Cationic Photopolymerization Process Research Articles

Double Role of Diphenylpyridine Derivatives as Fluorescent Sensors for Monitoring Photopolymerization and the Determination of the Efficiencies of the Generation of Superacids by Cationic Photoinitiators.

Novel fluorescent sensors with electron-donating or electron-withdrawing substituents incorporated into a chromophore group based on 2,6-diphenylpyridine were designed and synthesised. The spectroscopic properties of these compounds were studied. Moreover, the positive solvatochromism of 2,6-bis-(4-methylsulphanylphenyl)pyridine (PT-SCH3) in selected solvents was studied by measurement of the absorption and emission spectra and analysed using the Dimroth–Reichardt solvent parameter set. After that, the performance of a series of 2,6-diphenylpyridine derivatives as fluorescent molecular sensors for monitoring free-radical and cationic photopolymerization processes by the Fluorescence Probe Technique (FPT) was studied. As a consequence of this stage of research, the effect of substituents on the sensitivity of the 2,6-diphenylpyridine derivatives as sensors during photopolymerization has been evaluated and discussed. It has been found that compounds containing strong electron-donating substituent (PT-SCH3) slightly shift their fluorescence spectrum during the free-radical polymerization of monomer, which enables the monitoring of the polymerization progress using the fluorescence intensity ratio measured at two different wavelengths as the progress indicator. The position of the fluorescence spectrum of 2,6-diphenylpyridine derivatives with electron-withdrawing substituents is practically insensitive to changes occurring in their environment. Hence, it is recommended to use these compounds with different indicators of the progress of the photopolymerization process based on normalised intensity of fluorescence (Imax/I0). Among the compounds studied, 2,6-bis(4-methylsulphanylphenyl)pyridine (PT-SCH3) turned out to be the best fluorescent sensor for the purpose of monitoring free-radical polymerization by FPT. Consequently, the dual application of the selected 2,6-diphenylpyridine derivatives is proposed: (a) as fluorescent sensors for monitoring the free-radical photopolymerization progress, and (b) as spectroscopic sensors for the determination of efficiencies of the generation of superacids by cationic photoinitiators during the cationic photopolymerization process. Finally, a new method for determining the relative efficiency of the photogeneration of superacids during the photo cleavage of onium salt has been devised and applied for the evaluation of the performance of 2,6-diphenylpyridine derivatives.

Copper Complex: A Key Role in the Synthesis of Biocidal Polymer Coatings

A specific copper complex is used here for the development of new antibacterial coatings against two different bacteria strains i.e. Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). Remarkably, the cationic polymerization of a glycerol-derived monomer was performed using an efficient Cu complex as a photoinitiator. The synthesized coatings which were successfully developed under UV–visible light exposure and under a solvent-free cationic photopolymerization process show excellent adhesion on stainless steel plate according to nanoindentation and scratch tests. The resulting glycerol-derived coatings have been conducted to assess the antibacterial activities against E. coli and S. aureus: a tremendous decrease of 99.9% and 96% of the adhered Escherichia coli and Staphylococcus aureus on the surface of copper containing coatings has been demonstrated in comparison with bare stainless steel supports. Finally, our investigation suggests from live/dead assays data that the synthesized polymer films show biocidal properties due to the release of Cu2+ ions, which are responsible for inhibiting bacterial proliferation.

The Applicability of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile Sensors for Monitoring Different Types of Photopolymerization Processes and Acceleration of Cationic and Free-Radical Photopolymerization Under Near UV Light.

The performance of a series of 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives as fluorescent molecular sensors for monitoring photopolymerization processes of different monomers by the Fluorescence Probe Technique (FPT) was studied. It has been shown that the new derivatives are characterized by much higher sensitivity than the commercially available 7-diethylamino-4-methylcoumarin (Coumarin 1) and trans-2-(2′,5′-dimethoxyphenyl)ethenyl-2,3,4, 5,6-pentafluorobenzene (25ST) probes. It has been discovered that the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives accelerate the cationic photopolymerization process initiated with diphenyliodonium photoinitiators at the wavelength where the photoinitiator alone does not work. They are particularly efficient for the photoinitiation of cationic photopolymerization of an epoxide and vinyl monomers. Consequently, the application of the 2-amino-4,6-diphenyl-pyridine-3-carbonitrile derivatives in a dual role: (a) as fluorescent sensors for monitoring the free-radical, thiol-ene and cationic polymerization progress, and (b) as long-wavelength co-initiators for diphenyliodonium salts initiators, is proposed.

