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     

Novel N‐ethyl‐2‐styrylquinolinum iodides as sensitizers in photoinitiated free radical polymerization of trimethylolopropane triacrylate (TMPTA), part 3

Three‐component systems, which contain a light‐absorbing species (dye), an electron donor (n‐butyltriphenylborate salt), and a third component (N‐alkoxypyridinum salt or 1,3,5‐triazine derivative), have emerged as efficient, visible‐light sensitive photoinitiators of free radical polymerization. It was found that three‐component systems are more efficient than their two‐component counterparts. Kinetic studies based on microcalorimetry revealed a significant increase in polymerization rate with increasing concentration of N‐alkoxypyridinum salt. Such results were not obtained for photoinitiating systems possessing 1,3,5‐triazine derivative as a second coinitiator. Based on the experimental results we concluded that the primary photochemical reaction involves electron transfer from the borate anion to the excited dye followed by the reaction of resulting dye‐based radical with second coinitiator that regenerates the original dye and simultaneously produces the alkoxy radical or triazynyl radical which could start the polymerization chain reaction. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Electron Transfer Photoinitiating Systems. The Effect of the Co‐Initiator Structure on the Photoinitiation Ability of a Photoredox Pair Containing Neutral Hemicyanine Dyes as Sensitizers

Summary: The photoinitiation ability of photoredox pairs composed of a neutral hemicyanine dye and different co‐initiators for the free radical polymerization of 2‐ethyl‐2‐(hydroxymethyl)propane‐1,3‐diol triacrylate is investigated. p‐(N,N‐dimethylaminostyryl)benzthiazole, p‐(N,N‐dimethylaminostyryl)benzoxazole, p‐(N,N‐dimethylaminostyryl)α‐naphthiazole are tested as dyes, and, as co‐initiators, an aromatic amino‐acid, an aromatic thio‐ and oxycarboxylic acid, and alkyltriphenylborate are applied as electron donors. N,N′‐dialkoxybipyridinium salts are used as ground‐state electron acceptors. The experimental results show that the photoinitiating ability of the tested photoredox pairs are controlled by both the driving force of the electron transfer process between an electron donor and an electron acceptor and the reactivity of the free radical that results from the secondary reactions occurring after the photoinduced electron transfer process. The greatest photoinitiation ability of free radical polymerization is observed when the tested dyes are applied as electron donors in their singlet excited states in combination with N,N′‐dialkoxybipyridinium salts acting as ground‐state electron acceptors.

Schematic of the investigated photoinitiation systems.     

Novel comb‐structured‐polymer‐grafted carbon black by surface‐initiated atom transfer radical polymerization and ring‐opening polymerization

Novel comb‐structured‐polymer‐grafted carbon black (CB) was synthesized with a combination of surface‐initiated atom transfer radical polymerization and ring‐opening polymerization. First, poly(2‐hydroxyethyl methacrylate) (PHEMA) was grafted onto the CB surface by surface‐initiated atom transfer radical polymerization. The prepared CB‐g‐PHEMA contained 35.6–71.8% PHEMA, with the percentage depending on the molar ratio of the reagents and the reaction temperature. Then, with PHEMA in CB‐g‐PHEMA as the macroinitiator, poly(?‐caprolactone) (PCL) was grown from the CB‐g‐PHEMA surface by ring‐opening polymerization in the presence of stannous octoate. CB‐g‐PHEMA and CB‐g‐(PHEMA‐g‐PCL) were characterized with Fourier transform infrared, ¹H‐NMR, thermogravimetric analysis, dynamic light scattering, and transmission electron microscopy. The resultant grafted CB had a shell of PHEMA‐g‐PCL. On the whole, the CB nanoparticles were oriented in dendritic lamellae formed by these shells. This hopefully will result in applications in gas sensor materials and nanoparticle patterns. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Allyl ether‐modified unsaturated polyesters for UV/air dual‐curable coatings. II: UV and air‐curing behavior

