一类高效复合型光引发剂的合成研究

硫鎓盐是一类有效的阳离子光引发剂,同时它在光解时也有自由基生成,实质上它是一种阳离子-自由基复合型光引发剂.硫鎓盐广泛地应用于涂料、油墨、电子工业、微细加工和快速成型等领域.它的出现使原本不能发生光聚合的单体,如环氧化合物发生光聚合反应,同时,它具有不受氧干扰,引发效率高、表面硬度高、深层收缩小,且可在光固化后用加热使固化反应更彻底等优点.     

香豆素肟酯类双光子引发剂的合成及性能研究

开发高效的双光子引发剂是提升双光子聚合速度的关键。本文基于光致脱羧机制,设计并合成了两种以共轭香豆素作为生色团、肟酯作为引发基团的双光子引发剂,并通过实验测试结合模拟计算对该类引发剂的光物理和光化学行为进行了研究。结果表明,该类引发剂在400~500 nm区域具有较强吸收,在LED可见光辐照下发生分解,具有光漂白特性,光解后释放的活性种可引发丙烯酸酯类单体聚合。利用双光子三维微纳成型技术,该类香豆素肟酯化合物可有效用于构建高分辨率的三维微纳结构。并通过量子化学计算,对该类引发剂的引发机理进行了探讨。     

光引发阳离子聚合反应的研究——Ⅱ.硫鎓盐DPTS引发乙烯基正丁醚光聚合动力学

以二苯基-4-苯硫基代苯基硫鎓盐(DPTS)为光引发剂,研究了乙烯基正丁醚的本体和溶液光聚合。在本体聚合中,聚合速率(R_p)与引发剂浓度成正比;在15～35℃范围内,聚合活化能几乎为零。分别以CHCl₃(CH₂Cl)₂和C₆H₅Cl作溶剂的溶液聚合,其R_p均比本体聚合者大,同时单体浓度对R_p的影响则表现出复杂的关系。根据普遍接受的硫鎓盐光解机理并假设溶剂和单体均可不同程度地参与引发反应,解释了溶液聚合中单体影响的动力学规律。     

用吸收光谱法测定鎓盐光解生成酸的量子产率

近年来,鎓盐化合物,如碘鎓盐、硫鎓盐和氧鎓盐等,作为光引发剂在酸催化微电子器件加工技术中得到了广泛的应用。我们曾对它们的稳态和瞬态光解及机理进行过比较详细的研究,也发现它们在光解时能以不同途径生成很强的无机酸(Bronsted酸),进而可引发单体阳离子聚合或高分子薄膜的交联等。很显然,在这一工作中准确测定它们光解时生成酸的量子产率将与微电子器件加工中光刻质量(如分辨率等)密切相关。在过去的工作中,一般采用酸碱滴定法困,即用氢氧化钠,氢氧化钾水溶液测定嗡盐光解生成酸的量子产率,但由于嗡盐在水中溶解度不很理想,因而结果往往不能重复,测定的酸量子产率误差较大,如Pappas用此法测得的三苯基硫嗡盐在254 nm光解生成酸量子产率为0.74,误差在正负20%。     

氨基甲酸酯乙烯基醚类化合物光聚合性能研究

本文合成了一种双官能度的氨基甲酸酯乙烯基醚和一种三官能度的氨基甲酸酯乙烯基醚,并用实时傅立叶红外光谱分别监测了单官能度、双官能度和三官能度的乙烯基醚化合物在三芳基六氟锑酸锍鎓盐阳离子光引发剂(PAG-201)引发下的光聚合情况,对其光聚合动力学性能进行了比较,研究了引发剂PAG-201的浓度对双官能度单体光聚合的影响.结果表明,随着官能度的增加,乙烯基醚化合物的转化率和聚合速率降低.此外,对它们的聚合产物进行的热失重分析表明,随着官能度的增加,聚合产物的热稳定性增加.本文的结果对于研究开发基于氨基甲酸酯乙烯基醚单体的阳离子聚合体系具有较好的指导意义.     

