Photocrosslinking of elastomer systems. II. Ultraviolet light-induced reactions in an EPDM modified by grafting of benzoin derivatives

Photocrosslinking experiments were performed on elastomeric polymer films (EPDM) previously modified by grafting a photosensitive initiator (benzoin derivative) onto the macromolecular backbone. This modification was performed by a series of Friedel–Crafts reactions and the resulting materials were characterized by infrared (IR) spectroscopy in conjunction with model reactions. After ultraviolet (UV) irradiation the photocrosslinked samples were studied by IR spectroscopy in conjunction with the measurement of physical properties. It apperared that grafting the photosensitizer onto the elastomer considerably enhances the crosslinking reaction even with a limited quantity of grafted benzoin derivative. Moreover, the results obtained suggest that the structure of the resulting networks is strongly dependent on the crosslinking process used; that is, curing the elastomer with peroxide or UV irradiation either of a blend of elastomer and photosensitizer or of the same elastomer modified by grafting the chromophore.     

不饱和环缩醛/多硫醇体系的光交联

本文研究了3,9-二丙烯基-2,4,8,10-四氧螺[5,5]十三烷(DPTST)和四巯基醋酸季戊四醇酯(PTMA)以苯乙酮衍生物、安息香醚和芳酮作光引发剂时的光交联。通过测定双键在1680cm^-1和巯基在2570cm^-1处的红外吸收随光照时间的变化以及凝胶转化率和硬度随光照时间的变化来表征光交联动力学。 光交联速度与组分配比、光引发剂性质及含量有明显关系。以苯乙酮衍生物和α,α-二甲氧基-α-苯基苯乙酮为光引发剂、DPTST/PTMA的摩尔比为2:1到3:1时,得到较好的实验结果。     

A convenient and selective synthesis of unsymmetrical benzoins via the cyanide ion catalyzed cleavage of benzils

The cyanide ion-catalyzed cleavage of benzils is used for the generation of various ‘masked’ acyl intermediates. The reaction of these intermediates with various aldehydes furnishes the corresponding esters of unsymmetrical benzoins in very good yields. A variety of unsymmetrical benzoin derivatives are synthesized in this way, including ferrocene derivatives. The hydrolysis of benzoin esters and their subsequent oxidation affords the corresponding unsymmetrical benzoins and benzils in high yield.     

SBS光交联反应及其性能研究

利用测定凝胶含量的方法 ,对SBS热塑性弹性体在紫外光辐照下的交联反应进行了研究。研究表明 ,SBS经光交联剂的引发能很好地发生交联 ,在所采用的光引发剂蒽醌、苯芴酮、三硝基芴酮、安息香乙醚中 ,安息香乙醚的交联效果最佳。另外 ,通过红外光谱对交联反应动力学进行了研究 ,结果发现SBS中乙烯双键含量的增加对交联反应影响不大 ,因为乙烯双键含量的增加 ,只会加速分子内反应 ,对分子间的交联反应没有贡献。辐照膜的差示扫描量热及热失重分析表明 ,交联后的SBS膜热稳定性增大 ,且随交联程度的增加 ,热稳定性增大 ,并用扫描电镜对交联膜的微观结构进行了表征     

苯偶姻单酯无溶剂微波加热合成2-取代-4,5-二芳基咪唑衍生物

以醛为原料,在维生素B1作用下,经安息香缩合反应制得相应的苯偶姻衍生物,进而以此为原料与不同的酰化试剂酯化生成苯偶姻单酯.苯偶姻单酯与醋酸铵附着在固载体酸性氧化铝上,在无溶剂条件下微波加热合成了17种2-取代-4,5-二芳基咪唑,其中7种未见文献报道.该方法具有反应条件温和、反应时间短,且无需有机溶剂,是一种节能环保、易操作的合成方法.另外,所合成化合物的结构通过IR、高分辨质谱和核磁共振谱进行了确认.     

