Real-time FTIR Spectroscopy Research Articles

Low migration and high performance thioxanthone based photoinitiators

Photopolymerization technology has been limited in the application of the field of food packaging and biomedicine due to the high migration of the small molecule which are mostly from the photoinitiators. To improve migration stability of photoinitiators, polymerizable 2-vinyl thioxanthone (ETX) was synthesized by thiosalicylic acid and 4-fluorobenzaldehyde. Moreover, to further reduce the migration of photo- or co-photoinitiator, two macromolecular photoinitiators (PPI1, PPI2) were prepared by copolymerization of ETX with dimethylaminoethyl methacrylate (DMAEMA). The initiation activity of the prepared photoinitiators was studied by real-time FTIR spectroscopy. The results indicated ETX/triethanolamine (TEOA) system exhibited higher initiation performance than ITX/TEOA system by irradiation of 405 nm LED lamp, PPI2 as a one component photoinitiator displayed favorable initiation ability. In addition, the migration of ETX, PPI1 and PPI2 in the photocured film was declined obviously. ETX, PPI1 and PPI2 with low migration have potential application in the field of food package and biological materials.

Synthesis and photochemistry of flavonol camphorsulfonates photoinitiator with different substituents

In this study, we synthesized five novel flavonol camphorsulfonates (HFSs) photoinitiators using a flavonol scaffold as the chromophore. These HFSs demonstrated photoinitiating properties in both one-component (Norrish Type I) and two-component photoinitiating systems, with high final reaction function conversion and excellent polymerization rates of acrylates in free radical photopolymerization. Additionally, HFSs exhibited thermal stability in thermogravimetric tests. To explain the photoinitiating mechanisms, we used various complementary approaches, including real-time FT-IR spectroscopy, UV–Vis absorption spectroscopy, fluorescence spectroscopy, analysis of photolysis products, cyclic voltammetry, free radical capture experiments and molecular modelling calculations.

Design, synthesis and properties of carbazole-indenedione based photobleachable photoinitiators for photopolymerization

In order to investigate the properties of carbazole-indenedione based photoinitiators for photopolymerization, two visible light-sensitive photoinitiators (CAs) were designed and synthesized. Their structures were confirmed by nuclear magnetic resonance (NMR) and high resolution mass spectrometry (HR-MS). Additionally, their properties concerned photophysical/photochemical and photoinitiating were determined by electron paramagnetic resonance (EPR), UV–vis spectrophotometer and real-time FT-IR spectroscopy. The results have showed that CA-2 could be regarded as an effective one-component photobleachable photoinitiator for free-radical polymerization (FRP). Meanwhile, its photoinitiating property could be enhanced or optimized by adding the additional hydrogen donor or iodonium salt, and the interpenetrated polymer networks (IPN) were synthesized by the hybrid polymerization of TMPTA (trimethylolpropane triacrylate)/EPOX (3,4-epoxycyclohexylmethyl 3,4-epoxycycohexanecarboxylate) initiated by two-component CA-2/Iod (iodonium salt). The results of theoretical calculation experiments showed that it is also an effective way to improve the photoinitiating efficiency by the introduction of the electron-donating piperidine group in the ortho-position of the double bond on carbazole skeleton. The curing depth experiments showed that the photobleaching performance could be enhanced by introduction of Iod in acrylic/epoxy resin and a colorless polymer with the thickness of 5.8 mm was obtained under visible LED light irradiation for 6 min. Thus, the carbazole-indenedione based photobleachable dye CA-2 has great potential in deep curing materials (e.g. dental materials, biomedical materials and 3D printing).

Synthesis of a Curing Agent Derived from Limonene and the Study of Its Performance to Polymerize a Biobased Epoxy Resin Using the Epoxy/Thiol-Ene Photopolymerization Technique.