应用化学专业综合实验设计:光电子转移可行性判断

针对于光化学基本理论的实验教学对于应用化学专业的学生培养具有重要意义,将蒽与碘鎓盐的光电子转移可行性判断,以及蒽/碘鎓盐引发丙烯酸酯单体的聚合实验设计为应用化学专业的综合实验,以培养学生对光化学基本理论的理解。学生通过紫外-可见吸收光谱、荧光激发光谱和循环伏安实验获得实验数据,依据Rehm-Weller方程计算获得蒽与碘鎓盐之间光电子转移的自由能变,并通过光聚合实验学习光电子转移增感引发体系的应用。     

香豆素衍生物与碘鎓盐间的光诱导电子转移研究

研究了3种碘鎓盐对3种香豆素荧光的猝灭,发现猝灭曲线符合Stern-Volmer方程,并且猝灭过程受扩散控制.研究证实了猝灭的机理是由于发生了光诱导电子转移.通过香豆素衍生物-碘鎓盐体系能在光照下引发甲基丙烯酸甲酯单体的聚合进一步证实了这种机理.尽管香豆素有较强的分子内电荷转移倾向,但由于碘鎓盐阳离子很强的拉电子能力,它们间还是能发生快速的电子转移.     

双官能度单组分光引发剂的制备及其光引发活性研究

本文利用4-甲基二苯甲酮、哌嗪等原料合成了一种双官能度的单组分光引发剂（MBPPA）,其分子结构中具有两个二苯甲酮基团。通过紫外光谱研究了光引发剂的紫外吸收和光降解性能,并利用实时红外测试了光引发剂的光引发活性以及不同单体对光聚合动力学的影响。结果表明,在光照10 min后,MBPPA在257.2 nm处的吸光度降低了18.76%,光降解速度明显高于MBP。当光强为50 mW·cm^-2时,0.2%（摩尔分数）MBPPA单独引发乙氧基乙氧基丙烯酸乙酯（EOEOEA）聚合的转化率可达90%。在同等条件下,多官能度丙烯酸酯单体的聚合速率要明显高于单官能度丙烯酸酯单体,但其转化率有所降低。     

吩噻嗪席夫碱可见光引发剂的合成与性能

利用吩噻嗪衍生物的供电子能力及紫外吸收强的特点, 通过引入推-拉电子结构, 设计并合成了4种D-π-A型吩噻嗪席夫碱类可见光引发剂, 并利用核磁共振氢谱和高分辨质谱表征了其结构. 该系列光引发剂在350~450 nm范围内具有摩尔消光系数达10⁴ L·mol^-1·cm^-1的较强吸收, 与商品化Ⅱ型可见光引发剂硫杂蒽酮（ITX）相比, 其与405 nm LED光源具有更好的匹配性, 与碘鎓盐（Iod）组成的复合光引发体系也具有更高的引发效率和交联基团转化率. 通过光解、 电子自旋共振波谱和循环伏安（CV）实验证明了吩噻嗪席夫碱可见光引发剂与Iod复合光引发体系的光致电子转移（PET）机理. 最后, 利用吩噻嗪席夫碱可见光引发剂/碘鎓盐复合引发体系, 实现了光致发光器件的数字光处理（DLP）3D打印.     

新型感可见光的染料鎓盐光引发体系

本文报道了一种新型感可见光的引发体系-曙红双(二苯基碘鎓盐)(Eo(IPh_2)_2).在基态,这种体系具有良好的热稳定性,而在激发态时能发生离子对内光诱导电子转移反应,导致其发生漂白和碘鎓盐的分解反应,产生具有引发作用的自由基.该体系适用于一般烯类单体的自由基聚合,其中时丙烯酸酯类单体效果最好.在以甲基丙烯酯甲酯(MMA)为单体时,聚合反应速度满足动力学方程:R_p=l[Eo(IPh_2)_2]~(0.38)[MMA],并求得聚合反应的活化能E_c=7.00kcal/mol.氧在Eo(IPh_2)_2光敏引发聚合中,既起自由基聚合阻聚剂的作用,又起引发剂三重态猝灭剂作用     

