synthesis and investigation of properties of thiacalix [4] arene‐based polyurethane elastomers

Research ArticleReceived: 15 June 2014 Revised: 26 August 2014 Accepted article published: 17 September 2014 Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/pi.4807

Synthesis and investigation of propertiesof thiacalix[4]arene-based polyurethaneelastomersAbbas Mohammadi,a Moslem Mansour Lakouraja* and Mehdi Barikanib

Abstract

A series of polyurethane elastomers (PUEs) derived from three thiacalix[4]arene derivatives (TC4As), namelyp-tert-butylthiacalix[4]arene, tetrasodium thiacalix[4]arenetetrasulfonate and thiacalix[4]arenetetrasulfonic acid, as a por-tion of chain extender in a mixture with glycerol were synthesized. The effects of the chemical structure of TC4As used aschain extenders on the various properties of the prepared PUEs were investigated and compared with PUE extended with onlyglycerol as chain extender using Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), ther-mogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy and a universal tensile tester. Moreover,the effect of the introduction of TC4As as a portion of chain extender on the hydrophobicity of the PUEs was also evaluated.DSC, FTIR spectroscopy and XRD revealed that the degree of phase separation and crystallinity in TC4A-based PUEs was muchhigher than that of the glycerol-based ones. Thus, it was concluded that the presence of TC4As in TC4A-based PUEs seems tofavour the formation of a more ordered structure due to an increase in the degree of phase separation. The TGA results alsoshowed that, with incorporation of TC4As into the polyurethane backbone, the thermal stability of PUEs was improved.© 2014 Society of Chemical Industry

Supporting information may be found in the online version of this article.

Keywords: polyurethane; elastomers; supramolecular structures; phase separation; morphology

INTRODUCTIONPolyurethanes are a category of highly significant engineeringpolymers with excellent properties and a broad range of com-mercial applications in many areas, such as coatings, adhesives,construction, automotive industries, medical devices, sealants andtextiles industries.1 –4 The urethane chemical bonds that they con-tain are synthesized through a polyaddition reaction between iso-cyanate and hydroxyl functional groups.5

Polyurethane elastomers (PUEs) are widely used because theycan show quite interesting properties with a varying chemicalstructure depending on starting materials. They can be preparedtypically by reacting together three chemical constituents: a diiso-cyanate, a long-chain diol (or polyol) and a small molecule as chainextender.6 PUEs are formed from soft segment and hard segmentsequences. The soft segment is derived from the polyol, while thehard segment is derived from diisocyanate and chain extender.7,8

Phase separation may occur in many polyurethanes due to the dif-ference in the chemical structure of soft and hard segments, andthe presence of physical and chemical crosslinks which can con-trol the morphology, crystallinity and thermomechanical proper-ties of PUEs.9 The degree of phase separation and domain forma-tion depend on the chemical structure of the diisocyanate, polyoland chain extender employed to produce the PUE.9,10 The spe-cific domain structure formed by microscopic phase separation, inwhich the hard segment acts as filler-like reinforcement for the softsegment, imparts elastomeric properties to PUEs.11 – 13

It is important to be able to modify PUEs using various methodssuch as the use of specific diisocyanate, polyol and chain extenderto provide new features as well as to improve the thermal andmechanical properties. The effect of various diisocyanates, polyolsand chain extenders on the properties of polyurethanes have beeninvestigated and well documented.9,11

Thiacalix[4]arenes (TC4As), as a new subclass of classic cal-ixarenes, are macrocyclic compounds possessing four phenolunits linked by four bridging sulfur atoms instead of four methy-lene bridging groups of the classic calix[4]arenes. The cavityshape, host–guest properties and self-assembling nature of thesemacrocycles make them attractive candidates for wide applica-tions in the fields of supramolecular chemistry and moleculardetection and as potential adsorbents for heavy metals and dyemolecules.14 – 16 Thus, the incorporation of the thiacalix[n]arenederivatives into PUEs makes them potential candidates for theadsorption of industrial effluents such as heavy metals and dyes.Moreover, TC4A derivatives, because they contain four aromaticrings, are highly thermally stable, so that excellent thermal stabil-ity of polymers derived from these compounds can be expected.

