research article the synthesis of hydroxybutyrate-based...

Research ArticleThe Synthesis of Hydroxybutyrate-Based BlockPolyurethane from Telechelic Diols with Robust Thermal andMechanical Properties

Dan Xue1 Xiaodong Fan1 Zengping Zhang2 and Wei Lv3

1School of Science Northwestern Polytechnical University Xirsquoan Shaanxi 710072 China2Key Laboratory for Special Area Highway Engineering of Ministry of Education Changrsquoan UniversityXirsquoan Shaanxi 710064 China3Oil and Gas Technology Research Institute Changqing Oilfield Company Xirsquoan Shaanxi 710018 China

Correspondence should be addressed to Dan Xue xdnwpu163com

Received 28 May 2016 Revised 19 August 2016 Accepted 24 August 2016

Academic Editor Ewa Schab-Balcerzak

Copyright copy 2016 Dan Xue et alThis is an open access article distributed under the Creative Commons Attribution License whichpermits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

A series of novel amphiphilic block polyurethanes (PUHE) have been successfully synthesized by solution polymerization of thederived PHB-diol and poly(ethylene glycol) with a coupling agent of 16-hexamethylene diisocyanate (HDI) while the PHB-diolwas prepared via the transesterification of PHB and ethylene glycol The hydroxyl contents in PHB-diols range from 136 to 199(the molar ratio) as determined by nonaqueous titration The molecular weight and chemical compositions of PUHE and PHB-diol were investigated by GPC 1HNMR and FTIR in detail which confirm the successful synthesis of PUHEThe tensile strengthand elongation at break of PUHE could reach as high as 20MPa and 210 as the content of PHB in PUHE is 33 TGA curvesindicate that block-bonding between PHB-diol and PEG increases the thermal stability of PHB-diol Film degradation of PUHEwas studied by weight loss and scanning electron microscope (SEM) It could be concluded that degradation occurred graduallyfrom the surface to the inside and that the degradation rate could be controlled by adjusting the PHBPEG ratios These propertiesmake PUHE able to be used as a biodegradable thermoplastic elastomer

1 Introduction

Polyhydroxybutyrate (PHB) originated from bacteria hasbeen considered one of the most prospective bioplastics [1 2]due to excellent strength close to that of isotactic polypropy-lene and favorable melt processability [3 4] for conventionalprocess such as extrusion [5 6] moulding [7 8] andspinning [9 10] Therefore PHB is widely used in the fieldsof food packaging [11] tissue engineering [12] drug deliveryand so forth [13ndash15]However it should bementioned that theapplication of PHB is greatly limited by the brittleness highhydrophobicity [16ndash18] and the narrow processing window[19 20]Thusmany attempts have been developed to improvethe properties of PHB including the preparation of block orgraft copolymers or blending with suitable polymers [21ndash26]Among them block copolymerization is regarded as a simpleand effective approach

Polyurethane elastomer is a kind of block copolymercomposed of soft and hard segments [27ndash29] which canbe synthesized by the reaction between polymer terminatedwith free hydroxyl groups and difunctional isocyanates [30ndash34] And the easy control over the domain structure ofpolyurethanes through the selection ofmonomer unitsmakesit superior to other kinds of PHB material In the synthesisof polyurethane elastomer mole ratio of NCOOH shows asignificant effect on the mechanical and hydrophilic perfor-mance As NCOOH molar ratio increases the proportionof hard segments of polyurethane will increase leading to adecrease of the flexibility of chain Meanwhile the increase ofNCOOHmolar ratio results in an increase in the number ofhydrogen bonds which leads to an increase in crosslink den-sity (hydrogen bonds formed from the cross-linking) thusthe hydrophobicity of polyurethane will increase accordinglyNCO content could be accurately determined by chemical

Hindawi Publishing CorporationJournal of ChemistryVolume 2016 Article ID 9635165 10 pageshttpdxdoiorg10115520169635165

2 Journal of Chemistry

analysis method [35] However few researches focus on themeasurement of the content of free hydroxyl groups

PHB oligomers terminated with free hydroxyl groupsmay be produced by the transesterification of alkane-diolswith high molecular weight of PHB Saad et al syn-thesized macrodiols by transesterification of PHB in 12-dichloroethane with 110-decanediol and p-toluenesulfonateas catalysts [36] Hirt et al obtained telechelic dihydroxy-PHB by glycolysis of bacterial derived high molecular weightdihydroxy-PHB [37] However it is still a challenge toquantify the terminal hydroxyl content in PHB oligomersand to study its effect on properties of the correspondingpolyurethanes

Herein a promising polyurethane elastomer was syn-thesized by solution polymerization of PHB-diol andpoly(ethylene glycol) with a coupling agent of 16-hexameth-ylene diisocyanate (HDI) While the PHB-diol was preparedvia the transesterification of PHB with ethylene glycolthe hydroxyl content of PHB-diol was quantified by thetitration of acetic anhydride-pyridine Then chemicalcompositions were investigated with GPC 1H NMR andFTIR in detail The relationship between block structureand degradation profiles was performed Furthermorethe thermal and mechanical properties of as-preparedPUHE were studied to exploit its potential application asthermoplastic biodegradable elastomer

2 Experimental

21 Materials Polyhydroxybutyrate (PHB Mn of 70 times 105 plusmn10gmol) was purchased from Zhejiang Tianan Tech CoLtd (Zhejiang China) All PHB samples were purified by dis-solving in chloroform followed by filtration and precipitationin ether before use 16-Hexamethylene diisocyanate (HDI)(99 Sigma USA) was used without further purificationChloroform p-toluenesulfonic acid (PTSA) and ethyleneglycol were all from Kemiou Reagent Development Center(Tianjin China) and were used as received

22 Preparation of Dihydroxy-Terminated PHB Oligomers(PHB-Diol) Dihydroxyl-terminated PHB oligomers (PHB-diol) were prepared by transesterification between thepurified PHB materials and ethylene glycol using p-toluenesulfonic acid as catalyst [38ndash40] Typically purifiedPHB (10 g) was dissolved in 100mL of chloroform andrefluxed in nitrogen Subsequently p-toluenesulfonic acid(48 g) and ethylene glycol (20 g) were added The reactiontemperature was controlled at 60∘CThe reaction was carriedout under reflux for 6sim10 h depending on required molecularweight of PHB-diol The resultant solution was washed withdistilled water for 3 times concentrated and dried underreduced pressure

