Non-extractable photoinitiators based on thiol-functionalized benzophenones and thioxanthones

Non-extractable photoinitiators could be advantageous for use in biological, electronic, and food packaging applications. Therefore, thioxanthone and benzophenone derivatives were synthesized from 1,6-hexane dithiol and chlorinated benzophenone or thioxanthone. The efficiency of thiol-functionalized photoinitiators in combination with amine co-initiators was compared to benzophenone and isopropylthioxanthone with amine co-initiators, and the cleavage of photoinitiator 2,2-dimethoxy-1,2-diphenylethan-1-one in acrylic resins. The reaction kinetics were analyzed using photo-differential scanning calorimetry and real-time FTIR. Coating physical properties were evaluated by pendulum and pencil hardness, steel-wool scratch and mandrel bend tests. The non-extractable photoinitiators had higher absorbance than their benzophenone or isopropylthioxanthone counterparts due to the sulfide substitution on the phenyl ring, and the free thiol groups reacted with the acrylate by either an amine catalyzed Michael addition or a free-radical chain process. The combination of thiol-functionalized photoinitiators with secondary amines provides an efficient photoinitiator system that is locked into the photopolymerized network and cannot be extracted with typical solvents.     

Photochemical reactions of high polymers. XIV. Syntheses and photochemical reactions of copolymers bearing O-acyloxime groups

Copolymers bearing pendant O-acyloxime groups were synthesized by two methods: copolymerizations of oxime acrylate (methyl β-naphthyl ketone oxime acrylate or benzophenone oxime acrylate) and styrene, condensation of acrylic acid—styrene copolymer with oximes (benzophenone oxime, p-nitrobenzophenone oxime, methyl β-naphthyl ketone oxime, benzalacetone oxime or 9-fluorenone oxime). The photochemical behavior of the O-acyloxime copolymers changed markedly with the irradiation conditions: irradiation of benzene solutions led to degradation in air and crosslinking under nitrogen, while irradiation of solid films in air resulted in simultaneous degradation and crosslinking. Photolysis of methyl β-naphthyl ketone oxime acetate, a model for the O-acyloxime copolymer, in benzene solution under nitrogen resulted in scission of the N? O bond. The same reaction was observed in the irradiation of the O-acyloxime copolymers. It is suggested that formation of free radicals on the polymer chains via scission of the N? O bond is followed by decarboxylation. In the absence of oxygen, crosslinking of the polymer by recombination of the free radicals competes with degradation via β-scission. In the presence of oxygen, autoxidative degradation predominates.     

Functional polysiloxanes as photoinitiators for UV-curable compositions: Evidence for a polymer effect

Functional silicone copolymers containing one or several types of pendant ester groups including a benzophenone or a thioxanthone chromophore, and/or a tertiary amine were used to prepare novel photo-initiating systems based on the phenone - amine photogeneration of radicals. The influence of the nature and relative amounts of the functional pendant units on the overall efficiency of the various initiating systems was evaluated by measuring the rate of polymerization of an acrylate based composition. By comparing the results obtained from different combinations of polymeric or low molecular weight reactants, a neat polymer effect inducing a greater initiation efficiency is evidenced, especially when a polysiloxane containing only aromatic carbonyl ester groups is associated with free 4-dimethylaminobenzoic esters as hydrogen donors. Time-resolved spectroscopy performed with thioxanthone functional systems indicates that the favourable effect on the apparent polymerization rate is not correlated with the rate of quenching of the triplet excited state by a tertiary amine. The polymer effect can rather be explained by the microheterogeneity of the distribution of the partners in the complex initiation process.     