∗ Correspondence to: Moslem Mansour Lakouraj E-mail: [email protected]

a Department of Organic Chemistry, Faculty of Chemistry, University ofMazanadaran, PO Box 47416, Babolsar, Iran

b Department of Polyurethane, Iran Polymers and Petrochemicals Institute, POBox 14965-115, Tehran, Iran

Polym Int (2014) www.soci.org © 2014 Society of Chemical Industry

www.soci.org A Mohammadi, MM Lakouraj, M Barikani

Up to now, although the classic calixarene-based polymers havebeen extensively studied,17 – 20 only a few attempts have beenundertaken to incorporate TC4As into various polymers.16,21,22

For instance, Tabakci et al.21 reported the synthesis of two newpolymeric TC4As by the reaction of some TC4A derivatives withterephthaloyl dichloride and chloromethylated polystyrene (Mer-rifield’s resin). Moreover, in our previous study, we describedthe preparation of p-tert-butylthiacalix[4]arene-embedded flexi-ble polyurethane foam as an efficient cationic dye adsorbent.

The objective of the investigation reported here was to syn-thesize and characterize a series of PUEs containing TC4As as aportion of the chain extender. Structural, morphological, thermaland mechanical properties of these prepared PUEs were studiedand compared to those of a glycerol-based PUE elastomer. Tothe best of our knowledge, no investigation has been reportedof the preparation of TC4A-based PUEs. For this purpose, a seriesof NCO-terminated polyurethanes was firstly prepared frompoly(𝜀-caprolactone) (PCL) and isophorone diisocyanate (IPDI)and extended with either glycerol or glycerol in a mixture withTC4As as chain extender. It was thought that the presence ofTC4As in the polyurethane backbone might lead to elastomericmaterials with desired thermal and mechanical properties. Inaddition, considering the excellent intelligent structural andhost–guest properties of TC4As, the produced PUEs could begood candidates for application as ion-exchange polyurethanemembranes. The synthesized PUEs were characterized using spec-troscopic methods, and their thermal stability and morphologicaland mechanical properties were also investigated.

EXPERIMENTALMaterials and methodsPCL diol with a molecular weight of 2000 g mol−1 was obtainedfrom Solvay Chemicals Co. IPDI and glycerol were purchased fromMerck. Polyol and chain extenders were dried at 60 ∘C under vac-uum for 6 h before use to ensure the removal of all air bubblesand water vapour that may otherwise interfere with the isocyanatereactions. Other chemicals used in the synthesis of TC4A deriva-tives were as follows: sulfur, p-tert-butylphenol, sodium hydroxide,tetraethylene glycol dimethyl ether (tetraglyme) and sulfuric acid.All chemicals used in this study were of analytical grade.

Synthesis of p-tert-butylthiacalix[4]arene (p-BTC4A)p-BTC4A was prepared based on an already reported method.14 Amixture of p-tert-butylphenol (8 g), elemental sulfur (S8; 3.5 g) andNaOH (1.20 g) in tetraethylene glycol dimethyl ether (2.5 mL) wasstirred under nitrogen. The stirred mixture was heated gradually to230 ∘C over a period of 4 h and kept at this temperature for further3 h under nitrogen atmosphere. The obtained dark red mixturewas cooled to room temperature and diluted with 35 mL of tolueneand 50 mL of 4 mol L−1 aqueous sulfuric acid solution, followed byaddition of 50 mL of diethyl ether with stirring to give a suspension.The precipitate was separated by filtration, recrystallized fromethanol and dried under vacuum at 100 ∘C for 2 h.

FTIR (KBr, cm−1): 3247 (O—H), 2958 (C—H), 1559 (C&dbond;C),1457 (C—H), 1196 (C—O), 690 (C—S). 1H NMR (400 MHz, CDCl3; 𝛿,ppm): 9.61 (s, 4H, OH), 7.56 (s, 8H, ArH), 1.24 (s, 36H, t-Bu). 13C NMR(400 MHz, CDCl3; 𝛿, ppm): 155.6, 144.7, 136.4, 120.5 (C, Ar), 34.2 (C,t-Bu), 31.2 (C, t-Bu).

Table 1. Sample codes and formations of prepared PUEs

Sample code Chain extenderBlock ratioa

(CAPA 225:IPDI:glycerol:TC4A)

PUE Glycerol 1:2:1:0CPUE1 Glycerol+ p-BTC4Ab 1:2:0.9:0.1CPUE2 Glycerol+ TSTC4ASc 1:2:0.9:0.1CPUE3 Glycerol+ TC4ASd 1:2:0.9:0.1

a Molar ratio of polyol:diisocyanate:chain extender.b p-tert-Butylthiacalix[4]arene.c Tetrasodium thiacalix[4]arenetetrasulfonate.d Thiacalix[4]arenetetrasulfonic acid.