The photoinduced and peroxide‐induced polymerization behavior of dual‐curable allyl ether‐modified unsaturated polyester (AUPE) and vinyl ether (VE) used as a reactive diluent for dual‐curable coating have been studied by infrared spectroscopy (IR). For UV curing systems in N₂ atmosphere, the maleate's conversion and total conversion decrease with the increasing of allyloxy content. However, the rate and of copolymerization and conversion of VE are independent of allyloxy concentration. The copolymerization of allyl ether (AE) and vinyl ether occurs in the presence of maleate (MA) under UV irradiation. For air curing, the rate of copolymerization increases with allyloxy content. The ultimate conversion is the same irrespective of the allyloxy concentration. Because the electron‐rich double bond of allyloxy would become an electron‐deficient one through oxidation, the conversion of maleate decreases with increasing of the allyloxy content due to the enhancement of copolymerization of AE with VE. The ATR‐IR showed that different curing mechanisms occur in AUPE/VE system during air‐curing process. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2771–2776, 2004     

Preparation and antidehydration of interpenetrating polymer network hydrogels based on 2‐hydroxyethyl methacrylate and N‐vinyl‐2‐pyrrolidone

This work reports the preparation of 2‐hydroxyethyl methacrylate (HEMA)/N‐vinyl‐2‐pyrrolidone (NVP) interpenetrating polymer network (IPN) hydrogels by UV‐initiated polymerization in the presence of free radical photoinitiator Darocur 1173 and cationic photoinitiator 4,4′‐dimethyl diphenyl iodonium hexafluorophosphate. The polymerization mechanism was investigated by the formation of gel network. The structure and morphology of the HEMA/NVP IPN hydrogels were characterized by fourier transform infrared spectroscopy (FTIR) and scanning electron microscope (SEM). The results showed that the IPN gels exhibited homogeneous morphology. The dehydration rates of HEMA/NVP IPN hydrogels were examined by the gravimetric method. The results revealed that the hydrogels had a significant improvement of antidehydration ability in comparison with poly(2‐hydroxyethyl methacrylate)(PHEMA) hydrogel embedded physically with poly(N‐vinyl‐2‐pyrrolidone)(PVP). © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of Photodegradable o‐Nitrobenzyl Nanogels on the Photopolymerization Process

A series of partially photodegradable o‐nitrobenzyl nanogels (NBNG) with different caged functional groups (COOH, OH, SH) are prepared and compared with a nondegradable nanogel as additives in photocurable materials. Photoinduced nanogel network disruption and photoinitiated polymerization of infiltrating and dispersing monomer could be controlled independently. In triethylene glycol dimethacrylate (TEGDMA), o‐NBNGs that release a COOH or OH functional group upon photodegradation of the o‐nitrobenzyl crosslinker, the reduced chemical crosslinking density of the nanogel network allows greater penetration of monomer into the partially degraded nanogel network, which results in an increase in volumetric shrinkage and polymerization stress. In contrast, the formulation of o‐NBNGs with caged SH groups also can be photodegraded but is able to rebuild the chemical crosslinking through thiol‐based chain transfer reactions when photocured as a dispersion in TEGDMA. As such, it behaves like a photo‐inert nanogel. Dynamic thermomechanical analysis and testing by three‐point bending further confirms the photoinduced crosslink density variation influences mechanical properties of the final polymer networks. This work demonstrates the inherent properties of the nanogel network and the type of crosslinking can alter the performance of the photocured resin while a separate photochemical process can be used to regulate photoinduced polymerization.     

Designing of fullers‐earth‐containing poly(vinyl alcohol)‐g‐poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) nanocomposites: Swelling and deswelling behaviors

In this study, polymer–clay nanocomposites (PCNs) composed of poly(vinyl alcohol)s (PVAs), poly(2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid), and fullers earth were prepared by the effective dispersal of inorganic nanoclays in the organic PVA matrix via in situ free‐radical polymerization with potassium persulfate as an initiator and N,N‐methylene bisacrylamide as a crosslinker. The monomer, 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid, was grafted onto the PVA backbone, and at the same time, fullers earth layers were intercalated and exfoliated into the grafted copolymer, especially at a low or moderate loading of the fullers earth. The synthesized PCN materials were characterized by Fourier transform infrared spectroscopy and wide‐angle X‐ray diffraction techniques. The morphological features of the synthesized materials were studied by scanning electron microscopy; this revealed that the swelling ratio of this nanocomposite increased with increasing fullers earth content. The X‐ray diffraction results indicated that the fullers earth was exfoliated in the nanocomposite matrix, and its introduction into the polymer matrix enhanced the percentage crystallinity of the polymer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Comparison of poly(o‐anisidine) and poly(o‐anisidine‐co‐aniline) copolymer synthesized by chemical oxidative method

