C NMR Characteristics and Thermal Properties of Hydroxyethyl Cellulose Grafting Poly(caprolactone) Copolymer

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1 Asia Joural of Chemistry; Vol., No. 8 (0), C NMR Characteristics ad Thermal Properties of ydroxyethyl Cellulose Graftig Poly(caprolactoe) Copolymer MING GU, XIN XIN YIN ad PENG WANG Departmet of Chemistry, Zhejiag Agriculture ad Forestry Uiversity, Li'a 00, P.R. Chia Correspodig author: Fax: ; Tel: ; tdky@hotmail.com (Received: 0 May 0; Accepted: February 0) AJC-997 ydroxyethyl cellulose (EC) graftig poly(caprolactoe) (PCL) copolymer (EC-g-PCL) was successfully sythesized by the protective techology of trimethylsilyl group. The poly(caprolactoe) was grafted oto hydroxyethyl cellulose after the partial hydroxyl groups were firstly protected with trimethylsilyl group, the protective trimethylsilyl groups were take off ad the ew graft copolymer was geerated. The product was characterized by C NMR, the thermal properties aalysis was also tracked with quadrate hyperthermic treatmet. The results of the structure aalysis idicated that poly(caprolactoe) was coected to hydroxyethyl cellulose by chemical bod ad the test showed that the thermal stability was chaged alog with the modified structure. Key Words: ydroxyethyl cellulose, Polycaprolactoe, Trimethylsilyl groups, Copolymer. INTRDUCTIN It is most sigificat i developig cellulosic modificatio materials which have advatages of low processig cost, otoxicity ad biodegradability etc. - As typical cellulose ester, hydroxyethyl cellulose ca be used i the field of thickeig aget, fluxio coditioer, medicie, etc. -6 owever, hydroxyethyl cellulose hardly dissolves i o-water solvet, which limits its further applicatio. Poly(caprolactoe) (PCL) is oe kid of polymers of hydrophobicity ad biocompatility. It plays a importat role i polymers ad i the biomedical material area 7,8. accout of poly(caprolactoe)'s structure of molecule chai ad high crystalliity, its costacy is better tha others ad the biodegradability of poly(caprolactoe) is ot perfect. If the modificatio material through the chemical graft reactio betwee the hydrophilic hydroxyethyl cellulose ad the hydrophobic poly(caprolactoe) could be successfully sythesized, the the ew biodegradatio material (EC-g- PCL) will be gaied. Meawhile, the obtaied ew material with special structure should be edowed a lot of peculiar thermal properties. To our best of kowledge, the C NMR characteristics ad thermal properties of hydroxyethyl cellulose graftig poly(caprolactoe) (EC-g-PCL) is still the ew result for this kid of copolymer. EXPERIMENTAL ydroxyethyl cellulose (EC, Mw: 000, Ms =.0) was supplied by Ruitai Cellulose Co. Ltd., (Shadog, Chia); ε-caprolactoe (CL, 99 %) was supplied by Acros rgaics Co.; examethyldisilazae (MDS, AR, Shaghai Medical Chemical Reaget, Chia). ther chemical reagets were aalytical grade ad redistilled water was used throughout the experimet. Preparatio of EC-g-PCL: The experimetal istallatio was uder a water-free ad oxyge-free coditio. g hydroxyethyl cellulose was dissolved i 0 ml N,N-dimethyl formamide with the protectio of itroge ad 0. g N Cl was added i the reactio flask. The temperature was raised to 0 ºC, the ml hexamethyldisilazae was slowly titrated ito this flask for 8 h reactio by stirrig. The excessive redistilled water was added ito a vessel ito which the reactio mixture has bee trasferred. The crude product was obtaied after the reactio mixture was stirred vigorously, precipitated ad filtered. The, the crude product was dissolved i acetoe ad filtered, excessive redistilled water was added ito the filtered liquor ad the process of stirrig, suckig filtratio was take. The solid hydroxyethyl cellulose trimethyl-silicificatio itermediate (TMSEC) was obtaied. 