Photolysis of polymers using the medium pressure mercury lamp: Part 2—Photolysis of poly(methyl acrylate), alone and in presence of benzoin,fluorenone and 2-chlorothioxanthone

Poly(methyl acrylate) (PMA) films, 44 μm thick, have been irradiated and the yields of the four principal condensable volatile photolysis products (methyl formate, formaldehyde, methanol and carbon dioxide) have been determined quantitatively, using subambient TVA, for periods of irradiation up to 6 h. Spectral changes (ir and uv) occurring in the films as a result of irradiation have been examined. The crosslinking reaction has been followed by sorption measurements using radioactive styrene dichloride. Results have been compared with those of earlier studies using the low and high pressure mercury lamps.The effects of benzoin, fluorenone and 2-chlorothioxanthone on the photolysis of PMA have been investigated. Each compound reduces the yield of the normal photolysis products; benzaldehyde is observed as a new product from films containing benzoin. For photolysis in the presence of these compounds, which decompose within 30 min under the conditions used, sorption measurements suggest that crosslinking is reduced and, when sufficient concentration of additive is present, chain scission predominates. After the additive has been destroyed, however, the crosslinking reaction proceeds as in pure PMA.     

Detection of molecular weight changes in solid polymer samples without dissolution: A novel approach

Changes in the molecular weight of poly(methyl acrylate) (PMA) films as a result of crosslinking during photolysis in vacuo at 30°C have been followed by sorption of styrene dichloride, labelled with chlorine-36, from a solvent/non-solvent medium and radiochemical measurement of the absorbed solvent. The count rate falls sharply with extent of irradiation, showing a clear indication of the development of crosslinks in the film. Corresponding behaviour with several concentrations of benzoin as additive has also been examined: the sorption method gives a valuable insight into the effect of benzoin on the crosslinking process.Sorption has also been applied to films of a series of heterodisperse linear PMA samples, with interesting results. A clear molecular weight dependence of the amount of styrene dichloride absorbed in a fixed time has been observed.     

Photoinitiated polymerization of methyl methacrylate and methyl acrylate with 14C-labeled benzoin methyl ethers

Three ¹⁴C-labeled benzoin methyl ether (α-methoxy-α-phenylacetophenone) derivatives were utilized as photoinitiators in the polymerization of methyl methacrylate (MMA) and methyl acrylate (MA). The results of polymer end-group analysis are in accord with a mechanism of benzoin ether photocleavage into initiator radicals and dispute earlier labeling studies which were interpreted as evidence for copolymerization of excited-state benzoin ethers with reactive monomers. In MMA polymerization, the results indicate a preference for termination by disproportionation (～60%) and provide evidence for primary radical termination at 0.041M photoinitiator (optically dense solutions) in neat MMA. Evidence for chain branching by initiator radical hydrogen abstraction from poly(methyl acrylate) (PMA) is also presented. The benzoyl and α-methoxybenzyl radicals, produced on photolysis of benzoin methyl ether, appear to be equally effective in both initiation and hydrogen-abstraction processes. Quantum yields at 366 and 313 nm indicate the absence of a wavelength effect.     

High-performance liquid chromatographic measurement of guanidino compounds of clinical importance in human urine and serum by pre-column fluorescence derivatization using benzoin

High-performance liquid chromatographic microanalyses for guanidino compounds in human physiological fluids have been accomplished by means of a pre-column fluorescence derivatization method using benzoin. The guanidino compounds in urine or deproteinized serum after ultrafiltration are converted to the fluorescent derivatives with benzoin in an alkaline medium, and the derivatives are separated simultaneously within 25 min on a reversed-phase column (mu Bondapak Phenyl) with a linear gradient elution of methanol in aqueous mobile phase (pH 8.5). The method permits the quantitative determination of guanidinosuccinic acid, methylguanidine, taurocyamine and guanidinobutyric acid at concentrations of as low as 8-78 pmol/ml in human urine and serum.     

Chiral micellar electrokinetic chromatography-atmospheric pressure photoionization of benzoin derivatives using mixed molecular micelles

In the present work we report, for the first time, the successful on-line coupling of chiral MEKC (CMEKC) to atmospheric pressure photoionization MS (APPI-MS). Four structurally similar neutral test solutes (e.g. benzoin (BNZ) derivatives) were successfully ionized by APPI-MS. The mass spectra in the positive ion mode showed that the protonated molecular ions of BNZs are not the most abundant fragment ions. Simultaneous enantioseparation by CMEKC and on-line APPI-MS detection of four photoinitiators, hydrobenzoin, BNZ, benzoin methyl ether, benzoin ethyl ether, were achieved using an optimized molar ratio of mixed molecular micelle of two polymeric chiral surfactants (polysodium N-undecenoxy carbonyl-L-leucinate and polysodium N-undecenoyl-L,L-leucylvalinate). The CMEKC conditions, such as voltage, chiral polymeric surfactant concentration, buffer pH, and BGE concentration, were optimized using a multivariate central composite design (CCD). The sheath liquid composition (involving %v/v methanol, dopant concentration, electrolyte additive concentration, and flow rate) and spray chamber parameters (drying gas flow rate, drying gas temperature, and vaporizer temperature) were also optimized with CCD. Models built based on the CCD results and response surface method were used to analyze the interactions between factors and their effects on the responses. The final overall optimum conditions for CMEKC-APPI-MS were also predicted and found in agreement with the experimentally optimized parameters.     