In this study, poly(o‐anisidine) [POA], poly(o‐anisidine‐co‐aniline) [POA‐co‐A], and polyaniline [PANi] were chemically synthesized using a single polymerization process with aniline and o‐anisidine as the respective monomers. During the polymerization process, p‐toluene sulfonic acid monohydrate was used as a dopant while ammonium persulfate was used as an oxidant. N‐methyl‐pyrolidone (NMP) was used as a solvent. We observed that the ATR spectra of POA‐co‐A showed features similar to those of PANi and POA as well as additional ones. POA‐co‐A also achieved broader and more extended UV–vis absorption than POA but less than PANi. The chemical and electronic structure of the product of polymerization was studied using Attenuated Total Reflectance spectroscopy (ATR) and UV–visible spectroscopy (UV–vis). The transition temperature of the homopolymers and copolymers was studied using differential scanning calorimetry and the viscosity average molecular weight was studied by using dilute solution viscometry. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Applicability of hemicyanine phenyltrialkylborate salts as free‐radical photoinitiators in the visible‐light polymerization of acrylate

The photoinitiation ability of photoredox pairs composed of a hemicyanine dye cation and different borate anions for the radical polymerization of 2‐ethyl‐2‐(hydroxymethyl)‐1,3‐propanediol triacrylate was investigated. In such a system, the excited dye chromophore is reduced by different tetraorganylborate anions. Upon irradiation at 488 nm, reductive carbon–boron bond cleavage occurs, producing reactive radicals, which start the chain reaction. The efficiency of bond‐breaking processes was found to be dependent on the nature of both the acceptors and the donors. The experimental results show that the photoinitiating ability of the tested photoredox pairs were controlled by both the driving force of the electron‐transfer process between the electron donor and the electron acceptor and the reactivity of the free radical that resulted from the secondary reactions occurring after the photoinduced electron‐transfer process. Using the nanosecond flash photolysis method, we studied the spectral and kinetic characteristics of the triplet state of cyanine dye and determined the rate constants of the triplet quenching by phenyltrialkylborate salts. The results obtained show that the tetramethylammonium phenyl‐tri‐n‐butylborate (TB7) has a faster electron‐transfer rate than the tetramethylammonium n‐butyltriphenylborate (TB2) salt, which bore only one butyl group attached to the boron. The relative initiator efficiency of the triphenylbutylborate salts, as compared to the corresponding phenyltrialkylborate salts with a common chromophore, was determined. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Fabrication and drug release properties of poly(5‐benzyloxy‐trimethylene‐co‐glycolide) microspheres

Poly(5‐benzyloxy‐trimethylene carbonate‐co‐glycolide) random copolymers were synthesized through the ring‐opening polymerization of 5‐benzyloxy‐trimethylene carbonate and glycolide (GA). The copolymers with different compositions, PBG‐1 with 17% GA units and PBG‐2 with 45% GA units, were obtained. Using these copolymers, microsphere drug delivery systems with submicron sizes were fabricated using an “ultrasonic assisted precipitation method.” The in‐vitro drug release from these microspheres was investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of polystyrene/poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] fluorescent microspheres by miniemulsion polymerization

Fluorescent microspheres have great potential for use as probes in biological diagnostics. In this context, poly[2‐methoxy‐5‐(2′‐ethylhexyloxy)‐p‐phenylenevinylene] (MEH‐PPV), a conjugated polymer which has high quantum yield, controllable emitting wavelength and facile processing in manufacture, was used as a fluorescent material for the preparation of polystyrene (PS)/MEH‐PPV fluorescent microspheres via miniemulsion polymerization. We demonstrate that the emitting wavelength of the PS/MEH‐PPV fluorescent microspheres can be regulated by changing the amount of azobisisobutyronitrile initiator in the polymerization process. Using acrylic acid comonomer, poly[styrene‐co‐(acrylic acid)]/MEH‐PPV fluorescent microspheres with functional carboxyl groups were also prepared. All the microspheres were characterized using transmission electron microscopy, scanning electron microscopy, fluorescence microscopy and fluorescence spectrophotometry. The functional carboxyl groups were characterized using Fourier transform infrared spectroscopy. This work provides a novel platform for the preparation of conjugated polymer fluorescent microspheres for biological applications. © 2012 Society of Chemical Industry     