23 Hydroxyl Titration Nonaqueous titration was employedto determine the hydroxyl content in PHB oligomers [41]010 g of PHB oligomers was added to 5mL solution of aceticanhydride in pyridine (20 vv) and then heated up to 100∘Cfor acetylation of 1 h After that 1mL H

2O was added to the

reaction mixture that was left alone for another 05 h Thesolution of KOH in methanol (20 gL) was used to titrate thereactionmixture inwhich several drops of thymol bluecresolred solution (31 04wv) were added as the indicator Theblank titrating experiment without PHB oligomers followedthe same procedure as above

24 PHB-PEG Urethane Preparation A series of polyure-thanes (PUHE) were synthesized by different molar ratiosof polyethylene glycol (Mn = 1500 gmol) and PHB-diolswith different molecular weight 18 g of PHB-diol andpolyethylene glycol were dried in a 25mL two-necked tubeat 40∘C under vacuum overnight Then 20mL of anhydrous12-dichloroethane was added to the flask and any traceof water in the system was removed through azeotropicdistillation with only 5mL of 12-dichloroethane being left inthe flask When the flask was cooled down to 75∘C 020 g ofHDI (12 times 10minus3mol) and two drops of tin octoate (8 times 10minus3 g)were added sequentially The reaction mixture was stirredat 80∘C under nitrogen atmosphere for 48 h The resultantcopolymer was precipitated in diethyl ether and furtherpurified in a mixture of methanol and diethyl ether

25 1H NMR Spectrum The chemical structure and mon-omer composition were determined by 1H NMR usinga ADVANCEIII 400MHz NMR spectrometer The NMRspectrum was obtained at room temperature in CDCl

3

(20mgmL) with tetramethylsilane (TMS) as an internalstandard

26 Fourier Transform Infrared (FTIR) Spectroscopy Fouriertransform infrared (FTIR) spectroscopy was measured by aBio-Rad FTS135 (Bio-Rad USA) spectrophotometer PHB-co-PEG block polyurethane (PUHE) was dissolved in chlo-roform coated on a KBr pellet and dried before test

27 Gel Permeation Chromatography Average molecularweights were determined by gel permeation chromatography(GPC) using chloroform as an eluent at a flow rate of10mLmin in Waters 1525 pump with a combination of fourStyragel columns series (Styragel HR 5mm) and equippedwith a 2414 differential refractive index detector and UVdetector (Agilent Technologies PL-GPC 50 Integrated GPCSystem USA) The sample concentration was 2mgmL and150 120583L of the injection volume The calibration curve wasobtained using polystyrene standards (Shodex Japan) Allsamples were carried out with 64 scans at a resolution of2 cmminus1 at room temperature

28 Differential Scanning Calorimetry (DSC) MeasurementsDifferential scanning calorimetry (DSC) measurements wereperformed on TA Instruments Q100 differential scanningcalorimeter equipped with an auto-cool accessory and cal-ibrated using indium The following protocol was used foreach sample heating from room temperature to 150∘C at aheating rate of 5∘Cmin holding at 150∘C for 3min coolingfrom 150 to minus50∘C at a heating rate of 5∘Cmin beingisothermal at minus50∘C for 3min and finally reheating from minus50

Journal of Chemistry 3

H O CH C C OH +

O

x

H O CH C C

O

m

Cat

CH3

H2

H2

OCH2CH2OH

CH3

HOCH2CH2OH

Scheme 1 Synthesis of PHB oligomer

to 150∘C at a heating rate of 5∘Cmin Data collected fromboth first cooling and second heating runs were analyzed andpeak maxima were taken as transition temperatures

29 Thermogravimetric Analysis Thermogravimetric analy-sis (TGA) was carried out on TA Instruments SDT 2960Samples were heated at 20∘Cmin from room temperatureto 500∘C in a dynamic nitrogen atmosphere (flow rate70mLmin)

210 Mechanical Property The tensile experiment was con-ducted on a WD-10E electronic universal tensile machine(made in Changchun Second Material Experiment Factorytype WD-10E) at room temperature with the loading speedof 2mmmin

211 Degradation Experiments Copolymer films were pre-pared by solvent casting from a 10wt chloroform solutionThe resultant films were dried in vacuo at 50∘C for 2 dayscut into discs (diameter 25mm thickness 2mm) and usedfor the degradation experiments The polymer films (approx200mg) were placed in small bottles containing 10mL buffersolution (pH 74) under a constant temperature of 37∘CThe PBS buffer solution contained 80 g NaCl 02 g KCl144 g Na

2HPO4and 024 g of KH

2PO4in 1 L solution Buffer

solution in small bottles was renewed every 2 weeks andsamples were removed periodically washed with distilledwater and subsequently dried in vacuum to a constant weightbefore analysis

Theweight loss of the polymer films after degradationwasevaluated with residual weight () which was defined by

Residual Weight () = (119908119905

1199080

) times 100 (1)

where 1199080and 119908

119905were the initial weight and the weight at

time 119905 respectively 119908119905was obtained after drying the samples

at 50∘C under vacuum for 1 week

212 Scanning Electron Microscopy (SEM) The microscopicmorphology of the PHB and PUHE copolymers duringdegradation was also investigated with SEM (Hitachi X-650Japan) For the morphological measurements the sampleswere coated with gold to provide conductive surfaces

3 Results and Discussion

31 Synthesis of PHB-co-PEG Block Polyurethane (PUHE)and Its Oligomer As described in the experimental partdihydroxyl-terminated PHB oligomers (PHB-diols) wereobtained through transesterification between high molec-ular weight natural PHB and ethylene glycol using p-toluenesulfonic acid as catalyst

The synthetic schematic route of the controlled alcohol-ysis of bacterial PHB is shown in Scheme 1 As shown inScheme 1 the ethylene glycol broke the ester bond producingthe double-hydroxyl terminated product Since the alcoholy-sis proceeds according to a random cleavage mechanism themolecular weight of the degraded product decreases rapidlyat the initial stage As the reaction continues the decreasingrate will fall

PUHE was synthesized by the solution polymerizationbetween PHB-diol and polyethylene glycol at 80∘C andHDI was chain extender in the reaction system Becausethe reaction is moisture-sensitive azeotropic distillation wascarried out to remove any trace of water in the systembefore HDI was added in HDI was carefully dropped intothe stirring reaction mixture at 1 drop10min to keep thehomogeneous reactants and prevent the insoluble byproductsas less as possible And the reaction proceeded in dried12-dichloroethane under a nitrogen atmosphere The targetpolyurethane PUHE was isolated and purified from thereaction mixture by repeated precipitation from a mixture ofmethanol and diethyl ether The reaction process is shown inScheme 2 In the molecular chain of PUHE PHB acts as hardsegment andPEGacts as soft segment withHDI as a couplingagent andmany urethane groups (-NH-COO-) are across themolecular chain A number of hydrogen bonds can be formedbetween -NH and -CO- groups acting as crosslinking bondsfor the linear molecular chains to assemble into a physicalcrosslinked network which endows the synthetic segmentedcopolymer a certain degree of toughness