1,5‐Diphenyl‐1,4‐diyn‐3‐one: A highly efficient photoinitiator

In a continuation of our research on new chromophores for photoinitiators (PIs), we investigated a triple‐bond‐containing benzophenone derivative. 1,5‐Diphenyl‐1,4‐pentadiyn‐3‐one ( 2 ) was prepared from phenylacetylene and ethyl formate by a one‐pot reaction. Differential scanning photocalorimetry experiments in lauryl acrylate of 2 showed surprisingly high activity for the double‐bond conversion and rate of polymerization at the lowest PI concentrations and even without any coinitiator. By the application of monomers with abstractable hydrogens, significant improvement in the photoreactivity was observed. Ultraviolet–visible spectroscopy revealed strong absorption up to 350 nm. Steady‐state photolysis experiments proved that the photochemistry of this compound was faster than that of benzophenone. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 101–111, 2005     

Cationic photopolymerization with the aid of pyridinium‐type salts

Pyridinium‐type salts containing an N‐ethoxy group belong to the family of onium salts and are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers which are not polymerizable by a free radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the onium ion, with the former being restricted to the wavelength range of self absorption, the latter being applicable at wavelengths of visible light. An additionally useful tool, namely free radical‐mediated generation of initiating species enlarges the versatility of pyridinium salts as photoinitiators. In this connection, the oxidation of free radicals by pyridinium‐type ions and the free radical‐induced fragmentation of alkoxy pyridinium ions are addressed in this article. Moreover, an interesting application is noted concerning the synthesis of novel block copolymers with the aid of the onium salt‐based photopolymerization technique.     

Phenacyl onium salt photoinitiators: synthesis, photolysis, and applications

Onium salts, namely sulfonium, phosphonium, ammonium, and pyridinium salts containing phenacyl group are photoinitiators appropriate for the polymerization of monomers such as oxiranes and vinyl ethers, which are not polymerizable by a free-radical mechanism. The initiation is accomplished by direct or indirect (sensitized) photolysis of the salts. Depending on the type of the salt, the direct photoinitiation of cationic polymerization involves reversible or irreversible processes. The photolysis of phenacylsulfonium compounds proceeds by a reversible process, while the other types undergo irreversible photolysis leading to complete fragmentation of the photoinitiator. An additionally useful tool, namely photosensitized generation of initiating species enlarges the versatility of these salts as photoinitiators. Photoinitiated free-radical and zwitterionic polymerizations by using phenacyl-type salts are also addressed. Keto-enol tautomerization of phenacyl pyridinium salts is discussed. Moreover, an interesting application concerning in situ synthesis of clay-poly(methyl methacrylate) nanocomposites with the aid of the phenacyl anilinium salt-based photopolymerization technique is noted.     

N‐alkoxypyridinium salts as coinitiators in radical polymerization: Synthesis and Photochemical Properties

A few N‐alkoxypyridinium salts are developed as photoinitiators for efficient polymerization reactions. They are characterized by absorption properties below 300 nm, and generate alkoxy radicals on UV‐Vis light exposure. The squarylium dye was used as a blue‐light photosensitizer. Polymerization results are correlated with the photochemistry of N‐alkoxypyridinium salts. The quenching of the excited singlet state of squarylium dye by pyridinium salt and the formation of the semioxidized species of squaraine suggests an electron transfer from an excited dye to a coinitiator, and that the resulting oxygen‐centered radical initiates the polymerization process. The chemical mechanism was investigated by steady state photolysis and nanosecond laser flash photolysis experiments. Photoinitiating activity of new photoinitiators for initiation of polymerization of trimethylolpropane triacrylate in the UV‐blue light region was compared with photoinitiating ability of selected commercially available initiators. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2840–2850     

Design of ketone derivatives as highly efficient photoinitiators for free radical and cationic photopolymerizations and application in 3D printing of composites