Synthesis of tetrasodium thiacalix[4]arenetetrasulfonate(TSTC4AS)TSTC4AS was synthesized based on a literature method.23 First,1.5 g of p-BTC4A was mixed with 80 mL of sulfuric acid (98%),and the suspension was heated at 80 ∘C for 4 h with stirring. Thesolution was then cooled and poured into 500 mL of ice-coldwater, and the resulting purple solid was filtered. Then, 100 g ofsodium chloride was added to the filtrate to afford sodium salt.The obtained salt was dried and dissolved in 20 mL of water, andthen ethanol was added to form a milky precipitate. The whiteprecipitate was filtered and dried in a vacuum oven at 90 ∘C for 4 h.

FTIR (KBr, cm−1): 3449 (O—H), 1182 and 1138 (S&dbond;O). 1HNMR (400 MHz, D2O; 𝛿, ppm): H of —OH disappeared on exchangewith D2O, 7.91 (s, 8H, ArH). 13C NMR (400 MHz, D2O; 𝛿, ppm): 160.81,134.80, 134.28, 121. 49.

Synthesis of thiacalix[4]arenetetrasulfonic acid (TC4AS)TC4AS was synthesized based on the method of Shinkai et al.24

FTIR (KBr, cm−1): 3359 (O—H), 1047 and 1165 (S&dbond;O). 1H NMR(400 MHz, D2O; 𝛿, ppm): H of —OH disappeared on exchange withD2O, 7.71 (s, 8H, ArH). 13C NMR (400 MHz, D2O; 𝛿, ppm): 151.3,135.80, 128. 49.

Synthesis of PUEsIn this investigation, NCO-terminated polyurethane prepolymerwas synthesized according to a recommended procedure.25

For this purpose, appropriate amounts of IPDI and previouslydegassed PCL (with a mole ratio of 2:1) were reacted by stepgrowth polymerization in a three-necked flask equipped withreflux condenser, mechanical stirrer, heating oil bath, droppingfunnel and nitrogen inlet and outlet. The prepolymer reaction wascarried out at 90 ∘C for 2 h to form polyurethane prepolymer. Toobtain the final PUEs in a chain extension step, prepolymers weremixed with suitable amounts of chain extenders which containedglycerol alone or glycerol in a mixture with TC4A derivatives withan equal ratio of NCO/OH at 90 ∘C for 30 min according to theformulations given in Table 1. Then the final viscous polymerswere poured into Teflon moulds and cured for 24 h in a hotair-circulating oven at 100 ∘C to form uniform sheets. The curedsamples were stored for a week at room temperature for furthercharacterization and measurements. The chemical routes for thesynthesis of PUEs are shown schematically in Fig. 1.

MeasurementsThe chemical structures of all the prepared PUEs were investi-gated using attenuated total reflection (ATR) Fourier transform

wileyonlinelibrary.com/journal/pi © 2014 Society of Chemical Industry Polym Int (2014)

Synthesis and investigation of properties of thiacalix www.soci.org

Figure 1. Schematic of chemical routes for synthesis of (a) PUE and (b) TC4A-based PUEs.

infrared (FTIR) spectroscopy. ATR-FTIR spectra were obtained withan EQUINOX55 (Bruker Co.). All spectra were collected with 32scans and at a resolution of 2 cm−1 over the wavenumber range500–4000 cm−1. 1H NMR and 13C NMR spectra of prepared TC4Aswere recorded with a 400 MHz Bruker Avance DRX NMR spectrom-eter. Deuterated dimethylsulfoxide (DMSO-d6) and D2O were usedas solvents, and tetramethylsilane served as an internal standard.

DSC was carried out with a Netzsch DSC 200. Accurately weigheddry material was placed in an aluminium cup and hermeticallysealed. Sample weights employed were 10–15 mg. The measure-ments were carried out from −100 to 200 ∘C under dry nitrogenatmosphere at a scanning rate of 10 ∘C min−1. The onset of theheat capacity change was chosen to represent the glass transi-tion temperature and melting point refers to the endotherm peaktemperature. TGA and derivative thermogravimetry (DTG) analysiswere performed with a thermal analysis system (PerkinElmer Pyris

1) under nitrogen atmosphere at a heating rate of 10 ∘C min−1 fromroom temperature to 600 ∘C.

