Polymer Journal (2011) 43, 869–873 & The Society of Polymer Science, Japan (SPSJ) All rights reserved 0032-3896/11 $32.00 www.nature.com/pj RAPID COMMUNICATION Synthesis of rosin allyl ester and its UV-curing characteristics Polymer Journal (2011) 43, 869–873; doi:10.1038/pj.2011.78; published online 31 August 2011 Rosin has been recognized as a potential EXPERIMENTAL PROCEDURE acid value of 182.5 mg KOH per g (185.8 mg important renewable resource in the forest General KOH per g by theory). chemical industry. It is a complex mixture of Materials were obtained from commercial high-molecular-weight organic acids and sources and used without further purifica- Synthesis of rosin allyl ester related materials. The acidic constituents tion. Infrared ray (IR) spectra (max in To obtain a solid product, 7.4 g NaOH (dis- that make up rosin are called resin acids, cmÀ1) were obtained using a MAGNA-550 solved in 150 ml ethanol) was added dropwise which include abietic acid, neoabietic acid (Nicolet, Waltham, MA, USA) spectrophoto- to 50 g rosin acids (dissolved in 150 ml and palustric acid. They can be used to meter. Gas chromatography-mass spectro- ethanol). The mixture was stirred at room synthesize many types of fine chemicals,1–3 metry (GC-2010, Shimadzu, Kyoto, Japan) temperature for 1 h and then filtered to and are widely used as raw materials to was conducted to analyze the composition obtain sodium rosinate. The product was produce functional polymers.4–8 Woo-Sik of resin acids and rosin allyl ester. Separation dried at room temperature to produce a Kim5 provided a method to synthesize poly was performed in an HP-5 column, yield of 92.2% (49.5 g). (vinylbenzyl abietate) using poly(vinylbenzyl 30 mÂ0.25 mmÂ0.25 mm, under the follow- Rosin allyl ester was synthesized by the chloride) and sodium abietate as raw materi- ing working conditions: 100 1C, 5 1CminÀ1 esterification of sodium rosinate with allyl als. Tae Hoon Kim6 reported the synthesis of to 200 1C, 2 1C min to 250 1C, hold for chloride as shown in Figure 1 (abietate as polymethacrylate by the reaction of poly 25 min. Acid values were determined accord- representative). A mixture of sodium rosi- (glycidyl methacrylate) with abietic acid. In ing to the China National Standards: Test nate (10.0 g, 0.0309 mol) and allyl chloride these two methodologies, the resin derivatives methods for rosin (GB/T 8146–2003); (6.2 ml, 0.076 mol), including a trace of p- were not used as monomers in the polymer- polymerization instrument: Intelli-ray 600 benzoquinone as a polymerization inhibitor ization. That is, these polymers were based on (Shenzhen Wisbay M&E Co., Ltd., Shenzhen, and hexadecyltrimethylammonium bromide the polymerization of other kinds of mono- China) shuttered UV Floodlight (the Intelli- as phase-transfer catalyst (PTC) (0.3 g, 3% mers besides resin derivatives. The final ray 600 utilizes a metal halide-type arc mass fraction of sodium rosinate), was product did not provide a suitable resin lamp and the radiation flux is 315–400 nm); heated at 40–65 1C for 6–8 h. Thereafter, structure; the conversion of the reaction was wave band: 315–400 nm; intensity 100%; unreacted allyl chloride was recovered by relatively low.5–6 Moreover, a large amount of and timer 300 s. GPC was performed at distillation. The mixture was cooled and solvent was used to purify the product after room temperature on a Waters 515 (Waters, filtered to produce 10.0 g of the product reaction. Recently, vinyl compounds have Milford, MA, USA) apparatus equipped with with a yield of 94.7%. become well known as photosensitive mono- a Waters 2414 refractive-index detector. Styr- mers. Therefore, Woo-Sik Kim7 and Byoung- agel HR1 and HR2 (300Â7.8 mm) columns Polymerization Woo Park8 developed methods to polymerize from Waters were used. High-purity liquid- Tinplate panels (Shanghai Xiandai Environ- abietate derivatives by introducing a vinyl- chromatography-grade tetrahydrofuran was ment Engineering Technique Co., Ltd., Shan- benzyl group into the molecular structure. used as the eluent at a flow rate of ghai, China) (120Â50Â2.8 mm) were used However, it is difficult to remove the 1mlminÀ1. The columns were calibrated by as substrates for film preparation. The sub- unreacted vinylbenzyl chloride by vacuum using polystyrene standards with molecular strates were cleaned with distilled water distillation because of its high boiling point weights in the range between 580 and and acetone and then dried. The formula- (192 1C), which would bring thermal insta- 1.96Â104 gmolÀ1 (with NMD for 1.1). tions were made by taking the synthesized bility to vinylbenzyl abietate. rosin allyl ester and mixing it with 5% In this study, we tried to introduce a vinyl Purification of rosin acids photoinitiator Darocure 1173 (Tokyo Chemi- group into the structure of rosin monomer to Twenty grams of rosin was dissolved in 15 ml cal Industry Co. Ltd., Tokyo, Japan). The synthesize rosin allyl ester. The ultraviolet acetone by stirring at 60 1C for 10 min. Then, films on the tinplate panel were irradiated (UV)-curing reaction of the rosin allyl ester the mixture was cooled to room temperature under UV light to be cured; then they were was investigated, and the cured product was to obtain a solid product. The solid obtained stored in a dust-free cabinet for testing pur- characterized by thermogravimetry (TG), dif- was filtered and recrystallized twice in poses. The UV-curing conditions were as ferential scanning calorimetry (DSC) and gel acetone. After purification, the total yield of follows: wave band 315–400 nm, intensity permeation chromatography (GPC). the product was approximately 35% with an 100% and time 300 s9. Rapid Communication 870 RESULTS AND DISCUSSION Recrystallization of rosin Several types of solvent, such as ethanol, H H + NaOH acetone, ether, ethyl acetate, trichloro- + H2O methane, methylbenzene and N,N-dimethyl- H H formamide, were compared with respect to COOH COONa rosin recrystallization. Acetone was deter- mined to be the most suitable solvent. The total rosin acids yield was B35% in rosin recrystallization. To identify the components H H CH CH Cl + NaCl of the rosin acids, gas chromatography–mass + CH2 2 spectra (GC–MS) analysis was performed. H H The main components identified by GC–MS COONa COOCH2CH CH2 are illustrated in Table 1. The results show that the total rosin acids content is 98.3%. Figure 1 Synthesis of rosin allyl ester (abietate as representative). Synthesis of rosin allyl ester In this study, allyl chloride was chosen for Table 1 Results of recrystallization of rosin using acetone as solvent reaction because of its low boiling point, which makes it easy to remove after reaction Contents after recrystallization (%) under vacuum at low temperature to avoid polymerization of the product. It can be seen Serial Contents First Second Third that the reaction was greatly enhanced by a number Constituents (%) in rosin run run run PTC (0.3 g, 3% mass fraction of sodium 1 Pimaric acid 3.1 2.7 3.2 2.9 rosinate). Different types of PTCs were 2 Pinus elliottii acid 3.0 1.4 0.7 0.3 compared, and the most suitable catalyst 3 Sandaracopimaric acid 1.9 1.6 2.1 1.9 was determined to be hexadecyltrimethylam- 4 Isopimaric acid 13.0 14.0 13.2 15.2 monium bromide, with a product yield 5 Palustric acid and levopimaric acid 22.8 23.5 23.3 21.7 of 90.2%. Detailed information regarding 6 Dehydroabietic acid 3.6 4.1 4.2 5.2 the PTC tests is shown in Table 2. 7 Abietic acid 26.0 32.1 36.9 41.7 The factors that influence the yield of the 8 Neoabietic acid 19.8 16.2 14.1 9.4 reaction, such as the amount of catalyst used, reaction time, reaction temperature and Total (%) 93.2 95.6 97.7 98.3 molar ratio, were investigated. The optimum reaction conditions obtained were as follows: reaction temperature 45 1C, n (sodium rosin): Table 2 Effect of different kinds of catalyst on product yield n (allyl chloride)¼1:2.5, amount of the catalyst (hexadecyltrimethylammonium bro- Catalyst Yield of product (%) mide) 0.3 g (3% mass fraction of sodium Blank 69.7 rosinate) and reaction time 7 h. The Hexadecyltrimethylammonium bromide 90.2 main components identified by GC–MS are Tetrabutylammonium chloride 87.0 illustrated in Table 3. Tetrabutylammonium bromide 79.0 Table 3 shows that the esterification of Tetraethylammonium bromide 83.8 sodium rosinate and allyl chloride was per- Tetracesium 4,4¢-carbonylbisphthalate 83.3 formed efficiently under a PTC to produce a total rosin allyl ester yield of 94.7% at a purity of 98.9%. The IR spectra of rosin acids and rosin allyl Table 3 Main components in rosin allyl ester ester are shown in Figure 2. The spectra Constituents Retention time (min) Contents (%) clearly show that the structure of rosin allyl ester was different from that of the rosin Allyl pimarate 43.9 1.4 acids. The greatest difference between the Allyl pinus elliottiate 44.1 1.0 rosin acids and rosin allyl ester is the stretch- Allyl sandaracopimarate 44.6 0.9 ing of the carbonyl acid group (3000– Allyl isopimarate 45.8 11.9 3500 cmÀ1). The C¼C-H stretching vibra- Allyl palustriate 46.3 16.2 tions between 3000 and 3100 cmÀ1 indicate Allylevopimarate 46.6 1.2 that the allyl group was successfully intro- Allyl dehydroabietate 47.3 5.0 duced into the product. The C–H stretching Allyl abietate 49.1 56.8 vibrations between 2800 and 3000 cmÀ1,and Allyl neoabietate 51.8 4.5 C–H deformation vibrations between 1350 Total 98.9 and 1475 cmÀ1 indicate the presence of Polymer Journal Rapid Communication 871 methyl and methylene in the rosin structure.