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Energy and Buildings 48 (2012) 206–210

Contents lists available at SciVerse ScienceDirect

Energy and Buildings

j our na l ho me p age: www.elsev ier .com/ locate /enbui ld

reparation of poly(decaglycerol-co-ethylene glycol) copolymer as phase changeaterial

ing Guoa,∗, Hengxue Xiangb, Qianqian Wanga, Chengnv Hua, Meifang Zhub, Lili Lib

College of Chemistry Engineering & Material, Dalian Polytechnic University, Dalian 116034, PR ChinaState Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, PR China

r t i c l e i n f o

rticle history:eceived 23 August 2011eceived in revised form 9 January 2012ccepted 28 January 2012

a b s t r a c t

In this work, a novel phase change material poly(decaglycerol-co-ethylene glycol) [P(DG-co-EG)] copoly-mer was prepared by free-radical solution polymerization based on two macromonomers, polyethyleneglycol acrylate (PEGA) and polydecaglycerol acrylate (PDGA), which were synthesized via acryloyl chlo-ride modification. The results showed that the crystallization enthalpy of P(DG-co-EG) achieved to

eywords:olydecaglycerololyethylene glycolcryloyl chloridehase change materialsicrogel

141.3 J/g, and its soaking time increased up to 15 min with the increase of molar ratios of PEGA toPDGA:TGA results indicated that P(DG-co-EG) degraded in two steps and its maximum degradation ratewas at 420 ◦C.

© 2012 Elsevier B.V. All rights reserved.

. Introduction

Phase change material (PCM) is the material that uses the heatbsorbed or released during the phase-change process to store theatent heat, which has the ability to control temperature within

certain range [1–4]. Therefore, PCM plays an important role inots of fields, such as solar energy storing, smart housing, phasehange energy storage fibers and agricultural greenhouse [5–8].olyethylene glycol (PEG) is also academically classified as a kindf solid–liquid latent heat-storage material with excellent perfor-ance, higher phase transition enthalpy, low thermal hysteresis;

owever, the reactivity of terminal hydroxyl limits its furtherpplications in the field of phase change materials. To overcomehis shortcoming, Liu et al. [9] used direct condensation reactionetween polyethylene glycol-400 and acrylic acid and preparedolyethylene glycol acrylate (PEGA); Cheng and Pan [10] usedethacryloyl chloride to modify polyethylene glycol and prepared

olyethylene glycol double methyl acrylate with the active dou-le bond. Shi et al. [11] used photo-induced radical polymerizationo obtain polyethylene glycol methyl ether acrylate. Based onEGA studies, Lin et al. [12] prepared PEGA copolymers of a series

ross-linked degree and studied its solubility and gas permeabil-ty; Fu and Kao [13] studied the medicine delivery and transport

echanisms of semi-interpenetrating network polymer formed by

∗ Corresponding author. Tel.: +86 13704091879; fax: +86 411 84428309.E-mail address: guojing8161@163.com (J. Guo).

378-7788/$ – see front matter © 2012 Elsevier B.V. All rights reserved.oi:10.1016/j.enbuild.2012.01.035

PEGA with gelatin. As mentioned above, PEGA with active dou-ble bonds can be used to prepare the multi-form and functionalPCM.

Currently, PEGA was reported in literatures, most of whichused the PEG with a molecular weight below 1000 and the slowheat response. Herein, PEG molecular weight was reached to4000, with a higher enthalpy and better thermal behavior. More-over, a new type of cross-linked agent-polydecaglycerol acrylate(PDGA) was synthesized, with each molecular chain having 12active double bonds. Based on the highly active macromonomer,poly(decaglycerol-co-ethylene glycol) [P(DG-co-EG)] copolymerphase change materials were synthesized. The results show thatP(DG-co-EG) had better solid–solid phase transition properties, andits phase transition enthalpy achieved to 141.3 J/g.

2. Experiment

2.1. Materials

The main chemicals used are following: polyethylene glycol-4000, CP, National Pharmaceutical Group Chemical Reagent Co.,Ltd.; polydecaglycerol (PDG), CP, Jinan Dong Run Refined Tech-nology Co., Ltd.; acryloyl chloride, AP, Shandong Swiss Chemical

Technology Co., Ltd.; dichloromethane, AP, Tianjin Kai Xin Chem-ical Industry Co., Ltd.; triethylamine, AP, Tianjin Kai Xin ChemicalIndustry Co., Ltd.; anhydrous ether, AP, National PharmaceuticalGroup Chemical Reagent Co., Ltd.