Emulsion copolymerization of vinyl acetate and butyl acrylate in the presence of fluorescent dyes

This article describes our first experiments for preparing dye‐labeled latex particles by the emulsion copolymerization of a 4/1 (w/w) mixture of vinyl acetate‐butylacrylate (VAc‐BA). We discuss the synthesis of acrylate derivatives of phenanthrene, anthracene, and pyrene [9‐acryloxymethyl phenanthrene ( 7 ), 9‐acryloxymethyl‐10‐methyl anthracene ( 8 ), and 1‐acryloxymethyl pyrene ( 10 )] and an allyl ether derivative of anthracene [9‐allyoxymethyl‐10‐methyl anthracene ( 9 )]. Although the phenanthrene derivative 7 gave latex particles with high monomer conversion and good dye incorporation, the pyrene acrylate and both anthracene comonomers strongly inhibited the free‐radical reaction. To assist our search for a dye that would serve as a useful energy acceptor for phenanthrene and without suppressing VAc‐BA polymerization, we also examined batch emulsion polymerization in the presence of a variety of dye derivatives—substituted anthracenes, acridines, a coumarin, and two benzophenone derivatives. All of the anthracene derivatives, as well as acridine, strongly inhibited monomer polymerization. The coumarin dye 7‐hydroxy‐4‐methyl coumarin ( 22 ) that had only limited solubility allowed more than 90% monomer conversion. Most promising were 2‐hydroxy‐5‐methyl benzophenone ( 23 ) and 4‐N,N‐dimethylamino benzophenone ( 24 ) that at 1 mol % in the monomer mixture permitted virtually quantitative monomer conversion to latex. 4′‐Dimethylamino‐2‐acryloxy‐5‐methyl benzophenone ( 25 ) copolymerized well with the VAc‐BA mixture, yielding latex particles in high yield and with a narrow size distribution. These dyes appear to be useful acceptor dyes for energy‐transfer experiments with phenanthrene. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1594–1607, 2002     

The polymerization of acrylates using a combination of a carbonyl compound and an amine as a photo-initiator system

Photo-initiator systems for the polymerization of acrylates, based on a mixture of an aryl ketone and an α,ω-diaminoalkane, have been investigated. Rate constants for the photoreduction of fluorenone by α,ω-diaminoalkanes have been evaluated: it was found that CH₃N groups are more relative than CH₃CH₂N groups. The relative rates of photo-oxidation of α,ω-diaminalkanes sensitised by benzophenone have been determined. Surprisingly, little correlation exists between the susceptibility of an amine towards oxidation and its ability to reduce excited carbonyl groups. Several mixtures composed of an aryl ketone and an α,ω-diaminoalkane were found to initiate the polymerization of methyl methacrylate. The efficiency of initiation appears to be related to the efficiency of reaction of the triplet carbonyl compound with the amine. The efficiency of a particular combination of an aryl ketone and an amine to cure films of acrylate oligomers is also governed to some extent by the efficiency of reaction of the triplet carbonyl compound with the amine. However, the structure of the amino alkyl radical produced in the initiation reaction appears to be of greater importance in determining the efficiency of polymerization. Radicals of the type R₂N?HCH₂OR were found to be highly efficient.     

Exploring Bis(cyclometalated) Ruthenium(II) Complexes as Active Catalyst Precursors: Room‐Temperature Alkene–Alkyne Coupling for 1,3‐Diene Synthesis

Described is the development of a new class of bis(cyclometalated) ruthenium(II) catalyst precursors for C? C coupling reactions between alkene and alkyne substrates. The complex [(cod)Ru(3‐methallyl)₂] reacts with benzophenone imine or benzophenone in a 1:2 ratio to form bis(cyclometalated) ruthenium(II) complexes ( 1 ). The imine‐ligated complex 1 a promoted room‐temperature coupling between acrylic esters and amides with internal alkynes to form 1,3‐diene products. A proposed catalytic cycle involves C? C bond formation by oxidative cyclization, β‐hydride elimination, and C? H bond reductive elimination. This Ru^II/Ru^IV pathway is consistent with the observed catalytic reactivity of 1 a for mild tail‐to‐tail methyl acrylate dimerization and for cyclobutene formation by [2+2] norbornene/alkyne cycloaddition.     

