Radical Polymerization Of Acrylic Monomers Research Articles

High compatible free radical UV-curable fluorine-containing polyacrylic acrylate prepolymer

Abstract Fluorine-containing polyacrylic acrylate prepolymers, with different molecular weight and fluorine content, were successfully synthesized by solution radical polymerization of acrylate monomer and following esterification. The compatibility of the prepolymers with solvents and acrylate monomers could be improved markedly with introduction of butyl acrylate as co-monomer and decreasing the polymer molecular weight. It could form homogeneous solution in solvents and monomers and transparent cured film combined with commercial photoinitiator and monomer, evidenced with vision, transmittance, dynamic mechanic and graphic analysis. At the same time, this kind of prepolymers could perform rapid photopolymerization and reach about 95% double bond conversion after 90 s ultraviolet irradiation. It also showed unique surface tension as low as 24.9 dyn/cm and lower glass transition temperature ( T g ) with higher fluorine concentration. This kind of novel prepolymer could be widely used in photopolymerization for low surface tension and high optical demands.

Experimental Evidence Shedding Light on the Origin of the Reduction of Branching of Acrylates in ATRP

Intramolecular chain transfer to polymer and subsequent propagation of tertiary radicals cause extensive branching in radical polymerization of acrylic monomers. Studies in the literature have shown that under controlled radical polymerization conditions the extent of branching is significantly reduced. There are two competing theories to explain this effect. In one, the cause of reduced branching is attributed to a reduction in the number of backbiting events, and in the other that has been specifically applied to atom-transfer radical polymerization (ATRP), the cause is due to trapping of the tertiary radical by a fast deactivation step. In this article we show that trapping of the tertiary radical is not the cause for the reduction in branching fraction. This is shown by the absence of the corresponding patched midchain bromide structure as revealed by quantitative 13C NMR and by the ability to chain extend from a poly(butyl acrylate-co-butyl 2-bromoacrylate) copolymer by ATRP. These results are comple...

A Tris(triphenylphosphine)ruthenium(II) Complex as a UV Photoinitiator for Free-Radical Polymerization and in Situ Silver Nanoparticle Formation in Cationic Films

The characterization and the photochemical investigation of a RuII complex (Ru(PPh3)3Cl2) having phosphine ligands are reported. DFT calculations and ESR spin trapping experiments revealed for the first time that the photodecomposition of the complex is governed by a homolytic cleavage of the P–(C6H5) bond generating phenyl radicals Ph• which are able to initiate the free radical polymerization of acrylate monomers. The addition of a H-donor HD plays a key role in the cationic photopolymerization of epoxides: (i) the reaction efficiency is enhanced using [Ru(PPh3)3Cl2]/HD and (ii) the in situ formation of Ag nanoparticles is observed in the presence of Ru(PPh3)3Cl2/HD/AgSbF6 according to the following reactions: Ph•/DH hydrogen abstraction yielding a D• radical and oxidation of D• by the silver salt.

Recoverable Reusable Polyisobutylene (PIB)-Bound Ruthenium Bipyridine (Ru(PIB-bpy)3Cl2) Photoredox Polymerization Catalysts.

Polyisobutylene (PIB)-bound ruthenium bipyridine [Ru(PIB-bpy)3]2+ metal complexes were prepared from PIB ligands formed by alkylation of 4,4'-dimethylbipyridine with polyisobutylene bromide. The product Ru(PIB-bpy)3Cl2 complexes with at least one PIB ligand per bipyridine unit function as soluble recyclable photoredox catalysts in free radical polymerization of acrylate monomers under visible light irradiation at 25 °C with ethyl 2-bromoisobutyrate as the initiator in the presence of diisopropylethylamine. The polyacrylate products contained only about 1 ppm Ru contamination. This PIB-bound catalyst was recyclable and showed about 50-fold less Ru leaching as compared to Ru leaching in a polymerization catalyzed by the low molecular weight Ru catalyst, Ru(bpy)3(PF6)2.