J. Guo et al. / Energy and Buildings 48 (2012) 206–210 207

tic of

2

pm

Fig. 1. Schema

.2. Preparation of P(DG-co-EG) phase change material

P(DG-co-EG) copolymer was prepared by free-radical solutionolymerization based on PEGA and PDGA. The synthesis of theseaterials is described as follows:

Preparation of the PDGA: PDG and triethylamine were dissolvedin N,N-dimethylformamide (DMF), triethylamine was added, andthen acryloyl chloride was dropped slowly, the molar ratio of acry-loyl chloride to PDG was 1:12. After that, the reaction system washeated up to 35 ◦C and reacted in a nitrogen atmosphere for aperiod of time. With ether as the precipitation agent, the PDGAwas obtained after vacuum filtering.Preparation of PEGA: PEG-4000 and triethylamine were dissolvedin dichloromethane, and then acryloyl chloride was dropped withequimolar of PEG-4000. The PEGA was obtained by ether as theprecipitating agent after reacted a period of time in nitrogen pro-tection.Preparation of P(DG-co-EG): PEGA and PDGA with a certain ratio

were dissolved in deionized water, and then the appropriateamount of initiator was added. The system reacted at 75 ◦C inwater bath for 15 min, forming semi-IPN copolymer phase changematerial. The schematic was shown in Fig. 1.

Fig. 2. Schematic diagram of

P (DG-co-EG).

2.3. Performance test

FTIR: PEG, PEGA and P(DG-co-EG) were observed by Fouriertransform infrared spectroscope (Elmer Instruments Platinum (PE),America). For the solid samples, the tests used KBr pellet method:1 mg sample was mashed into powder using a mortar and a pes-tle, and then 200 mg KBr powder was added and the mixture wascompressed to make FTIR specimen.

Crystallization morphology: the crystallization morphologies ofpure PEG, PEGA, and P(DG-co-EG) were observed by polarized opti-cal microscopy (POM) (XPB-01, China). A digital camera was usedto capture images in cross-polarized light condition.

DSC determination: the thermal properties of P(DG-co-EG) weredetermined by differential scanning calorimeter (Mettler-ToledoDifferential Scanning Calorimeter, Switzerland) using nitrogen aspurge gas. Indium and zinc were used for temperature calibra-tion. Firstly, samples were heated from 0 ◦C to 80 ◦C at a heatingrate of 10 ◦C/min, and subsequently cooled to 0 ◦C at a cooling rateof 10 ◦C/min. The reliability properties of P(DG-co-EG) also weretested through thermal cycling in accordance with above operationby Diamond DSC (PerkinElmer, USA).

Thermal insulation test: accurately weight 3.0 g P(DG-co-EG) ina small test tube was heat for 5 min at 90 ◦C in water bath, andthen removed out in the laboratory environment at 22 ◦C withoutforced convection cooling, while the temperature loggers was used

thermal insulation test.

208 J. Guo et al. / Energy and Buildings 48 (2012) 206–210

4000 800160024003200

P(DG -co-EG)

PEGA

Wavenu mber/c m-1

PEG1620

1715

173 0

fi

EAr

3

3

saCamuu

tai1ti

3

EsraibiiiwPcwm

Fig. 3. FT-IR spectra of PEG4000, PEGA and P (DG-co-EG).

or recording temperature curves. Schematic diagram of thermalnsulation test is shown in Fig. 2.

TG test: the thermal properties of PEG, PEGA, and P(DG-co-G) were tested by Q50 Thermogravimetric Analysis (TA Company,merica). The samples were heated from 25 to 700 ◦C at a heatingate of 20 ◦C/min.

. Results and discussion

.1. FTIR analysis

The FTIR spectrums of PEG4000, PEGA and P(DG-co-EG) arehown in Fig. 3, in which the characteristic absorption of PEGAppears at 1715 cm−1, which corresponds to the unsaturated ester

O group; the C C bond stretch vibrational frequencies enhancedt 1620 cm−1, which can be explained that after acryloyl chlorideodification, the –OH of PEG is esterified, and then the PEG molec-

lar chain has been given C C functional groups and turns into annsaturated ester.

From the spectrum of P(DG-co-EG) in Fig. 1, it can be seen thathe characteristic absorption of saturated ester C O groups appearst 1730 cm−1 [14]. Besides, in the FTIR spectrum, the character-stic absorption peak of C O groups is offset from 1715 cm−1 to730 cm−1, because of the terminal double bond of PEGA and PDGAhat occurring free radical polymerization in the presence of annitiator in the preparation process of P(DG-co-EG).

