Synthesis of a novel UV-curable prepolymer neopentyl glycol diglycidyl ether diacrylate and its cure

J Shanghai Univ (Engl Ed), 2009, 13(5): 396 401Digital Object Identifer(DOI): 10.1007/s11741-009-0511-3Synthesis of a novel UV-curable prepolymer neopentyl glycol diglycidylether diacrylate and its cured film tensile propertyHUANG Bi-wu (黄笔武)，HUANG Bo-fen (黃伯芬)，CHEN Wei-qing (谌伟庆)，OUYANG Zhi-qiang (欧阳志强)School of Material Science and Engineering, Nanchang University, Nanchang 330031, P. R. ChinaAbstract A novel UV-curable prepolymer neopentyl glycol diglycidyl ether diacrylate (NPGGEA) was synthesized by usingneopentyl glycol diglycidyl ether (NPGGE) and acrylic acid (AA) as starting materials, N, N-dimethylbenzylamine as catalystand p-hydroxyanisole as inhibitor. The optimum synthetic conditions were taken as fllows: The concentration of N,N-dimethylbenzylamine, 0.80% of reactants; the concentration of p-hydroxyanisole, 0.3% of reactants; the reaction temperature,90-110 °C; the molar ratio of NPGGE to AA, 12.2. Meanwhile, 1-hydroxycyclohexyl phenyl ketone of a UV-cured initiatorwas added to the synthesized NPGGEA to prepare a kind of UV-cured coating. Mechanical properties of the UV-cured filmswere determined, giving 28.75 MPa of tensile strength, 923.82 MPa of Young's modulus and 5.51% of elongation at tear.Keywords synthesis, neopentyl glycol digycidyl ether diacrylate (NPGGEA), Bcryic acid (AA), UV-curable prepolymer,fimIntroductioncal properties of its cured film are also investigated, andthe results show that the flexibility of the cured flm isUV-radiation curing has become a well- acceptedsuperior to that of the other cured film prepared by u8-technology, which has found many industrial applica-ing the BPGEA as the prepolymer for the UV-curabletions due to its distinct advantages, mainly as protectivecoating.coatings, printing ink and adhesives. A liquid resin can1 Experimental procedurebe transformed almost instantly into a solid polymermaterial by simple exposure to the UV-light at ambi-1.1 Materialsent temperaturel1-6]. In UV-curable coatings, bisphe-nol A diglycidyl ether diacrylate (BPGEA) is generallyNPGGE was supplied by the Baling Petrol Chem-used as prepolymer(7- 10]. However, the BPGEA pos-icals Co. Ltd., China. BPGEA was purchasedfrom the Wuxi Resin Factory.AA was purchasedsesses some rigid phenyl rings in its molecular chainfrom the Dongfeng Chemcals Factory, Bejing. 1-to cause its high viscosity and the very poor flexibil-ity of its UV-cured materials. Furthermore, with thehydroxycyclohexyl phenyl ketone was supplied byBPGEA as prepolymer to prepare UV-curable coat-Ciba-Geigy, Switzeland. N,N- dimethylbenzylamine, p-ings, some small molecular weight reactive diluents musthydroxyanisole and butyl acrylate were purchased frombe added, regulating working viscosity and the rheol-the First Reagent Company of Shanghai.ogy property of the coatingl1-12. The reactive dilu-1.2 Instrumentationents have great volatility and irritant to human skin,IR spectra of NPGGEA and its UV-cured film werend diluents pollute the environment[13]. The presentcharacterized by a Bruker FT-IR EQUINOX55 spec-paper describes the method for synthesizing neopentyltrometer made in Germany. The viscosity of NPGGEAglycol diglycidyl ether diacrylate (NPGGEA), which iswas measured with an NDJ-1A model spinning viscome-the product of reacting commercial neopentyl glycolter from the Ande Instrument Co., China. UV-curablediglycidyl ether (NPGGE) with commercial acrylic acidcoatings were irradiated by a 1 000 W high-pressure mer-(AA). Because NPGGEA has flexible ether bonds, itscury lamp built into a UV-chamber with a distance ofviscosity is medium, and it can directly prepare the UV-15 cm from lamp to specimens made in the Wuhancurable coatings without adding diluents. The mechani-Binhu中国煤化工_2o. The mechanicalReceived Sept.23, 2008; Revised May 4, 2009Prject supported by the National High-Technology Research and DevelTYHC N M H Gat No.20202623088)Corresponding author HUANG Bi-wu, PhD, Prof, E-mail: hbwhzkj@tom.comJ Shanghai Univ (Eagl Ed), 2009, 13(5); 396 401397properties of the cured films were tested with a WDW-the reaction systerm. The methodl14I for analyzing the50 universal testing machine made in Shenzhen, China.acid value was as follows: The mixture (0.5 -1.0 g) in the.3 Synthesis of neopentyl glycol diglycidylflask was precisely weighted to place in a 250 mL conicalether diacrylate (NPGGEA)bottle, then it was dissolved in acetone, and phenolph-1.0 mol NPGGE was placed in a 1000 mL four-thalein indicator was added to the conical bottle. Potas-neck round-bottom fiask with a stirrer, a thermome-sium hydroxide ethanol standard solution (0.1 mol/L)er, a condenser and a dropping funnel. 