XRD patterns of the prepared samples were obtained using aSiemens D-5000 X-ray diffractometer at room temperature withFe anode radiation (1.93604 Å) generated at 35 kV and 25 mA. TheXRD spectra were recorded with a scan rate of 1∘ min−1 for 2𝜃between 5∘ and 40∘.

The surface morphology of prepared samples was evaluatedusing SEM with a Vega-II from TESCAN Co. equipped with anenergy dispersive X-ray analysis (EDX) system (INCA, Oxford Instru-ments). Samples were fractured in liquid nitrogen and coveredwith a gold layer to obtain better conductivity.

The mechanical properties of the samples were also studied atroom temperature with an Instron model 1011 universal testingmachine. A 1 kN load cell was used and the crosshead speedwas 50 mm min−1. Pneumatic grips were required to hold the

Polym Int (2014) © 2014 Society of Chemical Industry wileyonlinelibrary.com/journal/pi


test specimens. Tensile tests were performed according to theASTM D 412 standard procedure. An average of three individualmeasurements was used for each sample.

Water contact angle measurements were also performed atroom temperature using a Kruss-G10 instrument. All the datapresented were averages of three measurements. Milli-Q waterwas used as a medium to measure the contact angle. For eachmeasurement, a water drop was placed on the sample surfaceand the drop shape was recorded with a high-frame-speed videocamera. Stills from the videos thus obtained were taken whichwere then used to measure the contact angle via the sessile dropmethod using a software program.

RESULTS AND DISCUSSIONThe main purpose of this research was to study the effect of incor-poration of TC4As as a portion of chain extender used in the back-bone of polyurethane. The structural, thermal, mechanical andmorphological characterization of the synthesized PUEs was car-ried out. Synthesis of TC4A-based PUEs was performed accord-ing to the synthetic route as presented in Fig. 1. The reaction ofone equivalent of polyol with two equivalents of IPDI leads toNCO-terminated polyurethane prepolymer, which is subsequentlyextended with one equivalent of different mixtures of glycerol andTC4As to prepare final PUEs (Table 1). The synthesized PUEs werecharacterized using spectroscopic methods, and their thermal sta-bility, crystallinity, morphology and mechanical properties werealso investigated.

Structural characterization of PUEsFigure 2 shows the ATR-FTIR spectra of the prepared PUE sam-ples. The PUE spectrum is characterized with stretching vibra-tions of urethane N—H bond at 3366 cm−1, stretching vibrationsof urethane carbonyl at 1727 cm−1, which is overlapped withesteric carbonyl of PCL polyol, and urethane N—H out-of-planebending vibration at 1525 cm−1. The C—H asymmetric and sym-metric stretching vibrations of alkyl groups appear at 2941 and2862 cm−1, respectively. The absorption bands at 1460, 1359and 1303 cm−1 are assigned to CH2 bending, CH3 bending andCH2 wagging vibrations, respectively. The C—O—C asymmet-ric and symmetric stretching vibrations of PCL are observed at1231 and 1157 cm−1, respectively. The absorption bands at 1098and 1038 cm−1 are also assigned to asymmetric and symmetricC—O—C stretching vibrations of urethane groups.25,26 All the FTIRspectra confirm the formation of a polyurethane structure. Theasymmetric stretching vibration of the NCO group at 2270 cm−1

is used to determine the completeness of the reaction. Thereis no peak related to free isocyanate groups at approximately2270 cm−1, and this confirms the complete conversion of iso-cyanate groups.

TC4A-based PUEs (CPEU1, CPUE2 and CPUE3) show bands similarto those of the PUE sample without significant shifts that providesevidence for the completion of reaction. Furthermore, a slight shiftis found in carbonyl band position of CPUE1, CPUE2 and CPUE3 to alower wavenumber of 1720 cm−1 compared to PUE without TC4As.This shift is attributed to an increase in hydrogen bonding betweenthe urethane linkages which could result from an enhancementin phase separation on incorporation of the TC4As into the PUE.Moreover, it is observed that the characteristic peak at 1157 cm−1

related to C—O—C symmetric stretching vibrations of PCL polyolis divided into two peaks in the spectra of CPUE1, CPUE2 and

CPUE3 which implies the presence of amorphous and crystallinemorphology for soft segments in the TC4A-based PUEs.

