Polymeric amine bearing side-chain thioxanthone as a novel photoinitiator for photopolymerization

Novel polymeric photoinitator (PTX) was synthesized by introducing thioxanthone (TX) moieties to polymeric amine side-chain. Compared with low-mulecular weight model compound, PTX has similar UV-vis absorption and weaker fluorescence emission, and some radicals are trapped in the macromolecular coil cage. The kinetics for polymerization of trimethylolpropane triacrylate using PTX as photoinitiator was studied by photo-DSC. It shows that PTX is an efficient photoinitiator, and that PTX concentration and light intensity have similar effect on photopolymerization. The increase in PTX concentration and light intensity leads to the increase in the polymerization rate and the final conversion. The increase in temperature also results in the increase in the polymerization rate and final conversion, due to the enhanced molecular mobility and delay in vitrification at high temperature. At the late stage of polymerization, the reaction becomes more diffusion-controlled than that at early stage of polymerization.     

Amphipathic hyperbranched polymeric thioxanthone photoinitiators (AHPTXs): Synthesis, characterization and photoinitiated polymerization

Amphipathic hyperbranched polymeric thioxanthone (TX) photoinitiators (AHPTXs) were synthesized by introducing TX, and polyethylene glycol monoethylether glycidyl ether (E-PEO), which contained short poly (ethylene oxide) (PEO) chain, into periphery of hyperbranched poly(ethylene imine) (HPEI), as well as low-molecular weight analogue 2-(2-hydroxy-3-(methyl(2,3,4,5,6-pentahydroxyhexyl)amino)propoxy) thioxanthone (MGA-TX). AHPTXs possess UV-vis absorption spectra similar to TX derivatives, and weaker fluorescence emission in comparison to low-molecular weight analogues. AHPTXs can be not only dispersed easily in many solvents and acrylate monomers, but also are soluble in water. AHPTXs are very efficient in photopolymerization of acrylamide (AM), poly(ethylene glycol) diacrylate (PEGDA) and 2,2-bis[4-(acryloxypolyethoxy)phenyl] propane (A-BPE-10). In comparison to low-molecular weight analogues photoinitiator systems 2-(2,3-epoxypropyloxy) thioxanthone/triethylamine (ETX/TEA) and MGA-TX/TEA, AHPTX1 is very efficient for photoinitiation of A-BPE-10 and AM in aqueous solution     

聚氨酯型高分子硫杂蒽酮光引发剂的制备及性能研究

通过三种二异氰酸酯、2-（2,3-二羟基）丙氧基硫杂蒽酮（HPTX）及N-甲基二乙醇胺(MDEA)进行逐步聚合反应,将硫杂蒽酮结构及共引发剂胺结构引入到同一高分子链上,得到侧链含有硫杂蒽酮,主链含有共引发剂胺的聚氨酯型高分子光引发剂。傅立叶红外变换光谱和核磁共振氢谱证实了高分子光引发剂的结构。紫外光谱证实了高分子链的结构对硫杂蒽酮单元的最大紫外吸收几乎没有影响。用光致差示量热计（photo-DSC）研究聚氨酯型高分子光引发剂引发聚氨酯丙烯酸酯树脂（PUA）的光聚合反应,发现PU-IMTX是本文合成的引发剂中引发PUA光聚合最有效的光引发剂。     

Study of macrophotoinitiator containing in-chain thioxanthone and coinitiator amines

Three kinds of macrophotoinitiator, PTXB, PTXE and PTXP, were synthesized by step-polymerization of thioxanthone and different amino monomers. The UV-vis spectra of PTXP, PTXE and PTXB are similar with slightly-shifted maximum absorption, and the fluorescence emission varies. The photopolymerization of three monomers with different functionality, methyl methacrylate (MMA), poly(propylene glycol) diacrylate (PPGDA) and trimethylolpropane triacrylate (TMPTA), initiated by these three types of macrophotoinitiators was studied through dilatometer and photo-DSC. The results show different photoinitiators behaviors towards monomers efficiently: PTXP is the most efficient for MMA, PTXE is the most efficient for PPGDA and PTXB is the most efficient for TMPTA. The efficiency of the photopolymerization is mainly effected by structure of amine in macrophotoinitiator.     