Photoinitiating behavior of benzophenone derivatives covalently bonded tertiary amine group for UV‐curing acrylate systems

A series of benzophenone derivatives (N‐BPs) containing tertiary amine group used as hydrogen abstraction‐type (type II) photoinitiators were synthesized through the addition reaction of secondary amines with 4‐(2,3‐epoxypropyloxy) benzophenone. The chemical structures were characterized with ¹H NMR, FTIR spectroscopy, and UV spectrum measurements. The N‐BPs showed the higher absorption in 300–400 nm than benzophenone (BP). The photoinitiating activity was examined based on the photopolymerization of 1,6‐hexanediol diacrylate using photo‐DSC method. The results showed that the photoinitiating efficiency was negatively affected by the molecular structure of alkyl group connected to the tertiary amine with the order of isopropyl (N‐BPI) < methyl (N‐BPM) < ethyl (N‐BPE) < propyl (N‐BPP). Moreover, the diethanolamine‐modified benzophenone derivative (N‐BPOH) had the highest‐photoinitiating efficiency for free radical polymerization systems among the N‐BPs. Copyright © 2011 John Wiley & Sons, Ltd.     

Surface modification. II. Functionalization of solid surfaces with vinylic monomers

A new method to functionalize surfaces of solid substrates such as glass, silicon crystals, and silica microspheres with appropriate vinylic monomers, i.e., methyl vinyl ketone, methyl acrylate, methacrolein, and acrolein, is described. The surface modification process was performed through the following sequence of reactions: (a) derivatization of the surfaces with to-nitrile groups by interacting the substrates with SiCl₃(CH₂)₃CN; (b) subsequent reduction of the a)-nitrile groups with diborane to w-amine groups; (c) binding of the vinylic monomers to the surfaces via the to-amine groups. pK_1/2 of the surface primary amine groups, as determined by contact angle titration, was found to be 2–4 units lower than the pK_1/2 values of primary amine analogous in solution. Methyl vinyl ketone and methyl acrylate were covalently bound to the amine surfaces only under basic conditions via the Michael addition reaction. Methacrolein and acrolein were covalently bound to the amine surfaces under both acidic and basic conditions via two major reactions: the Michael addition reaction and Schiff base bond formation. The concentration of the aldehyde groups of the surfaces obtained by the reaction with methacrolein and acrolein was significantly higher than that obtained using the common, published method in which glutaraldehyde interacts with the amine surfaces.     

Preparation of a copolymer of methyl methacrylate and 2‐(dimethylamino)ethyl methacrylate with pendant 4‐benzyloxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy and its initiation of the graft polymerization of styrene by a controlled radical mechanism

The macroinitiator of a copolymer (PMD_BTM) of methyl methacrylate (MMA) and 2‐(dimethylamino)ethyl methacrylate (DAMA) with 4‐benzyloxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (BTEMPO) pendant groups was prepared by the photochemical reaction of tertiary amine groups of the copolymer with benzophenone in the presence of BTEMPO. The radical copolymerization of MMA and DAMA was carried out first with azo‐bis‐isobutyronitrile (AIBN) as an initiator; then, the dimethylamine groups of the copolymer constituted a charge‐transfer complex with benzophenone under UV irradiation, and the methylene of ternary amine and diphenyl methanol radicals were produced. The former was capped by BTEMPO, and the nitroxide (BTEMPO) was attached to the polymeric backbone. The amount of pendant BTEMPO on PMD_BTM was measured by ¹H NMR. PMD_BTM initiated the graft polymerization of styrene via a controlled radical mechanism, and the molecular weight of the PMD‐g‐polystyrene increased with the polymerization time. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 604–612, 2001     

Synthesis and photoinitiating behavior of hyperbranched polymeric photoinitiators bearing coinitiator amine

