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Ultraviolet-cured powder coatings (abbreviated as UV-cured powder coatings) represent a new technology that combines traditional powder coating techniques with UV curing technology, offering the advantages of both. They are particularly suitable for applications where environmental protection, painting at low temperatures, rapid curing, and efficient production are required【j1]. Currently, UV-cured powder coatings have solved the problem that conventional thermosetting powder coatings cannot be used on heat-sensitive materials【21». UV-cured powder coatings belong to the “4E” technology category, and they possess enormous market potential; as a result, research on them is advancing at an unprecedented pace. The components of uV-curable powder coatings include: a photoinitiator, a base resin, a curing agent, and various additives. This type of coating uses high-energy ultraviolet light as the curing energy source; the photoinitiator in the coating absorbs the ultraviolet light, causing the molecules to transition from their ground state to an active excited singlet state, and they can further undergo intersystem crossing to reach an excited triplet state. In its excited singlet state, or possibly after the excited triplet state undergoes single-molecule or double-molecule chemical reactions, reactive fragments are generated; these fragments can be radicals or ions, thereby triggering the polymerization of the unsaturated bonds in the photosensitive resin and reactive diluents within the system, allowing the coating to cure. Therefore, the photoinitiator is an essential component in the formulation, and its physical and chemical properties are crucial for controlling the photoinitation and photopolymerization processes. Classified according to the photoinitiation mechanism, the photoinitiators used in UV-curable powder coatings are mainly of the radical type and cationic type【6–1.】Date of receipt: 2006–03–23 Cationic photoinitiator-based systems suffer from drawbacks such as long curing times, slow increase in molecular weight, and the significant inhibitory effect of even small amounts of water on the polymerization reaction, which makes it difficult to achieve commercialization and industrial application. Currently, radical-type photoinitiators are those that are widely used in commercial applications. Their advantages include the fact that water does not inhibit polymerization in such systems, they enable fast curing rates, and they allow for the creation of coatings with excellent decorative properties and good weather resistance. Free-radical photoinitiators are divided into two main categories: cleavable types and hydrogen-evolving types. Hydrogen-donating initiators mainly include diphenylmethane derivatives and thioxanthene derivatives; such initiators require a hydrogen donor (amine, alcohol amine) as a co-component, otherwise they will not exhibit any initiating effect. Pyrolytic photoinitiators are mainly composed of arylalkyl and related derivatives; notable examples include benzoin and its derivatives, benzoyl acetal derivatives, dialkoxyphenylethanes, monohydroxyalkylbenzenes, monoaminoalkylbenzenes, acyl phosphoxides, aryl peroxide compounds, and benzoyl acetates. Although there are a great variety of photoinitiators available on the market today, they are not suitable for producing thicker cured materials, mainly because the photosensitivity and photoinitiating activity of these photoinitiators are not high enough ； Furthermore, these photoinitiator types all contain benzene rings or heteroatom structures; since the radicals containing benzene rings or heteroatoms tend to collide with each other, larger conjugated systems with chromophoric groups are formed, which causes the product to turn yellow over time during use. The two issues of insufficient photosensitivity of photoinitiators and their tendency to cause \"yellowing\" of the products during use have become bottlenecks restricting the development of UV-curable materials. Therefore, by designing and developing a new type of highly efficient photoinitiator, methyl acrylate triacetyl methane, which contains multiple acetyl groups, both its light sensitivity and initiation activity will be extremely high. Moreover, since the acetyl groups serve as the free radicals in this new initiator and do not contain benzene rings, it is difficult for large conjugated systems to form, thereby effectively addressing the issue of yellowing. To synthesize this compound, 2 synthetic routes were designed. Synthesis route I: Me／／, V, \\\Me + CH3COC1– >／ + deletion. Synthesis route II: + e MeOOC–) O O ll ll / + CH3COC1 MeOOC／ O O Na ll ll. Delete Ether ⋯ ～ 1 Experimental Section 1.1 Instruments and Reagents HNMR, \"CNMR: Bluck400 (using tetramethylsilane as a standard)\" ； GC: Agilent 6890 ； GC—MS: GC (6890N), MS (5973N from Agilent). Both reagents and solvents are of analytical grade or chemical grade available commercially. 