Plasma‐induced,solid‐state polymerization of N‐isopropylacrylamide

The radio‐frequency plasma‐initiated polymerization of N‐isopropylacrylamide (NIPAM) in the solid state was performed. The isolated linear polymer was characterized by ¹³C‐NMR, ¹H‐NMR, and Fourier transform infrared spectroscopy, and the effects of selected operational plasma parameters (discharge power and time) on the conversion rates were studied. Reversible transitions at the volume‐phase‐transition temperatures of the swelled poly(N‐isopropylacrylamide) hydrogels were investigated by differential scanning calorimetry. The surface morphologies before and after plasma treatment were followed by scanning electron microscopy. With the obtained X‐ray diffraction results, we propose a solid‐state plasma polymerization mechanism for the NIPAM. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis of poly(epichlorohydrin‐g‐methyl methacrylate) and poly(epichlorohydrin‐g‐styrene) graft copolymers by a combination of cationic and photopolymerization methods

Poly(epichlorohydrin‐g‐styrene) and poly (epichlorohydrin‐g‐methyl methacrylate) graft copolymers were synthesized by a combination of cationic and photoinitiated free‐radical polymerization. For this purpose, first, epichlorohydrin was polymerized with tetrafluoroboric acid (HBF₄) via a cationic ring‐opening mechanism, and, then, polyepichlorohydrin (PECH) was reacted ethyl‐hydroxymethyl dithio sodium carbamate to obtain a macrophotoinitiator. PECH, possessing photolabile thiuram disulfide groups, was used in the photoinduced polymerization of styrene or methyl methacrylate to yield the graft copolymers. The graft copolymers were characterized by ¹H‐NMR spectroscopy, differential scanning calorimetry, and gel permeation chromatography. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Functionalization of poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) films via surface‐initiated atom transfer radical polymerization: Comparison with the conventional free‐radical grafting procedure

We modified hydrophobic poly(3‐hydroxybutyrate‐co‐3‐hydroxyvalerate) (PHBHV) films with hydrophilic chains to control their surface properties. We designed and investigated surface‐initiated atom transfer radical polymerization (SI‐ATRP) to modify the PHBHV films by grafting poly(2‐hydroxyethyl methacrylate) (PHEMA) from the surface. This method consisted of two steps. In the first step, amino functions were formed on the surface by aminolysis; this was followed by the immobilization of an atom transfer radical polymerization initiator, 2‐bromoisobutyryl bromide. In the second step, the PHEMA chains were grafted to the substrate by a polymerization process initiated by the surface‐bound initiator. The SI‐ATRP technique was expected to favor a polymerization process with a controlled manner. The experimental results demonstrate that the grafting density was controlled by the reaction conditions in the first step. The grafted films were analyzed by Fourier transform infrared spectroscopy, contact angle testing, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. The results show that grafted chains under the SI‐ATRP method were preferentially located on the surface for surface grafting and in the bulk for conventional free‐radical polymerization initiated by benzoyl peroxide. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Two‐stage grafting onto polyethylene fiber by radiation‐induced graft polymerization and atom transfer radical polymerization

Two‐stage graft polymerization onto polyethylene (PE) fiber was demonstrated. The graft side chain was formed by radiation‐induced graft polymerization. A PE fiber was irradiated with an electron beam and immersed in a vinyl monomer solution. The terminal of the formed graft chain was halogenated using N‐bromosuccinimide. The halogenated graft chain was then extended by atom transfer radical polymerization to obtain block‐copolymer grafted PE fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Miniaturized biocatalysis on polyacrylate‐based capillary monoliths

