Photopolymerization Rate Research Articles

Oxygen-Accelerated Photopolymerization of Methyl Methacrylate in the Presence of Amides

Abstract The photopolymerization of methyl methacrylate (MMA) was accelerated by amides such as N-methylpyrrolidone (NMP), pyrrolidone (PD), and dimethylacetamide (DMA) in the following order: NMP > PD > DMA. the rates of photopolymerization of styrene and vinyl acetate were also increased by NMP. the results suggest that the free radicals produced by the photodecomposition of these amides initiate the polymerization. Moreover, the rate of photopolymerization of MMA in the presence of the amides was enhanced by oxygen after an induction period. the UV absorption spectra of these amides were measured under nitrogen and oxygen; the extra absorptions observed under oxygen were ascribed to charge-transfter complexes between oxygen and the amides. the reaction mechanism is discussed on the basis of the photoreaction of the complex

Diene-containing 1,3-diacylglycero-2-phosphoric acid

A polymerizable 1,3-diacylglycero-2-phosphoric acid, 1,3-bis(octadeca-trans-2, trans-4-dienoyl)-rac-glycero-2-phosphoric acid 1, was synthesized. The lipid bilayer formation and its pH-dependence were elucidated by ultraviolet, fluorescence, DSC and 1H- and 31P-NMR measurements. The rate of photopolymerization as bilayer assemblies was sensitive to pH, i.e. the the degree of dissociation of the phosphoric group of 1.

Thioxanthone photopolymers I: A kinetic study of methyl methacrylate polymerization using 2-benzyloxy thioxanthone, free and polymer bound, as photoinitiator

The general photochemistry and photopolymerization activity of free and polymer-bound 2-benzyloxy thioxanthone were studied. The polymeric photoinitiator was prepared by chemical modification of an atactic polystyrene ( M̄ n = 97 500). The spectroscopic properties of free and polymer-bound 2-benzyloxy thioxanthone were examined in various solvents and the data were compared with their behaviour as photoinitiators of polymerization. Quantitative steady state and microsecond flash photolysis studies in the absence and presence of a tertiary amine were also related to their photopolymerization activity. The dependence of the photopolymerization rates and quantum yield of polymerization of methyl methacrylate on the concentration of amine, photoinitiator and monomer was studied by photodilatometry. Furthermore, all the polymers obtained were characterized by gel permeation chromatography and the ratio of the propagation constant to the square root of the termination rate constant k p/ k t 1 2 was obtained.

Effect of the medium on the photopolymerization of butyl methacrylate initiated by benzophenones in the presence of amines

Using methods of dilatometry and pulsed photolysis a study was made of the influence of the medium on the photopolymerization of butyl methacrylate initiated by benzophenones in the presence of amines. It was found that irrespective of the nature of the medium the photopolymerization has a free-radical character; at the same time in polar media a relationship was observed between the photopolymerization rate on the one hand, and the σ-constants of Hammett substituents in benzophenone and the ionization potential of the amine on the other hand. The photopolymerization rate was significantly reduced with increasing polarity of the medium. According to the results of the pulsed photolysis, this is attributable to a change in deactivation of the excited state of the benzophenone by the monomer.

Photochemistry and photopolymerization activity of novel perester derivatives of fluorenone

The photochemistry and photopolymerization activity of three novel t-butylperester derivatives of fluorenone have been examined and compared with unsubstituted fluorenone and a tetra-t-butylperester of benzophenone. The longest wavelength absorption bands of all three derivatives are blue-shifted from that of fluorenone itself with a marked increase in the corresponding extinction coefficients, associated with the electron withdrawing effect of the peroxyester groups and a concurrent increase in the charge transfer content of the molecule due to substitution. The fluorescence quantum yields of the fluorenone derivatives are also greater than those of fluorenone in a range of solvent systems; this effect is associated with an increase in the degree of charge transfer content in the lowest excited singlet state. Photoreduction quantum yields are also higher in 2-propanol solvent, that for the bis-perester derivative being twice that of the monoperester. The presence of a tertiary amine (triethylamine) enhances the photoreduction quantum yields due to an increase in the probability of electron abstraction. Conventional micro-second flash photolysis in 2-propanol solution indicates that free radical formation occurs from an upper excited triplet n-π ∗ state. Rates of photopolymerization in bulk poly(methyl methacrylate) on a percentage basis are also higher for the three perester derivatives with those for the monoesters being greater than for the bisperester. The latter is associated with a much higher probability of self termination reactions. The presence of methyldiethanolamine enhances the rate of photopolymerization with both fluorenone and the monoperester derivatives but reduces that with the 2-t-butylperester, 7-nitro and bisperester derivatives due to competitive termination reactions. The results are discussed on the basis of the photophysical data and subsequent spectroscopic analysis of the polymer samples by second-order derivative u.v. spectroscopy and fluorescence analysis, both of which are shown to be valuable methods for the determination of chromophoric initiator fragments.