.2. Crystallization morphology analysis

The polarization pictures of pure PEG4000, PEGA and P(DG-co-G) are shown in Fig. 4, in which PEG-4000 modified by chloridetill has the crystalline extinction phenomenon, and the spheruliteadius decreases. This is due to the ester bond forming between PEGnd acryloyl chloride, and the C C double bond being introducednto the terminal molecular chain of PEG when PEG was modifiedy acryloyl chloride. The phenomenon makes the structure regular-

ty of molecular chain declined. Therefore, when the temperatures dropped to the crystallization temperature, the melt itself is eas-ly nucleated, resulting in crystal radius decreases. P(DG-co-EG)

as prepared by free radical polymerization between PEGA andDGA, forming the comb-like and lightly cross-linked molecular

hain structure. The crystallization ability of PEG molecular chainas further hindered by the above structure, so PEG chain formedicro-crystals, as shown in Fig. 4(c).

Fig. 4. POM images of pure PEG4000, PEGA, P(DG-co-EG). (a) Pure PEG4000, (b)PEGA, and (c) P (DG-co-EG).

3.3. Thermal performance analysis

The DSC curves of P(DG-co-EG) are shown in Fig. 5. It can beseen that the melting and crystallization enthalpy of P(DG-co-

EG) are 163.51 J/g and 141.31 J/g, respectively. The melting andcrystallization temperature are 51.13 ◦C and 42.02 ◦C, respectively.In comparison, the crystallization enthalpy of copolymer phase

J. Guo et al. / Energy and Buildings 48 (2012) 206–210 209

80706050403020-30

-20

-10

0

10

20

30

40

Normalized -163.51Jg^-1

Onset 51.13ºC

Peak 57.58ºC

Endset 64.25ºC

Heating Rate 10.0ºC min^-1

Normalized 141.31Jg^-1

Onset 42.02ºC

Peak 38.97ºC

Endset 32.91ºC

Heating Rate -10.0ºC min^-1

Hea

t F

low

/mW

ccTbcttbmt

Fibioeg

opi1relw

706050403020

cycl e-5

cycl e-4

cycle-3

cycl e-2

Endo

Temperatur e / oC

cycle-1

Fig. 7. DSC cycling cooling curves of P (DG-co-EG).

2500200015001000500020

30

40

50

60

n(PEGA)/n(PDGA)=8:1

n(PEGA)/n(PDGA)=4:1T

emper

ature

/ºC

Time/s

n(PEGA)/n(PDGA)=12:1

3.4. Thermal stability analysis

Temperature/ºC

Fig. 5. DSC heating curves of P (DG-co-EG).

hange material significantly is less than melting enthalpy, andrystallization temperature is lower than melting temperature.his is due to molecular chains of PEG being made as a moleculeranched-chain of copolymer and its interspersion between theomb networks of copolymer after the free radical polymeriza-ion of phase change monomer between PEGA and PDGA. Whenhe temperature dropped to the crystallization temperature of PEG,ecause the main chains of PEG were bounded by the copolymerain chain and the copolymer molecular chain network, the crys-

allization integrity and enthalpy decreased.The reliability properties of P(DG-co-EG) are shown in

igs. 6 and 7, in which it can be seen that the first heating scans different from those of the following thermal cycling. This occursecause of the different thermal history of samples. After the reliev-

ng of the heat history, the DSC curves indicate that the peak areaf endothermic and exothermic change is little in each cycle. Thenthalpy has not obviously changed. As a result, P(DG-co-EG) hasood thermal reliability properties.

The cooling curves of P(DG-co-EG) with different molar ratiof PEGA to PDGA are shown in Fig. 8, in which the temperaturelatform of cooling curves occurred in 43.8 ◦C, the holding time

ncreased with the molar ratios of PEGA to PDGA, and reached5 min. This can be explained that P(DG-co-EG) is obtained by freeadical polymerization with different molecular structure, differ-

nt ratio of PEGA to PDGA, different structure. PDGA contains aarge number of unsaturated double bonds, so the cross-linked net-

ork density of P(DG-co-EG) increased with the PEGA dosage and

756555453525

cycle-5

cycle-4

cycle-3

cycle-2

Endo

Temperature / oC

cycle-1

Fig. 6. DSC cycling heating-up curves of P (DG-co-EG).

Fig. 8. Cooling curves of P(DG-co-EG) with different molar ratio of PEGA to PDGAafter heating in 90 ◦C water for 5 min.

the activity space of the PEG molecule branched-chain reduced;therefore, the crystallization capacity was limited, and temperaturestabilization effect was reduced.

The TG curves of P(DG-co-EG) are shown in Fig. 9, in whichthe weight loss of P(DG-co-EG) occurs in three temperature ranges

70060050040030020010000

20

40

60

80

100

Temperatur e/ºC

Wei

ght/

%

0.0

0.5

1.0

1.5

2.0

2.5

Deriv

.Weig

ht/( %

·ºC-1)

Fig. 9. TG curves of P (DG-co-EG).