0. g TMSEC was trasferred to a reactio flask which has 8 ml xylee. The temperature was raised to 80 ºC for. h reactio uder the protectio of itroge. The ml ε-caprolactoe moomer ad 0. ml S(ct) were added ad the reactio was cotiued for h at 0 ºC. The reactio product was dissolved with CCl ad the reactio product was precipitated i petroleum ether ad the washed several times with petroleum ether. The white polymer TMSEC-g-PCL was obtaied. %

2 0 Guo et al. Asia J. Chem. NaC diluted solutio, 6 % Cl diluted solutio were prepared respectively. Isopropaol ad diluted hydrochloric acid were measured ad mixed to a prepared alcoholysis solutio of isopropaol/water/hydrochloric acid (:, v/v). The sythetic TMSEC-g-PCL was added to the isopropaol/ water/hydrochloric acid alcoholysis solutio. The alcoholysis reactio bega at 7 ºC for mi with stirrig ad the NaC was used to adjust the solutio system p = 7.. The precipitate was a filtered depositio ad the graft copolymer (EC-g-PCL) was fially obtaied. Characterizatio of reactat, itermediate product ad graft copolymer: The Fourier trasform ifrared spectra of hydroxyethyl cellulose, itermediate product TMSEC, TMSEC-g-PCL ad ed product EC-g-PCL were measured with a spectrophotometer (Prestige-, Shimadzu, Japa). The NMR ad C NMR spectra of hydroxyethyl cellulose, TMSEC, TMSEC-g-PCL ad EC-g-PCL samples were measured by usig a Bruker ADVANCEB/00Mz uclear magetic resoace spectrometer (NMR, Bruker, Switzerlad). The solvet of NMR used was D, CD CCD, d 6 -DMS ad d -pyridie ad the iteral stadard was tetramethylsilae. Thermal properties aalysis: The DSC measuremet of reactat, itermediates ad ed product usig twice rise temperature treatmet begi of low temperature were operated with DSC Q00 differetial scaig calorimeter (TA, America). The test begi with -00 ºC, the speed-rate of heatig is set as 0 ºC mi - util the temperature reached 00 ºC after 0 mi, this temperature is kept for mi, the the system temperature was cooled util it reached 0 ºC ad the speed-rate of coolig was also stetted as 0 ºC mi -. The temperature should be raised immediately agai whe 0 ºC was fiished, the speedrate of heatig was kept at 0 ºC mi - util the system touchs 00 ºC ad the this quadrate hyperthermic experimet is fiished. The flow uit of N is ml mi - uder whole test ad the mass of samples are from.60 mg to.9 mg. RESULTS AND DISCUSSIN Sythesis of EC-g-PCL: The sythesis of EC-g-PCL follows three steps (Fig. ). examethyl-disilazae as hydroxyl protectio reaget reacts with the hydroxyl of hydroxyethyl cellulose to produce TMSEC. The caprolactoe occurs opeig loop reactio ad polymer reactio, graft polymerizatio of poly(caprolactoe) with TMSEC is achieved, which geerates the graft polymer TMSEC-g-PCL. The TMS group of TMSEC-g-PCL is take off ad EC-g-PCL ca thus be completely sythesized. The graftig ratio (G %) ad graft efficiecy (G E ) ca be calculated ad are. % ad. % respectively. The experimetal data idicates