Topochemistry of the solid-state polymerization of diacetylenes containing unsaturated side groups

The electronic spectra of polymers in the monomer matrix have been investigated for two structurally similar diacetylenes one of which has side substituents containing the allyl bond which is responsible for degradative chain transfer in the case of liquid-phase polymerization. Melting points and phase transition temperatures were determined for the monomers and polymers by the DSC method. A study of the integral absorption of the polymers in the visible portion of the spectrum shows that the photopolymerization rate for the diacetylene containing the allyl double bond is only one-third of that for the diacetylene that is without the allyl bond. This fact is attributed to a high degree of topotacticity of the solid-state polymerization of crystalline diacetylenes.

Photopolymerisation mit der initiatorkombination 9,10-phenanthrenchinon-aryloniumverbindungen

The rate of photopolymerization of methyl methacrylate (MMA) intiated by phenanthrene quinone (PQ, light absorbing initiator) increases when arene onium salts (co-initiators, Ar 3S +, Ar 2I +, ArN 2 +) are added. By means of flash photolysis studies and quantum yield measurements in dependence on onium salt, MMA and hydrogen donor concentrations, a mechanism of this reaction was deduced. The main effect on photopolymerization rate is caused by oxidation of the inhibiting nucleophilic initiator radicals (semiquinone or semiquinone anion radicals, radical adducts of PQ to MMA) by arene onium salts to give reactive arene radicals which initiate MMA polymerization. At higher co-initiator concentrations, the reaction of exciten PQ singlet state with the onium compounds is probable.

Photochemistry of thioxanthones—III. Spectroscopic and flash photolysis study on hydroxy and methoxy derivatives

The spectroscopic properties of 9 oil soluble hydroxy and methoxy thioxanthone derivatives have been examined in various solvents and the data compared to their photopolymerization efficiency and flash photolysis behaviour in solution. Absorption maxima, extinction coefficients, fluorescence and phosphorescence spectra and quantum yields have been measured. Generally, most of the compounds exhibit low fluorescence and high phosphorescence quantum yields except 1-substituted derivatives where intra-molecular hydrogen bonding is involved. These observations are consistent with the high photoreactivity of the molecules occurring via the lowest excited triplet state. Photopolymerization rates of n-butyl methacrylate, using N-diethylmethylamine as co-initiator, correlate to some extent with the absorption maxima and extinction coefficients of the thioxanthones. Transient formation on micro-second flash photolysis is associated with the ketyl radical formed by the lowest excited triplet state of the thioxanthones abstracting a hydrogen atom from the solvent. In the presence of a tertiary amine, a new longer wavelength transient absorption is produced and is assigned to a radical-anion formed by the lowest excited triplet state of the thioxanthones abstracting an electron from the amine. A correlation was observed between the transient absorption due to the radical-anion and the ionisation potential of various amines. Flash photolysis studies in acid and base media confirmed the identity of the radical and radical-ion species. Intra-molecular hydrogen bonding in the α-position to the carbonyl group deactivates both the lowest excited singlet and triplet states of thioxanthone but has little effect on polymerization efficiency. The latter is associated with competition of the carbonyl group with the amine co-initiator for hydrogen bonding and consequent electron abstraction to give an active radical-anion. This is confirmed using micro-second flash photolysis.

Photochemistry of thioxanthones—IV. Spectroscopic and flash photolysis study on novel n-propoxy and methyl, n-propoxy derivatives

The spectroscopic properties of seven oil soluble n-propoxy and methyl, n-propoxy substituted thioxanthone structures have been examined in various solvents and the data compared to their photopolymerization efficiencies, photochemical stabilities and flash photolysis behaviours in solution. Absorption maxima, extinction coefficients, fluorescence and phosphorescence spectra and quantum yields have been measured. Generally, all the compounds exhibit low fluorescence and high phosphorescence quantum yields but the ratio is solvent dependent. These observations are consistent with the high photoreactivity of the molecules operating in the lowest excited triplet state which is nπ* in character. Photopolymerization rates of n-butyl methacrylate with N-diethylmethylamine co-initiator correlate with the absorption maxima and extinction coefficients of the thioxanthones and also the degree of quenching of their fluorescence by the amine, indicating the importance of electron transfer. In the absence of a tertiary amine, transient formation on micro-second flash photolysis in 2-propanol is associated with the ketyl radical formed by the lowest excited triplet state abstracting a hydrogen atom from the solvent. In the presence of a tertiary amine, both ketyl radical and radical anion (at longer wavelengths) are observed, the latter being formed via abstraction of an electron from the amine. This is confirmed by a flash photolysis study using amines of various ionization potentials where a correlation is observed with radical anion absorbance. A pH study confirms the identity of the transient species. Activation of the thioxanthone molecule in the 3 and 4 positions with a methyl group enhances initiator activity whereas substitution in the t-position deactivates the molecule through intra-molecular hydrogen atom abstraction.