Photochemical study and photoinitiation activity of macroinitiators based on thioxanthone

In this work we studied the photopolymerization of methyl methacrylate using polymeric initiators based on thioxanthone chromophore. As co-initiator were used low molecular weight tertiary amines and bound to a polymer chain. The photoinitiation efficiency of these systems was compared with that of the corresponding low molecular weight analogue. A higher efficiency was obtained with the system comprising the thioxanthone bound to a polymer chain and the free amine. The results carried out with low molecular weight TX and the polymeric co-initiator showed that the efficiency is independent of the amount of amine units in the polymer chain. The photophysics of the different systems show that the polymer chain does not affect the emission characteristics of the thioxanthone chromophore. Bimolecular rate constants for the singlet and triplet quenching of thioxanthone by the amine were determined using fluorescence and laser flash photolysis techniques. The dependence of the photoinitiation efficiency with the amine concentration was simulated from the measured quenching rate constants, and shows that the active radicals are produced from the interaction of the ketone triplet with the amine. The ketyl radical yield was slowly higher for the thioxanthone bound to the polymer. The difference between the photoinitiation activity of the polymeric system and the low molecular weight models is explained in terms of the effect of the polymer chain on the reactivity of the amino radicals.     

Difunctional monomeric and polymeric photoinitiators: Synthesis and photoinitiating behaviors

The first methacrylate monomers with two type I or type II side-chain photoinitiating groups (PI1, PI2 and PI3) are synthesized from reactions of 2-(chloromethyl)acryloyl chloride and 4-hydroxybenzophenone, 4-hydroxyacetophenone or 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959), and polymerized, giving polymeric photoinitiators (PPI1, PPI2 and PPI3). PI1 is also copolymerized with N,N-dimethylaminoethyl methacrylate (DMAEM) to investigate the photoinitiation efficiency of the resulting polymer featuring built-in amine coinitiator. Activities of these photoinitiators together with acetophenone (AP), benzophenone (BP) and Irgacure 2959 are investigated in photopolymerizations of hexane-1,6-diol diacrylate, using photodifferential scanning calorimeter and the kinetic parameters are correlated with the structures of the photoinitiating systems. The results show different photoinitiating activities compared to small molecule commercial analogs: BP-based photoinitiators, PI1, PPI1 and PPI(PI1-co-DMAEM), are found to be particularly efficient compared to BP. The Irgacure 2959-based ones appear to be promising as type I photoinitiators.     

Photopolymerization of methyl methacrylate initiated by thioxanthone derivatives: photoinitiation mechanism

The photopolymerization of methyl methacrylate initiated by substituted thioxanthones in the presence of an amine has been investigated. The polymerization rates in acetonitrile were measured at several amine concentrations. The dependence of the polymerization rates with the amine concentration and the photoinitiation efficiency at a given amine concentration are highly dependent on the ketone structure. The rate constants for the quenching of thioxanthones excited states by the monomer and the amine were measured by fluorescence and laser flash photolysis, under the polymerization conditions. These data show that the reactivity of the ketone is also highly dependent on the ketone structure. The values of the quenching rate constants show that the initiation efficiency is controlled by the competition between the quenching of the excited states by the monomer and also the amine. From the latter a mechanism is proposed to simulate the dependence of the polymerization rates with amine concentration.     

Synthesis and photoinitiating behavior of benzophenone-based polymeric photoinitiators used for UV curing coatings

Three benzophenone-based type II polymeric photoinitiators, poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane maleate)) (PBM), poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane succinate)) (PBS), and poly(2-(4-benzophenone methylene ether)-1,3-dihydroxypropane-co-2-(phenyl-methylene-ether)-1,3-dihydroxypropane maleate)) (PBPM) used for free radical UV curing systems, were prepared through the step-growth polymerization of 4-(2,3-epoxypropyloxy) benzophenone (EBP) with maleic anhydride and succinic anhydride, as well co-polymerization with phenyl glycidyl ether and maleic anhydride, respectively. The molecular structures were characterized with ¹H NMR and FT-IR spectroscopy, and GPC analysis. For equimolar EBP and MA reaction system, the M_n led to the maximum of 6868 g/mol with the PDI of 1.22. The UV spectroscopy analysis showed that the synthesized polymeric photoinitiators possess higher UV absorption intensity in the wavelength range of 300–400 nm compared with benzophenone (BP). The photoinitiating activity was examined based on the photopolymerization of tripropyleneglycol diacrylate (TPGDA) in the presence of triethylamine as a coinitiator by using Photo-DSC method. It was found that PBM and PBS showed higher photoinitiating efficiency than BP in the photopolymerization of TPGDA. Moreover, the side BP moiety incorporated into the polymeric chain possessed higher initiating activity than end-capped BP moiety. Moreover, PBM with higher molecular weight was more efficient to photoinitiate TPGDA UV-cured. The side chromophore group distribution in the molecular chain also affected the photoinitiating activity. The highest photopolymerization rate at the peak maximum was obtained by the photoinitiation with PBM prepared with the molar feed ratio of 1.0 of EBP to MA.     

