fluorinated siloxane-containing waterborne polyurethaneureas with excellent hemocompatibility,...

European Polymer Journal 46 (2010) 472–483

Contents lists available at ScienceDirect

European Polymer Journal

journal homepage: www.elsevier .com/locate /europol j

Fluorinated siloxane-containing waterborne polyurethaneureas withexcellent hemocompatibility, waterproof and mechanical properties

Teng Su, Gui You Wang, Shao Lei Wang, Chun Pu Hu *

Key Laboratory for Ultrafine Materials, Ministry of Education, Shanghai 200237, PR ChinaSchool of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237, PR China

a r t i c l e i n f o

Article history:Received 29 June 2009Received in revised form 1 November 2009Accepted 1 December 2009Available online 14 December 2009

Keywords:DispersionsFluorinated polysiloxanesHemocompatibilityMechanical propertiesPolyurethaneureaWater resistance

0014-3057/$ - see front matter � 2009 Elsevier Ltddoi:10.1016/j.eurpolymj.2009.12.009

* Corresponding author. Address: School of MEngineering, East China University of Science and T200237, PR China. Tel.: +86 21 64253037; fax: +86

E-mail addresses: [email protected], chunpuhHu).

a b s t r a c t

Two series of polyurethaneurea (PUU) aqueous dispersions consisting of fluorinated siloxanesegments were prepared from a high-molecular-weight (Mn = 8361) a,x-dihydroxy-poly[(3,3,3-trifluoropropyl)methylsiloxane] (PTFPMS), dimethylolpropionic acid, isopho-rone diisocyanate and ethylenediamine, with poly (tetramethylene oxide) andpolycarbonate polyols as soft segments, respectively. These anionic aqueous dispersionswere stable at the ambient temperature for more than 6 months, with particle sizes rangingfrom 45 to 98 nm. Both series of PUU films showed the excellent waterproof properties, i.e.the decrease in water absorption and surface energy upon the incorporation of PTFPMS seg-ments. The phase mixing increased in the fluorinated siloxane-containing polyether-basedPUUs and the phase separation increased first then decreased in the fluorinated siloxane-con-taining polycarbonate-based PUUs, with increasing PTFPMS content. All the PTFPMS-modi-fied PUU films showed excellent mechanical properties. The polycarbonate-based PUU filmconsisting of 5 wt.% PTFPMS had a tensile strength of 60.7 MPa and a breaking elongationof 632%, owing to the increase in the ordered hydrogen bonding degree and the micro-phase-separation degree between the hard and soft segments in the system. In vitro hemo-lysis and dynamic clotting time measurements indicated that the thromboresistance wasenhanced markedly with increasing PTFPMS content for both series of PUUs, which couldbe ascribed to the synergistic effect between the carboxylate groups and the PTFPMS seg-ments migrating onto the surfaces of the films.

� 2009 Elsevier Ltd. All rights reserved.

1. Introduction

The combination of unique physical–mechanical proper-ties and good biocompatibility has made polyurethane (PU)one of the most attractive materials used in various biomed-ical applications, such as intra-aortic balloons, heart valves,pacemaker leads, catheters, facial prostheses and gene carri-ers [1]. Driven by the stringent environmental requirementon minimizing the emission of volatile organic compounds,

. All rights reserved.

aterials Science andechnology, Shanghai21 [email protected] (C.P.

waterborne PU or polyurethaneurea (PUU), and polyureth-aneurea/acrylate aqueous dispersions [2,3] have receivedincreasing attention, and have been gradually replacingthe conventional solvent-borne PU products in the areas ofcoatings, adhesives and surface finishes for textiles. Sincethe PU incorporating negatively-charged carboxylategroups has shown better antithrombogenicity than thenon-ionic or sulfonate-containing one [4], some carboxyl-ated waterborne PUs have also been studied recently forapplications in blood-contacting and tissue engineering[5–7]. However, the insertion of hydrophilic ionic groupinevitably renders waterborne PU or PUU with undesirablewater absorption, and affects the mechanical properties ofthe final materials [5]. Poussard et al. [8] designed and syn-thesized two series of waterborne PUs based on a polybuta-

http://dx.doi.org/10.1016/j.eurpolymj.2009.12.009

mailto:[email protected]

mailto:[email protected]

http://www.sciencedirect.com/science/journal/00143057

http://www.elsevier.com/locate/europolj

T. Su et al. / European Polymer Journal 46 (2010) 472–483 473

diene soft segment, with the carboxylate groups insertedeither into the hard segments or into the soft segments.The results showed that the insertion of carboxylate groupsinto the soft segments not only limited the water absorptionamount of PU film (within 5 wt.%), but also reduced theplatelet and fibrinogen adhesion on the surface of PU.