Silver Nanoparticles Coated with Thioxanthone Derivative as Hybrid Photoinitiating Systems for Free Radical Polymerization

A new type of photoinitiator for free radical polymerization was synthesized and characterized. 2-(11-Mercaptoundecyloxy)thioxanthone (1) was anchored at the surface of silver nanoparticles (NPs), and the interaction of plasmon field generated in the immediate vicinity of Ag NPs carrying the chromophores was evaluated. The optical features and structure of the silver-initiator nanoassemblies (Ag@1) were characterized by UV-vis and fluorescence spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). TEM and XRD studies revealed the presence of ca. 5-6 nm diameter Ag NPs, and XPS also confirmed the successful anchorage of 1 at their periphery. The nanoassemblies Ag@1 were successfully used as macroinitiator for radical polymerization of acrylate monomers, triggered photochemically, to obtain Ag(0)-polyacrylate nanocomposite materials. The nanocomposite materials synthesized with the use of Ag@1 exhibit attractive possibilities for patterning the surface of thin films.

Free radical formation in three-component photoinitiating systems

N,N′-diethylthiacarbocyanine iodide (Cy) with two different compounds acting as co-initiators were used in the three-component photoinitiating systems for free radical polymerization of acrylate monomer. The steady state and time-resolved techniques were used to study the fluorescence quenching by co-initiators, as well as laser flash photolysis to investigate an electron transfer process, that occurs in these photoinitiating system (PIS). To investigate the key factors involved with visible-light activated radical polymerizations involving three-component photoinitiators, we used thermodynamic feasibility and kinetic considerations to study photopolymerizations initiated with thiacarbocyanine dye as a photosensitizer. The Rehm–Weller equation was used to verify the thermodynamic feasibility for electron transfer reaction. Experiments show, that the main interaction between the dye and both co-initiators occurs through its excited singlet state. It was concluded, that the key kinetic factors for efficient visible-light activated initiation process are summarized in two ways: (1) to retard back electron transfer and recombination reaction steps and (2) to use a secondary reaction step to consuming dye-based radical and regenerating the original photosensitizer.Basing on the study, it is known that, there are two possible mechanisms of generation of free radicals, which can start polymerization involving photoreducible series mechanism and parallel series mechanism (photoreducible–photooxidizable series mechanism).

Multicationic monomethine dyes as sensitizers in two- and three-component photoinitiating systems for multiacrylate monomers

This paper is focused on the description of the synthesis, spectroscopic and electrochemical properties, and the free radical photoinitiation abilities of new multi-cationic monomethine dyes. The new monomethine dyes were employed both as the visible light photoinitiators of acrylate monomer polymerization and as fluorescence probes for monitoring the progress of polymerization. A degree of polymer cure from the measurement of the changes in the probe emission intensity and position shift during the thermally initiated polymerization of monoacrylate was obtained. A distinct increase in the intensity of the dyes fluorescence was observed during polymerization when the degree of monomer conversion was gradually increasing. The second part of this work is the possibility of an application of the dyes synthesized in combination with borate anions, as photoinitiating systems. Novel multi-cationic monomethine dyes paired with n-butyltriphenylborate anions are very efficient visible light photoinitiators of free radical polymerization of acrylate monomers. Their photoinitiating abilities were compared with the photoinitiation ability of Rose Bengal derivative, e.g. typical triplet state photoinitiator. The addition of a second co-initiator to the two-component photoinitiating system (monomethine borate salts) enhances their photoinitiating abilities.

Synthesis and performance of alkyd–acrylic hybrid binders

Preparation and properties of alkyd–acrylic hybrids have been studied. Hybrids with different alkyd–acrylic ratios and acrylic parts were prepared via free radical polymerization of acrylic monomers in a presence of an unsaturated alkyd resin using emulsion polymerization technique. The binders were characterized according to their solid content, conversion, viscosity, pH and particle size. Evidence on formation of true copolymer was obtained via NMR spectroscopy and molecular weight and glass transition temperature measurements, as well as via performance studies. The performance evaluation was focused on investigation of drying, penetration and water repellency ability, as well as on film formation and surface topography studies. The binders were compared to references of an alkyd emulsion, acrylic latex and a blend made of them. The results showed that alkyd–acrylic hybrids with synergistic and improved properties can be prepared.