A novel ferrocenium salt as visible light photoinitiator for cationic and radical photopolymerization

A novel hybrid photoinitiator for visible light photopolymerization, (η⁶-3-benzoyl-4-chlorodiphenylamine) (η⁵-cyclopentadienyl) iron hexafluorophosphate (Fc-NBP), was synthesized and studied. Its absorption in the UV and visible light regions showed much stronger activity than those of either the commercialized cationic photoinitiator I-261 or the conventional free radical photoinitiator benzophenone, especially above wavelengths of 350 nm. When exposed to visible light, the photoinitiator under study initiates both cationic polymerization and radical polymerization. The photoinitiator's abilities in the photopolymerization of acrylates and epoxides were evaluated by near infrared (NIR) spectroscopy. The results from NIR clearly indicate that Fc-NBP exhibited high efficiency in photopolymerizing acrylate monomers. In the same lamp, however, benzophenone showed no photoinitiating ability. The photopolymerization rate of the diglycidyl ether of the bisphenol-A epoxy (DGEBA) oligomer was found to be slower than that of acrylates when using Fc-NBP as the photoinitiator. This study shows that the polymerization of epoxide DGEBA can be speeded up by adding a photosensitizer benzoyl peroxide (BPO), but BPO and tertiary amines do not affect the free radical photopolymerization of tripropylene glycol diacrylate (TPGDA). We conclude by providing a possible photoinitiation mechanism.     

Determination of photoinitiated polymerization of multifunctional acrylates with acetic acid derivatives of thioxanthone by RT-FTIR

Photopolymerization of multifunctional acrylates with 2-thioxanthone-thioacetic acid (TXSCH₂COOH) and 2-(carboxymethoxy) thioxanthone (TXOCH₂COOH) as the one-component photoinitiator has been investigated by real-time Fourier transform infrared (RT-FTIR) spectroscopy. The photobleaching of these one-component nature initiators was performed in air. The irradiation time for total bleaching was 240 s for TXSCH₂COOH and 540 s for TXOCH₂COOH.     

Polymer-bound hydroxamic dithiobenzoic anhydride: a new heterogeneous photoinitiator

Poly(methylmethacrylate) resins crosslinked with divinyl benzene, ethyleneglycol dimethacrylate and N,N′-methylene-bis-acrylamide were functionalized to generate a photodissociable chromophore, S-benzoyl-o-dithiohydroxamate. These polymeric mixed anhydrides were found to be efficient heterogeneous initiators in the light-induced polymerization of acrylic and vinyl monomers. On UV irradiation, both homopolymers and graft polymers were obtained. Polymerization of MMA was followed at various time intervals and as a function of monomer and initiator concentrations. On varying the initiator concentration, the rate of polymerization passed through a maximum. © 1998 SCI.     

央速成型光固化树脂用光引发剂的种类与应用

快速成型光固化技术是绿色环保的新型技术,主要是利用激光或者紫外光引发固化。然而光引发剂是快速成型光固化体系中重要的组成部分,对研究和发展光固化产品有着十分重要的影响,筛选高效的光引发剂已经成为当前研究的热点。本文主要介绍和分析了常用光引发剂的引发固化的原理,不同类型光引发剂的性能、结构与应用。     

Novel polymeric photoinitiators with side-chain benzophenone: Facile synthesis and photopolymerization properties without coinitiator

A novel polymeric photoinitiator, poly(glycidyl benzophenone ether) (PGBE), with a side-chain benzophenone (BP) group was synthesized from poly(epichlorohydrin) and 4-hydroxybenzophenone. The structure of PGBE was characterized by IR and ¹H NMR. The light absorption of PGBE was detected by UV spectrophotometer with the maximum absorption wavelength at 283 nm in acetonitrile solvent, which were red-shifted compared with BP. The obvious advantage of this initiator was the elimination of amine based hydrogen donors and to provide alternative hydrogen donors with easy availability and non-toxicity. The photopolymerizations of tripropylene glycol diacrylate (TPGDA) and trimethylolpropane triacrylate (TMPTA) initiated by PGBE and BP/EDAB were studied by real-time FT-IR. The polymeric initiator was found to have higher efficiency than BP/EDAB.     