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[13] Y. Fu, J.W. Kao, Drug release kinetics and transport mechanisms from semi-interpenetrating networks of gelatin and poly(ethylene glycol) diacrylate,

10 J. Guo et al. / Energy and

s the thermal decomposition of P(DG-co-EG) is segmented. Theeight loss during 210–240 ◦C was caused by the small amount of

riethylamine hydrochloride which decomposed into gaseous tri-thylamine and hydrochloric acid. The thermal weight loss during10–330 ◦C was related to the destruction of the ester bond in P(DG-o-EG); the weight loss during 330–420 ◦C was mainly caused byhe thermal degradation of PEG chains. From the TG curves wean see that the degradation of PEG was the main reason lead-ng to weight loss. The maximum degradation rate of P(DG-co-EG)ccurred at 420 ◦C.

P(DG-co-EG) completely degraded at 460 ◦C.

. Conclusions

Phase change monomer PEGA and cross-linked monomer PDGAith end-double bond were synthesized by acryloyl chloride mod-

fication. Based on above two high activity monomers, P(DG-co-EG)opolymer phase change materials were prepared by free radi-al polymerization. P(DG-co-EG) had the characteristic absorptioneaks of the saturated ester C O group. The crystallization enthalpyf P(DG-co-EG) achieved to 141.3 J/g, and its soaking time increasedp to 15 min with the increase of molar ratios of PEGA to PDGA.(DG-co-EG) degraded in two steps and its maximum degradationate was at 420 ◦C. This result has also proved that we can preparehape-stabilized phase change material using polyatomic alcoholodification.

cknowledgements

This research is financially supported by the Key Laboratoryoundation of the Educational Department of Liaoning ProvinceLS2010010) and the Specialized Research Fund for the Doctoralrogram of Higher Education (20100075110007).

[

ings 48 (2012) 206–210

References

[1] J. Guo, H.X. Xiang, X.Y. Gong, Y.P. Zhang, Preparation and performance of thehydrolyzate of waste polyacrylonitrile fiber/poly(ethylene glycol) graft copoly-merization, Energy Source A 33 (2011) 1067–1075.

[2] L.W. Fan, J.M. Khodadadi, Thermal conductivity enhancement of phase changematerials for thermal energy storage: a review, Renewable and SustainableEnergy Reviews 15 (2011) 24–46.

[3] F. Berroug, E.K. Lakhal, M. El Omari, M. Faraji, H. El Qarnia, Thermal performanceof a greenhouse with a phase change material north wall, Energy Buildings 43(2011) 3027–3035.

[4] I. Ceron, J. Neila, M. Khayet, Experimental tile with phase change materials(PCM) for building use, Energy Buildings 43 (2011) 1869–1874.

[5] C. Hasse, M. Grenet, A. Bontemps, R. Dendievel, H. Sallee, Realization, testand modelling of honeycomb wallboards containing a Phase Change Material,Energy Buildings 43 (2011) 232–238.

[6] Y. Wang, T.D. Xia, H. Zheng, H.X. Feng, Stearic acid/silica fume composite asform-stable phase change material for thermal energy storage, Energy Build-ings 43 (2011) 2365–2370.

[7] J. Zuo, W. Li, L. Weng, Thermal performance of caprylic acid/1-dodecanoleutectic mixture as phase change material (PCM), Energy Buildings 43 (2011)207–210.

[8] S. Wu, G. Fang, Dynamic performances of solar heat storage system with packedbed using myristic acid as phase change material, Energy Buildings 43 (2011)1091–1109, 6.

[9] Y.L. Liu, Z.L. Lei, J.C. Zhao, Synthesis and characterization of polyethylene glycolacrylate, Progress in Modern Biomedicine 6 (2006) 41–43.

10] S.X. Cheng, C.Y. Pan, Synthesis of polyethyleneglycol methacrylate and inves-tigation of its photochemical initiated polymerization, Polymeric MaterialsScience and Engineering 14 (1998) 22–24.

11] Y. Shi, H. Gao, L.C. Lu, Y.L. Cai, Ultra-fast RAFT polymerisation of poly(ethyleneglycol) acrylate in aqueous media under mild visible light radiation at 25 ◦C,Chemical Communications 11 (2009) 1368–1370.

12] H.Q. Lin, T. Kai, B.D. Freeman, S. Kalakkunnath, D.S. Kalika, The effect of cross-linking on gas permeability in cross-linked poly(ethylene glycol diacrylate),Macromolecules 38 (2005) 8381–8393.

Pharmaceutical Research 26 (2009) 2115–2124.14] Y.M. Dong, Polymer Analysis Handbook, China Petrochemical Press, Beijing,

2004.