Polymeric oxidizing reagents based on polyacrylamides: Effect of the nature and extent of crosslinking on reactivity

Acrylamide was copolymerized with N,N′-methylene-bis-acrylamide (NNMBA), tetraethyl-eneglycol diacrylate (TEGDA), and divinyl benzene (DVB) in different proportions to afford crosslinked polyacrylamides with varying nature and extent of crosslinking. These insoluble polymers were functionalized with the N-bromoamide function and the reactivity of the resulting polymeric N-bromoamide was investigated under different conditions. The capacities of the reagents varied from 6.7 mequiv / g for the linear polymeric reagent to 1.1 mequiv / g for the 15% DVB-crosslinked reagent. Oxidation of benzoin to benzil was used as the model reaction. Investigation of the reaction under different conditions of solvent and varying molar excess revealed a significant influence of the nature and extent of crosslinking in deciding the extent of reaction. In the case of NNMBA-crosslinked reagents, the reactivity increased up to 10% crosslinking and then decreased. The reactivity of the reagents increased up to 15% crosslinking in the case of TEGDA-crosslinked ones and for DVB-crosslinked reagents the reactivity decreased with crosslinking. The polarity of the crosslinking agent and its molar percentage on the polymeric reagent (crosslink density) are factors affecting the solvent compatibility, which in turn, is decisive in the facilitation of the reactions.     

Side products in the rosenmund reduction of benzofuran-2-carboxylic acid chlorides

The corresponding 1,2-bis(2-benzofuryl)ethylenes and 2-methylbenzofurans were isolated as side products, along with the principal reaction products (2-formylbenzo-furans), in the Rosenmund reduction of 3-, 5-, and 7-alkylbenzofuran-2-carboxylic acid chlorides. The bis(2-benzofuryl)ethylene structure was confirmed by the IR and PMR spectra data and alternative synthesis by reduction of the corresponding benzofuroins, obtained by benzoin condensation of 2-formylbenzofurans, with zinc amalgam in acidic media. The side formation of desoxybenzofuroin derivatives was noted in some cases in the benzoin condensation.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 744–748, June, 1977.     

Photocrosslinking of poly(methyl acrylate)s containing the 1,3-dioxolane structure as a pendant group

(2-Ethyl-2-methyl-1,3-dioxolan-4-yl)methyl- and (2-methyl-2-phenyl-1,3-dioxolan-4-yl) methyl acrylates were synthesized and polymerized. The photochemical behavior of the resulting polymers was investigated to determine whether the polymers pending on the 1,3-dioxolane structure were readily crosslinked with ultraviolet (UV) irradiation. The degree of crosslinking was estimated by the weight-loss method by immersion in acetone, with the result that the polymer with an aromatic substituent was more photocrosslinkable than the polymer that bore the aliphatic substituent. The catalytic effect on photocrosslinking of polymers was also studied by using benzoin and cobalt naphthenate. The infrared (IR) spectra of polymers irradiated in air that showed the new band at 3450 cm^?1 were attributed to a hydroxyl group; however, the spectra of polymers irradiated in vacuum displayed little absorption at 3450 cm^?1. To explain the mechanism of crosslinking model compounds were prepared and irradiated with UV light. It was concluded that crosslinking proceeds mainly from the fission of the 1,3-dioxolane ring and the coupling of the yielding radicals, together with autooxidation by atmospheric oxygen.     

Regio- and stereochemical aspects in the synthesis of homoallylic alcohols from benzoins and their iodocyclisation to 2,3-diphenyltetrahydrofurans

Indium mediated allylation, crotylation and cinnamylation of benzoins and its substituted derivatives in THF-H₂O (2/1) provide a range of homoallylic alcohols. In general, the benzoins undergo allylation and crotylation in a sluggish manner compared to those observed earlier in the case of α-hydroxy aldehydes and are significantly affected by the electronic features of both the benzoin and indium organometallic reagent. The reactions exhibit higher order of diastereoselectivities than those observed for α-hydroxy aldehydes. The cinnamylation though proceeds in a highly diastereoselective manner but is restricted to only benzoin and 4,4′-dichlorobenzoin. The homoallylic alcohols undergo I₂ mediated intramolecular diastereoselective cyclization to provide 2,3-diphenyltetrahydrofuran derivatives. The relative stereochemistries in tetrahydrofurans and homoallylic alcohols have been assigned by coupling constants, NOE experiments and in one case by X-ray crystallography.     

