Ethylene glycol aluminum as a novel catalyst for the synthesis of poly(ethylene terephthalate)

Available online at www.sciencedirect.comCHINES EScienceDirectCHEMICALL ETTERSEL SEVIERChinese Chemical Letters 22 (2011) 741-744www. elsevier.com/locate/ccletEthylene glycol aluminum as a novel catalystfor the synthesis of poly(ethylene terephthalate)Bin Xiao a,b,e, Li Ping Wang a,b.c, Ren Hao Mei a,b.c, Gong Ying Wang a,b,c,*: Chengdu Institute of Orgaric Chemistry, Chinese Academy of Sciences, Chengdu 610041, Chinab Changzhou Key Laboratory of Green Chemistry and Technology, Changzhou Instiute of Chemistry, Changzhou 213164, ChinaC Graduate School of Chinese Academry of Sciences, Bejing 100039, ChinaReceived 14 September 2010AbstractEthylene glycol aluminum was prepared eficiently and characterized by FT-IR and NMR. It exhibited higher catalytic activityand had proftable effect than titanium glycolate and ethylene glycol antimony for the synthesis of poly(ethylene terephthalate)(PET). It was only used as polycondensation catalyst because it was sensitive to water. For this catalyst, the degree of esterificationof the theoretical amount of water was produced up to 95% at 260 °C, while the intrinsic viscosity and content of terminal carboxylgroups of the corresponding PET polyester, polymerized at 280。C, 70 Pa for 39 min, was 0.87 dL/g and 23.0 μmolg, respectively.Ethylene glycol aluminum was a promising catalyst for the synthesis of PET polyester.◎2010 Gong Ying Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.Keywords: Aluminum alkoxide; PET; Polycondensation; Catalyst; Ethylene glycol; Terephthalic acidPoly(ethylene terephthalate) (PET) is used as a commodity as well as engineering product for diverse applications.Its main end products are fibers, packaging articles and films [1,2]. PET has one of the fastest growing markets and willcontinue this trend in the future boosted by world economic growth and continuous development of new applicationfields. In the production of high molecular weight PET by the polycondensation of ethylene terephthalate, the presenceof a catalyst is essential.Despite the large number of papers and reviews published in the literature on the kinetic and catalytic aspects of theformation of PET [3- -6], the report is rare which aluminum alkoxide is used as the polycondensation catalyst. In thiswork, ethylene glycol aluminum was prepared and used as a new catalyst for the synthesis of PET polyester.1. ExperimentalEthylene glycol aluminum was prepared from aluminum isopropoxide and ethylene glycol (EG) in a molar ratio of2/3 in quantitative distilled isopropanol at 190 °C for 8 h. The solution was cooled to room temperature, then 200 mLtoluene was added to precipitate the product as a white solid. Then the white solid sample was dried in vacum at roomtemperature [7].* Corresponding author at: Chengdu Institute of Organic Chemistry, Chinese A中国煤化工,ChineE-mail addresses: gywang@cioc.ac.cn, bxwisdom. _886@yahoo.com.cn (G.Y:MYHCNMHG1001-8417/S- see front matter心2010 Gong Ying Wang. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All nights reserved.doi: 1.016/.cet.2010.12.036742B. Xiao et al./Chinese Chemical Lters 22 (2011) 741-744PET synthesis was carried out in the reactor of the polyesterifcation apparatus with terephthalic acid (TPA) and EGin a molar ratio of EG/TPA = 1.2 and ethylene glycol aluminum 0.5% of TPA mole was adding. Esterfcation reactionwas operated at 260 °C under purified nitrogen atmosphere, until no water was distilled out, then polycondensationreaction was carried out at 280。C. 