that poly(caprolactoe) as a brach chai grafted o the hydroxyethyl cellulose backboe successfully. The mass ratio of poly(caprolactoe) brach chai ad hydroxyethyl cellulose backboe is about :. I other words, the ratio deotes poly(caprolactoe) brach chai occupies about / of the mass of the graft product. G E =. % meas the active hydroxyl belogig to hydroxyethyl cellulose molecule is oly left i a limited amout after trimethyl-silicificatio substitutio. By itself the limited activity, most of ε-caprolactoe has a homo polymerizatio reactio ad the resultat is fially washed. C 6 C -(C C ) X - R -(C C ) X - S(oct) i-pr/ /Cl R : or -(C C -) X - MDS/DMF R 6 C -(C C ) X -TMS 6 C -(C C ) X -TMS R -(C C ) X - R -(C C ) X -(C -(C ) -C-) m - 6 C -(C C ) X - -(C C ) X -(C -(C ) -C-) m - R : or -(C C -) X - or -(C C -) X -TMS R : or -(C C -) X - or -(C C -) X -TMS or -(C -(C ) -C--) m - R : or -(C C -) X - or -(C -(C ) -C--) m - The structural formula of graft caprolactoe uit Fig.. Graft polymerizatio scheme of EC-g-PCL The IR ad NMR of spectra of EC, TMSEC, TMSEC-g-PCL ad EC-g-PCL have bee ivestigated. IR spectra of EC (ν max, cm - ): 0 (-), (-C ), (-C -) ad (C-), (C--C); IR spectra of TMSEC (ν max, cm - ): 80 (-), (-C ), (-C -) ad (C-), (Si-Me), (Si-Me), 8 (Si-Me), 7-79 (Si-Me), (C--C); IR spectra of TMSEC-g- PCL (ν max, cm - ): (-), (-C ), (-C -) ad (C-), (Si-Me), (Si-Me), 80 (Si-Me), 7-78 (Si-Me), (C--C), 70 (C=); IR spectra of ECg-PCL (ν max, cm - ): 6 (-), (-C ), (-C -) ad (C-), (C--C), 70 (C=). NMR of EC (ppm):.98,.,.-.8,.8,.8; NMR of TMSEC:.98,.,.-.8,.8,.8, 0.; NMR of TMSEC-g- PCL:.,.0,.8,.,.,.0, 0.; NMR of EC-g- PCL:.,.0,.8,.,.,.0. These spectra of IR ad NMR show that the EC-g-PCL has bee successfully sythesized. Aalysis of C NMR spectroscopy: C NMR is a high performace approach for characterizig the cellulose derivatives 9. Fig. shows the C NMR of hydroxyethyl cellulose. The C 6 carbo sigal of cellulose rig ca be observed at δ = 69. ppm, δ = 7.6 ppm for C of cellulose rig, δ = 7.7 ppm for C of cellulose rig, δ = 8. ppm for C of cellulose rig, δ = 8.6 ppm for C of cellulose rig, δ = 0. ppm for C of cellulose rig, respectively. The peak at δ = 60. ppm is due to -C - (f, g) carbo of the hydroxyethyl group. The C NMR of TMSEC was recorded i Fig.. The peaks at δ = ppm are due to C -C 6 carbo of cellulose rig ad carbo sigal at 0.0 ppm for C of cellulose rig. The peak at δ = 6. ppm is due to -C - (f, g) carbo of

3 Vol., No. 8 (0) Properties of ydroxyethyl Cellulose Graftig Poly(caprolactoe) Copolymer ppm Fig.. C NMR spectra of hydroxyethyl cellulose ppm Fig.. C NMR spectra of TMSEC hydroxyethyl group. The ew peak at δ =.8 ppm is origiated from the sigal of -(C ) Si-, it cofirms that the trimethyl-silicificatio reactio of hydroxyethyl cellulose has actually occurred. C NMR of TMSEC-g-PCL shows the peak at ear δ = 0 ppm is due to C carbo sigal o the hydroxy-ethyl cellulose backboe, δ = ppm are attributed to C -C 6 carbo sigal of cellulose rig, δ =.7 ppm is origiated from the carbo sigal of -(C ) Si-, δ = 7. ppm is due to carboyl group(i) carbo sigal i the polycaprolactoe uit. The multiple peaks at δ = 6. ppm are well assiged to -C - (e, f, g) carbo sigal. The peaks at δ =.8 ppm ad δ = 8. ppm are attributed to -C - (a, d) carbo sigal respectively. The two sites of -C -(b) ad -C - (d) i the polycaprolactoe uit have bee distiguished