Water‐soluble and polymerizable thioxanthone photoinitiator containing imidazole

A novel free radical photoinitiator, 3‐allyl‐1‐[2‐hydroxy‐3‐(thioxanthen‐9‐one‐2‐yl)oxypropyl]imidazolium chloride ([AIPTX]Cl), is synthesized by the addition reaction of 2‐(2,3‐epoxy)propoxylthioxanthone (ETX) with a heterocyclic compound imidazole firstly, and the achieved intermediate 1‐[2‐hydroxy‐3‐(thioxanthen‐9‐one‐2‐yl)oxypropyl]imidazole (IPTX) is then reacted with allyl chloride. IPTX is chosen to evaluate the photoefficiency of [AIPTX]Cl. FTIR and ¹H‐NMR confirm the structures of [AIPTX]Cl and IPTX. UV‐Vis spectra of the two photoinitiators are similar and both exhibit the maximal absorption about 400 nm. Fluorescence spectra show [AIPTX]Cl/IMZ has slightly higher fluorescence intensity than IPTX system. Photopolymerization studies indicate that [AIPTX]Cl/IMZ is more efficient for the polymerization of water‐soluble monomer than IPTX. Moreover, due to its advantages of water solubility and polymerizability, [AIPTX]Cl is an environmental‐friendly photoinitiator and has potential for application in UV‐curing systems. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40659.     

两亲性苯甲酰甲酸酯类光引发剂及其引发性能

以苯甲酰甲酸和三乙二醇为原料合成了一种水油两亲性光引发剂苯甲酰甲酸三乙二醇单酯（TGBF），并利用紫外-可见分光光度计、电子自旋共振仪及实时红外光谱仪等手段探究了TGBF的光吸收性能、光降解机理、水中溶解性以及引发光聚合的能力。研究结果表明，TGBF在300 nm以上波长的摩尔消光系数较低，但在405 nm LED光源照射下，能够发生分子内或者分子间的夺氢反应，并产生烷基自由基引发单体聚合。TGBF具有良好的水溶性，可高效地引发油性单体三丙二醇二丙烯酸酯（TPGDA）与水性单体聚乙二醇400二丙烯酸酯（PEG（400）DA）的聚合，最终双键转化率可达到80%以上。更重要的是，TGBF具有优异的引发油性单体TPGDA与水性单体深度聚合的能力，聚合深度分别达到5.6cm和6.5 cm以上,在深层LED光聚合领域表现出极大的应用潜力。     

New photochemical approach to cellulose fabric and photoinitiator system

The surface modifications of cellulose substrate based on the photo‐induced reaction are closely related with the radicals introduced on the surface of cellulose substrates by light irradiation. We have evaluated the ability of radical formation in lyocell fabric and two water‐soluble photoinitiator systems by using photoluminescence analyses. Namely, the relative quantum yields of fluorescence and phosphorescence were estimated by the integrated emission intensity under the same values of light absorbance and the identical measuring conditions. First of all the [2‐(acryloyloxy)ethyl](4‐benzoylbenzyl)dimethylammonium bromide (PIA) system had larger UV absorbance values below 287 nm than [3‐(3,4‐dimethyl‐9‐oxo‐9h‐thioxanthene‐2‐yloxy)‐2‐hydroxypropyl]trimethylammonium chloride (PIB) system at the same concentration. The relative quantum yields of fluorescence and phosphorescence emission in PIA system were smaller than those in PIB system even if the two systems had the same values of light absorbance. Therefore it was found that the PIA system was more easily transited to the triplet‐state and the transited molecules reacted with the cellulose substrates more effectively. The modified cellulose fabric with 2‐(dimethylamino)ethyl chloride hydrochloride (AM1) and PI system had only a little different UV absorbance and photoluminescence properties from the untreated fabric system. However, the fabric modified with 2‐(4‐chlorophenyl)‐ethylamine (AM2) and PI system showed relatively big differences. The UV absorbance values were increased and the relative quantum yields of photoluminescence were decreased remarkably. We have acquired that the tertiary amine treated cellulose fabric were very effective in photo‐induced modification of cellulose. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

A novel polymeric gel electrolyte systems containing magnesium salt with ionic liquid

