and ¹H NMR measured the structure of the macroinitiator and copolymers. The contact angle measurement indicated that the water contact angles decreased gradually with the increasing of PMMA block content. The self-assembly behaviors of the triblock polymer were studied by transmission electron micrograph, scanning electron microscopy, and dynamic light scattering measurement. The results indicated that the polymers could self-assemble into various complex morphologies in different solvents and the morphologies depended on the properties of solvents. The possible molecular packing models for self-assembly behaviors of the ABA triblock polymers were proposed.     

AGET ATRP of methyl methacrylate catalyzed by FeCl3/iminodiacetic acid in the presence of air

The recently developed living free-radical polymerization system, atom transfer radical polymerization using activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), was used for methyl methacrylate (MMA) polymerization in the presence of a limited amount of air, using a novel catalyst system based on iron (FeCl₃) complexes with iminodiacetic acid (IDA) and using ascorbic acid (VC) as a reducing agent. The kinetics of AGET ATRPs of MMA with different amounts of VC in the presence of air was investigated. The results of the polymerizations demonstrated the features of “living”/controlled free-radical polymerization such as the number-average molecular weights increasing linearly with monomer conversion and narrow molecular weight distributions (M_w/M_n = 1.31–1.44).     

The effect of co-initiator structure on photoinitiating efficiency of photoredox couples composed of quinoline[2,3-b]-1H-imidazo[1,2-a]pyridinium bromide and phenoxyacetic acid or N,N-dimethylaniline derivatives.

Summary  Two groups of electron donors (phenoxyacetic acid derivatives, PAADs, and the family of N,N-dimethylaniline derivatives DMADs) in combination with quinoline[2,3-b]-1H-imidazo[1,2-a]pyridinium bromide (QIPB) were applied as photoinitiator for free radical polymerization induced with UV emission of an argon-ion laser (351 and 361 nm). Analysis of the data obtained for the initial time of photoinitiated polymerization indicates that both, the rate of electron transfer process between QIPB and tested co-initiators as well as the structure of obtained free radical can affect the overall photoinitiation ability of tested photoredox pairs.     

Sulfur-substituted and α-methylated fatty acids as peroxisome proliferator-activated receptor activators

FA with varying chain lengths and an α-methyl group and/or a sulfur in the β-position were tested as peroxisome proliferator-activated receptor (PPAR)α,-δ(β), and-γ ligands by transient transfection in COS-1 cells using chimeric receptor expression plasmids, containing cDNAs encoding the ligand-binding domain of PPARα,-δ, and-γ. For PPARα, an increasing activation was found with increasing chain length of the sulfur-substituted FA up to C₁₄-S acetic acid (tetradecylthioacetic acid=TTA). The derivatives were poor, and nonsignificant, activators of PPARδ. For PPARγ, activation increased with increasing chain length up to C₁₆-S acetic acid. A methyl group was introduced in the α-position of palmitic acid, TTA, EPA, DHA, cis9,trans11CLA, and trans10,cis12 CLA. An increased activation of PPARα was obtained for the α-methyl derivatives compared with the unmethylated FA. This increase also resulted in increased expression of the two PPARα target genes acyl-CoA oxidase and liver FA-binding protein for α-methyl TTA, α-methyl EPA, and α-methyl DHA. Decreased or altered metabolism of these derivatives in the cells cannot be excluded. In conclusion, saturated FA with sulfur in the β-position and increasing carbon chain length from C₉−S acetic acid to C₁₄−S acetic acid have increasing effects as activators of PPARα and-γ in transfection assays. Furthermore, α-methyl FA derivatives of a saturated natural FA (palmitic acid), a sulfur-substituted FA (TTA), and PUFA (EPA, DHA, c9,t11 CLA, and t10,c12 CLA) are stronger PPARα activators than the unmethylated compounds.     

原子转移自由基聚合在纳米粒子改性方面的研究进展

介绍了原子转移自由基聚合(ATRP)在纳米粒子改性方面的研究进展,综述了基于 ATRP 的多种不同催化体系的衍生技术在纳米粒子表面改性方面的应用,其中主要包括反向原子转移自由基聚合（RATRP）和电子转移活化再生催化剂原子转移自由基聚合(AGET ATRP),并对其特点进行了概述,对纳米粒子表面引发ATRP的发展进行了展望。     

Synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid

Poly(styrene‐co‐divinylbenzene) microspheres with size ranging from 1.6 to 1.8 μm were prepared in acetic acid by precipitation polymerization. The particle size and particle size distribution were determined by laser diffraction particle size analyzer, and the morphology of the particles was observed with scanning electron microscope. Besides, effects of various polymerization parameters such as initiator and total monomer concentration, divinylbenzene (DVB) content, polymerization time and polymerization temperature on the morphology and particle size were investigated in this article. In addition, the yield of microspheres increased with the increasing total monomer concentration, initiator loading, DVB concentration and polymerization time. In addition, the optimum polymerization conditions for synthesis of monodisperse crosslinked poly(styrene‐co‐divinylbenzene) microspheres by precipitation polymerization in acetic acid were obtained. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Synthesis of crosslinked polyacrylonitrile via atom transfer radical polymerization with activators regenerated by electron transfer and use of the resin in mercury removal after modification

Crosslinked polyacrylonitrile (PAN) was synthesized with divinylbenzene as the crosslinker with an iron(III)‐mediated atom transfer radical polymerization method with activators regenerated by electron transfer. The polymerization exhibited first‐order kinetics with respect to the polymerization time. Hydroxylamine hydrochloride (NH₂OH·HCl) was used to modify the cyano groups of the crosslinked PAN to obtain amidoxime (AO) groups. The AO‐crosslinked PAN was used to remove Hg(II). The optimum pH, adsorption kinetics, and adsorption isotherms were investigated. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

The synthesis, spectroscopic and electrochemical properties, and application of new dyeing photoinitiator systems for acrylate monomers polymerization

New symmetrical bicationic polymethine dyes were synthesized and their spectroscopic and electrochemical properties were described. The bichromophoric dyes (benzothiazole, benzoxazole, indolinium derivatives) were investigated as sensitizers in the free radical photopolymerization initiated by their borate salts. The obtained kinetic results shown that bicationic polymethine dyes as the organoborate salts are much efficient photoinitiating systems of acrylate monomers polymerization than monocationic parent dyes. The rate of polymerization depends on ΔG_ET of electron transfer from borate anion to the excited singlet state of bicationic polymethine dye. The relationship between the rate of polymerization and the free energy of electron transfer process shows the dependence predicted by the classical theory of electron transfer.     

Synthesis of small-molecule initiators derived from fluorinated acrylates and their application in atom transfer radical polymerization (ATRP)

The bromo-terminated small-molecule initiator was prepared by the direct addition reaction of 2,2,3,4,4,4-hexafluorobutyl methacrylate (HFMA) or dodecafluoroheptyl methacrylate (DFMA) with hydrobromic acid in acetic acid under mild conditions. This greatly widened the initiators used for atom transfer radical polymerization (ATRP). The successful polymerization of isobutyl methacrylate (IBMA) or methyl methacrylate (MMA) derived from HFMA-Br or DFMA-Br indicated that fluorinated acrylates could be used as initiators for ATRP. The data of GPC showed the well controlling of the initiator system. FTIR and ¹H NMR characterized the structures of the initiators and their polymers. Contact angle measurement indicated that although only one molecule of fluorinated acrylate was introduced, the surface properties of polymers were improved greatly.     

Synthesis of Hydrophobic Polymeric Cryogels with Supermacroporous Structure

A versatile approach to synthesis of hydrophobic polymeric cryogels is proposed using acetic acid crystals instead of ice crystals as porogen through cryo‐polymerization. In the range of 60 to 90 vol% of acetic acid, polymerization at ambient temperature gives rise to particulate polymers in beaded or amorphous shape, while polymerization at 4 °C, lower than the melting point of acetic acid (16.6 °C), leads to the formation of cryogel‐like monoliths with supermacroporous structure, which is mainly ascribed to cryo‐concentration effect. According to the measurements by scanning electron microscopy and mercury intrusion porosimetry, the dried samples are supermacroporous with pore size mainly ranging from several micrometers to several hundred micrometers, which can be feasible for rapid mass transfer. The forming cryogels display a superfast responsiveness to organic solvents, possibly stemming from their supermacroporosity and distinctive hydrophobicity.