A series of benzophenone (BP)‐terminated hyperbranched polyester (BoltornTM P1000), bearing amine moieties as synergists by reacting with piperidine, were synthesized as yellowish liquids with low viscosity, and used as polymeric photoinitiators (HPPIs). For comparison, acrylate groups were introduced to the terminals of hyperbranched polyester for obtaining a polymerizable photoinitiator. The chemical structures were characterized by FTIR and ¹H NMR spectroscopy. HPPIs and BP exhibited the similar absorptions by UV–vis spectroscopy. The photoinitiating behavior of HPPIs with trimethylolpropane triacrylate (TMPTA) as a trifunctional monomer was investigated by using photo‐DSC analysis. The results indicated that the maximum photopolymerization rate and unsaturation conversion of TMPTA initiated by HPPIs were both lower than that by BP. Among them, the HPPI with double tertiary amine moiety of BP moiety was found to be the most efficient photoinitiator. Additionally, the films cured with bisphenol A epoxy acrylate EB605 initiated by HPPIs were uniform and possessed high T_g from DMTA. Copyright © 2010 John Wiley & Sons, Ltd.     

电荷转移聚合法合成聚丙烯酸叔丁酯的研究

本文以丙烯酸叔丁酯为单体,苯胺与二苯甲酮络合物为引发剂,四氢呋喃为溶剂,在紫外光照射下通过电荷转移聚合(CTP)合成了具有苯亚胺基链端的聚丙烯酸叔丁酯(PtBA),并用FT-IR、1H-NMR和GPC等对其进行了表征.同时考察了反应时间、引发剂浓度、反应温度等因素对单体转化率和聚合物分子量的影响.结果表明,聚合反应动力...     

芳香叔胺引发烯类单体聚合研究——单体结构与聚合的关系

不同烯类单体在芳香叔胺存在下的聚合机构不一样。甲基丙烯酸甲酯等有α-甲基的烯类单体在不照光的条件下即可被芳香叔胺引发聚合,其聚合机构认为是首先α—甲基被胺-氧复合物氧化,生成单体过氧化物。再与胺形成氧化还原体系,分解产生自由基。 丙烯酸酯,丙烯腈等没有α-甲基的单体,只有光照时才被芳香叔胺氧化聚合,不光照时完全不聚合。这是因为这些单体不被胺-氧复合物氧化。光照下聚合的机构认为是因光的激发,这些单体与芳香叔胺形成电子转移激发络合物,再分解产生自由基。 研究了单体结构,胺结构对光聚合速度的影响。不同单体的活性次序是: AN>MA>VA>St 不同芳香叔胺的活性次序是: DMT>DMA>DMB>DNA 表明单体双键电子云密度越小,芳香叔胺氮原子上电子云密度越大,越容易形成激发态电子转移络合物,从而越容易聚合。     

TREN versus Me6‐TREN as ligands in SET‐LRP of methyl acrylate

The commercially available tris(2‐aminoethyl)amine (TREN) was used as ligand to mediate the single‐electron transfer‐living radical polymerization (SET‐LRP) of methyl acrylate in dimethyl sulfoxide initiated with the bifunctional initiator bis(2‐bromopropionyl)ethane and catalyzed by both nonactivated and activated Cu(0) wire. A comparative study between TREN and tris(2‐dimethylaminoethyl)amine (Me₆‐TREN) ligand, that is more commonly used in SET‐LRP, demonstrated that TREN provided a slower polymerization but the chain‐ends functionality of the resulting bifunctional poly(methyl acrylate) was near quantitative and comparable to that obtained when Me₆‐TREN was used as a ligand. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.     