Mechanism of interaction of aminocoumarins with reaction medium during cationic photopolymerization of triethylene glycol divinyl ether

Applicability of a series of coumarin derivatives as fluorescent probes for monitoring progress of cationic photopolymerization processes by Fluorescence Probe Technique (FPT) has been studied using triethylene glycol divinyl ether as a model monomer and diphenyliodonium hexafluorophospate as a cationic photoinitiator. The following coumarins were evaluated: Coumarin 1, Coumarin 6H, Coumarin 102, Coumarin 120, Coumarin 151, Coumarin 343 and Coumarin 466. It has been found that despite the presence of an amino group in their structure, at low concentrations of the order of 0.1%, the Coumarins 1, 102, 343 and 466 can be used as the fluorescent probes for the cationic photopolymerization, while Coumarin 343 exhibits the best performance. At high concentrations, the aminocoumarins slow down the photopolymerization rate and extend induction period. All of the aminocoumarins are applicable as long-wavelength sensitizers for diphenyliodonium photoinitiators, enabling photopolymerization at the irradiation wavelengths, where the photoinitiator does not absorb. At short wavelengths, where both photoinitiator and probe absorb light, and at the probe concentrations below 0.1%, Coumarin 343 and Coumarin 1 accelerate the cationic photopolymerization by supplying an additional route for the photoinitiator cleavage beside its direct cleavage upon light absorption. The direct initiation and sensitization mechanisms are proposed.

Visible Light Induced Cationic Polymerization of Epoxides by Using Multiwalled Carbon Nanotubes.

The visible light induced cationic polymerization of epoxides can be achieved by means of multiwalled carbon nanotubes (MWCNTs), which act as visible light photoinitiators via a radical-induced cationic photopolymerization process. When MWCNTs are irradiated with longer wavelengths (above 400 nm), they generate carbon radicals, by means of hydrogen abstraction from the epoxy monomer; these radicals are oxidized in the presence of iodonium salt to a carbocation that is sufficiently reactive to start the cationic ring-opening polymerization of an epoxy monomer. These mechanisms have been supported by electron paramagnetic resonance analysis.

New Horizons in Cationic Photopolymerization.

In this review, we report some recent advances and new horizons in UV-induced cationic photopolymerization. In particular, after a brief introduction on the discovery and affirmation of the cationic photopolymerization process, new efforts in the synthesis of cationic photoinitiators are reported. Subsequently, an interesting and absolutely new application is reported, related to the combination of Radical-Induced Cationic Photopolymerization with Frontal Polymerization, achieving the cross-linking of epoxy composites.

Application of a carbazole derivative as a spectroscopic fluorescent probe for real time monitoring of cationic photopolymerization

Abstract The performance of 1-(9-ethylcarbazol-3-yl)-4,4,4-trifluorobutane-1,3-dione (1) as a fluorescent probe for the monitoring of cationic photopolymerization processes by Fluorescence Probe Technique (FPT) has been evaluated in comparison with the response of 7-diethylamino-4-methylcoumarin (Coumarin 1) (2). Triethylene glycol divinyl ether and diphenyliodonium hexafluorophosphate were used as an example monomer and a cationic photoinitiator respectively. It has been found that the probe 1 withstands the cationic polymerization conditions and provides correct probe response. 1-(9-ethylcarbazol-3-yl)-4,4,4-trifluorobutane-1,3-dione shifts its fluorescence spectrum with progress of cationic photopolymerization of the monomer, which enables the monitoring of the polymerization progress using the fluorescence intensity ratio measured at two different wavelengths as the progress indicator. By comparing the behavior of 1 and 2, it has been documented that the fluorescence spectrum of probe 1 shows a spectacular hypsochromic shift (Δλ = 33 nm) upon the monomer polymerization, while the shift of 2 is three times smaller (Δλ = 11 nm). Moreover, the sensitivity of probe 1 is more than 2.5-times higher than that of any other probes suitable for monitoring cationic polymerization processes, reported previously. Therefore, application of the carbazole derivative (1) as a new probe for the monitoring of the crosslinking process of coatings cured by cationic photopolymerization has been proposed.

The performance of 7‐hydroxycoumarin‐3‐carbonitrile and 7‐hydroxycoumarin‐3‐carboxylic acid as fluorescent probes for monitoring of cationic photopolymerization processes by FPT

AbstractThe applicability of 7‐hydroxycoumarin‐3‐carbonitrile (1) and 7‐hydroxycoumarin‐3‐carboxylic acid (2) as fluorescent probes for monitoring of cationic photopolymerization processes by fluorescence probe technique (FPT) was evaluated in comparison to the response of 7‐diethylamino‐4‐methylcoumarin (C1). Triethylene glycol divinyl ether and diphenyliodonium hexafluorophosphate were used as an example monomer and a cationic photoinitiator, respectively. It has been found that the probe 1 withstands the cationic polymerization conditions and provides correct probe response. The probes 2 and C1 undergo side reactions under the cationic polymerization conditions that make them unusable for monitoring of the polymerization progress at high monomer conversions. The application of 1 as an amine‐free probe for monitoring of curing progress of photocurable coatings cured by cationic photopolymerization is proposed. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