1.2 Test Procedure 1.2.1 Synthesis Route I (1) Synthesis of the intermediate triacetyl methane: Add 30 mL of ether to a 100 mL four-necked reaction flask equipped with a thermometer, a reflux condenser, and a stirrer. Then add 6 g (0.06 mol) of acetylpropane, and start stirring to dissolve acetylpropane in the ether. Then 0.69 g (0.03 mol) of metallic sodium was added. After the reaction between acetopropion and sodium was complete with no bubbles being released, 2.355 g (0.03 mol) of acetyl chloride was added dropwise, followed by heating under reflux; GC was used to monitor the progress of the reaction. Since acetopropion exists in both the ketal and enol forms, and the hydrogen atom on the methyl group attached to the carbonyl group is also somewhat reactive, the reaction is very complex. The yield of the target product, triacetyl methane, is very low, at around 30%, and it is difficult to purify. The same method was tried with various catalysts such as potassium carbonate, sodium tert-butoxide, DBU, and NaH, but the yield of the target product, triacetyl methane, was very low in all cases. When using the above basic catalysts, since most acrolein exists in the enol form, substituted by-products are easily formed at the oxygen site of acrolein. Therefore, BF3 was intended to be used to form a complex with the oxygen of acrolein in order to reduce the formation of by-products. The specific reaction is as follows: F F F F 0 . . 0 . . B, B\\0 0 . . +BF3–. Although this reaction does not produce by-products resulting from substitution at the oxygen site, the yield is very low, at only 18.2%. The reason for this may be the strong complexing ability of the intermediate products, which prevents the reaction from proceeding further. By attempting the above methods for synthesizing the intermediate triacetyl methane, using acetopropionitrile and acetyl chloride as starting materials and metallic sodium as a catalyst, a relatively high yield was obtained. An acetylpropionyl compound using 1 tool is used for an amplification reaction to yield triacetylmethane, which is then used in the next reaction step. (2) Synthesis of the target product, methyl acrylate triacetyl methane. In a 100 mL four-necked reaction flask equipped with a thermometer, a reflux condenser, and a stirrer, 3 g (0.021 mol) of triacetyl methane and 30 mL of dry THF were added. Then, 0.15 g (0.001 mol) of DBU was slowly added; the temperature rose rapidly as observed on the thermometer, indicating that the reaction was quite vigorous. After the temperature stabilized, 1.81 g (0.021 mol) of methyl acrylate was added dropwise to the reaction flask. The reaction is carried out under heating and reflux conditions, with the reaction monitored using GC. From the GC graph, it can be seen that the yield of the target product is very low. After 2 hours of reaction, 0.2 g of metallic sodium was added, which increased the yield slightly, but it still remained at a maximum of 12.3%. Then, as the reaction time increases, the yield decreases instead, presumably due to the decomposition of the target product. Triacetyl methane is also very unstable because three triacetyl groups are attached to the same carbon atom, and it decomposes easily when heated. Therefore, this reaction route is not suitable for synthesizing the target compound. 1.2.2 Synthesis Route II (1) Synthesis of the intermediate methyl acrylate acetylpropanide: 80 g (0.8 mol) of acetylpropanide was added to a 500 mL four-necked reaction flask equipped with a thermometer, a reflux condenser, and a stirrer. Next, 0.3 g (0.013 mol) of metallic sodium was added, and it was observed from the thermometer that the temperature rose rapidly, indicating a vigorous reaction. After cooling to room temperature, keep the reaction temperature below 35°C, and add methyl acrylate slowly in an amount of 34.4 g (0.4 mol). After adding it over 1 hour, lower the reaction temperature to room temperature. The products of single addition and double addition were identified using GC-MASS; based on the GC chromatogram, 92% were products of single addition. The pH of the reaction mixture was adjusted to neutral using hydrochloric acid, then the salts were filtered out. The reaction mixture was subjected to vacuum distillation to yield 72 g of the target intermediate, methyl acrylate ethyl acetylpropanoate, with a purity of 98%. (2) Synthesis of the target product, methyl acrylate triacetyl methane. In a 