Polysiloxanes and fluorocarbon compounds exhibit un-ique low surface energy, biocompatibility and biostability.The incorporation of polydimethylsiloxane (PDMS) or fluo-rocarbon segments proved to significantly reduce plateletdeposition and activation [9,10], hence could be consideredan effective approach to enhance both the water resistanceand blood compatibility of waterborne PUs. However, manyinvestigators also observed the loss of tensile strength forthe solvent-borne and waterborne PUs bearing PDMS orfluorocarbon segments as grafts or blocks in the macromo-lecular chains [11–13].

In the previous studies [14,15], we reported a series ofpolyadipate-based anionic PUU aqueous dispersions incor-porating a,x-dihydroxypoly[(3,3,3-trifluoropropyl)meth-ylsiloxane] (PTFPMS, number-average molecular weight(Mn) = 798) units into the macromolecular chains. Thewater-resistant and mechanical properties were found tobe enhanced markedly and simultaneously for these water-borne PUU films containing both silicon and fluorine groupsin the same unit. In this work, two series of polyether- andpolycarbonate-based PUU aqueous dispersions consistingof long fluorinated siloxane segments were prepared fromPTFPMS (Mn = 8361), dimethylolpropionic acid, isophoronediisocyanate and ethylenediamine. The physical propertiesof these aqueous dispersions, and the surface and bulk prop-erties of the PUU films prepared from the two series of aque-ous dispersions were investigated. The experimental datashow that all the aqueous dispersions are quite stable notonly at ambient temperature but also at high and low tem-peratures. Furthermore, the excellent hemocompatibility,waterproof and mechanical properties can be achievedsimultaneously for these environmentally-friendly water-borne PUU films.

2. Experimental section

2.1. Materials

PTFPMS {HO[(CF3CH2CH2)MeSiO]nH, n = 53, Mn = 8361,polydispersity index = 1.31} was kindly provided by Shang-hai Friend Rubber and Plastic Material Technology Corp.,China. Poly (tetramethylene oxide) diol (PolyTHF 2000, hy-droxyl number = 56 mg KOH/g) was supplied by BASF andwas dried under vacuum at 100 �C for 2 h. Polycarbonatediol (PCDL S6002, hydroxyl number = 56 mg KOH/g) wassupplied by Asahi Kasei Corp., Japan and was produced from1,6-hexanediol and 1,5-pentanediol by transesterificationwith ethylenecarbonate. The polycarbonate diol was driedunder vacuum at 80 �C for 3 h before use. Dimethylolprop-ionic acid (DMPA) was provided by Perstorp AB, Swedenand was dehydrated under vacuum at 60 �C for 24 h. Isoph-orone diisocyanate (IPDI) was supplied by Degussa-Hüls,Germany. N,N-Dimethylacetamide (DMAc) was dried overCaH2 for 2 days at room temperature, distilled under vac-

uum and stored in the presence of 0.4 nm molecular sieves.Other materials were standard laboratory reagents andwere used as received, except that triethylamine (TEA) andethylenediamine (EDA) were treated with 0.4 nm molecularsieves for over 1 week before use.

2.2. Synthesis of the PTFPMS-containing prepolymer

The prepolymer based on IPDI, PTFPMS, DMPA and poly-ether (or polycarbonate), was synthesized using a two-steppolymerization. In the first step, IPDI (0.006 mol, dissolvedin DMAc: IPDI/DMAc = 1/1, w/w) and dibutyltin dilaurate(DBTDL, 0.03 wt.% based on the total reaction mass) wereintroduced into a dry 250-mL, four-necked flask equippedwith a mechanical stirrer, a nitrogen inlet, a condenser,and a thermometer. PTFPMS (0.003 mol, dissolved in DMAc:PTFPMS/DMAc = 2/1, w/w) was then dropped slowly intothe system for 1 h at 70 �C under a dry nitrogen atmosphere.After that, the reaction was continued at 85 �C to obtain theNCO-terminated PTFPMS (FS-NCO) until the NCO contentreached the theoretical value determined by using a stan-dard dibutylamine back-titration method. In the secondstep, a stoichiometric amount of FS-NCO and IPDI ([NCO]/[OH] = 1.9, molar ratio) were added to a well-stirred mixtureof PolyTHF 2000 (or PCDL S6002) and DMPA (dissolved inDMAc: DMPA/DMAc = 1/1, w/w) at 60 �C. The reaction tookplace at 85 �C for 5 h under the dry nitrogen atmosphere un-til the theoretical NCO value was reached to synthesize theNCO-terminated prepolymer containing PTFPMS segments.