     

Nitroxide polymer brushes as efficient and recoverable catalysts for the selective oxidation of primary alcohols to aldehydes

2,2,6,6‐Tetramethylpiperidinyloxyl (TEMPO)‐containing polymer brushes were grafted onto crosslinked polystyrene microspheres via surface‐initiated activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) of 2,2,6,6‐tetramethyl‐4‐piperidyl methacrylate, followed by an oxidation process with 3‐chloroperoxybenzoic acid as oxidant. The synthesized nitroxide polymer brushes included homopolymer brushes, block copolymer brushes, and random copolymer brushes with various TEMPO contents and molecular weights. They were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, nuclear magnetic resonance spectroscopy, and gel permeation chromatography. These nitroxide brushes bearing high TEMPO contents were used as recoverable catalysts for the hypochlorite and aerobic oxidation of primary alcohols to aldehydes. The effects of polymer brush structure on the catalytic properties were studied and discussed. The results showed that these nitroxide polymer brushes had excellent catalytic properties and good recycling performances. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44365.     

Synthesis, characterization and morphology of polyanthranilic acid micro- and nanostructures

Polyanthranilic acid (PANA) nanofibres, nanorods, nanospheres and microspheres were synthesized by polymerization of anthranilic acid using ammonium peroxydisulfate (APS) as oxidant without hard or soft templates. Polymerization of anthranilic acid was carried out in aqueous solutions of strong (hydrochloric) and weak (acetic) acids. The influence of synthetic parameters such as oxidant, initiator, dopant acid and its concentration, redox initiator, and reaction medium on the morphology and particle size of PANA have been investigated. PANA nanofibres and nanorods were obtained via redox polymerization of anthranilic acid initiated by FeSO₄ as redox initiator. PANA nanospheres and nanofibres were also obtained when used aromatic amines as initiators. When polymerization carried out in the solution of weak (acetic) acid the microsphere morphology obtained and the particle size increase with increasing the concentration of weak acid. PANA nanorods were obtained also by polymerization of anthranilic in ethanol-water mixture unlike interfacial polymerization of anthranilic acid (in chloroform-water) that give PANA microspheres. The morphology and particle size of PANA was studied by scanning electron microscope (SEM) and transmission electron microscope (TEM). The average diameter of nanostructures obtained ≤100 nm. The optical bandgap of microspheres and nanofibers polymeric products were determined using UV-vis spectroscopic technique and found to be 2.0 eV and 1.6 eV, respectively. The bandgap decreased with decreasing the particle size. IR spectrum confirmed the structure of PANA nanofibres (synthesized with FeSO₄ as redox initiator) in emeraldine form. The thermal stability of polymer obtained was determined by thermal gravimetric analysis (TGA). The molecular weight was determined also by gel permeation chromatography (GPC).     

Photoinitiating free‐radical polymerization electron‐transfer pairs applying amino acids and sulfur‐containing amino acids as electron donors

A series of free‐radical polymerization initiation systems, based on xanthene dyes as the absorbing chromophores [Rose bengal derivative, 3‐(3‐methylbutoxy)‐5,7‐diiodo‐6‐fluorone and 3‐acetoxy‐2,4,5,7‐tetraiodo‐6‐fluorone] and sulfur‐containing amino acids as the electron donors, were investigated. The photoredox pair xanthene dye/sulfur‐containing amino acid was effectively used for photoinitiation of free‐radical polymerization of the mixture composed of poly(ethylene glycol)diacrylate–1% NH₄OH (3 : 1). The highest initiating efficiencies were observed for the system composed of methionine derivatives as the electron donor. The mechanism of photoinduced electron transfer between sulfur‐containing amino acids and triplet state of xanthene dye was investigated using laser‐flash and steady‐state photolysis techniques. Based on photochemistry of xanthene dyes, photochemistry of sulfur‐containing amino acids, and obtained results, the mechanism describing the major processes occurring during the photoinitiated polymerization by a photoinduced intermolecular electron‐transfer process was postulated. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 358–365, 2005     

Polymerization on heating up of bio‐oil: A model compound study

Understanding of the condensation reactions in bio‐oil is the key for efficient conversion into transportation fuel or value‐added chemicals. In this study, the roles of the typical compounds representing the sugars, sugar derivatives, and aromatics found in bio‐oil were investigated for their contribution to condensation reactions. Glucose played a key role for the polymer formation due to its decomposition to reactive compounds with multiple hydroxyl groups, carbonyl groups or conjugated π bonds. The sugar derivatives, including furfural, hydroxyl aldehyde and hydroxyl acetone, were also found to be reactive toward polymerization. The carboxylic acids were shown to be the catalysts for polymerization and formic acid was much more efficient to catalyze polymerization than acetic acid. The phenolic compounds also promoted the acid‐catalyzed reactions. Vanillin contains reactive a carbonyl group, leading to its high tendency toward polymerization. In methanol, various kinds of methanolysis reactions dominated, which significantly suppressed the decomposition of glucose and the polymerization of other compounds. © 2012 American Institute of Chemical Engineers AIChE J, 59: 888–900, 2013     