500 mL four-necked reaction flask equipped with a thermometer, a reflux condenser, and a stirrer, 35 g (0.188 mol) of methyl acrylate acetylpropanone and 200 mL of dry ether were added. Then, 4.33 g (0.188 mol) of metallic sodium was slowly added; the temperature rose rapidly as observed on the thermometer, indicating that the reaction was quite vigorous. Once the temperature stabilized and no changes occurred, the absence of methyl acrylate acetylpropionate detected by GC indicated that sodium metal had completely reacted with methyl acrylate acetylpropionate. Lower the temperature to 20°C, then add 14.76 g (0.188 mol) of acetyl chloride, which has been distilled, to the reaction flask. The reaction was carried out under heating and reflux conditions for 3 hours, and the reaction was monitored using GC. Based on the GC graph, the yield of the target product can reach 88.3%, with few by-products, making it much more effective than synthesis route I. The yield of the target product is relatively high; through vacuum distillation, 33.9 g of the target compound with a purity of 98.6% was obtained, giving an overall yield of 85%. The structure of the target compound was characterized by H—NMR, 13C—NMR, and GC—MS as follows: H—NMR: (proton same as d6); 13C—NMR: (carbon same as d6); GC—MS: 3.61 (3H, s, –O–CH3) ； O ll 2.38(2H, t, –C—CH2—CH2—C—O) O 2.33(2H, t, –C—CH2—CH2—C—O) O ll 2.08(9H, s, –C—CH3) O ll 200.9(s, H3C—C—C) O ll 173.2(s, –C—O) O ll 51.6(s, –C—O—CH3) O lI 33.2(s, –C—CH2—CH2—C—O) O ll 31.3(s ； One C—CH3) ll 14(s, one C—CH2—CH2—C—O) molecular ion peak: 228 ； Base peak: 43 ； Other major fragment peaks: 186, 143, 111, 43 2 Results and Discussion 2.1 Synthesis Route I Synthesis Route I involves first synthesizing triacetylmethane, and then preparing the target compound, methyl acrylate triacetylmethane. However, the synthesis of triacetylmethane is extremely difficult. Various methods described in the experimental section were tried, but the results were unsatisfactory: either the yield of the reaction was very low, or the reaction was very difficult to carry out. The main reason is that the acetyl group is a highly reactive functional group; the presence of three acetyl groups attached to the same carbon atom makes triacetylmethane extremely unstable. In the second-step reaction: the addition of triacetylmethane to methyl acrylate, the target product can be obtained, but the yield is very low. This is because the acetyl groups readily detach under basic conditions, which also demonstrates that triacetylmethane is highly unstable. 2.2 Synthesis Route II: Synthesis Route II involves first synthesizing methyl acrylate acetylpropanide, and then synthesizing the target product, methyl acrylate triacetylmethane. Since the intermediate, methyl acrylate acetylpropanoate, is relatively stable, the synthesis process is relatively simple ； Moreover, the addition reaction between methyl acrylate and acetopropionone proceeds relatively easily; experiments have shown that sodium metal as a catalyst is highly suitable for this type of Michael addition reaction, offering high efficiency. To minimize the di-addition byproducts, the amount of acetylpropionyl group must be at least twice that of methyl acrylate. Since there is a significant difference in boiling points between the mono-addition and di-addition products, they can be separated by vacuum distillation, thereby yielding the high-purity target intermediate, methyl acrylate acetylpropionyl. Then, the intermediate methyl acrylate acetylpropanoate is reacted with acetyl chloride to synthesize the target product, and this reaction also proceeds relatively easily. Using metallic sodium as a catalyst and ether as a solvent yields good results, with a high yield of the target product, making it very suitable for this type of substitution reaction. High-purity target compound can be obtained through vacuum distillation, with an overall yield of 85%. The basic strength of the catalyst is very important for this substitution reaction. Due to increased steric hindrance in methyl acrylate-based acetylpropanes, the reactivity of their –H groups is reduced; therefore, the catalyst must have a sufficiently high basic strength in order to increase the reaction yield. The structure of the target product was confirmed by H—NMR, 13C—NMR, and GC—MS. 2.3 Evaluation results The target product, methyl methacrylate, was evaluated in UV-curable powder coatings, and it exhibited a very high level of UV light initiation efficiency; patents have been filed in various countries including China, India, Japan, the United States, Germany, the United Kingdom, and France. The industrialization and commercialization of the product are in progress.