0.40%-was used to titrate the mixture solution in the conical1.00% N, N-dimethylbenzylamine and 0.20%- 0.40% pbottle, and the appearance of rose pink was the titratedhydroxyanisole were also placed in the fAask, and theend point. The conversion of reaction was defined asmixture was then stirred and heated. AA in the drop-the fraction of carboxyl group that had reacted at timeping funnel was added dropwise to the mixture at 80-t. It was calculated from the acid value of the mi120 °C. After the completion of AA addition, the reac-ture which was a measure of the concentration of car-tion was kept at 90-120°C for 2-6 h. The acid valueboxyl groups using the following equation: conversionof the mixture in the flask was determined at definite(%)=100 (1- M/Mo), where Mo is the initial acid valuetime intervals. The reaction was terrminated when theof the mixture in the flask, and M the acid value of thecid value was lowered to 5 mg KOH/g. The obtainedmixture in the flask at time t.product was slightly yellow viscous liquid, its acid value2 Results and discussionwas 5.0 mg KOH/g, and its viscosity was approximately930 mPas at 25 °C.2.1 Synthesized reaction formula1.4 Determination of conversion percent-When a small amount of N, N-dimethylbenzylamineage of NPGGE into NPGGEAexisted in NPGGE with N, N-dimethylbenzylamine be-With the synthetic reaction proceeding, NPGGEing the catalyst, the epoxy rings of NPGGE was easilygradually turned into NPGGEA, and the embodimentopened, and AA was easily incorporated with NPGGE.was decrease of'the epoxy value and the acid value inThe main reaction formula is as follows:CH3CH2- -CH-CH2-0- -CH2 -C- -CHz-0-CH2 -CH- -CH2 + 2CH2-CH-C -0H→NPGGECH2= =CH-C- -0-CH2- -CH- -CH2- 0- -CH2-C- -CH2- -0-CH2-CH- -CH2-0-C-CH=CH2.OHNPGGEA2.2 Infuentialfactors inpreparinginhibitor. The increase of catalyst clearly had positiveinfuence on the conversation of NPGGEA. The yield ofIn order to obtain UV-curable NPGGEA, theNPGGEA was approximate 69% after reaction for 6 hNPGGE was modifed by AA, which provided acrylatein 0.4% catalyst. The yield increased with the catalystNPGGE with unsaturated double bonds. The reactionincreasing, especially in the initial stage. The optimumrate was affected by the catalyst, inhibitor, reactioncatalyst concentration was 0.8% of reactants, becausethe further increasing of the catalyst could not effec-temperature and the concentration of reactants.tively enhance the yield of NPGGEA.2.2.1 Effect of the catalystIn this study, the synthetic reaction catalyst was N,2.2.2 Effect of temperatureN-dimethylbenzylamine. Figure 1 shows the relation-Fi中国煤化工of NPGGEA at dif-ship between catalyst concentration and the yield offerent;YHhe presence of N, N-NPGGEA when NPGGE reacted with AA at 110C indime. C N MH Gi phyroxyanisole ofthe presence of 0.3% p-hydroxyanisole as the reaction0.30%. The reaction rate and the yield were greatly398J Shanghai Univ (Engl Ed), 2009, 13(5): 396- 401affected by temperature. Conversion of NPGGEAreaction, acrylic acid must be excessive. Figure 3 showsonly reached 82% when NPGGE reacted with AA atdiferent yields of NPGGEA with 1.0 mol NPGGE re90°C for 6 h, reached 89% at 100°C for 6 h, andacting with different amount of AA at 100°C in thereached 98% at 110C for 6 h. Enhancing temperaturepresence of N, N-dimethylbenzylamine of 0.80% and p-had positive infuence on reaction rate. However, exor-hydroxyanisole of 0.30%.bitant temperature resulted in gelation because of thereaction between double bonds such as the reaction at120 °C.80 t100 r0t8040- 1.0 mol+ 1.8 mol20 t士2.0 molg 60-12言40- +←1.00%Reaction time/h十0.80%- +0.60% .Fig,3 Effect of conversion on adding diferent amount of-*-0.40%AAIn Fig.3, the conversion of NPGGEA only reachedReaction timeh48% when 1.0 mol NPGGE reacted with 1.0 mol AA at100°C for 6 h, the conversion was 79% when 1.0 molFig.1 Effect of catalyst concentration on reactionNPGGE reacted with 1.8 mol AA, the conversion was90% when 1.0 mol NPGGE reacted with 2.0 mol AA,100pand conversion had already reached 97% when 1.0 molNPGGE reacted with 2.2 mol AA. Thus the optimumratio of reactants was 1:2.2 (NPGGE:AA).60 t2.2.4 Choice of inhibitors and amount of in--◆90C .