i the C NMR spectrum, the carbo sigal of -C - (b) ad -C -(d) separately locate at δ =.9 ppm ad δ = 8. ppm. The peak at δ =.8 ppm is due to -C -(c) carbo sigal. Fig. shows the C NMR of EC-g-PCL. The peak at δ = 00 ppm is due to C carbo sigal o the hydroxyethyl cellulose backboe, δ = ppm are attributed to C -C 6 carbo sigal of cellulose rig; δ = 7. ppm is due to carboyl group (i) carbo sigal i the polycaprolactoe uit. The multiple peaks at δ = 6. ppm are due to -C - (e, f, g) carbo sigal. δ =.9 ppm ad δ = 8. ppm ca be assiged to -C - (a) ad -C - (d) carbo sigal, δ =. ppm ad δ =.6 ppm for the -C - (c) ad -C - (b) carbo sigal. The experimetal data idicated that the caprolactoe molecule has a rig-opeig polymerizatio reactio ad is liked to hydroxyethyl cellulose by ester bod ad the EC-g-PCL was successfully sythesized. I additio, the peaks correspodig to glucoside ad poly(caprolactoe) segmet also exist ad the carbo chemical shift of every group i Fig., but the peak at δ =.7 ppm, which is due to the chemical shift of -(C ) Si carbo disappeared i Fig.. This C NMR spectrum idicates that the TMS group has bee successfully removed. Aalysis of thermal properties: The thermal stability has a importat meaig i processig, fusio characteristics, mechaical properties etc. of the cellulose-base derivatives 0,. I this paper, the hyperthermic experimet of hydroxyethyl cellulose, TMSEC, TMSEC-g-PCL ad the graft product EC-g-PCL has bee doe ad the thermal stability aalyzed. Fig. shows the quadrate hyperthermic curves of hydroxyethyl cellulose ad TMSEC. From the Fig., the iitial fusio peak (8.9 ºC) of hydroxyethyl cellulose has bee observed uder the DSC experimetal temperature, but the apparet thermal effect is ot occurred i the procedure of the secod heatig-up process. After the hydroxyethyl cellulose is protected, the apparet thermal effect ad fusio peak are also ot occurred throughout the experimetal temperature, it idicates that the thermal stability of TMSEC is proved. Fig. 6 shows the quadrate hyperthermic curve of the TMSEC-g-PCL. The fusio temperature (T m) ad crystallizatio temperature (T c) of TMSEC-g-PCL ca be obtaied from Fig. 6. The T m ad T c are 6.70 ºC ad 8.9 ºC for pure poly(caprolactoe). After poly(caprolactoe) is liked to the skeleto of TMSEC successfully, the T ml ad T c of TMSEC-g-PCL are 60.6 ºC ad. ºC respectively. It is also kow from Fig. 6, the quadrate fusio temperature T m is 0.8 ºC, T m is lower tha the iitial fusio temperature T m. Fig. 7 shows the quadrate hyperthermic curve of EC-g- PCL. Compared to Fig. 6, the DSC curves of two products are similar except that the exothermal peak ad edothermic peak of TMSEC-g-PCL become more sharper, it could be deduced that the micro-structure ad thermal properties of EC-g-PCL is similar to TMSEC-g-PCL. Fig. 7 showed the T m ad T c of EC-g-PCL are 8. ºC ad 8.6 ºC, which decreased sigificatly compared with TMSEC-g-PCL. Fig. 7 also shows that the quadrate meltig temperature T m is lower tha iitial meltig temperature T m ad the T m is 8. ºC. Fig. 8 showed the quadrate hyperthermic curve of the hydroxyethyl cellulose, TMSEC, TMSEC-g-PCL ad EC-g-PCL, the DSC curves with the time as their abscissa. As show i Fig. 8, hydroxyethyl cellulose holds a wide