Thermal propertiesThe DSC thermograms of the PUEs extended with various compo-sitions of TC4As and glycerol are shown in Fig. 3. All the PUEs showone glass transition temperature (T g) associated with T g of softsegments. In contrast to the PUE sample, for CPUE1, CPUE2 andCPUE3, as well as a T g transition peak, one sharp melting endother-mic peak appears, indicating the presence of crystalline regionsin these samples corresponding to melting of the crystalline por-tions of PCL in soft segments (Table 2).27 The single T g for the PUEsample suggests that there may not be any phase separation intosoft and hard domains, which occurs for the other PUEs (CPUE1,CPUE2 and CPUE3). Crystalline regions in soft segment domainscan be formed due to strong phase separation compared to thePUE sample.10

The DSC thermograms also show that the introduction of TC4Asin polyurethane backbones leads to a slight increase in T g forCPUE1, CPUE2 and CPUE3 compared to the PUE sample. Thisphenomenon is attributed to a decrease in the segmental mobilityof the polymer chains due to phase separation and highly orderedstructure of soft segments that restricts the molecular motion ofthe polymer chains.28

As can be seen from Fig. 3, T m of the soft segments in CPUE2 andCPUE3 are lower than that in CPUE1. This is because p-BTC4A inhard segments has a much lower affinity with PCL in soft segmentsdue to the hydrophobic nature of p-BTC4A which cannot mix wellwith polar PCL. This leads to much greater phase separation anddegree of crystallinity of PCL in soft segments compared to CPUE2and CPUE3.

The thermal stability and decomposition behaviour of the pre-pared PUEs was evaluated using TGA and DTG analysis under nitro-gen atmosphere. The results are collected in Figs 4 and 5 andTable 2. Many studies confirm that the urethane group is unstableat high temperature and that, depending on the structure of diiso-cyanate, polyol and chain extender, thermal degradation reactionscan occur during heating.13 The thermal decomposition of all PUEsamples was evaluated at three different percentages of weightloss (T onset, T 10% and T 50%) and the results are given in Table 2.

The decomposition of PUE starts at an onset degradation tem-perature (T onset) of 271 ∘C, which is related to the simple depoly-merization of urethane bonds. The temperature for mass loss of10% as a most valuable criterion for thermal stability is 323 ∘C forPUE. It is quite clear from the TGA results that the TC4A-based PUEshave higher T onset, T 10% and T 50% than the PUE sample and are morethermally stable than the PUE sample extended with glycerol only.This increase in T onset, T 10% and T 50% for CPUE1, CPUE2 and CPUE3compared to PUE is attributed to the high thermal stability of TC4Adue to its four aromatic rings which delays polyurethane degrada-tion under a nitrogen atmosphere.29

The thermal degradation of polyurethane samples usually takesplace in two main steps. The first degradation stage occurs from200 to 350 ∘C and is primarily the decomposition of the hard seg-ment, which includes the dissociation of urethane to the originalpolyol and isocyanate, which then forms a primary amine, alkeneand carbon dioxide. The second main stage occurs from 350 to500 ∘C and proceeds by polyol degradation mechanisms and isinfluenced by the soft segment structure and morphology.30,31

The DTG curves in Fig. 5 also obviously reveal that there are twomain degradation stages as mentioned above. The second stageis further divided into two stages which are associated with the



Figure 2. FTIR spectra of (a) PUE, (b) CPUE1, (c) CPUE2 and (d) CPUE3.

Figure 3. DSC thermograms of PUE samples.

presence of two amorphous and crystalline regions within the softsegments (PCL). An inspection of the data in Table 2 indicatesthat the values of T max (temperature at the maximum thermaldegradation rate) in DTG curves increase with the incorporationthe TC4As into the PUEs as a portion of chain extender comparedto the PUE sample.

Table 2. Thermal properties of prepared PUEs

SampleTonset

(∘C)aT10%

(∘C)bT50%

(∘C)cTmax

(∘C)dTg

(∘C)eTm

(∘C)f

PUE 271 323 363 366 −50 Not seenCPUE1 303 347 386 380 −46 47CPUE2 295 335 372 373 −48 44CPUE3 291 340 378 373 −44 42

a Onset degradation temperature (temperature at which polymerdegradation starts).b Temperature at 10% weight loss.c Temperature at 50% weight loss.d Temperature at maximum thermal degradation rate.e Glass transition temperature.f Melting temperature.