32 Effects of Alcoholysis on Molecular Weight and ThermalProperties of PHB-Diols DSC is a useful measurement forestimation of the thermal transition of PHB-diols Meltingtemperature (119879

119898) and melting enthalpy (Δ119867

119898) of PHB-diol

can be obtained from the DSC curves as listed in Table 1Thereaction conditions Mn MwMn and other characteristicsof the PHB-diols are also presented in Table 1The PHB-diolsare denoted as PHB I PHB II PHB III and PHB IV for


H O CH C C

O

m+ + HO H

x

O CH C C

O

C C

O O

mx

CH3

H2

OCH2CH2OH

OCH2CH2O OCH2CH2O

OCN(CH2)6NCO CH2CH2O

CH3

H2

NH(CH2)6NH

Scheme 2 Synthesis of PHB-co-PEG block polyurethane (PUHE)

Table 1 Reaction conditions thermal and molecular weight characteristics of PHB-diols

Sample Alcoholysistime (h)

Mna

(times103 gmol)Mwa

(times103 gmol) MwMna119879119898

b (∘C) Δ119867119898

c (Jg) 119883119888

d Hydroxyl content(molar ratio)

PHB mdash 70 175 7186 490PHB I 1 217 347 159 1695 7174 489 199PHB II 5 698 121 174 1564 6857 468 136PHB III 6 618 972 157 1562 559 381 197PHB IV 8 442 733 166 1583 3438 235 192aMn Mw and polydispersity (MwMn) were determined by GPC (in gmol)bMelt point 119879119898 was from the DSC second heating runcMelting enthalpy was calculated from the endothermal peak in the DSC second heating rundCrystallinity calculated from the melting enthalpy in DSC second heating run Reference value of 100 crystallized PHB was Δ119867119898

120579= 146 Jg and 119883119888 =

100 times Δ119867119898Δ119867119898120579

PHB-diols with Mn of 21700 gmol 6980 gmol 6180 gmoland 4420 gmol prepared with various alcoholysis timerespectively It is noticeable that melting temperature andmelting enthalpies of PHB-diol decrease with the increase ofthe alcoholysis time It can be observed from Table 1 that the119879119898values of PHB-diols are directly related to the molecular

weight 119879119898of PHB-diol decreases by approximately 17∘C as

Mn decreases to 4420 gmol compared with precursor Therelatively high enthalpy of melting (Δ119867

119898) of the PHB-diols

indicates a high degree of crystallinity Based on the reportedvalue for the heat ofmelting of 100 crystalline PHB (146 Jg)[24] the degree of crystallinity for our samples was calculatedto be in the range of 235sim489 The lowered 119883

119888and 119879

119898of

PHB-diols compared to the precursors might be due to thepresence of ethylene glycol restricting the crystallization ofthe PHB

GPC is employed to determine the molecular weight andits distribution of PHB-diol The results are listed in Table 1It shows that the molecular weight of PHB-diol declinedquickly in the initial 5 h of alcoholysis reaction The Mnwas 217 times 103 gmol after 1 h alcoholysis When the reactiontime reached 5 h Mn was decreased by almost two ordersof magnitude compared with precursor reduced to 698 times103 gmol The decreasing rate of Mn slowed down when thereaction time exceeds 5 h All of PHB-diols show the narrowmolecular weight distribution despite undergoing differentreaction time (MwMn = 159sim174)

33 The Hydroxyl Contents in PHB Oligomers HigherNCOOH molar ratio in PUHE yields a high crosslinkingdegree resulting in rigid and brittle copolymer which makes

it difficult to the subsequent processes In this study nonaque-ous titration was employed to quantify the terminal hydroxylcontentThemolar ratio of PHB to PEGwas fixed at 1 1 in thesynthesis of PUHEThe amount ofHDIwas equivalent to thatof the reactive hydroxyl groups in the solution The hydroxylcontents in PHB-diol range from 136 to 199 determined bynonaqueous titration as shown in Table 1 which are in goodagreement with the calculated values

34 Characterization of Infrared Spectroscopy To investi-gate the compositions of as-prepared PHB-diol and PUHEelastomer FTIR is employed as shown in Figure 1 It isconfirmed by the band at 3435 cmminus1 corresponding to thehydrogen-bonded hydroxyl groups with alkoxy and thisband appears in the spectrum of PHB-diol while it appearsvery weak in that of original PHB As shown in Figure 1(c)the band near 3435 cmminus1 attributed to bonded -NH-groupsis overlapped with hydrogen-bonded hydroxyl groups withPEG and absorption peak becomes more distinct The bandnear 1723 cmminus1 corresponds to C=O stretching modes Theamide absorption at 1546 cmminus1 is the characteristic peak ofurethane which demonstrates the copolymerization betweenPHB and PEG

35 Characterization of Proton Nuclear Magnetic ResonanceSpectra (1H NMR) The NMR spectra of PHB-diols areshown in Figure 2 1H NMR (CDCl

3) 521ndash529 (due to

protons b) 421ndash423 (due to protons b1015840 and e) 381 (dueto protons d) 241ndash266 (due to protons a and a1015840) 122ndash132(due to protons c) and 116 (due to protons c1015840) This provedthat the hydroxyl-terminated PHB oligomers were producedsuccessfully


Table 2 Compositions and molecular weights of resulting PUHE copolymers

Sample 119865PHB () 119865PEG () 119865HDI () Molecular weightMn (gmol) Mw (gmol) PDI

PUHE-1 873 114 13 27635 40585 147PUHE-2 848 137 15 18237 29201 160PUHE-3 806 165 29 17370 26382 152

3500 3000 2500 2000 1500

1546

3435c

b

a

Wavenumber (cmminus1)