A new polymeric gel electrolyte system consisting of poly(ethylene oxide)-modified polymethacrylate (PEO-PMA) with organic ionic liquid dissolving magnesium salt, Mg[(CF₃SO₂)₂N]₂, has been developed. The ionic conductance and electrochemical properties of the gel films were investigated. The obtained gel film was self-standing, transparent and flexible with sufficient mechanical strength. Thermal analysis of the gel film showed that it is homogeneous and amorphous over a wide temperature range. The highest conductivity, ca. 3.5 mS cm⁻¹ at 60 °C, was obtained for the polymeric gel containing 80 wt.% of the liquid component that consists of 80 mol% of EMITFSI (1-ethyl-3-methylimidazolium bis(trofluoromethylsulfonyl)imide) and 20 mol% of Mg[(CF₃SO₂)₂N]₂. The sort of the ionic liquid affected much on the ionic conductivity of the gel. The dc polarization of a Pt/polymeric gel electrolyte/Mg cell proved that the magnesium ion (Mg²⁺) can mobile in the present polymeric gel system.     

Copolymeric photoinitiators containing in‐chain thioxanthone and coinitiator amine for photopolymerization

Two kinds of copolymeric macromolecular photoinitiator, PTXPM and PTXPC, were prepared by introducing methylacryloyl or cinnamoyl groups to the side chain of PTXP. The photopolymerizations of poly(propylene glycol)diacrylate (PPGDA) and trimethylolpropane triacrylate (TMPTA), using PTXPM and PTXPC as photoinitiators, were studied by photo‐DSC. PTXPM and PTXPC have UV–vis spectra similar to that of PTXP with blue‐shift absorption maxima. The photopolymerization behavior of TMPTA, initiated by three photoinitiators, appears similar to that of PPGDA. Compared with PTXP and PTXPC, PTXPM gives higher polymerization rate and final conversion, in photopolymerization of PPGDA and TMPTA, which shows that the introduction of methyl acrylate to the PTXP chain has a greater effect on photopolymerization of PPGDA and TMPTA than that of cinnamoyl acrylate. The polymerization rate and final conversion, for photopolymerization of PPDGA initiated by PTXP, can be more effectively increased by the introduction of methyl acrylate group to the PTXP chain, than are those for TMPTA. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 2395–2400, 2004     

Polymeric Michler's ketone photoinitiators: The effect of chain flexibility

Through introducing Michler's ketone (MK) moiety and diglycidyl ether monomers of different molecular chain into the same polymeric chain, polymeric photoinitiators of different chain flexibility, PMKPR, PMKPG and PMKPP were synthesized. These polymeric photoinitiators possess the similar characteristic UV–vis absorption of parent MK, and their photobleaching behavior is similar. The T_g of PMKPR, PMKPG and PMKPP is 58.1 °C, −24.9 °C and −12.5 °C, respectively. Three types of monomer with different functionality, phenoxy ethyleneglycol acrylate (AMP-10G), 2,2-bis[4-(acryloxypolyethoxy) phenyl]propane (A-BPE-10) and trimethylopropane triacrylate (TMPTA), were chosen to be initiated by these photoinitiators. The result indicates the chain structure of photoinitiators has significant influence on the polymerization of monomers. PMKPG is the most efficient polymeric photoinitiator for initiating the polymerization of AMP-10G and A-BPE-10, while PMKPP is the most efficient for TMPTA.     

Copolymerization of n‐butylacrylate with styrene by a novel photoinitiator, 1‐(bromoacetyl)pyrene

A comparative study on photoinitiated solution copolymerization of n‐butylacrylate (BA) with styrene (Sty) using pyrene (Py), 1‐acetylpyrene (AP), and 1‐(bromoacetyl)pyrene (BP) as initiators showed that the introduction of a chromophoric moiety, bromoacetyl (? COCH₂Br), significantly increased the photoinitiating ability of pyrene. The kinetics and mechanism of copolymerization of BA with Sty using BP as photoinitiator have been studied in detail. The system follows nonideal kinetics (R_p ∝ [BP]^0.34 [BA]^1.07 [Sty]^0.97). The nonideality was attributed to both primary radical termination and degradative initiator transfer. The monomer reactivity ratios of Sty and BA have been estimated by the Finemann–Ross and Kelen–Tudos methods, by analyzing copolymer compositions determined by ¹H NMR spectra. The values of r₁ (Sty) and r₂ (BA) were found to be 0.78 and 0.25, respectively, which suggested the high concentration of alternating sequences in the random copolymers obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3233–3239, 2006