Three‐cationic carbocyanine dyes as sensitizers in very efficient photoinitiating systems for multifunctional monomer polymerization

AbstractThis article is focused on the description of the synthesis, spectroscopic, electrochemical properties, and the free radical photoinitiation abilities of new three‐cationic carbocyanine dyes. A new synthestic strategy for preparation of symmetrical cyanine dyes has been developed based on the 2‐methylbenzothiazole, 2‐methylbenzoxazole and 2,3,3‐trimethylindolinium quaternization by α‐bromo‐ω‐tertiary ammonium salts followed by the condensation of obtained product with triethyl ortho‐formate. Resulted dyes possess in one molecule three quaternary nitrogen atoms, for example, they are three‐cationic in character. Novel three‐cationic symmetric carbocyanine dyes paired with n‐butyltriphenylborate anions are very efficient photoinitiators of free radical polymerization of acrylate monomers, for example, (TMPTA) when irradiated with the visible emission of an argon‐ion laser. The photoinitiating abilities of the novel photoredox pairs were compared to the photoinitiation properties of their monocationic equivalents, for example, N,N′‐diethylthia‐, N,N′‐diethyloxa‐ and N,N′‐dimethylindocarbocyanine n‐butyltriphenylborates (SB2, OB2, and IB2) and also compared to the initiation ability of Rose Bengal derivative, for example, typical triplet state photoinitiator. The kinetic studies clearly demonstrated that the three‐cationic carbocyanine borate photoredox pairs exhibit a significant increase in the efficiency of TMPTA free radical polymerization in comparison to the photoredox pairs containing structurally related, mono‐cationic carbocyanine borates. It was also shown that, the addition of a second coinitiator to the cyanine borate salts enhances their photoinitiating abilities. The best results were obtained for three cationic carbocyanine borates in the presence of second coinitiator being N‐methoxypyridinium n‐butyltriphenylborate. The photoinitiating abilities of the systems of these types are more effective than those composed of carbocyanine cation/borate anion exclusively. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4636–4654, 2009

Dual-curable acrylic pressure-sensitive adhesives based on UV and thermal processes

Several dual-curable acrylic pressure-sensitive adhesives (PSA) were synthesized by the radical polymerization of acrylic monomers containing benzophenone, hydroxyl, and alkyl groups. The optimum extent of UV-induced cure was determined by varying the content of the benzophenone groups (the photoinitiator) from 0.5 to 1.5 wt%. The weight average molecular weight of the polymers obtained ranged from 300,000 to 700,000 amu. The coated pressure-sensitive adhesives were cured either by short UV exposure to induce the grafting of acrylic polymers, or by heating for 6 h at 60 °C to promote the reactions between the polyisocyanates and hydroxyl groups. The dual-curing behavior was determined by monitoring both processes quantitatively by infrared spectroscopy. The developed dual-curable acrylic pressure-sensitive adhesives were found to compensate for the limitations in UV-induced curing of thick coatings.

Low-temperature postradiation quasi-living radical polymerization of acrylic monomers in the presence of fullerene C 60

Water-soluble fullerene C 60 -containing polymers of acrylamide and acrylic acid were obtained by low-temperature radiation-induced quasi-living radical polymerization.

Dual-curable fluorinated poly(methacrylate) copolymers for optical adhesives

In pursuit of photo-curable adhesive for optical communication, dual-curable acrylic oligomers (AOs) having alkoxy silane group, fluorine atoms and vinyl group as a pendent group were synthesized by two-stage reactions. The isocyanate group containing oligomers were firstly synthesized via radical polymerization of acrylic monomers, and followed by urethane reaction with 2-hydroxy ethyl methacrylate. The dual curing behaviors, e.g. thermal and photo-cure, were studied by using photo-differential scanning calorimetry (DSC) and real-time IR. An optimum adhesive formulation, based on AO (15 g), epoxy acrylate (80 g), isobonyl methacrylate (17 g) and photo-initiator (3 g), was obtained. As the content of AO was increased in the optical adhesive formulation, refractive index decreased but transmittance increased due to the increase in fluorine content. The optical transmittance at the range of 1.3 to 1.55 μm was higher than 90%. The addition of colloidal silica with the earlier mentioned formulation was helpful in decreasing crosslinking volume shrinkage and the increasing of glass fiber adhesion. The required properties for the optical adhesive, including chemical resistance and thermal resistance, dimension stability, etc. were also investigated. Copyright © 2005 John Wiley & Sons, Ltd.