Figure 1 FTIR spectra of (a) PHB (b) PHB-diol and (c) PUHE

5 4 3 2 1

O OOH

m

O

HO

O

c

b a

e

d

425 420 385 380

d

(ppm)

b

d

c

b998400 e

b998400 e

a998400b998400

c998400

CH3CH3

a a998400

c998400

Figure 2 1H NMR spectra of PHB-diol

The 1H NMR (CDCl3) spectra of polyurethanes (PUHE)

are shown in Figure 3 521ndash529 (due to protons b) 493 (dueto protons a and a1015840) 420 (due to protons f and f1015840) 126 (due toprotons c) 244ndash263 (due to protons d) 317 (due to protonsg and g1015840) 366 (due to protons e e1015840 f and f 1015840) 148 (due toprotons h and h1015840) and 132 (due to protons i and i1015840)

36 Compositions and Molecular Weights of PUHE Copoly-mers In order to overcome the brittleness of PHB basedblock copolymer a short PHB segment in PUHE is requiredto reduce the crystallinity Herein PHB content in the blockcopolymers could be tuned by adjusting the molar ratio ofPHB-diol and PEG Three series of PUHE were synthesizedfrom PEG with Mn of 1500 gmol and PHB-diols with Mn of6180 gmol respectivelyThe compositions of PUHE could becalculated by comparing the integration value of resonancesat 120575 = 525 ppm assigned to methine in repeating units ofPHB block and that at 120575 = 366 ppm assigned to methylene

6 5 4 3 2 1

H O OO H

N NHm

b d e

f

O

Oc

a

x

g

h

i

O

O O

H

d

27 26 25 2453

b

(ppm)

b d

c

a a998400 f f 998400

e e998400

g g998400

h h998400 i i998400

CH3

e998400 a998400 h998400 f 998400

i998400 g998400

Figure 3 1H NMR spectra of polyurethane PUHE

Elution time (min)

cba

a998400

b998400

c998400

Figure 4 GPC diagrams of PHB-diols (a b c) and PUHE copoly-mers (a1015840 b1015840 c1015840) (a) Reaction time 8 h (b) reaction time 6 h (c)reaction time 5 h

in repeating units of PEG block The compositions of thepolymers are presented in Table 2 As is shown from Table 2the molecular weight of PUHE gradually declines with thedecrease of PHB-diol content

37 Characterization of Gel Permeation ChromatographyGPC chromatograph was taken to measure the molecularweight of PHB-diols and block copolymers Figure 4 shows


150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)

Figure 5 TGA curves of PHB-diol (a) and PUHE (b)

100 200 300 400 500

ab

Temperature (∘C)

Figure 6 DTG curves of PHB-diol (a) and PUHE (b)

the typical GPC curves of the block copolymers as com-pared with those of PHB-diols In GPC chromatographthe unimodal peaks of the purified polyurethanes PUHEwith nonoverlapping compared with those of correspondingprecursors indicate that a complete reaction took place withno unreacted precursor remaining All the polyurethanesPUHE showed narrow molecular weight distribution withpolydispersity ranging from 147 to 160 and high molecularweight with Mn from 173 times 104 gmol to 276 times 104 gmol Itshows that the peaks of block copolymers are shifted towarda high molecular weight region compared with that of theoriginal PHB-diols Together with the results of FTIR and1H NMR this confirms the successful synthesis of PUHE byPHB-diol and PEG via the solution polymerization

38 Thermal Properties Thermal stability of polymers playsa crucial role in the determination of their working temper-ature and the application conditions Figures 5 and 6 show

0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()

PUHE-25PUHE-33PUHE-50

Figure 7 Typical stress-strain curves of PUHE with differentcomposition

the typical TGA curves and the corresponding differentialthermogravimetric (DTG) curves of PHB-diol and PUHErespectivelyThe degradation of pure PHB-diol starts at 128∘Cand completes at 227∘C (Figure 5(a)) PUHE (Figure 5(b))undergoes two-step thermal degradation with the first stepoccurring between 230 and 290∘C and the second stepsbetween 290 and 400∘C It has been reported that the firstweight loss is assigned to the degradation of PHB hard seg-ments as a consequence of its relatively low thermal stabilitywhereas the second weight loss is dominated by the thermaldegradation of the PEG soft segments [42] DTG curvesshow that the degradation velocity of PHB chain segment incopolymer was obviously lower than PHB-diol It indicatesthat block-bonding between PHB-diol and PEG increases thethermal stability of PHB-diol This is in accordance with theresult of other PHB segmented copolymers

39 Mechanics Performance Testing Toughness is an impor-tant mechanical property for engineering polymers Figure 7gives the stress-strain curves of PUHE with different compo-sitionThe PUHE with different compositions are denoted asPUHE-25 PUHE-33 and PUHE-50 for PHB content with 2533 and 50 respectively

As shown in Figure 7 PUHE-50 with a PEG contentof 50 is brittle with a yield strength of 1292MPa andelongation at break of only about 236 When PEG contentincreases to 67 the breaking strength of PUHE reaches ashigh as 20MPa with the elongation at break being about210 The elongation at break and tensile strength of PUHEare markedly increased which is mainly attributed to theregularity of PHB structure being broken and the crystallinitybeing declined A certain amount of PEG plays internalplasticization role in the copolymer At the same time it isfound that the fracture characteristic of PUHE is obviouslytransformed from brittleness into ductility with a gradual


0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)

Period of hydrolysis (weeks)

Figure 8 Residual weight () of the PUHE films after degradation

Week 0 Week 12Week 4

Figure 9 SEM micrographs of PUHE-50 film at various stages of degradation at pH 74

increase in PEG content When polyethylene glycol contentincreases to 75 the matrix gives priority to polyethyleneglycol and the mechanical strength and elongation at breakare substantially decreased

310 Degradation Investigation A degradation study wascarried out using the solution-cast films submerged in phos-phate buffer solution at 37∘C The residual weights of theselected polymers prior to and after hydrolysis were studied(Figure 8) A linear decrease in the residual weight of thePUHE films was observed from week 2 onwards with a finalweight loss of about 10sim15 by 12 weeks of degradationCompared with degradation profiles of samples PUHE-50and PUHE-25 the former showed a slower degradation ratein the investigated period Polymer PUHE-25 containing75wt PEG in hydrolytic degradation recorded the mostdramatic decrease in physical weight of the polymer filmrevealing that the strong polymer hydrophilicity was in favorof faster degradation [43] As expected the copolymerserosion could be controlled by adjusting the PHBPEG ratios