2.3. Preparation of the PUU aqueous dispersions and theirfilms

The obtained prepolymer was cooled to 45 �C and neu-tralized with TEA for 40 min, then dispersed into deionizedwater under vigorous stirring. The polyether-based or poly-carbonate-based PUU aqueous dispersions containing dif-ferent PTFPMS contents were prepared after the chainextension by the dropwise addition of EDA. For simplicity,they were designated as T2000-FS-X or C2000-FS-X, whereX indicates the PTFPMS content. The preparation processfor these two series of PUU aqueous dispersions is shownin Scheme 1. The concentration of DMPA in the PUU macro-molecular chains was 4 wt.% (based on the total mass ofPUU). All the aqueous dispersions had a solid concentrationof about 30 wt.%. The formulations in the preparation ofthese PUU aqueous dispersions were presented in Table 1.

The PUU films were prepared by casting the aqueousdispersions into Teflon molds. Then, they were dried at35 �C for 7 days and under vacuum at 60 �C for 24 h untila constant weight was obtained.

2.4. Characterization

The particle size and distribution of the aqueous disper-sions were measured by dynamic laser light scattering on aMalvern Zetasizer 3000 at 25 �C.

The high-temperature stability of the aqueous dispersionswas determined by the observation of whether the aqueousdispersions were deposited or not after being placed in anoven at 60 �C for 40 h. For freeze–thaw stability measure-

Scheme 1. Preparation process of the anionic PUU aqueous dispersions consisting of PTFPMS segments.

474 T. Su et al. / European Polymer Journal 46 (2010) 472–483

ments, the PUU aqueous dispersions were subjected to anumber of testing cycles in which the samples were frozenat�30 �C for 18 h and then allowed to thaw at room temper-aturefor 6 h. At least five cycles were performed for each sam-ple to observe whether any precipitation could be detected.

The stability of the aqueous dispersion was expressed bythe recycle times of the freeze–thaw test.

The transmission Fourier transform infrared (FTIR) spec-tra of the PUU films were recorded with a Nicolet Magana IR5700 FTIR spectrometer at 25 �C. Differential scanning calo-

Table 1Formulations of the anionic PUUs (based on molar ratios).

Sample IPDI FS-NCO PolyTHF 2000orPCDL S6002

DMPA EDA

T2000-FS-0 1 – 0.274 0.252 0.474T2000-FS-5 0.995 0.005 0.265 0.261 0.474T2000-FS-30 0.962 0.038 0.210 0.316 0.474C2000-FS-0 1 – 0.274 0.252 0.474C2000-FS-5 0.995 0.005 0.265 0.261 0.474C2000-FS-30 0.962 0.038 0.210 0.316 0.474


rimetry (DSC) analysis was performed with a TA Instru-ments 2910 modulated DSC analyzer over the range from�120 �C to +260 �C at a heating rate of 10 �C/min underthe nitrogen atmosphere (nitrogen flow rate: 60 mL/min).

The mechanical properties for all the specimens weremeasured on a SANS CMT2203 universal testing machineunder a 50 mm/min crosshead rate at 25 �C, and the spec-imens were made in accordance with GB1040-79.

The amount of the water absorption of the PUU film(25 mm � 25 mm � 1 mm) was tested in water for 24 hat 25 �C and was calculated as follows:

Water absorptionð%Þ ¼ ðW2 �W1Þ=W1 � 100% ð1Þ

where W1 and W2 are the weights of the PUU film beforeand after soaking, respectively.

The static contact angle of water or ethylene glycol on thePUU film surface was measured with the sessile drop meth-od at 25 �C by using a JC2000A series instrument, and the re-sults reported are the mean values of five replicates.

The surface molecular structure of the PUU films wasanalyzed by attenuated total reflectance Fourier transforminfrared (ATR-FTIR) spectroscopy, which was performed bymeans of a Nicolet Magana IR 5700 spectrometer. ATRspectra were recorded with a Smart OMNI-Sampler acces-sory equipped with a ZnSe crystal (45�, single reflection).Data were collected with a resolution of 4 cm�1 and128 scans. In our experimental setup, the penetrationdepth relative to 1000 cm�1 frequency resulted in 2.0 lmapproximately [16,17].

The atomic force microscopy (AFM) studies were per-formed with a Nanoscope IIIa scanning probe microscopy(Digital Instruments, Santa Barbara, CA) under tappingmode in air at ambient temperature. Topographic and phaseimages were recorded simultaneously using a standard sili-con probe (RTESP7, VEECO Instruments, CA) at a set-pointoscillation amplitude to cantilever free-oscillation ampli-tude ratio of 0.4 for all the reported images. Under this mod-erate force tapping conditions, phase data are sensitive tolocal stiffness difference of domains in the top several nano-meters from the uppermost surface. The root-mean-square(RMS) average of the surface roughness value was calculatedas the standard deviation of all the height values within thescanned area using NanoScope 5.12 software.