Stereocontrol in radical polymerization of acrylic monomers

A clear effect of Lewis acids, such as scandium trifluoromethanesulfonate [Sc(OTf) 3 ], on stereocontrol during the radical polymerization of a designed monomer, benzyl α-(methoxymethyl)acrylate was found. This Lewis acid also influenced the stereochemistry in the radical polymerization of methyl methacrylate giving a less syndiotactic and more isotactic polymer, although many Lewis acids were not effective. A catalytic amount of Lewis acids, such as Y(OTf) 3 and Yb(OTf) 3 , also significantly enhanced isotactic-specificity during the radical polymerization of acrylamide and its derivatives, N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide. Obvious solvent and temperature effects on tacticity were observed in these polymerizations, and poly(NIPAM) with >80% triad isotactic content has been obtained in the presence of Lewis acids.

Photolysis of N-phenylglycines sensitized by polycyclic aromatic hydrocarbons : Effects of sensitizers and substituent groups and application to photopolymerization

The effects of sensitizers and substituent groups on the rate of sensitized photodecomposition of N-phenylglycine (NPG) were investigated under irradiation using light of 366 nm. It was found that pyrene was the most effective polycyclic aromatic hydrocarbon as a sensitizer for the NPG photodecomposition. Introduction of an electron-donating group into the aromatic ring of NPG resulted in the enhancement of the pyrene-sensitized photodecomposition rate. Especially, the photodecomposition rate of N-(2,4-dimethylphenyl)glycine was larger than that of parent NPG by a factor of 4.6. The results were discussed on the basis of the free-energy change for the electron transfer from NPG or its derivatives to the excited sensitizer. Furthermore, the pyrene-sensitized photodecomposition of NPGs could be utilized for a photoinitiator for free radical polymerization of acrylate monomers.

UV curable acrylic dispersion for the cationic electro-deposition coating

The vinyl group containing polymer was synthesized via radical polymerization of acrylic monomers followed by reaction with methacrylic oxyethyl isocyanate(MOI). Stable dispersions of the vinyl group containing polymer, pentaerythritol triacrylate(PETA) and photo initiator were prepared by neutralization of the above synthesized polymer with lactic acid. Electro-deposition process was introduced to apply UV-curable acrylic dispersion into the nickel-plated plastic substrate. The prepared dispersion containing PETA has higher particle size and higher deposition yield than those of the dispersion without PETA. The electro-deposited film was cross-linked by UV radiation after 10 minutes flash-off stage at 80 °C. The kinetic study by real-time FT-IR revealed that the cross-linked films containing PETA gave higher conversion than those without PETA resulting in harder film.

Side chain organometallic polymers containing cyclopalladated potentially second order nonlinear optical active fragments as pendants

Three new organometallic homopolymers and a copolymer have been obtained by radical polymerization of acrylic monomers. The monomers were obtained by bridge splitting reaction from cyclopalladated dinuclear species and the appropriate imines. The polymers exhibit good thermal and chemical stability and are soluble in common organic solvents. Their potential ability to display second order nonlinear optical activity was tested by solvatochromic effect measurements on the corresponding monomers. In particular, the copolymer appears to be the most versatile in consideration of its thermal behaviour, solubility and inherent viscosity.