311 SEM Analysis of Film after Hydrolysis The morphologyof PUHE films degraded in PBS was observed by SEM It wasshown that degradation occurred gradually from the surfaceto the inside A surface morphology change accompaniedwith structural deterioration of the film and an increase inporosity and cracks were observed throughout the courseof degradation lasting over 12 weeks A PUHE-50 showedgreater hydrolytic stability to degradation probably due tothe higher PHB content in the copolymer preventing theentry of the hydroxyl and water molecules (Figure 9) [40]A PUHE-25 film presented with more extensive cracks andnetwork structures in progressiveweeks suggesting extensivedegradation (Figure 10)

4 Conclusion

The telechelic PHB with hydroxyl groups at both chainends was successfully prepared by alcoholysis of PHB in thepresence of p-toluenesulfonic acid as catalyst The molecularweight was decreased by almost two orders of magnitude of


Week 12Week 4Week 0


PHB DSC results show that the melting temperature (119879119898)

decreases with the molecular weight of PHB decreasingThe hydroxyl contents in PHB-diol are ranging from 136to 199 (the molar ratio) as determined by nonaqueoustitration in good agreement with theoretical value A seriesof novel biodegradable amphiphilic polyurethanes PUHEhasbeen successfully synthesized through the coupling reac-tion between hydroxyl groups in PHB-diol and PEG Thechemical compositions have been investigated by 1H NMRand FTIR GPC analysis confirmed the complete reactionproducing polyurethanes with relatively narrow molecu-lar weight distributions TGA curves indicate that block-bonding between PHB-diol and PEG increases the thermalstability of precursor Tensile strength and elongation at breakof PUHE could reach as high as 20MPa and 210 when thecontent of PHB in PUHE decreases to 33 It is shown thathydrolytic degradation of PUHE occurred gradually fromthe surface to the inside PUHE containing 75wt PEG inhydrolytic degradation recorded the most dramatic decreasein physical weight of the polymer filmThe in vitro hydrolysisof PUHE could be controlled by adjusting the PHBPEGratios These properties indicate that PUHE can be used asa biodegradable thermoplastic elastomer

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The authors gratefully acknowledge the financial supportfrom the National Natural Science Foundation of China (no81271008) (Grant no 02-05-23-SF0003)

References

[1] S Hiki MMiyamoto and Y Kimura ldquoSynthesis and character-ization of hydroxy-terminated [RS]-poly(3-hydroxybutyrate)and its utilization to block copolymerization with l-lactide toobtain a biodegradable thermoplastic elastomerrdquo Polymer vol41 no 20 pp 7369ndash7379 2000

[2] G-Q Chen and Q Wu ldquoThe application of polyhydroxyalka-noates as tissue engineeringmaterialsrdquo Biomaterials vol 26 no33 pp 6565ndash6578 2005

[3] E Hablot S Dharmalingam D G Hayes L C WadsworthC Blazy and R Narayan ldquoEffect of simulated weathering onphysicochemical properties and inherent biodegradation ofPLAPHA nonwoven mulchesrdquo Journal of Polymers and theEnvironment vol 22 no 4 pp 417ndash429 2014

[4] J J Bai J Dai and G Li ldquoElectrospun composites ofPHBVpearl powder for bone repairingrdquo Progress in NaturalScience Materials International vol 25 no 4 pp 327ndash333 2015

[5] N Le Moigne M Sauceau M Benyakhlef et al ldquoFoam-ing of poly(3-hydroxybutyrate-co-3-hydroxyvalerate)organo-clays nano-biocomposites by a continuous supercritical CO

2

assisted extrusion processrdquo European Polymer Journal vol 61no 1 pp 157ndash171 2014

[6] A A OlrsquoKhov A L Iordanskii and T P Danko ldquoMorphologyof poly(3-hydroxybutyrate)-polyvinyl alcohol extrusion filmsrdquoJournal of Polymer Engineering vol 35 no 8 pp 765ndash771 2015

[7] J P Reddy S AhankariMMisra andAMohanty ldquoA new classof injection moulded structural biocomposites from PHBVbioplastic and carbon fibrerdquo Macromolecular Materials andEngineering vol 298 no 7 pp 789ndash795 2013

[8] A N Hayati H R Rezaie and S M Hosseinalipour ldquoPrepara-tion of poly(3-hydroxybutyrate)nano-hydroxyapatite compos-ite scaffolds for bone tissue engineeringrdquoMaterials Letters vol65 no 4 pp 736ndash739 2011

[9] S G Karpova A L Iordanskii M V Motyakin et alldquoStructural-dynamic characteristics of matrices based on ultra-thin poly(3-hydroxybutyrate) fibers prepared via electrospin-ningrdquo Polymer Science Series A vol 57 no 2 pp 131ndash138 2015

[10] L Z Li W Huang B J Wang W F Wei Q Guand P Chen ldquoProperties and structure of polylactidepoly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PLAPHBV) blendfibersrdquo Polymer vol 68 pp 183ndash194 2015

[11] S Zhang J Y Xin L L Chen and Y Wang ldquoBiosynthesisof poly-120573- hydroxybutyrate as new material of food packingby various strains of methanotrophs from methanerdquo AdvancedMaterials Research vol 183ndash185 pp 924ndash928 2011

[12] S F Williams S Rizk and D P Martin ldquoPoly-4-hydroxybuty-rate (P4HB) a new generation of resorbablemedical devices fortissue repair and regenerationrdquoBiomedizinische Technik vol 58no 5 pp 439ndash452 2013


[13] G C Bazzo E Lemos-Senna and A T N Pires ldquoPoly(3-hydroxybutyrate)chitosanketoprofen or piroxicam compositemicroparticles preparation and controlled drug release evalua-tionrdquo Carbohydrate Polymers vol 77 no 4 pp 839ndash844 2009

[14] J Bidone A P P Melo G C Bazzo et al ldquoPreparationand characterization of ibuprofen-loaded microspheres con-sisting of poly(3-hydroxybutyrate) and methoxy poly (ethyleneglycol)-b-poly (DL-lactide) blends or poly(3-hydroxybutyrate)and gelatin composites for controlled drug releaserdquo MaterialsScience and Engineering C vol 29 no 2 pp 588ndash593 2009

[15] C B Packhaeuser J Schnieders C G Oster and T Kissel ldquoInsitu forming parenteral drug delivery systems an overviewrdquoEuropean Journal of Pharmaceutics and Biopharmaceutics vol58 no 2 pp 445ndash455 2004

[16] J Babinot E Renard and V Langlois ldquoControlled synthesisof well defined poly(3-hydroxyalkanoate)s-based amphiphilicdiblock copolymers using click chemistryrdquo MacromolecularChemistry and Physics vol 212 no 3 pp 278ndash285 2011