SBA-15/NiCl2催化超声合成喹喔啉衍生物

以苯偶姻和邻苯二胺为原料,SBA/NiCl2为催化剂,在超声条件下合成了喹喔啉衍生物,其结构经1H NMR和IR确证。考察催化剂类型、原料摩尔比和催化剂的用量对产率的影响。在最佳条件(苯偶姻和邻苯二胺物质的量比为1.0/1.0,催化剂用量为苯偶姻的10 mmol%,于70℃超声反应5 min)下,产率可达94.7%。     

Dielectric properties of some photo crosslinking acrylate ester copolymers

Photo crosslinking due to the photo polymerization of unsaturated acrylic side-groups attached to copolymers of glycidyl methacrylate and methyl methacrylate (GMA-MMA) by reaction with acrylic acid in the presence of benzoin methyl ether as photolabile initiator has been investigated. The composition of these copolymers based on (GMA-MMA, 30:70) were determined by [¹H] NMR spectroscopy. The reactivity ratios for the GMA-MMA system were determined using the Kelen-Tüdös method.

The dielectric properties of copolymers based on GMA-MMA acrylate ester (30:70) and homopolymers of MMA in combination with different polyfunctional acrylate ester monomers before and after exposure to UV irradiation have been studied in a solid state matrix, over a frequency range of 100 Hz to 50 kHz and at temperatures in the range 20–70°C.     

A catalyst- and solvent-free three-component reaction for the regioselective one-pot access to polyfunctionalized pyrroles

A facile method for the regioselective synthesis of tetrasubstituted pyrroles, from readily accessible 1,3-dicarbonyls, benzoin derivatives and ammonium acetate, has been developed. The one-pot three-component reactions were performed to afford tetrasubstituted pyrroles under solvent- and catalyst-free conditions.     

胶团噻唑衍生物对安息香不对称合成反应的催化作用

通过α-(1-萘基)-N-硫代甲酰乙胺与卤代酮反应制得六个光学活性的4-烷基-3-α-(1-萘基)乙基噻唑溴化物烷基碳链长=1,2,7.11,15,21). 将其用于催化水溶液中的安息香缩合反应, 所得产物收率约20-30%具有较高的光学纯度(47-57%). 在各种缓冲溶液中测定了S(+)-4-甲基-3-α-(1-萘基)乙基噻唑氯化物(Ta)的胶团性质和由它催化的不对称安息香缩合反应. 临界胶团浓度(cmc)证明(Ta)在反应中确以胶团形式催化. 在硼砂溶液中, 安息香的收率高达61%, 光学纯度23.6%.     

超声辅助合成喹喔啉类化合物

在超声辅助下,使用蒙脱土负载碘催化苯偶酰衍生物与邻苯二胺经缩合反应合成了4个喹喔啉类化合物,其结构经¹H NMR和IR确证。以苯偶酰（1a）和邻苯二胺（2）的反应为模板,对反应条件进行了优化。结果表明：最佳应条件为：1a 0.1 mmol, n(1a)：n(2)为1.0 ：1.2,催化剂蒙脱土负载碘用量为5 mol%,二氯甲烷为溶剂,于30 ℃超声反应5 min,收率97.2%。该催化体系回收利用3次后收率为82.0%,说明其具有一定的循环使用能力。     

Enantioselective reduction and deracemisation using the non-conventional yeast Pichia glucozyma in water/organic solvent biphasic systems: preparation of (S)-1,2-diaryl-2-hydroxyethanones (benzoins)

Water/organic solvent two-liquid-phase systems have been successfully applied in the synthesis of enantiomerically pure (S)-benzoin through two different methodologies catalysed by whole cells from the non-conventional yeast Pichia glucozyma: the stereoselective monoreduction of benzil and the deracemisation of benzoin. The presence of the organic solvent influences the redox systems implied in the reactions, avoiding the formation of the corresponding diols, increasing the enantioselectivity and allowing the easy isolation of the products in high yields and excellent enantiomeric excesses. The use of both strategies has been extended to the preparation of different chiral benzoin derivatives.