XRD studiesFigure 6 shows the XRD profiles for all PUE samples. XRD diffractionanalysis was carried out in order to investigate the crystalline stateof the PUEs. In segmented polyurethanes, phase separation of softand hard segments can take place depending on their relativecontents and structural regularity.

The XRD studies show that crystallinity much depends on thestructure of chain extender used in the polyurethane backbone.



Figure 4. TGA thermograms of PUE samples.

Figure 5. DTG thermograms of PUE samples.

The PUE sample exhibits only a broad and low-intensity amor-phous diffraction peak near 2𝜃 = 24.1∘, which implies that theglycerol disfavours the formation of an ordered structure dueto phase mixing. In contrast, the presence of two sharp peaksat 2𝜃 = 26.5∘ and 29.4∘ as well as an amorphous broad peak forTC4A-based PUEs confirms that soft segments tend to crystallize,from which it is concluded that the presence of TC4As seemsto favour the formation of a more ordered structure due to anincrease in phase separation compared to the PUE sample thatwas confirmed earlier using DSC and FTIR spectroscopy.32 The XRDprofile for PCL polyol also shows two crystalline peaks at 2𝜃= 26.5∘and 29.4∘. Since crystalline peak positions for CPUE1, CPUE2 andCPUE3 correspond well to those obtained for PCL (polyol), it islikely that the observed sharp peaks for PUEs are related to crys-tallization of soft segment domains, because the hard segmentsbased on IPDI chain extenders usually cannot crystallize. 33 How-ever, the XRD results clearly suggest that the TC4A-based PUEshave crystalline soft segment domains in them.34

SEM and EDX studiesThe morphology of the prepared PUEs was evaluated usingSEM. As can be seen from the SEM images presented in Fig. 7,

Figure 6. XRD patterns of PUE samples and PCL2000.

microphase separation morphology depends on the chemicalstructure of the chain extender used. The SEM photomicrographsshow that the hard domains (lighter regions) in the PUE sampleare not dispersed well in the polyurethane matrix. The discussionabove would account for the amorphous morphology and lowdegree of phase separation in the PUE sample. In the CPUE series,the formation and dispersion of the hard domains are enhanceddue to the presence of TC4As which cause an increase in inter-actions between hard segments, generating well-phase-separatedmorphology with homogeneously distributed hard domains in thewhole matrix.34

In the case of CPUE2, the SEM image in Fig. 7(c) reveals an unevensurface which can be reasoned from a weak interaction betweenpolyurethane chains in hard segments because of repulsion forcesbetween sulfonate groups. In order to better clarify the morphol-ogy of samples, AFM was carried out, the results of which are pro-vided in the supporting information.

In addition, Fig. 8 shows EDX results for the prepared PUEs. As canbe seen, EDX studies demonstrate that TC4As seem to be dispersedevenly within the polyurethane matrices. The presence of TC4Asin the polyurethane matrix is proved by the sulfur peak in the EDXspectra.

Mechanical studiesThe tensile stress–strain curve is a means to provide data fortensile strength, Young’s modulus and elongation at break. Thestress–strain curves of the prepared samples are shown in Fig. 9and the corresponding mechanical properties data are summa-rized in Table 3. The synthesized PUEs show a wide range ofmechanical properties depending on the crystallinity of the poly-mer backbone that arises from chain extender composition andstructure.10

Mechanical properties are discussed from the viewpoint ofphase domain separation of hard and soft segments. Addition of



Figure 7. SEM images of (a) PUE, (b) CPUE1, (c) CPUE2 and (d) CPUE3.

TC4As as a portion of the chain extender is accompanied by anincrease in the degree of phase separation, soft domain order andcrystallinity of PUEs which was earlier confirmed from DSC andXRD analysis.