[17] Q Liu C Wu H Zhang and B Deng ldquoBlends of polylactideand poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with lowcontent of hydroxyvalerate unit morphology structure andpropertyrdquo Journal of Applied Polymer Science vol 132 no 42Article ID 42689 2015

[18] K Huang B P Lee D R Ingram and P B Messersmith ldquoSyn-thesis and characterization of self-assembling block copolymerscontaining bioadhesive end groupsrdquo Biomacromolecules vol 3no 2 pp 397ndash406 2002

[19] A Daga A Muraglia R Quarto R Cancedda and GCorte ldquoEnhanced engraftment of EPO-transduced humanbone marrow stromal cells transplanted in a 3D matrix in non-conditioned NODSCID micerdquo GeneTherapy vol 9 no 14 pp915ndash921 2002

[20] H D Qiu D D Li X Chen et al ldquoSynthesis characterizationsand biocompatibility of block poly(ester-urethane)s based onbiodegradable poly(3-hydroxybutyrate-co-4-hydroxybutyrate)(P34HB) and poly(120576-caprolactone)rdquo Journal of BiomedicalMaterials Research Part A vol 101 no 1 pp 75ndash86 2013

[21] J Heller J Barr S Y Ng et al ldquoDevelopment and applicationsof injectable poly(ortho esters) for pain control and periodontaltreatmentrdquo Biomaterials vol 23 no 22 pp 4397ndash4404 2002

[22] S P Khanna andAK Srivastava ldquoRecent advances inmicrobialpolyhydroxyalkanoatesrdquo Process Biochemistry vol 40 no 2 pp607ndash619 2005

[23] T X Su R Zhang J J Wang W Shao and Y Hu ldquoStudyon the poly(3-hydroxybutyrate-cominus4-hydroxybutyrate)-basedcomposites toughened by synthesized polyester polyurethaneelastomerrdquo Journal of Applied Polymer Science vol 132 no 44Article ID 42740 2015

[24] G R Saad and H Seliger ldquoBiodegradable copolymers based onbacterial Poly((R)-3-hydroxybutyrate) thermal and mechani-cal properties and biodegradation behaviourrdquo Polymer Degra-dation and Stability vol 83 no 1 pp 101ndash110 2004

[25] F Ravenelle and R H Marchessault ldquoOne-step synthesis ofamphiphilic diblock copolymers from bacterial poly([R]-3-hydroxybutyric acid)rdquo Biomacromolecules vol 3 no 5 pp1057ndash1064 2002

[26] Q Zhao G Cheng C Song Y Zeng J Tao and LZhang ldquoCrystallization behavior and biodegradation of poly(3-hydroxybutyrate) and poly(ethylene glycol) multiblock copoly-mersrdquo Polymer Degradation and Stability vol 91 no 6 pp1240ndash1246 2006

[27] G Y Li P Li H DQiu D D LiM Su andK T Xu ldquoSynthesischaracterizations and biocompatibility of alternating blockpolyurethanes based on P34HB and PPG-PEG-PPGrdquo Journalof BiomedicalMaterials Research Part A vol 98 no 1 pp 88ndash992011

[28] L Vojtova V Kupka J Zıdek J Wasserbauer P Sedlacek andJ Jancar ldquoBiodegradable polyhydroxybutyrate as a polyol forelastomeric polyurethanesrdquo Chemical Papers vol 66 no 9 pp869ndash874 2012

[29] Y Niu Y Zhu R Gao W Yu L Li and K Xu ldquoSynthesis char-acterizations and biocompatibility of novel block polyurethanesbased on poly(lactic acid) (PLA) and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB)rdquo Journal of Inorganic andOrganometallic Polymers andMaterials vol 25 no 1 pp 81ndash902015

[30] J Brzeska P Dacko K Gębarowska et al ldquoThe structureof novel polyurethanes containing synthetic poly[(RS)-3-hydroxybutyrate]rdquo Journal of Applied Polymer Science vol 125no 6 pp 4285ndash4291 2012

[31] W F Ou H D Qiu Z F Chen and K T Xu ldquoBiodegradableblock poly(ester-urethane)s based on poly(3-hydroxybutyrate-co-4-hydroxybutyrate) copolymersrdquo Biomaterials vol 32 no12 pp 3178ndash3188 2011

[32] Z F Chen S T Cheng and K T Xu ldquoBlock poly(ester-urethane)s based on poly(3-hydroxybutyrate-co-4-hydrox-ybutyrate) and poly(3-hydroxyhexanoate-co-3-hydroxyocta-noate)rdquo Biomaterials vol 30 no 12 pp 2219ndash2230 2009

[33] X J Loh X Wang H Li X Li and J Li ldquoCompositionalstudy and cytotoxicity of biodegradable poly(ester urethane)sconsisting of poly[(R)-3-hydroxybutyrate] and poly(ethyleneglycol)rdquo Materials Science and Engineering C vol 27 no 2 pp267ndash273 2007

[34] X J Loh S H Goh and J Li ldquoHydrolytic degradation andprotein release studies of thermogelling polyurethane copoly-mers consisting of poly[(R)-3-hydroxybutyrate] poly(ethyleneglycol) and poly(propylene glycol)rdquo Biomaterials vol 28 no28 pp 4113ndash4123 2007

[35] SH S Siqueira R C LDutra andM FDiniz ldquoDeterminationof NCO contents in polyurethane adhesives using MIRNIRspectroscopiesrdquo Polimeros vol 18 no 1 pp 57ndash62 2008

[36] G R Saad Y J Lee and H Seliger ldquoSynthesis and thermalproperties of biodegradable poly(ester-urethane)s based onchemo-synthetic poly[(RS)-3-hydroxybutyrate]rdquoMacromolec-ular Bioscience vol 1 no 3 pp 91ndash99 2001

[37] T DHirt P Neuenschwander andUW Suter ldquoTelechelic diolsfrom poly[(R)-3-hydroxybutyric acid] and poly[(R)-3-hydroxybutyric acid]-co-[(R)-3-hydroxyvaleric acid]rdquo MacromolecularChemistry and Physics vol 197 no 5 pp 1609ndash1614 1996

[38] T D Hirt P Neuenschwander and U W SuterldquoSynthesis of degradable biocompatible and tough block-copolyesterurethanesrdquo Macromolecular Chemistry and Physicsvol 197 no 12 pp 4253ndash4268 1996

[39] X Li X J Loh K Wang C B He and J Li ldquoPoly(esterurethane)s consisting of poly[(R)-3-hydroxybutyrate] andpoly(ethylene glycol) as candidate biomaterials characteriza-tion andmechanical property studyrdquo Biomacromolecules vol 6no 5 pp 2740ndash2747 2005