Kinetic studies of the photopolymerization of methyl methacrylate in solution by benzophenones in presence of amines

The methods of dilatometry and pulse photolysis have been used to study the photopolymerization of methyl methacrylate in benzene initiated by benzophenones in presence of amines. The effect of various factors on the rate of photopolymerization has been studied: substituent in benzophenone, the structure of the amine, the concentrations of methyl methacrylate and benzophenones and the intensity of light. A kinetic scheme of the mechanism and the experimentally obtained equations for the rate of photopolymerization are presented. It is shown that the influence of the substituent detected in the benzophenone molecule on the rate of photopolymerization of methyl methacrylate is manifest not in the photochemical stage.

Photopolymerization of vinyl monomers in presence of silicon- and germanium-containing peroxides

The authors have studied the patterns of the photopolymerization of vinyl monomers in presence of silicon- and germanium-containing peroxides of different structure in solution in benzene at 303 K for an intensity of incident light 1·2 × 10 16 hv/cm 2·sec with the wavelength 320–400 nm. They have investigated the electron absorption spectra of the peroxide and their blends with the monomers. The rate of photopolymerization of the monomers in presence of the peroxides studied differs little from that initiated by organic peroxides. The photopolymerization of the monomers with organosilicon peroxides is subject to the patterns of radical polymerization. PMMA obtained by the photopolymerization of the monomer with trimethylcumylperoxysilane in thermal stability surpasses the polymer samples obtained with di-(tert-butyl) peroxide. The thermal stability of PMMA rises even further on polymerization in presence of trimethylcumylperoxysilane with additions of trichlorosilane, a good chain transmitter.

Use of Some Organic Acids and Amines as Photoinitiators of Vinyl Polymerization in the Absence and in the Presence of Benzophenone Photosensitizer

Abstract Preliminary studies on the suitability of some organic acids and amines, separately and in combination with each other, as photo-initiators for the polymerization of methyl methacrylate were made. Combinations of maleic acid or phthalic acid with any of the tertiary amines–triethyl amine, demethyl aniline, and diethylaniline-proved to be interesting photoinitiator systems in view of the fact that the initiator components in each combination were ineffective as initiators when used separately. The rate of photopolymerization in each of the above acid-amine combination system was much enhanced and the respective inhibition period largely reduced when benzophenone was used as the photoinitiator. Aliphatic diamine or polyamines such as ethylene diamine, diethylene triamine, and tri-ethylene tetramine, were ineffective as photoinitiators when used alone or in combination with maleic acid, but became effective

Investigation of the layered polymerization process

The photoinitiated layered polymerization of compositions based on polyvinyl compounds under UV irradiation has been investigated by methods of dilatometry and UV analysis. The reduction in the photopolymerization rate and lengthening of the induction period as the thickness of the forming polymer increases are due to a reduction in the rate at which light penetrates deeply into the layer of the composition in its region of photosensitivity. The illumination gradient decreases very slightly during photopolymerization. This effect is taken into account in the equation for the polymerization rate. The validity of this approach in determination of the wavelength of the photosensitivity maximum for the photopolmyerizing compositions has been demonstrated.

Studies on Photopolymerization of Methyl Methacrylate Using Sulfur Dioxide-Halogen Combinations as Initiators

Abstract Free radical photopolymerization of methyl methacrylate (MMA) in visible light was studied at 40°C using sulfur dioxide-halogen (Cl2, Br2, and I2) combinations as photoinitiators. Of the three SO2/halogen systems, only the SO2/Br2 combination formed an interesting initiating system due to 1:1 complexation between the two components resulting in pronounced enhancement of the rate of photopolymerization over those produced by each of the initiator components when used as a lone photoinitiator. Photopolymerization of MMA induced by (SO2-Br2) complex (1:1) as the photoinitiator exhibited a low initiator exponent value, 0.26, and a monomer exponent value of 1.5. Kinetic nonidealities were explained on the basis of (a) monomer-dependent chain initiation and (b) significant initiator-dependent chain termination along with the usual bimolecular mode of chain termination.

Mechanism of polymerization of vinyl monomers initiated by benzophenone and its derivatives

Pulse photolysis and dilatometry were used to study the mechanism of photopolymerization of methacrylic esters—methylmethacrylate and butylmethacrylate initiated by benzophenones. The kinetic system of the mechanism is described and the rate of photopolymerization calculated. It was shown that equations for the rate of photopolymerization derived using the kinetic system proposed are in satisfactory agreement with experimental results obtained.