+ 100"Chibitors- 110CWhen there was no inhibitor in the reaction fask, the+ 120Cviscosity of the reaction system quickly became high,and reactants easily produced gelation with the reac-tion going on. From Fig.4, it can be seen that vis-cosity changes in the reaction system when 1.0 molFig.2 Effect of conversion on reaction temperatureNPGGE reacts with 2.0 mol AA in the presence of N,N-dimethylbenzylamine of 0.80%.2.2.3 Efect of concentration of reactants7000Because one molecule NPGGE possesses two epoxy600groups, 1.0 mol NPGGE can completely convert into000 |1.0 mol NPGGEA to require only 2.0 mol AA accord-4000ing to the chemical reaction theory. However, if 2.0 mol000 tAA was added to 1.0 mol NPGGE, the epoxy groups ofNPGGE could not fully react, and residual epoxy group1000 twas left in the end. This phenomenon can be explained0.2 0.40.60.81.01.2as follows. Acrylic group reacted with the - -OH groupsproduced in the reaction of epoxy and acrylic groups. AtFig.4 Viscosity change as reaction time without addingthe beginning of these two competitive reactions, the reinhibitoraction of epoxy ring to be opened was the principal one.With the reaction proceeding, hydroxyl group increased中国煤化工ity of the reaction sys-sharply and esterification was obvious. Therefore, thetemE 1.0 h without addingacid value of AA decreased more quickly than the epoxyany:YHCNMHGnofgelationhadhap-value of NPGGE. In order to complete epoxy open ringpened.J Shanghai Univ (Engl Ed), 2009, 13(5): 396 -401399When there was hydroquinone as inhibitor in the re0.2% was only added in the reaction fask. This was theaction fAask, the synthetic reaction proceeded evenly, thereason why hydroquinone was easily oxidized to becomeviscosity of the reaction system rose stably, but the colorthe quinoid form. However, when p hydroxyanisoleof the reactive product was dark red. From Fig.5, theof 0.3% was added to the reaction fAask, not only itviscocity changed in the reaction system when 1.0 molcould inhibit to produce gelation reaction, but also theNPGGE reacted with 2.0 mol AA in the presence of N,color of the reaction product was good. Therefore, PN-dimethylbenzylamine of 0.80% and bydroquinone ofhydroxyanisole of 0.3% was best added to the reactive0.20%.system as inhibitor.2.3 Characteristics of the FT-IR spectra100010 g of NPGGEA and 0.25 g of 1-hydroxycyclohexyl800phenyl ketone were placed in a 50 mL beaker. The liquid00mixture in the beaker was fully stirred. The IR spec-400trum of the liquid mixture is given by the curve (a) inFig.7. A small amount of the liquid mixture was fetchedto coat on a small picce of glass, with the coated flm567being 0.100 mm in thickness. The piece of glass wasReaction time/hplaced in the UV-chamber, and irradiated by UV-lightFig.5 Viscosity changes 88 reaction time with adding hy-for 50 s. The cured flm on the piece of glass was peeleddroquinone as inhibitorwith a cut knife. The IR spectrum of the cured flm isshown by the curve (b) in Fig.7. Of many IR charac-In Fig.6 viscocity changed in the reaction systermteristic absorption peaks in the curve (a), the absorp-when 1.0 mol NPGGE reacted with 2.0 mol AA in thetion peak at 810 cm-1 is the C-H twisting vibrationpresence of N, N dimethylbenzylamine of 0.80% and p-absorption peak of the end double bond, and the ab-hydroxyanisole of 0.20%, 0.30% or 0.40%.sorption peak at 1 633 cm -1 belongs to the stretchingvibration absorption peak of the carbon-carbon double1600rbond. From the IR spectrum given by the curve (a),the liquid mixture possesses unsaturated carbon-carbondouble bond. This also shows that NPGGEA possessedunsaturated carbon-carbon double bond. However, theIR spectrum shown by the curve (b) has no absorption- + 0.20%peak at 810 cm - 1 and the