Herein, thirteen ketone derivatives composed of different cyclohexanone cores and peripheral moieties are designed, among which 10 ketones have never been synthesized before. These ketones are proposed as high-performance photoinitiators for both free radical polymerizations and cationic polymerizations under soft conditions (visible LED@405 nm irradiation at room temperature). In combination with an amine and an iodonium salt (Iod), these ketones could be used in three−component photoinitiating systems to initiate the free radical polymerization of acrylates with distinct final conversions, among which the ketone−1/amine/Iod combination proved to be the most efficient one. Besides, the ketone−1/Iod two−component system also showed a remarkable photoinitiation ability for the cationic polymerization of epoxides. The photochemical sensitivity of ketone−1 in the presence of an amine and an iodonium salt was systematically investigated by steady state photolysis and excited state fluorescence quenching characterizations, respectively. Interestingly, macroscopic 3D patterns with excellent spatial resolution could be generated using the ketone−1/amine/Iod photoinitiating system for the free radical polymerization of acrylates. This high performance is also found useful to overcome the light penetration issue for the access to filled samples (silica) and the preparation of composites.     

Synergistic interaction of epoxides and N‐vinylcarbazole during photoinitiated cationic polymerization

A kinetic study was conducted of the independent photoinitiated cationic polymerization of a number of epoxide monomers and mixtures of these monomers with N‐vinylcarbazole. The results show that these two different classes of monomers undergo complex synergistic interactions with one another during polymerization. It was demonstrated that N‐vinylcarbazole as well as other carbazoles are efficient photosensitizers for the photolysis of both diaryliodonium and triarylsulfonium salt photoinitiators. In the presence of large amounts of N‐vinylcarbazole, the rates of the cationic ring‐opening photopolymerization of epoxides are markedly accelerated. This effect has been ascribed to a photoinitiated free‐radical chain reaction that results in the oxidation of monomeric and polymeric N‐vinylcarbazole radicals by the onium salt photoinitiators to generate cations. These cations can initiate the ring‐opening polymerization of the epoxides, leading to the production of copolymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3697–3709, 2000     

Keto-coumarin scaffold for photoinitiators for 3D printing and photocomposites

The purposes of this paper are moving toward (a) the development of a new series of photoinitiators (PIs) which are based on the keto-coumarin (KC) core, (b) the introduction of light-emitting diodes (LEDs) as inexpensive and safe sources of irradiation, (c) the study of the photochemical mechanisms through which the new PIs react using different techniques such as Fourier transform infrared, UV–visible or fluorescence spectroscopy, and so on, (d) the use of such compounds (presenting good reactivity and excellent photopolymerization initiating abilities) for two specific and high added value applications: 3D printing (@405 nm) and preparation of thick glass fiber photocomposites with excellent depth of cure, and finally (e) the comparison of the performance of these KC derivatives versus other synthesized coumarin derivatives. In this study, six well-designed KC derivatives ( KC-C , KC-D , KC-E , KC-F , KC-G , and KC-H ) are examined as high-performance visible-light PIs for the cationic polymerization of epoxides as well as the free-radical polymerization of acrylates upon irradiation with LED@405 nm. Excellent polymerization rates are obtained using two different approaches: a photo-oxidation process in combination with an iodonium (Iod) salt and a photo-reduction process when associated with an amine (N-phenylglycine or ethyl 4-(dimethylamino)benzoate). High final reactive conversions were obtained. A full picture of the involved photochemical mechanisms is provided.     

Dimer liquid crystals with bent mesogenic units

Three series of dimer liquid crystals containing an aromatic and a cholesteryl mesogenic unit were synthesized and investigated The compounds within the series differ in the length of the spacer connecting the mesogenic groups. Two of the three series contain an aromatic mesogenic group that is connected to the spacer at a meta-position instead of the para-position. Due to the presence of this bent mesogenic group, the odd-even effect in the transitional properties that is normally observed for dimer liquid crystals is reversed as compared with that of the third series, which contains a para-substituted aromatic mesogenic group. The reversed odd-even effect is found for the isotropization temperatures, the associated enthalpy changes and also for the optical properties.