Alternating copolymerization of methyl acrylate with donor monomers having a protected amine group

Attempts were made to copolymerize p-aminostyrene, p-acetamidostyrene, N-methyl-p-aceta-midostyrene, N-(4-vinylphenyl) phthalimide, N-vinyl succinimide, and N-vinyl phthalimide with methyl acrylate complexed with ethyl aluminum sesquichloride. Only reactions involving N-(4-vinylphenyl)phthalimide and N-vinyl phthalimide yielded alternating copolymers. N-vinyl succinimide gave nonalternating copolymers insoluble in common solvents and the other monomers did not copolymerize. In some cases, the conventional radical copolymers were prepared for comparison purposes. The reactivity ratios of the free-radical initiated copolymerization of methyl acrylate (I) with N-(4-vinylphenyl)phthalimide (II) were r₁ = 0.14 and r₂ 1.56. The alternating copolymers were studied by ¹H-NMR and ¹³C-NMR spectroscopy. The alternating copolymer of N-(4-vinylphenyl)phthalimide with methyl acrylate was hydrazinolyzed to form the alternating copolymer of methyl acrylate with p-aminostyrene. Hydrazinolysis of the alternating copolymer of methyl acrylate with N-vinyl phthalimide removed the phthalimide moiety and generated vinyl amine units which readily cyclized with neighboring methyl acrylate units to form copolymers that contained five-membered lactam rings. The infrared (IR) spectra of the hydrazinolyzed products contain bands due to amine or amide groups and are devoid of the characteristic bands of the phthalimide ring.     

Photo-oxidative stability of electron beam and UV cured acrylated epoxy and urethane acrylate resin films

The post-cured photo-oxidative stability of urethane and bisphenol-A epoxyacrylate resins in mixed compositions with triacrylate and amine diacrylate resins are examined using UV and reflectance infra-red absorption spectroscopic techniques. Overall, by measuring the growth in hydroxyl absorption at 3400 cm⁻¹, electron-beam cured resin films are more photostable than UV curedfilms, indicating the high photo-activity of residual photoinitiator in the latter case. Regarding the UV cured systems benzophenone is found to be a more photo-active residual photoinitiator than the benzoyl ester photofragmenting types. Films containing the amine diacrylate resin are more photostable than those containing the triacrylate resin. This stabilising effect is associated with the oxygen and radical scavenging ability of the terminal amine groups. Photo-yellowing, as measured by the growth in an absorption band at 280 nm, is observed only in resin films containing the amine diacrylate resin and is associated with the formation of unsaturated carbonyl groups. The latter are, however, photobleached on prolonged irradiation whereas with resins containing the bisphenol-A epoxy acrylate resin, a longer term photo-yellowing is observed due to oxidation of the bisphenol-A to give stilbene-quinone products.     

Cu(0) Wire-mediated Single-electron Transfer-living Radical Polymerization of Oligo(ethylene oxide) Methyl Ether Acrylate by Selecting the Optimal Reaction Conditions

The efficient Cu(0) wire-catalyzed single-electron transfer-living radical polymerization (SET-LRP) in organic solvents and mixtures of the organic solvents with water has been thoroughly investigated.Oligo(ethylene oxide) methyl ether acrylate was used as an exemplar oligomer monomer to determine the optimum polymerization conditions for rapid,controlled,and quantitative production of well-defined polymers.The effects of Cu(0)-wire length (12.5 or 4.5 cm),ligand type (tris(dimethylaminoethyl)amine,Me6-TREN,or tris(2-aminoethyl)amine,TREN),and solvent type (dipolar aprotic solvents,cyclic ethers,alcohol,or acetone) on the polymerization have been evaluated.Kinetic experiments were performed for all polymerizations to assess the "living" behavior of each system employed.Importantly,TREN could be used as a replacement for Me_6-TREN in Cu(0) wire-catalyzed SET-LRP of oligomer monomer,which probably provides the most economical and efficient methodology since TREN is 80 times less expensive than Me6-TREN.The high chain-end fidelity of resulting polymer was experimentally verified by thiol-Michael addition reaction at the a-Br chain end and subsequent chain extension with methyl acrylate.     