[40] X J Loh K K Tan X Li and J Li ldquoThe in vitrohydrolysis of poly(ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] and poly(ethylene glycol)rdquo Biomaterials vol27 no 9 pp 1841ndash1850 2006


[41] X M Deng and J Y Hao ldquoSynthesis and characterization ofpoly(3-hydroxybutyrate) macromer of bacterial originrdquo Euro-pean Polymer Journal vol 37 no 1 pp 211ndash214 2001

[42] H FNaguibM S AAziz andG R Saad ldquoSynthesismorphol-ogy and thermal properties of polyurethanes nanocompositesbased on poly(3-hydroxybutyrate) and organoclayrdquo Journal ofIndustrial and Engineering Chemistry vol 19 no 1 pp 56ndash622013

[43] L J R Foster and B J Tighe ldquoCentrifugally spun polyhydrox-ybutyrate fibres accelerated hydrolytic degradation studiesrdquoPolymer Degradation and Stability vol 87 no 1 pp 1ndash10 2005

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


analysis method [35] However few researches focus on themeasurement of the content of free hydroxyl groups

PHB oligomers terminated with free hydroxyl groupsmay be produced by the transesterification of alkane-diolswith high molecular weight of PHB Saad et al syn-thesized macrodiols by transesterification of PHB in 12-dichloroethane with 110-decanediol and p-toluenesulfonateas catalysts [36] Hirt et al obtained telechelic dihydroxy-PHB by glycolysis of bacterial derived high molecular weightdihydroxy-PHB [37] However it is still a challenge toquantify the terminal hydroxyl content in PHB oligomersand to study its effect on properties of the correspondingpolyurethanes

Herein a promising polyurethane elastomer was syn-thesized by solution polymerization of PHB-diol andpoly(ethylene glycol) with a coupling agent of 16-hexameth-ylene diisocyanate (HDI) While the PHB-diol was preparedvia the transesterification of PHB with ethylene glycolthe hydroxyl content of PHB-diol was quantified by thetitration of acetic anhydride-pyridine Then chemicalcompositions were investigated with GPC 1H NMR andFTIR in detail The relationship between block structureand degradation profiles was performed Furthermorethe thermal and mechanical properties of as-preparedPUHE were studied to exploit its potential application asthermoplastic biodegradable elastomer

2 Experimental

21 Materials Polyhydroxybutyrate (PHB Mn of 70 times 105 plusmn10gmol) was purchased from Zhejiang Tianan Tech CoLtd (Zhejiang China) All PHB samples were purified by dis-solving in chloroform followed by filtration and precipitationin ether before use 16-Hexamethylene diisocyanate (HDI)(99 Sigma USA) was used without further purificationChloroform p-toluenesulfonic acid (PTSA) and ethyleneglycol were all from Kemiou Reagent Development Center(Tianjin China) and were used as received

22 Preparation of Dihydroxy-Terminated PHB Oligomers(PHB-Diol) Dihydroxyl-terminated PHB oligomers (PHB-diol) were prepared by transesterification between thepurified PHB materials and ethylene glycol using p-toluenesulfonic acid as catalyst [38ndash40] Typically purifiedPHB (10 g) was dissolved in 100mL of chloroform andrefluxed in nitrogen Subsequently p-toluenesulfonic acid(48 g) and ethylene glycol (20 g) were added The reactiontemperature was controlled at 60∘CThe reaction was carriedout under reflux for 6sim10 h depending on required molecularweight of PHB-diol The resultant solution was washed withdistilled water for 3 times concentrated and dried underreduced pressure

23 Hydroxyl Titration Nonaqueous titration was employedto determine the hydroxyl content in PHB oligomers [41]010 g of PHB oligomers was added to 5mL solution of aceticanhydride in pyridine (20 vv) and then heated up to 100∘Cfor acetylation of 1 h After that 1mL H

2O was added to the

reaction mixture that was left alone for another 05 h Thesolution of KOH in methanol (20 gL) was used to titrate thereactionmixture inwhich several drops of thymol bluecresolred solution (31 04wv) were added as the indicator Theblank titrating experiment without PHB oligomers followedthe same procedure as above

24 PHB-PEG Urethane Preparation A series of polyure-thanes (PUHE) were synthesized by different molar ratiosof polyethylene glycol (Mn = 1500 gmol) and PHB-diolswith different molecular weight 18 g of PHB-diol andpolyethylene glycol were dried in a 25mL two-necked tubeat 40∘C under vacuum overnight Then 20mL of anhydrous12-dichloroethane was added to the flask and any traceof water in the system was removed through azeotropicdistillation with only 5mL of 12-dichloroethane being left inthe flask When the flask was cooled down to 75∘C 020 g ofHDI (12 times 10minus3mol) and two drops of tin octoate (8 times 10minus3 g)were added sequentially The reaction mixture was stirredat 80∘C under nitrogen atmosphere for 48 h The resultantcopolymer was precipitated in diethyl ether and furtherpurified in a mixture of methanol and diethyl ether

25 1H NMR Spectrum The chemical structure and mon-omer composition were determined by 1H NMR usinga ADVANCEIII 400MHz NMR spectrometer The NMRspectrum was obtained at room temperature in CDCl

3

(20mgmL) with tetramethylsilane (TMS) as an internalstandard

26 Fourier Transform Infrared (FTIR) Spectroscopy Fouriertransform infrared (FTIR) spectroscopy was measured by aBio-Rad FTS135 (Bio-Rad USA) spectrophotometer PHB-co-PEG block polyurethane (PUHE) was dissolved in chlo-roform coated on a KBr pellet and dried before test

27 Gel Permeation Chromatography Average molecularweights were determined by gel permeation chromatography(GPC) using chloroform as an eluent at a flow rate of10mLmin in Waters 1525 pump with a combination of fourStyragel columns series (Styragel HR 5mm) and equippedwith a 2414 differential refractive index detector and UVdetector (Agilent Technologies PL-GPC 50 Integrated GPCSystem USA) The sample concentration was 2mgmL and150 120583L of the injection volume The calibration curve wasobtained using polystyrene standards (Shodex Japan) Allsamples were carried out with 64 scans at a resolution of2 cmminus1 at room temperature