All the PUEs display an elastic stress–strain behaviour. SamplesCPUE1, CPUE2 and CPUE3 display a considerable yield pointfollowed by necking indicating a high degree of phase sepa-ration and the presence of crystalline morphology for thesepolyurethanes. The PUE sample shows higher tensile strengthcompared the other samples. This behaviour is related to increasesin the sample crystallinity with drawing of the sample which makesthe polyol chains more ordered.34 On the other hand, if the hardand soft domains are extremely separated, a sharp phase bound-ary results and a localization of shear stresses can occur at thenarrow interface, giving rise to poor tensile properties for CPUE1,CPUE2 and CPUE3 compared to the PUE sample.35

In addition, for CPUE1, CPUE2 and CPUE3, the initial elas-tic modulus increases greatly with increases in crystallinity ofpolyurethanes in comparison to the PUE sample due to higherdegree of phase separation with incorporation of TC4As into thePUEs.28

Moreover, CPUE2 shows significantly poorer mechanical prop-erties of tensile strength, modulus and elongation at breakamong all samples. This behaviour can be assigned to a markeddecrease in intermolecular forces due to the presence of anionicsulfonate groups (SO3

−) in the polyurethane backbone. This leadsto electrostatic repulsion between sulfonate groups which can

reduce intermolecular forces in hard segments as mentioned inthe discussion of the SEM analysis.

Measurement of contact angleThe surface hydrophilicity of the PUEs was investigated by measur-ing the water contact angle between water drops and the surfaceof samples. Drops of water were placed on three different areasof the surface of samples using a microsyringe. The mean value ofthese measurements was recorded as the surface hydrophilicity.The results show that the contact angle of the PUE sample is71.2∘, while with addition of TC4As, the contact angle of CPUE1,CPUE2 and CPUE3 increases to 81.7∘, 79.3∘ and 77.1∘, respectively.These results show that the hydrophobicity of CPUE1, CPUE2 andCPUE3 is increased as a result of addition of TC4As which can beinterpreted in terms of the hydrophobic structure of the TC4Aderivatives compared to glycerol. It should be noted that thehydrophilicity of CPUE2 and CPUE3 is slightly higher than that ofCPUE1. This can be explained by the fact that the sulfonic acid andsulfonate salt substituents attached to phenolic rings in TC4ASand TSTC4AS, respectively, impart more hydrophilic character tothese PUEs compared to CPUE1 with p-tert-butyl substituent.

CONCLUSIONSA series of TC4A-based PUEs were prepared by the step-growthpolymerization technique. Polyurethane prepolymers were firstly



Figure 8. EDX results of (a) PUE, (b) CPUE1, (c) CPUE2 and (d) CPUE3.

prepared using PCL diol and IPDI with a [NCO]/[OH] ratio of2:1 and extended either with glycerol only or with glycerol ina mixture with various TC4A derivatives. The thermal stabil-ity of the PUEs increased with the incorporation of TC4As inthe polyurethane backbone, which makes these PUEs poten-tial candidates for heat-resistant elastomers for application asion-exchange polyurethane membranes. DSC and XRD analysesshowed that the addition of TC4As resulted in an increase inthe degree of phase separation and crystalline regions whilethe glycerol-based PUE showed no crystalline domains and

tended to show phase mixing without melting behaviour. Forthe TC4A-based PUEs, the initial elastic modulus increased withincreasing crystallinity compared to the glycerol-based PUE dueto a greater degree of phase separation which occurred withincorporation of TC4As into PUEs. The surface hydrophilicityof the prepared PUEs was investigated and the results showedthat the hydrophobicity of samples was increased as a resultof the addition of TC4As, which can be interpreted in termsof the hydrophobic structure of TC4A derivatives comparedto glycerol.



Figure 9. Stress–strain curves of PUE samples.

Table 3. Mechanical properties of prepared PUEs

Sample

Tensilestrength

(MPa)Young’s

modulus (MPa)Elongation at

break (%)

PUE 12.73± 0.67 2.41± 0.14 587± 24CPUE1 6.45± 0.31 45.62± 2.25 577± 21CPUE2 2.11± 0.12 38.58± 1.67 310± 14CPUE3 8.81± 0.42 48.13± 2.88 661± 31

ACKNOWLEDGEMENTSThe authors gratefully acknowledge the support of the Universityof Mazanadaran and the Polyurethane Center of Excellence in IranPolymer and Petrochemical Institute (IPPI).

SUPPORTING INFORMATIONSupporting information may be found in the online version of thisarticle.

REFERENCES1 Xia H and Song M, Soft Matter 1:386–394 (2005).2 Kuan HC, Ma CCM, Chang WP, Yuen SM., Wu HH and Lee TM, Compos

Sci Technol 65:1703–1710 (2005).3 Mai Y and Yu Z, Polymer Nanocomposites. Woodhead Publishing,

Cambridge (2006).