This study describes the synthesis of a curing agent derived from limonene as well as its application to prepare biobased thermoset polymers via the epoxy/thiol-ene photopolymerization (ETE) method. A biobased commercial epoxy resin was used to synthesize a crosslinked polymeric matrix of polyether-polythioether type. The preparation of the curing agent required two steps. First, a diamine intermediate was prepared by means of a thiol-ene coupling reaction between limonene and cysteamine hydrochloride. Second, the primary amino groups of the intermediate compound were alkylated using allyl bromide. The obtained ditertiary amine-functionalized limonene compound was purified and characterized by FTIR and NMR spectroscopies along with GC-MS. The curing agent was formulated with a tetrafunctional thiol in stoichiometric ratio, and a photoinitiator at 1 mol % concentration, as the components of a thiol-ene system (TES). Two formulations were prepared in which molar concentrations of 30 and 40 mol % of the TES were added to the epoxy resin. The kinetics of the ETE photopolymerizations were determined by means of Real-Time FTIR spectroscopy, which demonstrated high reactivity by observing photopolymerization rates in the range of 1.50–2.25 s−1 for the epoxy, double bonds and thiol groups. The obtained polymers were analyzed by thermal and thermo-mechanical techniques finding glass transition temperatures (Tg) of 60 °C and 52 °C for the polymers derived from the formulations with 30 mol % and 40 mol % of TES, respectively. Potential applications for these materials can be foreseen in the area of coatings.

Photoinitiator-free radical photopolymerization using polybrominated and polychlorinated aromatic methacrylates: Investigations on the mechanisms of initiation

In this study, pentabrominated and pentachlorinated phenyl methacrylate (PBPMA, PCPMA) were studied with respect to their suitability to initiate a photoinduced radical polymerization of an acrylic formulation without conventional photoinitiator. Real-time FTIR spectroscopy (RTIR) was used to study the kinetics of the polymerization reaction. Both halogenated monomers were found to be effective as initiators. Moreover, different experimental techniques such as laser flash photolysis (LFP), product analysis by GC/MS and FTIR spectroscopy as well as quantum chemical modeling were used to elucidate possible reaction pathways for the initiation of a photopolymerization reaction. A release of bromine radicals was observed by LFP after irradiation of PBPMA, which may initiate the polymerization similarly to the tetrabromophenyl methacrylate radicals. In contrast, no formation of free chlorine radicals from PCPMA was detected. Rather, GC/MS measurements after stationary photolysis indicated the formation of bicyclic isomers from PCPMA upon irradiation. Extensive quantum chemical modeling substantiated the formation of two different isomers. Accordingly, we propose that relocalization of the chlorine atom from the ortho position and subsequent ring closure via the methacrylate group may occur upon irradiation, which finally results in the formation of two bicyclic isomers with either a five- or a six-membered lactone ring. Spectra simulation and additional experiments by FTIR spectroscopy seem to indicate that the initiation of the photopolymerization with PCPMA might preferably proceed via the bicyclic molecule with the six-membered lactone ring and subsequent radical formation.

Real-time FTIR monitoring and modeling Bacillus amyloliquefaciens spore germination: Effect of temperature and sub-lethal treatment by nonthermal plasma

This study uses real-time FTIR spectroscopy to probe biochemical changes occurring in spores of Bacillus amyloliquefaciens during nutrient germination at T = 23 − 50°C and after sub-lethal injury by treatment with a nonthermal plasma (NTP). The FTIR identifies several spore structural components (e.g., stretching bands of the COO− group of dipicolinic acid at 1378 and 1616 cm−1; C−N vibrations in the DPA ring at 1570 cm−1, etc.) that are correlated to steps occurring during germination. The increase in peak intensity at 1570 cm−1 is interrelated to spore germination as measured with optical density at 600 nm (OD600) of refractile spores at T = 23 − 50°C and after NTP treatment. For the OD600 germination kinetics data, the Weibull model accurately fit the observed dynamics with values for the rate parameters α = 18.1 − 52.9 s−1 and shape parameter β = 0.9 − 1.2, and the Weibull model's performance was assessed by satisfactory values of the accuracy factor (1.00 < Af ≤ 1.15) and the bias factor (Bf in the ranges of 0.90 − 1.05), with the NTP-treated spores being the lone exception (Af = 1.22, Bf = 1.06).