UV-Cured Polysiloxane Epoxy Coatings Containing Titanium Dioxide as Photosensitive Semiconductor

UV-cured polysiloxane epoxy coatings containing titanium dioxide were prepared by means of a cationic photopolymerization process. A good distribution of the inorganic filler was achieved within the polymeric network with an average size dimension of around 500 nm. UV-vis analysis performed on organic dye (methylene blue) stained coatings showed a high efficiency of the titania photocatalytic activity: a complete degradation of the dye on the coating surface is reached after 60 min of UV irradiation without affecting the matrix photodegradation.

Germanes as efficient coinitiators in radical and cationic photopolymerizations

AbstractIn this article, germanes are presented as new coinitiators for both radical and cationic photopolymerization processes. For the free radical polymerization process, the newly proposed structures are characterized by efficiencies similar or better than the reference amine. Germyl radicals are also found to be excellent initiators for free radical promoted cationic photopolymerization (FRPCP) of an epoxy resin. The associated reactivity is even better under air. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3042–3047, 2008

Photopolymerization of hybrid monomer 3-(1-propenyl)oxypropyl acrylate

Hybrid monomer 3-(1-propenyl)oxypropyl acrylate, combining easy free radical and fast cationically polymerizable group, was synthesized by phase-transfer catalyzed substitution, isomerization and subsequently esterification. Its photopolymerization kinetics was monitored by Fourier transform real-time infrared spectroscopy (FTIR) with a horizontal sample holder. The results indicated that hybrid monomer showed inter-group interaction in photopolymerization process, which decreased moisture sensitivity to cationic photopolymerization process, and represented higher efficiency of photopolymerization when compared with blend system.

Kinetics of Cationic Photopolymerizations of UV‐Curable Epoxy‐Based SU8‐Negative Photoresists With and Without Silica Nanoparticles

AbstractSummary: This paper reports on the photocuring kinetics of protonic‐acid‐initiated cationic polymerizations of UV‐curable epoxy‐based SU8‐negative photoresist systems with and without silica nanoparticles, as assessed using photo‐DSC, FTIR spectroscopy, UV‐vis spectroscopy, and SEM. Photo‐DSC analysis using an autocatalytic kinetic model demonstrated that the cross‐link density and cure rate increased as the concentration of silica nanoparticles with surface silanol groups increased to 2.5 wt.‐%. This result was confirmed by FTIR spectroscopy, and suggests that the presence of silica nanoparticles of up to 2.5 wt.‐% promoted the cure conversion and cure rate of the UV‐curable hybrid organic/inorganic negative photoresists due to the synergistic effect of silica nanoparticles acting both as an effective flow or diffusion‐aid agent and as a proton‐donor cocatalyst during the cationic photopolymerization process. The decrease in the cross‐link density that occurred when the silica content was higher than 2.5 wt.‐% was attributed to aggregation between silica nanoparticles due to their high surface energy.SEM photograph at the film‐air interface of the UV‐cured hybrid organic/inorganic photoresist containing 10 wt.‐% silica nanoparticles.magnified imageSEM photograph at the film‐air interface of the UV‐cured hybrid organic/inorganic photoresist containing 10 wt.‐% silica nanoparticles.

Photoinitiated cationic polymerization of urethane vinyl ether crystalline monomers

AbstractPhotoinitiated cationic polymerization of crystalline monomers based on urethane vinyl ether has been investigated by means of differential photocalorimetry (DPC). The crystalline monomers in the melt state polymerized rapidly by exposure to UV light in the presence of a cationic photoinitiator such as an iodonium salt, sulfonium salt or iron arene salt. The kinetics of the cationic photopolymerization process were studied by following kp[M+] as a function of conversion. High conversions, of around 90 %, were obtained for most of the systems investigated. The efficiency of the cationic photoinitiators in initiating the polymerization of the vinyl ether monomers was in the order: iodonium salt > iron arene salt > sulfonium salt. Monomers modified with different saturated alcohols had different activities in photopolymerization, although they all carry the same functional group, i.e. vinyl ether. Copyright © 2005 Society of Chemical Industry

Photopolymerization of oxetane based systems

Oxetane based systems were investigated in cationic photopolymerization process. The effect on the rate of polymerization induced by the presence of epoxy monofunctional monomers and vinyl ether monomers were investigated. In both cases an increase of the rate of polymerization is evidenced either induced by a flexibilization effect due to a copolymerization or to a cross-propagation mechanism. Acrylate comonomers were also investigated and the formation of an IPN tightly cross-linked evidenced.