'H NMR (500 MHz, CDCI]yTFA (95:5 by weight): 8 3.45 (m, 2H, J= 8.7 H2),6.91 (m, 4H, Ar-H), 10.30 (s, 1H, -COOH).Intrinsic viscosity (IV) measurements were performed in Ubbelohde viscometer using 1,1 ,2,2 tetrachloro-ethane/phenol (40/60 by weight) as solvent.Content of terminal carboxyI group (- COOH) of the sample was determined by titrating a solution of the resin inphenol/chloroform (50/50 by weight) with standard KOH in ethanol in the presence of bromophenol blue as indicator.After the polymer samples were saponified by sodium hydroxide and methanol, the content of DEG was measuredon Shanghai Precision & Scientific Instrument Co., Ltd. gas chromatographic instrument.2. Results and discussionThe components and structure of ethylene glycol aluminum are demonstrated by FT-IR and NMR spectroscopies.FT-IR absorption bands from ethylene glycol aluminum (see Fig. 1) have been empirically assigned by comparisonwith the spectra of EG, because EG molecule is the part of the structure. Appearance of the peaks at 3320 cm- and1589 cm~ ! corresponds to vo H and δ H These peaks become weak in the spectrum of ethylene glycol aluminum at2939 cm-' , 2880 cm - I and 1460- 1250 cm~' due to the bond of Uc H and δc H This implies that the glycolate anioncannot move freely in ethylene glycol aluminum. It can be seen that the presence of VAL o and VC o bands at 658 and1090 cm . The data is coincided to the papers [7].NMR spectrum data of ethylene glycol aluminum in CD2O is shown in Figs. 2 and 3. The singlets at 3.60 and3.31 ppm are atrbuted to the proton in methylene group and CD4O. The triplets at 4.95 ppm are attributed to theproton in hydroxyl group or water in CD40. The singlet at 62.93 ppm is attributed to the carbon in methylene group.1401208 100Eerylene glyel80∞0星自g 40}20[ot4000 3500 3000 2500 2000 1500 1000 500Waveaumbers (cm* )Fig. 1. FT-IR of ethylene glycol aluminum.中国煤化工TYHCNMHG0108uppFig. 2. 'H NMR specrm of ethylene glycol aluminum.B. Xiao et al./Chinese Chemical Letters 22 (2011) 741- -744743100Fig 3. 'C NMR spectrum of ethylene glycol aluminum.The multiplets at 47.95 ppm are atributed to the solvent CD2O. From FT-IR and NMR spectrums, we can justify thatthe received sample is ethylene glycol aluminum.The IV data in Table 1 ilustrates that the catalytic activity of titanium glycolate is higher than ethylene glycolaluminum and ethylene glycol antimony. The catalytic activity is similar between ethylene glycol aluminum and ethyleneglycol antimony. This phenomenon could be caused by the coordinative ability ofTi to create some kinds of coordinativenetwork in the polymer melt that results in enhanced values of melt viscosity; Al and Sb are unable to form such networkand, as a consequence, lead to lower values of IV. The toxicity of ethylene glycol aluminum is lower than ethylene glycolantimony, so ethylene glycol aluminum can be considered a further advantage in their application.It is worthwhile noting that when titanium cormpounds are used for the production of PET, the polymer becomesmarkedly yellowish. From b* values of color measurement of PET samples of this work (Table 1), the PET sample oftitanium glycolate shows a clear visible yellow discoloration (b* = 29.3) due to titanium glycolate adding. A visibleyellow discoloration shows the samples with b* values >4.5, and all the other samples shows sensible discoloration.But the samples of ethylene glycol aluminum is whiter than the sample of titanium glycolate and b* value is lower.The result is shown in Table 1 that the polycondensation time is decreased with increasing catalyst amount. Itcan beseen from Table 1 that the catalytic activity is increased by increasing catalyst amount, but when the molar ratio ofcatalyst is 0.0025, the catalytic activity drops to a slightly lower level It seems likely that excess catalyst leads topolymerization of EG, disadvantageous to produce DEG. So, the optimal catalyst amount of ethylene glycol aluminummay be 0.005.Table 2 presents the property of PET versus the molar ratio of EG to TPA. When EG and TPA are added accordingto the stoichiometric reaction, the IV of PET is the lowest. This may ascribe that