Visible light-induced photopolymerization of Deep Eutectic Monomers, based on methacrylic acid and tetrabutylammonium salts with different anion structures

Deep Eutectic Monomers were prepared by dissolution of selected tetrabutylammonium salts serving as hydrogen bond acceptors (HBA) in methacrylic acid (MAA) acting both as hydrogen bond donor (HBD) and vinyl monomer. In this study, we systematically investigate the influence of chloride, nitrate, hydrogensulphate and fluoroborate anions on properties of DEMs and the course of radical photopolymerization. By Combining FTIR, 1H and 13C NMR spectroscopy we found the that degree of coordination of MAA in DEMs by anions follows the order: Cl− > NO3– > HSO4− ≫ BF4−. Moreover, the studies indicated that the strength of hydrogen bonds between HBD and HBA in DEMs is lower than in MAA dimers. Real-time FT-IR spectroscopy studies of photopolymerization of DEMs indicate that the mixtures formed from MAA and tetrabutylammonium fluoroborate show significant lower initial photopolymerization rate in comparison with other investigated DEMs, which polymerize with similar rates.

The inner mechanics of rhodopsin guanylyl cyclase during cGMP-formation revealed by real-time FTIR spectroscopy.

Enzymerhodopsins represent a recently discovered class of rhodopsins which includes histidine kinase rhodopsin, rhodopsin phosphodiesterases, and rhodopsin guanylyl cyclases (RGCs). The regulatory influence of the rhodopsin domain on the enzyme activity is only partially understood and holds the key for a deeper understanding of intra-molecular signaling pathways. Here, we present a UV-Vis and FTIR study about the light-induced dynamics of a RGC from the fungus Catenaria anguillulae, which provides insights into the catalytic process. After the spectroscopic characterization of the late rhodopsin photoproducts, we analyzed truncated variants and revealed the involvement of the cytosolic N-terminus in the structural rearrangements upon photo-activation of the protein. We tracked the catalytic reaction of RGC and the free GC domain independently by UV-light induced release of GTP from the photolabile NPE-GTP substrate. Our results show substrate binding to the dark-adapted RGC and GC alike and reveal differences between the constructs attributable to the regulatory influence of the rhodopsin on the conformation of the binding pocket. By monitoring the phosphate rearrangement during cGMP and pyrophosphate formation in light-activated RGC, we were able to confirm the M state as the active state of the protein. The described setup and experimental design enable real-time monitoring of substrate turnover in light-activated enzymes on a molecular scale, thus opening the pathway to a deeper understanding of enzyme activity and protein-protein interactions.

High Performance Redox Initiating Systems Based on the Interaction of Silane with Metal Complexes: A Unique Platform for the Preparation of Composites.

Currently, Redox Initiating Systems (RISs) of Free Radical Polymerization (FRP) are mainly based on the interaction of aromatic amines with peroxides (e.g., dibenzoyl peroxide (BPO)) that can be both toxic and unstable. In the present work, we aim to replace these hazardous substances in new RIS that can be peroxide-free and amine-free. Our redox two components (2K) initiating system is based on diphenylsilane (DPS) as reducing agent combined with different metal complexes (Mn(acac)2, Cu(AAEMA)2 or Fe(acac)3) as oxidizing agents. For the new proposed RIS, an excellent reactivity is found for the polymerization of benchmark methacrylate monomers under mild conditions (redox polymerization done under air and at room temperature); remarkably, it is also possible to finely control the gel time. Different techniques (optical pyrometry, Real-Time FTIR spectroscopy, Cyclic Voltammetry and Electron Spin Resonance (ESR)) were used to follow the polymerization processes but also to shed some light on the new redox chemical mechanisms.

The effect of organosilicon modifier structure on the efficiency of the polybutadiene hydrosilylation process

Real-time FT-IR spectroscopy permitted us to determine the influence of steoelectronic properties of functional groups on hydrosilylation. This allowed the synthesis of polybutadienes equipped with attractive silicon-based functional groups.