Alkyl halide/tertiary amine as novel initiators for free radical polymerizations of methyl methacrylate,methyl acrylate and styrene

A series of combinations of alkyl halide with tertiary amine such as ethyl α-bromophenylacetate/tris[2-(dimethylamino)ethyl)]amine (αEBP/Me₆TREN), ethyl 2-bromoisobutyrate/triethylamine (EBiB/TEA), and ethyl 2-chloropropionate/N,N,N′,N′,N′′-pentamethyldiethylenetriamine (ECP/PMDETA) have been developed as novel free radical initiators and used for the polymerizations of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (St). The effects of the structure of alkyl halide and tertiary amine on the polymerization of MA were investigated. Gel permeation chromatograph (GPC) and proton nuclear magnetic resonance (¹H NMR) have been utilized to analyze the end group of the obtained poly(methyl acrylate). Electron spin resonance (ESR) spectroscopy was employed to identify the structure of the radicals produced by αEBP/Me₆TREN, and the results indicated that αEBP reacted with Me₆TREN via a single electron transfer (SET) nucleophilic mechanism to produce corresponding ethyl α-phenylacetate radicals which subsequently initiated the polymerization of MA. As both alkyl halide and tertiary amine are commercially available at low cost, non-explosive, and ease of use and storage in comparison with conventional azo, peroxide or persulfate initiators, the combination of alkyl halide and tertiary amine as a free radical initiator is promising for large-scale practical applications.     

Novel PU‐type polymeric photoinitiator comprising side‐chain benzophenone and coinitiator amine for photopolymerization of PU acrylate

A novel diamine 3,5‐diamino‐4′‐phenoxylbenzophenone (DAPBP) was synthesized from the reaction of 3,5‐diamino‐4′‐chlorobenzophenone (DACBP) and phenol. Then through the polycondensation of DAPBP, toluene‐2,4‐diisocyanate (TDI), and N‐methyldiethanolamine (MDEA), we obtained a PU‐type polymeric photoinitiator containing side‐chain benzophenone (BP) and tertiary amine in the same macromolecule (PUSOA). Another polymeric photoinitiator without coinitiator amine in polymer chain (PUSO) was also synthesized for comparison. FT‐IR, ¹H NMR, and GPC analyses confirmed the structures of monomer and polymeric photoinitiators. The UV–Vis spectra of PUSOA, PUSO, and DAPBP are similar, and all exhibit the maximal absorption near 290 nm. ESR spectra indicate that PUSOA can generate active species most efficiently. The photopolymerization of PU acrylate, initiated by PUSOA, PUSO/MDEA, DAPBP/MDEA, and BP/MDEA, was studied by differential scanning photocalorimetry (photo‐DSC). The results show that the in‐chain coinitiator amine can significantly improve the photoefficiency of the polymeric photoinitiator and the PUSOA is more efficient for the polymerization of PU acrylate than its low‐molecular‐weight counterpart. Copyright © 2008 John Wiley & Sons, Ltd.     

大分子量二苯甲酮光引发剂的合成及动力学研究

以4-羟基二苯甲酮(HBP)、甲苯-2,4-二异氰酸酯(TDI)、4,4′-二羟基二苯甲酮(DHBP)为原料,通过两步反应,合成了一种大分子量二苯甲酮光引发剂:HBP-TDI-DHBP-TDI-HBP(HTDTH).通过实时红外研究了HTDTH的光聚合动力学.结果表明,HTDTH是一种有效的光引发剂.采用HTDTH/胺光引发体系引发二缩三丙二醇二丙烯酸酯(TPGDA)聚合时,随着胺和引发剂浓度的增大,反应速率(R_p)和单体最终转化率(P)同时增大.     

A recyclable perfluoroalkylated PCP pincer palladium complex

A new fluorous PCP pincer ligand has been coordinated to Ni(II), Pd(II) and Pt(II). The air stable palladium complex, which promotes Heck reactions between methyl acrylate and either aryl bromides or iodides, can be recovered intact by fluorous solid-phase extraction and was reused four times in the Heck reaction between methyl acrylate and 4-bromoacetophenone without loss in catalytic activity.