Synthesis, characterization of polyacrylate-g-carbon black and its application to soap-free waterborne coating

Polyacrylate-g-Carbon Black (abbrev. as gCB) was prepared by free radical polymerization of acrylate monomers on the carbon black surface, which was initiated by a redox system consisting of cerium ammonium nitrate and hydroxymethyl carbon black. gCB was ascertained by X-ray Photoelectron Spectrometry (XPS). The optimum conditions of synthesis were studied. The stabilities of gCB dispersing in water were studied by zeta potential measurement and spectrophotometric analysis. The results showed that gCB could disperse in water better than the ungrafted carbon black. gCB could be dispersed in the soap-free hydrosol forming a colored soap-free water-borne coating with satisfactory comprehensive performance. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1100–1106, 2001

Multiphoton-absorbing organic materials for microfabrication, emerging optical applications and non-destructive three-dimensional imaging

Non-resonant two-photon absorption (TPA) can be defined as the simultaneous absorption of two photons, via a virtual state, in a medium. TPA exhibits a quadratic dependence of absorption on the incident light intensity, resulting in highly localized photoexcitation. Recent developments in the design and synthesis of efficient, stable TPA organic materials are discussed. Microfabrication via two-photon induced free radical polymerization of acrylate monomers and cationic polymerization of epoxide monomers was accomplished using commercially available photoinitiators, and also a custom-made compound possessing high two-photon absorptivity. Two-photon facilitated photoisomerization of a fulgide in solution and in a polymer thin film demonstrated two-photon induced photochromism and its application in interferometric image recording, respectively. Greatly enhanced signal-to-noise ratios and resolution were achieved in the non-destructive three-dimensional two-photon fluorescence imaging of a polymer-coated substrate versus conventional single-photon laser scanning confocal microscopic imaging. Multifunctional TPA organic materials and fabrication of functional microstructures are also discussed. Copyright © 2000 John Wiley & Sons, Ltd.

Living Radical Polymerization of Acrylates Initiated and Controlled by Organocobalt Porphyrin Complexes

(Tetramesitylporphyrinato)cobalt(II) ((TMP)Co•) and the octabromo derivative ((Br8TMP)Co•) mediate an effective living radical polymerization of acrylate monomers through the formation of dormant organocobalt complexes ((por)Co−PA) with the growing acrylate polymer radical (•PA). Radical polymerization of methyl acrylate controlled by (Br8TMP)Co• is substantially faster than that for (TMP)Co• because of the higher concentration of radicals resulting from greater dissociation of the dormant organocobalt complex. Unusually large molecular weight low polydispersity acrylate homopolymers and block copolymers have been obtained by this method. Kinetic studies for the conversion of methyl acrylate (MA) to poly(methyl acrylate) (PMA) initiated and controlled by (TMP)Co−PMA are fully compatable with a living radical process mediated by the metallo radical ((TMP)Co•). Overall apparent activation parameters for the polymerization process (Δ = 28 ± 2 kcal mol-1; Δ = 4 ± 1 cal K-1 mol-1) are interpreted as sums of th...

Polymerization of methacrylic acid esters with the aged system of lanthanum versatate and p‐chlorobenzenediazonium tetrafluoroborate

AbstractThe aged system of lanthanum versatate (1) and p‐chlorobenzenediazonium tetrafluoroborate (2) was found to initiate effectively the radical polymerization of acrylic monomers including alkyl methacrylates, butyl acrylate and acrylonitrile, although its initiating activity is lower than that of the non‐aged system. The polymerization of methyl methacrylate (3) with the aged 1/2 system was studied kinetically in acetone. The initial polymerization rate (Rp) is expressed by Rp = Kċ[aged 1/2]0.80 ċ [3]1.1 at 50°C. The overall activation energy of the polymerization is 59.0 kJ ċ mol−1. The molecular weight of the resulting poly(3) formed in the early stage increases with increasing conversion. The polymerization system involves a persistent radical showing a four‐line EPR spectrum with a g‐value of 2.004. A three‐line spectrum due to the nitroxyl radical was also observed at lower monomer concentrations. The total concentration of persistent radicals was found to correspond well to the instantaneous polymerization rate. The copolymerization of styrene (M1) and 3 (M2) with the aged initiator system was examined at 50°C in acetone. r1 and r2 are 0.19 and 0.47, respectively. The former is considerably smaller than that (0.52) reported for the conventional radical polymerization.