CuBr2/Me6TREN-mediated living radical polymerization of methyl methacrylate at ambient temperature

A universal nitrogen based ligand, tris[2-(dimethylamino) ethyl] amine (Me₆TREN), was firstly employed as both reducing agent and ligand for atom transfer radical polymerization with activators regenerated by electron transfer (ARGET ATRP) of methyl methacrylate (MMA) in bulk and solution, using CuBr₂ as the catalyst and 2-bromoisobutyrate as the initiator. Remarkably high activity catalytic system (CuBr₂/Me₆TREN) enabled the ambient temperature polymerization and thus biradical termination reactions were low. The polymerization exhibited typical living radical polymerization features, including pseudo first-order kinetics of polymerization, linear increase in the molecular weight versus monomer conversion, and low polydispersity index values. Moreover, effects of solvent and reaction temperature on the polymerization were investigated in detail. The rate of polymerization increased with reaction temperature and the apparent activation energy of the polymerization was calculated to be 51.11 kJ/mol. Gel permeation chromatography and ¹H NMR analyses as well as chain extension experiment confirmed the living chain-end functionality.     

Integrating Catalyst and Co‐Catalyst Design in Olefin Polymerization Catalysis: Transferable Dianionic Ligands for the Activation of Late Transition Metal Polymerization Catalysts

Treatment of nickel and palladium α‐diimine catecholate complexes with alkylaluminum catecholates leads to active ethylene polymerization catalysts. Comparison of the catalytic activities achieved with combinations of α‐diimine catecholate or halide complexes as catalyst precursors with different activators (MMAO or alkylaluminum catecholates) reveals that the presence of the catecholate ligand in both catalyst components is beneficial for achieving high activity levels at very low M/Al ratios.     

Synthesis of novel high oil‐absorption resins of poly(methyl methacrylate–butyl methacrylate) by surface‐initiated atom transfer radical polymerization using activators regenerated by electron transfer for efficient removal of oil

Oil‐absorption resins are considered one of the effective materials to separate organic chemical compounds from oily water. In this work, well‐defined high oil‐absorption resins of poly(methyl methacrylate–butyl methacrylate) grafted onto silica gel were prepared by surface‐initiated atom transfer radical polymerization using activators regenerated by electron transfer mediated by FeCl₃/iminodiacetic acid. The grafted polymers were grown in a controlled manner. By considering the effect of different polymerization conditions, we prepared novel high oil‐absorption resins. The chemical structures of the resins were determined by Fourier transform IR spectroscopy. SEM and TGA were also used to characterize the resins. It was found that the resins had good heat‐resistant quality, higher oil absorbency and better oil retention and regeneration properties. The resins can absorb 31.2 g g^?1 for tricholoromethane and 23.3 g g^?1 for toluene. Copyright © 2012 Society of Chemical Industry     

Electroinitiated polymerization of some acetylenic derivatives,a polarographic study

The polarographic reduction of some acetylenic derivatives—phenylacetylene, diphenyldiacetylene and methyl propiolate, as well as of some quarternary salts (ammonium, phosphonium, arsonium and stibonium), was investigated in order to establish whether the electroinitiated polymerization process took place by direct electron transfer to the acetylenic monomer or indirectly. The half-wave potentials of the compounds mentioned at the dropping mercury cathode and at the stationary platinum electrode were measured. From the experimental data on the polymerization of the above acetylenic monomers, some statements on the kinetics of the polymerization process were made.     

Free radical polymerization and lipid binding of lysozyme reacted with peroxidizing linoleic acid

Insolubilization and polymerization of proteins exposed to peroxidizing lipids may be due either to cross-linking with incorporation of fragments of the lipid oxidation products, or to free radical transfer from lipid to protein and subsequent free radical polymerization of protein. The second mechanism which has been proposed was inferred from measurements of electron spin resonance signals in proteins. In this study, uniformly labeled linoleic acid, [¹⁴C(U)] LA, was reacted with lysozyme. Volatile oxidation products of LA were also used in some experiments. Incubation was done in the absence of water. Oligomers of lysozyme, as well as the monomer, were isolated after incubation, and the [¹⁴C] label incorporated into each fraction was determined. The results show that the dominant mechanism of protein polymerization after exposure to peroxidizing linoleic acid is the transfer of free radical from lipid to protein, and subsequent free radical polymerization.