the esterification reaction is reversible.Table 1Effect of different aluminum alkoxides on PET characters.CatalystCatalyst amountIV (dUg) -C0OH (μmolg)DEG (mol/t) Sample color(x 10 3 mo/mol TPA)b"Ethylene glycol aluminum for 60 min20.7228.460.9.2 12.9Ethylene glycol antimony for 60 min2:0.7023.87.259.7 1.1 10.5Titanium glycolate for 45 min2.0.8332.56.974.5 2.5 28.0Ethylene glycol aluminum for 39 mio0.8723.08.53.8 0.1 9.0Ethylene glycol antimony for 45 min0.8629.360.4 0.2 16.2Titanium glycolate for 30 min0.8926.68.673.4 3.0 29.3Ethylene glycol aluminum for 30 min1011.560.4 0.6 12.4Ethylene glycol antimony for 30 min0.8425.012.258.6 0.8 13.6Titanium glycolate for 18 min19.375.7 2.3 28.9Ethylene glycol aluminum for 24 min50.85中国煤化工59.9 1.3 14.8Ethylene glycol antimony for 24 min52.3 0.9 13.0Titanium glycolate for 15 minMYHCNMHG_74.5 2.8 29.5PET polymerization conditions: n(EG);:n(TPA) = 1.2. the TPA weight of 180 g. esterification at 260 °C, polycondensation at 280 °C. The reactionequipment is a I L stainless steel batch reactor equipped with a paddle agitator (50 H2) and the polycondensation time is calculated sirring powderfrom 40 to 70 Hz.744B. Xiao et al. /Chinese Chemical Letters 22 (2011) 741-744Table 2Effect of different mole/mole of EG/TPA on PET synthcsis,EG/TPA (mol/mol)IV (dL/g)Polycondensation reaction time (min)DEG (mol/t)-C0OH (μmo/g)1:0.78i01.51.2:10.87398.223.01.4:10.86428.626.21.6:1367.626.81.8:10.88300.82713.0PET polymerization conditions: ethylene glycol aluminum as catalys, esterifcation at 260 °C, polycondensation at 280°C.冬4000 3500 3000 2500 20000 15900 1000 500Wavenumber(cm")Fig. 4. FT-IR of PET.It is more favorable to the yield of water when EG is in excess compared with the amount ofTPA. When the molar ratioofEG/TPA is increased to 2:1, the yield of DEG increased greatly. The appropriate molar ratio of EG to TPA is about 1.2:1.The FT-IR spectrum of PET produced by the esterifcation of EG and TPA is shown as in Fig. 4. The FT-IRspectrum of PET coincided with papers [8]. Fig. 4 of PET FT-IR is complicated, but the characteristic absorption peaksare ester conformation and benzene ring. 1300cm~ and 1090cm 1 are due to stretching vibration of C-0.1720 cm~ I and 725 cm - I are assigned to the band of the carboxyl and benzene ring. The absorbencies of the signals at3430 and at 872 cm~ 1 are due to the end-group. H NMR spectrum of the sublimate in CDCl3-TFA (95:5 by weight)mixture is shown in Section 1. The multiplet observed in the 8 3.45 ppm region has been assigned to the protons ofmethylene groups present in PET [9]. The singlets observed at 8 6.91 and 10.30 ppm have been assigned to the protonsof the phenyl groups and terminal carboxyl groups. It can be concluded that the received sample is PET from thespectrum of FT-IR and 'H NMR.3. ConclusionsEthylene glycol aluminum exhibits similar catalytic activity to ethylene glycol antimony and whiter than titaniumglycolate for the synthesis of PET polyester in polycondensation reaction. Decreased catalyst cost, enhanced reactionrate and improved PET properties are the features of this new catalytic system. The experimental results testify thatethylene glycol aluminum is a more promising catalyst for the synthesis of PET polyester.References[1] B. Basu, s. Dey, B. Fischer, Radiat. Meas. 43 (8) (2008) 595.[21 A.K. Ahmed, H.W. Alan, Polymer 48 (8) (2007) 5069.[3] NL Vladimir, P. Francesco, B. Corado, J. AppL Polym. Sci, 58 (10) (1995) 771[4] D. Ben, Polymer 43 (11) (2002) 3147.中国煤化工[S] E.T. Faissal, PW. Jens, F Guner, Thermochim. Acta 432 (7) (2005) 99.[6] D.N. Bikiaris, D.S. Achilias, DJ. Giliopoulos, Eur. Polym. J.42 (12) (2006)MYHCNMHG[7] J.G. Graeme, K. Tim, B.M. Neil, Inorg. Chem. 34 (21) (1995) 5244.[8] M. Di Serio, R. Tesser, A. Ferrara, et al. J. Mol. Catal. A: Chem. 212 (1) (2004) 251.[9] Y. Kong, J.N. Hay, Polymer 43 (14) (2002) 3873.