4 0 Guo et al. Asia J. Chem ppm Fig.. C NMR spectra of EC-g-PCL T m 60.6 ºC.00 EC TMSEC TMSEC-g-PCL T m 0.8 ºC 67.J/g DSC/(mW/mg) DSC/(mW/mg).00 8.J/g J/g Temperature (ºC) Fig.. DSC curves of EC ad TMSEC edothermic peak, but the exothermic peak does ot appear ad the edothermic ad exothermic peaks ca ot be obviously observed for TMSEC. The DSC curves of TMSECg-PCL ad EC-g-PCL are very similar except that the former's edothermic ad exothermic peaks are much sharper. The explaatio of DSC curves is as followig: hydroxyethyl cellulose belogs to amorphous polymer. Whe it is heated, T c. ºC Temperature (ºC) Fig. 6. DSC curve of TMSEC-g-PCL the hydroge bods amog the molecules are destroyed ad they form a wide edothermic peak. Whe hydroxyethyl cellulose is beig cooled dow, the hydroge bods ca't recostruct, so hydroxyethyl cellulose does't exhibit a exothermic peak. The hydroge bods amog the TMSEC molecules are broke after hydroxyethyl cellulose trimethylsilicificatio, so TMSEC does't exhibit obvious edothermic

5 Vol., No. 8 (0) Properties of ydroxyethyl Cellulose Graftig Poly(caprolactoe) Copolymer 0 DSC/(mW /mg) eat Flow (W/g) EC-g-PCL T m 8. ºC.6J/g T c 8.6 ºC T m 8. ºC.J/g.0J/g Temperature ( ºC) 0 - Fig. 7. The DSC curve of EC-g-PCL EC TMSEC TMSEC-g-PCL EC-g-PCL Time (mi) Fig. 8. DSC curve of hydroxyethyl cellulose, TMSEC, TMSEC-g-PCL ad EC-g-PCL (with time as abscissa) ad exothermic peaks. The crystalliity of TMSEC-g-PCL icreases after poly(caprolactoe) graftig oto TMSEC molecule, thus, the crystallie area will be destroyed ad re-crystallized i the quadrate hyperthermic test ad the sharper edothermic ad exothermic peaks are formed. The molecule structure of EC-g-PCL is looser after the trimethylsilyl (TMS) groups are eluted. The crystalliity of EC-g-PCL is lower tha TMSEC-g-PCL, so the DSC curve of EC-g-PCL show less sharp peaks. Coclusio By usig the protective techology of trimethylsilyl (TMS) groups, the cellulosic chemical modificatio material EC-g-PCL was successfully sythesized by takig hydroxyethyl cellulose as the graftig skeleto ad poly(caprolactoe) as the graftig brach. C NMR was used to characterize the structure of the itermediates ad target product ad the results of sythesis verify the desiged reactio. The DSC experimet shows that the thermal behaviour characteristics of sythetic products chage whe a poly(caprolactoe) brach is itroduced ito the skeleto of amorphous hydroxyethyl cellulose. ACKNWLEDGEMENTS This work was supported by the Zhejiag Provicial Natural Sciece Foudatio (Y09079); the Foudatio of Sciece ad Techology Departmet of Zhejiag Provice (No. 0C0); the pe Fud of Zhejiag Provicial Top Key Disciplie of New Materials ad Process Egieerig (009). REFERENCES. R.A. Gross ad B. Kalra, Sciece, 97, 80 (00).. D. Klemm, B. eublei,.p. Fik ad A. Boh, Agew. Chem. It. Ed.,, 8 (00).. Y.X. Zhu, D.J. Che ad Y.J. Li, Polym. Bull.,, 8 (00).. S. Gorgieva ad V. Kokol, Carbohyd. Polym., 8, 66 (0).. C. Jiag, X.L. Wag, P.D. Su ad C. Yag, It. J. Biol. Macromol., 8, 0 (0). 6. Y.. Sog, Q. Zheg ad C. Liu, Id. Crops Prod., 8, 6 (008). 7. L. Dua, Z.F. Xu, K. Su, X.W. Zhao, J. Fag, X. Qi ad Z.Y. Gog, J. Biomed. Egg.,, 8 (007). 8. G.. Zhag, J.F. Zhu ad X.F. Xu, J. Cell. Sci. Techol.,, 60 (006). 9. C. Rodeau-Mouro,. Bizot ad D. Bertrad, Carbohyd. Polym., 8, 9 (0). 0. L.L. Wag, W. Dog ad Y.S. Xu, Carbohyd. Polym., 68, 66 (007).. M. Guo,.W. Meg, P. Wag, C.P. Wag ad F.X. Chu, Asia J. Chem.,, (00).. S. Nojima,. Nakao ad Y. Takahashi, Polymer,, 79 (99).