absorption peak at 1 633 cm-1甘0.30% .basically. This shows that double bond in the cured f6lm-★0.40%does not exist. Besides, the NPGGEA as a photosensi-tive prepolymer is very sensitive to the UV-light, and its+234567carbon-carbon double bond is easily ruptured to becomecarbon-carbon single bond when exposed to UV-light.Fig.6 VViscoaity changes as reaction time with adding Phydroxyanisole as inhibitorn \bFrom Fig.6 it is known that the pbenomenon ofgelation had produced in the reaction system withp-hydroxyanisole of 0.2%, indicating that adding p(.hydroxyanisole was not enough. When there was p-hydroxyanisole 0.30% or 0.40% as inhibitor in the re3500 3000 2500 2000 1500 1000 500action system, the synthetic reaction also proceededWave number/cm-1evenly, the viscosity of the reaction system also rose sta-bly, and the color of the reactive product was slightlyFig.7 FTIR spectra of the liquid mixture and its curedfilmyellow.According to the above experiment， both p中国煤化工of UV-curedhydroxyanisole and hydroquinone could be chosen asinhibitor. Although hydroquinone was effective, the reHCNMHGaction product appeared dark red when hydroquinone of20 g of NPGGEA was placed in a 100 mL beaker,400J Shanghai Univ (Engl Ed), 2009, 13(5): 396 401and 0.5 g of 1-hydroxycyclohexyl phenyl ketone was thenprepare the photosensitive coating were 28.75 MPa ofadded into the beaker. The mixture in the beaker wastensile strength, 923.82 MPa of Young's modulus andfully stirred. The mixture was coated on a clean glass5.51% of elongation at tear. Mechanical propertiesplate with the coated flm being 0.400 mm in thickness.with BPGEA 8s prepolymer were 39.83 MPa of tensileThe glass plate was placed in the UV-chamber, and ir-strength, 1 342.68 MPa of Young's modulus and 3.91%radiated by UV-light for 60 8. The UV-cured flm onof elongation at tear. As was seen from above, the UV-the glass plate was peeled with a cut knife. Accordingcured films with BPGEA as prepolymer have great valueto ASTM D882-91[15], the tensile properties were testedof Young's modulus, indicating that the UV-cured filmsfor the UV-cured films. The measured results are pre-with BPGEA as prepolymer is more rigid than that ofsented in Table 1.NPGGEA as prepolymer. However, the UV-cured filmsTable 1 Mechanical properties of UV- cured films withwith NPGGEA as prepolymer have great value of elon-NPGGEA a8 prepolymer to prepare photosensi-gation at tear, implying that the UV-cured flms withNPGGEA as prepolymer are more fexible than that oftive coatingBPGEA as prepolymer.TensileYoung'sElongationSample No.strength/MPa modulus/MPa at tear/%3 Conclusions128.33915.065.46With NPGGE synthesizing NPGGEA, the optimum228.27937.155.52synthesis conditions should be as follows: The con-329.02926.925.57centration of N,N dimethylbenzylamine, 0.80% of reac-29.49922.345.49tants; the concentration of p-hydroxyanisole, 0.3% of re28.64917.615.53actants; the reaction temperature, 90-110°C; the molarAverage value28.75923.82 :5.51ratio of NPGGE to AA, 1:2.2.The NPGGEA is very sensitive to the UV-light andNote: The tested temperature is 25 C, the humidity 70%，andhas good mechanical properties, especially good flexiblethe crosshead speed 20 mm/ minproperty. This implies that the NPGGEA has a goodSimilarly, 15 g of BPGEA, 5 g of butyl acrylate andapplication value in UV-cured materials.0.5 g of 1-hydroxycyclohexyl phenyl ketone were addedin another 100 mL beaker, and the mixture was fullyReferencesstirred. The mixture was coated on another clean glass[1] DIETLIKER K, CRIVELLO J V. Chemistry and technolplate, with the coated flm also being 0.400 mm in thick-ogy of UV and EB formulation for coatings, inks andness. The glass plate was placed in the UV-chamber,paints [M]. London: SITA Technology Limited, 1991:and irradiated by UV-light for 60 s. The UV- cured film1-on the glass plate was peeled with a cut knife, and their[2] DAVIDSON R S. Exploring the science technology andtensile properties are presented in Table 2.application of UV and EB curing [M]. London: SITATechnology Limited, 1999: 5- 12.Table 2 Mechanical properties of UV- cured films withBPGEA as prepolymer to prepare photosensitive[3] TAKIMOTO Y. 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