We developed a synthetic concept for the immobilization of enzymes onto monolithic supports. In addition, we elaborate on a generally applicable method for the rapid screening of the activity of such immobilized enzymes. For these purposes, we prepared monolithic acrylate‐based systems by electron‐beam (EB)‐triggered free‐radical polymerization within the confines of 200‐μm capillary columns. Aiming for protein immobilization, we subjected the polyacrylate‐based monoliths to EB‐mediated grafting processes to introduce functional surface‐located groups suited for the subsequent generation of functional units that themselves could bind different proteins. For the generation of the functional units, we used ring‐opening metathesis polymerization and free‐radical polymerization. The produced systems were tested for their ability to bind or repel proteins as exemplified by the use of the serine protease trypsin, which was used to catalyze the hydrolysis of N‐α‐benzoyl‐L ‐arginine ethyl ester (BAEE). Finally, the monolith‐immobilized trypsin systems were used for enzymatic peptide synthesis purposes, such as the acyl transfer of BAEE to amino acid amides. Complementarily, we used an immobilized trypsin variant, which we additionally subjected to on‐column chemical modification with succinic anhydride to alter its synthetic properties. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of prepolyurethane on the performances of poly(acrylates‐co‐urethane) copolymer

Poly(acrylates‐co‐urethane) copolymers were synthesized by the polymerization of acrylates and 2‐hydroxyethyl acrylate terminated polyurethane (prepolyurethane) at room temperature. The polymerization was initiated by the radicals, which were produced by the oxidation of tri‐n‐butylborane (TBB) from the mixing of TBB/hexamethylene diamine complex and diisocyanate decomplexer. The effects of prepolyurethane on the performances of copolymers were discussed. The results indicated that the damping property and flexibility of copolymers were obviously higher than that of pure polyacrylates. Dynamic mechanical analysis and transmission electron microscope results showed that PU was dispersed in polyacrylates phase very well. The copolymers were found to bond well to low surface energy materials because of introduction of PU. The lap shearing strength of copolymer bonding polypropylene or polyethylene both had the trend of first increase followed by decrease with the prepolyurethane content increase. The copolymers as adhesives were also shown to have a long working life and be suitable for utilization at low temperature especially at room temperature. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Rheokinetics of ring‐opening metathesis polymerization of norbornene‐based monomers intended for self‐healing applications

Constant shear rate rheokinetics was used to evaluate the polymerization of four norbornene‐based monomer systems as candidate healing agents in self‐healing composites: endo‐dicyclopentadiene (endo‐DCPD), exo‐DCPD, 5‐ethylidene‐2‐norbornene (ENB), and a 1:1 volume mixture of endo‐DCPD:ENB. The ruthenium catalyst induced ring‐opening metathesis polymerization of the healing agent candidates were measured experimentally under isothermal conditions while the influences of several different variables were considered (e.g., test temperature, catalyst concentration, catalyst form). Analyzing the increase in viscosity during the polymerization, comparisons of the reaction kinetics of the different monomers were quantified by defining two parameters, t_t and Δt, which correspond to the polymerization initiation and propagation rates respectively. Generally, ENB shows the fastest polymerization kinetics, and endo‐DCPD the slowest. POLYM. ENG. SCI. 46:1804–1811, 2006. © 2006 Society of Plastics Engineers     

Biodegradable poly(ester‐ether)s: ring‐opening polymerization of D,L‐3‐methyl‐1,4‐dioxan‐2‐one using various initiator systems

The synthesis and detailed characterization of racemic 3‐methyl‐1,4‐dioxan‐2‐one (3‐MeDX) are reported. The bulk ring‐opening polymerization of 3‐MeDX, to yield a poly(ester‐ether) meant for biomedical applications, in the presence of various initiators such as tin(II) octanoate, tin(II) octanoate/n‐butyl alcohol, aluminium tris‐isopropoxide and an aluminium Schiff base complex (HAPENAlOⁱPr) under varying experimental conditions is here detailed for the first time. Polymerization kinetics were investigated and compared with those of 1,4‐dioxan‐2‐one. The studies reveal that the rate of polymerization of 3‐MeDX is less than that of 1,4‐dioxan‐2‐one. Experimental conditions to achieve relatively high molar masses have been established. Thermodynamic parameters such as enthalpy and entropy of 3‐MeDX polymerization as well as ceiling temperature have been determined. Poly(D ,L ‐3‐MeDX) is found to possess a much lower ceiling temperature than poly(1,4‐dioxan‐2‐one). Poly(D ,L ‐3‐MeDX) was characterized using NMR spectroscopy, matrix‐assisted laser desorption ionization mass spectrometry, size exclusion chromatography and differential scanning calorimetry. This polymer is an amorphous material with a glass transition temperature of about ?20 °C. Copyright © 2010 Society of Chemical Industry