4 Santerre J, Woodhouse K, Laroche G and Labow R, Biomaterials26:7457–7470 (2005).

5 Barikani M, Zia KM, Bhatti IA, Zuber M and Bhatti HN, Carbohydr Polym74:621–626 (2008).

6 Kojio K, Fukumaru T and Furukawa M, Macromolecules 37:3287–3291(2004).

7 Daemi H, Barikani M and Barmar M, Carbohydr Polym 92:490–496(2013).

8 Hepburn C, Polyurethane Elastomers. Applied Science Publishers, NewYork (1982).

9 Zia KM, Zuber M, Bhatti IA, Barikani M and Sheikh MA, Int J BiolMacromol 44:23–28 (2009).

10 Chiou BS and Schoen PE, J Appl Polym Sci 83:212–223 (2002).11 Chen TK, Tien YI and Wei KH, Polymer 41:1345–1353 (2000).12 Chen TK, Chui JY and Shieh TS, Macromolecules 30:5068–5074 (1997).13 Eceiza A, Martin M, De La Caba K, Kortaberria G, Gabilondo N, Corcuera

M et al., Polym Eng Sci 48:297–306 (2008).14 Iki N, Kabuto C, Fukushima T, Kumagai H, Takeya H, Miyanari S et al.,

Tetrahedron 56:1437–1443 (2000).15 Lhoták P, Himl M, Stibor I and Petrıcková H, Tetrahedron Lett

43:9621–9624 (2002).16 Lakouraj MM, Mojerlou F and Zare EN, Carbohydr Polym 106:34–41

(2014).17 Memon S, Oguz O, Yilmaz A, Tabakci M, Yilmaz M and Ertul S, J Polym

Environ 9:97–101 (2001).18 Akceylan E, Bahadir M and Yilmaz M, J Hazard Mater 162:960–966

(2009).19 Alexandratos SD and Natesan S, Macromolecules 34:206–210 (2001).20 Adhikari BB, Kanemitsu M, Kawakita H, Jumina J and Ohto K, Chem Eng

J 172:341–353 (2011).21 Tabakci B, Beduk AD, Tabakci M and Yilmaz M, React Funct Polym

66:379–386 (2006).22 Mohammadi A, Lakouraj MM and Barikani M, React Funct Polym

83:14–23 (2014).23 Yuan D, Zhu WX, Ma S and Yan X, J Macromol Struct 616:241–246

(2002).24 Shinkai S, Araki K, Tsubaki T, Arimura T and Manabe O, J Chem Soc

Perkin Trans 1 2297–2299 (1987).25 Mohammadi A, Barikani M and Barmar M, Polym Adv Technol

24:978–985 (2013).26 Zia KM, Barikani M, Zuber M, Bhatti IA and Bhatti HN, Iran Polym J

17:61–72 (2008).27 Tatai L, Moore TG, Adhikari R, Malherbe F, Jayasekara R, Griffiths I et al.,

Biomaterials 28:5407–5417 (2007).28 Yeganeh H, Lakouraj MM and Jamshidi S, J Polym Sci A: Polym Chem

43:2985–2996 (2005).29 Saponar A, Popovici EJ, Perhaita I, Nemes G and Cadis AI, J Therm Anal

Calorim 110:349–356 (2012).30 Gong Q, Wu J, Gong X, Fan Y and Xia H, RSC Adv 3:3241–3248 (2013).31 Mohammadi A, Barikani M and Barmar M, J Mater Sci 48:7493–7502

(2013).32 Zia KM, Bhatti IA, Barikani M, Zuber M and Bhatti HN, Carbohydr Polym

76:183–187 (2009).33 Petrovic ZS and Ferguson J, J Prog Polym Sci 16:695–836 (1991).34 Kloss J, Munaro M, De Souza GP, Gulmine JV, Wang SH, Zawadzki S

et al., J Polym Sci A: Polym Chem 40:4117–4130 (2002).35 Martin DJ, Meijs GF, Gunatillake PA, Mccarthy SJ and Renwick GM, J

Appl Polym Sci 64:803–817 (1997).


synthesis and investigation of properties of thiacalix [4] arene‐based polyurethane elastomers

Documents