High-performance water-based UV-curable soft systems with variable chain architecture for advanced coating applications

Silicone-based materials and systems have played a key role over a century. In this work, surface and bulk characteristics of siloxane-modified water-based urethane-acrylate dispersions containing hydrophilic and hydrophobic soft segments with variable molecular weight and also a hard segment were tailored. Feeding and synthesis conditions were changed systematically to control over compatibility and softness of samples. FTIR, elemental analyses by proton and silicon nuclear magnetic resonances and dynamic light scattering were used to describe microstructure of dispersions. The effects of PDMS content and molecular weight on the composition-property relationship was discussed in terms of contact angle, water absorption and mechanical properties. Addition of PDMS having high-molecular-weight as hydrophobic soft segment in polyurethane-acrylate system improved water repellency, as featured by a rise in contact angle from 72 to 102°. The effect of photoinitiators type on C = C conversion rate was monitored by changing the polarity and hydroxyl group by real-time FTIR (RT-IR) spectroscopy. Physical and mechanical properties of UV-cured coatings like hardness, adhesion and flexibility were also examined. Siloxane-modified crosslinked films exhibited excellent flexibility and hydrophobic surface depending on soft segment type and content. Siloxane-modified water-based urethane-acrylate UV-cured film revealed high thermal-stability with negligible weight loss unless well-above 200 °C.

Synthesis and characterization of organozirconiums with type-II photoinitiator ligands as multifunctional photoinitiators for free radical photopolymerization

Two hydroxyl derivatives of benzophenone and anthraquinone were chosen as the ligands of zirconium complexes in the substitution of zirconium propoxide to obtain zirconium-based multifunctional photoinitiators (MPIs), ZrOBP and ZrOAQ. The MPIs were characterized in terms of molecular structures, UV absorption properties and photoinitiation ability. The absorption bands of the MPIs are similar to their low-molecular-weight counterpart with higher absorbance. These photoinitiators were used for the curing of a mixture of bisphenol A diacrylate and hexanedioldiacrylate. The kinetics of photopolymerization of the formulations was monitored by real-time FTIR spectroscopy, under the irradiation of a mercury-xenon lamp. Organozirconium complexes are known to tap the potential of overcoming the oxygen inhibition, thus the depth conversion profiles of the UV-cured films were followed by confocal Raman microscopy. Furthermore, the migration of residual photoinitiator was investigated via solvent extraction from the UV-cured film, the solution of which being measured by UV–vis spectroscopy.

Naphthalimide dyes: Polymerizable one-component visible light initiators

Two of acrylated naphthalimide one-component visible light initiators, 2-((2-(1,3-dioxo-6-(piperidin-1-yl)-1H-benzo[de] isoquinolin-2(3H)-yl)ethyl)(methyl) -amino)ethyl acrylate (ND-N-EA) and ((2-(1,3-dioxo-6-(piperidin-1-yl)-1H-benzo[de]isoquinolin-2(3H)-yl)ethyl)azanediyl)bis(ethane-2,1-diyl) diacrylate (ND-N-BEA) have been designed and synthesized. Their structures have been confirmed by HR-MS, 1H NMR and 13C NMR. The photochemical mechanisms are studied by cyclic voltammetry (CV), density functional theory (DFT) calculation, and electron paramagnetic resonance (EPR) spectroscopy. Their photopolymerization behavior and the extractability in the cured films are investigated by real-time FT-IR spectroscopy and UV-visible spectrometer, respectively. Results show that both of them exhibit good photopolymerization initiating performance and high migration stability in their initiated cured films.