28 Differential Scanning Calorimetry (DSC) MeasurementsDifferential scanning calorimetry (DSC) measurements wereperformed on TA Instruments Q100 differential scanningcalorimeter equipped with an auto-cool accessory and cal-ibrated using indium The following protocol was used foreach sample heating from room temperature to 150∘C at aheating rate of 5∘Cmin holding at 150∘C for 3min coolingfrom 150 to minus50∘C at a heating rate of 5∘Cmin beingisothermal at minus50∘C for 3min and finally reheating from minus50


H O CH C C OH +

O

x

H O CH C C

O

m

Cat

CH3

H2

H2

OCH2CH2OH

CH3

HOCH2CH2OH











1199080

) times 100 (1)

where 1199080and 119908











119898) of PHB-diol



H O CH C C

O

m+ + HO H

x

O CH C C

O

C C

O O

mx

CH3

H2

OCH2CH2OH

OCH2CH2O OCH2CH2O


CH3

H2

NH(CH2)6NH




Mna

(times103 gmol)Mwa


b (∘C) Δ119867119898

c (Jg) 119883119888



120579= 146 Jg and 119883119888 =

100 times Δ119867119898Δ119867119898120579






119888and 119879

119898of












PUHE-1 873 114 13 27635 40585 147PUHE-2 848 137 15 18237 29201 160PUHE-3 806 165 29 17370 26382 152

3500 3000 2500 2000 1500

1546

3435c

b

a



5 4 3 2 1

O OOH

m

O

HO

O

c

b a

e

d

425 420 385 380

d

(ppm)

b

d

c

b998400 e

b998400 e

a998400b998400

c998400

CH3CH3

a a998400

c998400





6 5 4 3 2 1

H O OO H

N NHm

b d e

f

O

Oc

a

x

g

h

i

O

O O

H

d

27 26 25 2453

b

(ppm)

b d

c

a a998400 f f 998400

e e998400

g g998400

h h998400 i i998400

CH3

e998400 a998400 h998400 f 998400

i998400 g998400


Elution time (min)

cba

a998400

b998400

c998400





150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)


100 200 300 400 500

ab

Temperature (∘C)




0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()







0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


H O CH C C OH +

O

x

H O CH C C

O

m

Cat

CH3

H2

H2

OCH2CH2OH

CH3

HOCH2CH2OH











1199080

) times 100 (1)

where 1199080and 119908











119898) of PHB-diol



H O CH C C

O

m+ + HO H

x

O CH C C

O

C C

O O

mx

CH3

H2

OCH2CH2OH

OCH2CH2O OCH2CH2O


CH3

H2

NH(CH2)6NH




Mna

(times103 gmol)Mwa


b (∘C) Δ119867119898

c (Jg) 119883119888



120579= 146 Jg and 119883119888 =

100 times Δ119867119898Δ119867119898120579






119888and 119879

119898of












PUHE-1 873 114 13 27635 40585 147PUHE-2 848 137 15 18237 29201 160PUHE-3 806 165 29 17370 26382 152

3500 3000 2500 2000 1500

1546

3435c

b

a



5 4 3 2 1

O OOH

m

O

HO

O

c

b a

e

d

425 420 385 380

d

(ppm)

b

d

c

b998400 e

b998400 e

a998400b998400

c998400

CH3CH3

a a998400

c998400





6 5 4 3 2 1

H O OO H

N NHm

b d e

f

O

Oc

a

x

g

h

i

O

O O

H

d

27 26 25 2453

b

(ppm)

b d

c

a a998400 f f 998400

e e998400

g g998400

h h998400 i i998400

CH3

e998400 a998400 h998400 f 998400

i998400 g998400


Elution time (min)

cba

a998400

b998400

c998400





150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)


100 200 300 400 500

ab

Temperature (∘C)




0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()







0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


H O CH C C

O

m+ + HO H

x

O CH C C

O

C C

O O

mx

CH3

H2

OCH2CH2OH

OCH2CH2O OCH2CH2O


CH3

H2

NH(CH2)6NH




Mna

(times103 gmol)Mwa


b (∘C) Δ119867119898

c (Jg) 119883119888



120579= 146 Jg and 119883119888 =

100 times Δ119867119898Δ119867119898120579






119888and 119879

119898of












PUHE-1 873 114 13 27635 40585 147PUHE-2 848 137 15 18237 29201 160PUHE-3 806 165 29 17370 26382 152

3500 3000 2500 2000 1500

1546

3435c

b

a



5 4 3 2 1

O OOH

m

O

HO

O

c

b a

e

d

425 420 385 380

d

(ppm)

b

d

c

b998400 e

b998400 e

a998400b998400

c998400

CH3CH3

a a998400

c998400





6 5 4 3 2 1

H O OO H

N NHm

b d e

f

O

Oc

a

x

g

h

i

O

O O

H

d

27 26 25 2453

b

(ppm)

b d

c

a a998400 f f 998400

e e998400

g g998400

h h998400 i i998400

CH3

e998400 a998400 h998400 f 998400

i998400 g998400


Elution time (min)

cba

a998400

b998400

c998400





150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)


100 200 300 400 500

ab

Temperature (∘C)




0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()







0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of




PUHE-1 873 114 13 27635 40585 147PUHE-2 848 137 15 18237 29201 160PUHE-3 806 165 29 17370 26382 152

3500 3000 2500 2000 1500

1546

3435c

b

a



5 4 3 2 1

O OOH

m

O

HO

O

c

b a

e

d

425 420 385 380

d

(ppm)

b

d

c

b998400 e

b998400 e

a998400b998400

c998400

CH3CH3

a a998400

c998400





6 5 4 3 2 1

H O OO H

N NHm

b d e

f

O

Oc

a

x

g

h

i

O

O O

H

d

27 26 25 2453

b

(ppm)

b d

c

a a998400 f f 998400

e e998400

g g998400

h h998400 i i998400

CH3

e998400 a998400 h998400 f 998400

i998400 g998400


Elution time (min)

cba

a998400

b998400

c998400





150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)


100 200 300 400 500

ab

Temperature (∘C)




0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()







0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


150 200 250 300 350 400 450

0

20

40

60

80

100

Resid

ual m

ass (

)

ab

Temperature (∘C)


100 200 300 400 500

ab

Temperature (∘C)




0 40 80 120 160 200

0

5

10

15

20

25

Stre

ss (M

Pa)

Strain ()







0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


0 2 4 6 8 10 1270

75

80

85

90

95

100


Resid

ual w

eigh

t (

)








4 Conclusion



Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


Week 12Week 4Week 0




Competing Interests


Acknowledgments


References






2



















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article the synthesis of hydroxybutyrate-based...

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