Penetration-depth Dependence of Photochemical Conversions in the Dye-sensitized Heterogeneous Photopolymerization of Acrylamide

Abstract The Amethyst violet-sensitized photolysis of p-tolyl p-anilinobenzenediazo sulfone initiated the polymerization of acrylamide in ethanol-water (9.3 : 0.7, v/v) to yield insoluble polymers. The polymer particles formed scattered the incident 546 nm light, leading to a change in the rate of photopolymerization. Using a 632.8 nm laser beam for viewing the sample at various penetration depths normal to the 546 nm light beam, a new method of determining the penetration-depth dependence of the yield of polymers was presented on the basis of the approximately linear relationship between the optical density at 632.8 nm and the polymer concentration. The method had the advantage that the progress of the photopolymerization, which takes place rapidly, can be easily followed with a high sensitivity below a 2.2% monomer conversion. From an evaluation of the magnitude of both the shadowing and forward scattering arising from the increasing number of polymer particles at various depths, it was confirmed that 546 nm light scattered by polymer particles brought about an effective photopolymerization over a wide range of the depths as a forward-scattering effect. Furthermore, the exposure to the 546 nm beam intensity range from 142 μW/ cm2 to 15.6 μW/ cm2 at sample depths up to 10 mm exhibited equal contributions of shadowing and forward scattering at the depth of ∼1.5 mm.

Vinyl Polymerization by Metal Complexes. XXIII. UV and Kinetic Studies on the Photopolymerization with Iron(III)-Amine-Carbon Tetrachloride Systems

Abstract In order to elucidate the initiation reaction of the photopolymerization with iron(III)-amine-carbon tetrachloride systems, the photochemical reaction process among iron(III), amine, and carbon tetrachloride in methanol solution was followed at 0°C by UV spectroscopy as for iron(III) ion. The rate constants of both the reduction of iron (III) under irradiation with light and the oxidation of iron(II) in the dark were measured, and were related to the rates of photopolymerization of methyl methacrylate. Kinetic study on the photopolymerization of methyl methacrylate with iron(III)-triethylenetetramine-carbon tetrachloride system was made in parallel in methanol solution at 0°C. The initiation mechanism of the photopolymerization was postulated.

The use of a recording dilatometer to study the photopolymerization of ethylene glycol dimethacrylate using the isobutyl ether of benzoin as photoinitiator

A simple recording dilatometer was adapted and used to determine or follow the rates of photopolymerization of ethylene glycol dimethacrylate with the isobutyl ether of benzoin as photoinitiator. The photopolymerization was recorded from 0% to 100% conversion of monomer to polymer, and the results from the dilatometer were compared with other methods (gravimetric, electrical resistance, and differential thermal analysis). The rates of photopolymerization were calculated as a function of initiator concentration, light intensity, and monomer concentration. Gel points could be directly determined along with the degree of conversion of monomer to polymer formation. The recording dilatometer can be used to measure rates of photopolymerization of ultraviolet crosslinking monomers, polymers, or coating systems.

Photoinitiated Polymerization onto Cotton

Polymerizations of acrylamide, diacetone acrylamide, methacrylamide, and N,1'-methylenebisacrylamide from water solutions with cotton were photoinitiated on exposure to near-uv light (3100-4100 Å, peak near 3500 Å). The rates of photopolymerization were as follows: diacetone acrylamide > acrylamide, methacrylamide > N,N-methylenebisacryla mide. Infrared spectra of the copolymer products showed increased carbonyl group absorption. The cotton—poly- (acrylamide) and cotton—poly (diacetone acrylamide) copolymer products were stable to solvent extraction and to acid hydrolysis, but only the.latter was stable to base hydrolysis. Differential dyeing indicated variation in the deposition of the photopolymers in the fabrics. Large increases were observed in the moisture regain of cotton—poty (N,N-methyl enebisacrylamide) and —poly (methacrylamide) fabric copolymers, as compared with cotton fabric controls.

Photopolymerization sensitized by metal acetylacetonate

AbstractPhotopolymerization of styrene and methyl methacrylate has been examined for twelve metal β‐diketonates. Mn(acac)3 and Co(acac)3 have a large sensitizing effect. In the photopolymerization of styrene sensitized by Co(acac)3, conversion increases linearly with time up to 10% conversion. Since sensitization is high in the wavelength region of charge transfer absorption and low in ligand field region, photoreduction of Co(III) to Co(II) is suggested during the formation of initiating radical.With the use of Mn(acac)3, photopolymerization rate of styrene was very high. The reduction of Mn(III) to Mn(II) was ascertained by ESR if 1‐methylstyrene was added as a radical scavenger. Without any radical scavenger, however, Mn(III) did not undergo reduction in benzene solution. In both cases of Co(acac)3 and Mn(acac)3, the initiation is by acetylacetonyl radical dissociated from the chelate. The central metal ion is simultaneously reduced. The initiation process is exactly the same as the thermal initiation.