실시간 FTIR 분광법을 이용한 경화제 함량 및 경화 온도에 따른 폴리우레탄 탄성체 경화반응속도

본 연구에서는 경화제의 함량과 경화 온도가 폴리우레탄 탄성체의 경화반응속도에 끼치는 영향에 대해 연구하였다. 톨루엔 디이소시아네이트와 폴리테트라메틸렌 에테르 글리콜을 질소 분위기 하에 80℃에서 한 시간 동안 반응시켜 폴리우레탄 프리폴리머를 합성하였으며 폴리우레탄 탄성체를 만들기 위해 4,4"-메틸렌 비스(2-클로로아닐린)을 경화제로 적용하였다. 아민-이소시아네이트 비율은 0.85에서 1.05까지, 경화온도는 각각 80℃에서 120℃까지 진행하여 폴리우레탄 탄성체의 경화반응성은 실시간 FTIR을 통해 확인하였다. 아민-이소시아네이트 비율과 경화온도를 높일수록 전환율과 반응속도가 증가함을 알 수 있었으며 수치 해석을 위해 Kamal 식을 적용하였다. The effects of stoichiometric ratios of curing agent to prepolymer and temperature on the curing reaction rates of polyurethane elastomer were investigated. The prepolymers were made from toluene diisocyanate (TDI) and polytetramethylene ether glycol (PTMEG) at 80℃ in nitrogen atmosphere for an hour. Then the prepolymers were mixed with the curing agent, 4,4"-methylene bis(2-chloroaniline) (MOCA) to produce polyurethane elastomer. The curing reactivities of polyurethane prepolymer with curing agent were measured by real time FTIR spectroscopy. The stoichiometric ratios were controlled from 0.85 to 1.05 at fixed curing temperatures from 80 to 120℃. Conversions and reaction rates were increased, as the stoichiometric ratios increased. And they were increased, as the reaction temperatures increased. Kamal’s equation was adopted for simulation as a kinetic model.

Physically and chemically gelling hydrogel formulations based on poly(ethylene glycol) diacrylate and Poloxamer 407

Poloxamer 407 (P407) and poly (ethylene glycol) diacrylate (PEG-DA) are well-characterized building blocks for physical and chemical hydrogels, respectively. P407 physical hydrogels alone can be used as injectable hydrogels, but lack mechanical stability. In this contribution, PEG-DA was added to physically gelling P407 solutions in order to introduce chemical curing ability. The resulting hydrogel formulations containing P407, PEG-DA (Mn = 700 g mol−1) and the photoinitiator 1-[4-(2-hydroxyethoxy)phenyl]-2-hydroxy-2-methyl-1-propan-1-one (Irgacure 2959) were characterized concerning their physical and chemical gelling behavior. Upon addition of PEG-DA to P407 solutions, their gel transition temperature Tgel was altered and could be adjusted between 10 °C and 39 °C. At P407 concentrations cPolox of <22.5 wt.-%, Tgel increased compared to P407 solutions by adding PEG-DA. At cPolox>22.5 wt.-% Tgel decreased. The different behavior at different cPolox could be explained by a combination of a decrease of P407 micelle size as well as a decrease of the critical mizellization temperature of P407 upon PEG-DA addition. Chemical gelation of the formulations was investigated by real-time FT-IR spectroscopy combined with photorheology as well as by the equilibrium degree of swelling and shear moduli of the cured hydrogels. Hydrogel curing was significantly faster without altering the double bond conversion when P407 was present in the formulations, probably due to prearrangement of the double bonds. The shear moduli and equilibrium degrees of swelling of the cured hydrogels could be adjusted by the PEG-DA concentration in the formulation, similar to pure PEG-DA hydrogels. The hydrogel formulations presented are promising candidates for injectable hydrogels with chemical curing ability.

One-component thioxanthone-based polymeric photoinitiators

The photochemical and photophysical properties of new polymeric photoinitiators (PPIs) containing pendant thioxanthone (TX) and amine moieties are studied. The PPIs are synthesized by copolymerization of tert-butyl 2-((9-oxo-9H-thioxanthen-2-yloxy)methyl)acrylate (TX1) with N,N-dimethylaminoethyl methacrylate (DMAEM) at two different ratios using free radical polymerization. UV–vis spectra indicate that PPIs possess similar absorption characteristics to TX1 in the violet range (∼400 nm; absorption red-shift 20 nm). The photochemical mechanisms are studied by electron spin resonance (ESR), steady state photolysis, laser flash photolysis, and cyclic voltammetry. ESR studies indicate formation of two different aminoalkyl radicals on the hydrogen donor amine. The triplet state of the PPIs is short-lived compared to isopropyl thioxanthone and TX1, due to the built-in amine functionality. Photopolymerization of trimethylolpropane triacrylate (TMPTA) initiated by these photoinitiators under LED exposure at 385 and 405 nm using real-time FTIR spectroscopy shows that they exhibit higher efficiency than TX/N-methyldiethanolamine (MDEA) and TX1/MDEA systems with the advantage of a much higher molecular weight that can be very helpful to overcome migration issues. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 3370–3378

A facile method to prepare a polyethylene glycol modified polysilane as a waterborne photoinitiator

Abstract Developing water-soluble or waterborne polysilane photoinitiators meets the demands for environmental friendly photopolymerization applications. By employing this photoinitiated strategy, a waterborne polysilane photoinitiator polysilane-co-poly(polyethyleneglycol acrylate) was prepared by an efficient photodecomposition of polymethylphenylsilane in the presence of acrylate functionalized polyethyleneglycol. The prepared polymer was characterized by 1H NMR, 13C NMR, 29Si NMR, FT-IR, UV–vis GPC, DSC and TGA. It could disperse in water easily and form micelle. The average micelle size (10 mg/mL) was measured to be 46 nm by dynamic light scatting technique. The course of photopolymerization of acrylamide in deuterated water initiated by it was investigated by the real-time FT-IR spectroscopy. The photopolymerization kinetic data revealed that the conversion of acrylamide reached 80% and 100% after 40 and 110 s irradiation, respectively. The photopolymerization of the water solution of acrylamide, hydroxyethyl methacrylate (HEMA) and acrylic acid (AA) initiated by this polymer at air atmosphere provided successfully polymeric jelly materials in high yields.

A novel high efficiency benzophenone based polymeric photoinitiator from ring-opening polymerization of benzoxazine

A novel polymeric photoinitiator based on benzoxazine was synthesized by introducing 4-hydroxy benzophenone, diglycolamine and paraformaldehyde into the macromolecular chain. Its molecular structure was characterized by 1H NMR, FTIR, and UV-Vis spectroscopy. Photopolymerization of tripropylene glycol diacrylate and trimethylolpropane triacrylate initiated by polybenzoxazine, benzoxazine, and benzophenone was studied by real time FTIR spectroscopy. The results obtained are discussed.

Morphology and properties of UV-curing epoxy acrylate coatings modified with methacryl-POSS

Abstract In this work, the morphology and properties of UV-curing epoxy acrylate (EA) coatings modified with methacryl polyhedral oligomeric silsesquioxanes (M-POSS) were studied. The M-POSS nanocages were introduced into EA UV-curing system via copolymerization at loadings between 0% and 10 wt%. The XRD and FTIR analysis indicated that M-POSS chemically incorporated into the hybrid materials and formed a cross-linked network between M-POSS and EA. The morphological analysis showed that the discrete spherical POSS-rich particles were dispersed in the EA matrix uniformly, and both of the number and mean diameter of POSS-rich particles increased with the increasing M-POSS loadings. The influence of M-POSS on the kinetics of the photopolymerization was determined by real time FTIR spectroscopy and the result showed that the addition of POSS enhanced both of the UV-curing rates and final double bond conversion. The DMA analysis showed that increasing the amount of M-POSS nanocages caused an increase on the nanocomposite's T g . TGA curves showed that at the later period of degradation process, the thermal stability of nanocomposites was enhanced by M-POSS. With respect to the mechanical properties, the most remarkable trend was an improvement on the impact resistance of nanocomposites with the increasing POSS contents. Because both of the craze and plasticity deformation caused by POSS nanocages would absorb impact energy, hinder the growth of craze.

Effect of Oxygen Inhibition on the Kinetic Constants of the UV-Radical Photopolymerization of Diurethane Dimethacrylate/Photoinitiator Systems

The kinetic constants of propagation (kp) and termination (kt) for a diurethane dimethacrylate/1-hydroxycyclohexyl phenyl ketone (Irgacure 184) system were measured using a dark polymerization technique that employs real-time FT-IR spectroscopy to measure the conversion and reaction rate of the methacrylate group at different time points. The sample was placed between two optically polished KBr plates with a 10 μm metal spacer. A series of measurements resulted in a gradual peak in the kinetic constants at a 0.15 conversion of the methacrylate group. The kinetic constants for the conversion, which ranged from 0.15 to 0.5, were used to obtain the parameters of the Anseth–Bowman model to generate a numerical simulation of the photopolymerization kinetics. The kinetic equations, the oxygen inhibition reaction-diffusion equation, and the macroradical mass balance model indicated that the gradual peak in the kinetic constant was caused by an oxygen inhibition reaction. The Anseth–Bowman model for kp and kt was...