The hemolytic potential of the PUU films was assessedby determining hemoglobin release under static conditions[18]. The blood sample was prepared by diluting 8 mL ofanticoagulated fresh human whole blood (purchased fromShanghai Blood Center) with 10 mL of 0.9% saline. Each

PUU film (5 g) was cut into small pieces and leached in0.9% saline for 24 h. Having been dried, the PUU film wasincubated for 30 min at 37 �C in 10 mL of 0.9% saline. Then,0.2 mL of the blood sample was added and the incubationcontinued at 37 �C for another 60 min without agitation. Apositive control (0.2 mL of blood sample with 10 mL ofdeionized water) and a negative control (0.2 mL of bloodsample with 10 mL of 0.9% saline) were also set for incuba-tion. After incubation, the immersion liquid was centri-fuged at 750g for 5 min and the supernatant wascarefully separated. The optical density (OD) of the super-natant was measured at 545 nm by a Unico UV-2800HUltraviolet spectrophotometer, and the reported valuewas obtained from three parallel experiments and ex-pressed as mean ± standard deviation. The percent ofhemolysis was calculated as follows:

Hemolysisð%Þ¼ ODðtest sampleÞ�ODðnegative controlÞODðpositive controlÞ�ODðnegative controlÞ�100%

ð2Þ

The dynamic clotting time measurement [19] wasadopted to study the thromboresistant property of thePUU films. 0.2 mL of anticoagulated fresh human wholeblood was dropped onto the film sample(20 mm � 20 mm � 1 mm). Blood clotting was then initi-ated by the addition of 20 lL of CaCl2 aqueous solution(0.2 mol/L) and proper mixing by a Teflon stick. After a pre-determined time, the sample was transferred into a beakercontaining 100 mL of deionized water and incubated at37 �C for 5 min. The concentration of free hemoglobin inthe water was measured as the absorbance at 540 nm witha spectrophotometer. The absorbance of the solution versustime was plotted against the contacting time of blood on thematerial surface. Each absorbance data point was obtainedby measuring three parallel samples and the standard devi-ation of the three tests were also determined. The siliconizedand nonsiliconized glass slides were investigated as nega-tive and positive controls, respectively, for comparison.

3. Results and discussion

3.1. PUU aqueous dispersions

Table 2 lists some physical properties of the PUU aque-ous dispersions with different PTFPMS contents. Withincreasing PTFPMS content, the particle sizes of both thepolyether-based and the polycarbonate-based series de-creased significantly; however, the particle size distribu-tion seemed unchanged. The particle size of a PUUaqueous dispersion is primarily dependent on the numberof the hydrophilic units, the flexibility of the macromolec-ular chain, as well as the chemical composition on the par-ticle surface. For a constant concentration of hydrophilicunits, the increase in chain flexibility was found to de-crease the particle size of the PU aqueous dispersion [20].Upon the incorporation of PTFPMS segments, the PUUmacromolecular chain would become more flexible andeasy to deform owing to the presence of siloxane linkages.Moreover, due to the strong hydrophobicity of the PTFPMS

Table 2Some physical properties of the polyether-based and polycarbonate-based anionic PUU aqueous dispersions with different PTFPMS contents.a

Sample PTFPMScontent(wt.%)

Hard segmentcontent(wt.%)

Averageparticlesize (nm)

Polydispersity Colloidalstabilityat 60 �C (h)

Freeze–thawstability(cycle)

T2000-FS-0 0 32.3 77 0.10 >40 7T2000-FS-5 5 31.6 54 0.07 >40 >10T2000-FS-30 30 28.0 45 0.08 >40 >10C2000-FS-0 0 32.3 98 0.11 >40 7C2000-FS-5 5 31.6 66 0.11 >40 >10C2000-FS-30 30 28.0 50 0.12 >40 >10

a None of the aqueous dispersions deposited after storage for 6 months at the ambient temperature.


segments, when the prepolymer consisting of PTFPMS wasdispersed into water, the hydrophobic PTFPMS segmentsentered the interior of the particle as much as possible,whereas the hydrophilic parts oriented at the polymer–water interface. As the PTFPMS content increased, thehydrophobicity for the inside of the particle was enhanced,and more hydrophilic carboxylate groups in the DMPAunits would be driven to orient at the polymer–waterinterface [14], leading to the increase in surface hydrophi-licity and the decrease in particle size. Therefore, the parti-cle diameter of the both series of PUU aqueous dispersionsdecreased in the following order: T2000-FS-0 > T2000-FS-5 > T2000-FS-30 and C2000-FS-0 > C2000-FS-5 > C2000-FS-30. Since the macromolecular chain composed of poly-ether is more flexible and hydrophilic than that of polycar-bonate, the polyether-based series of PUU aqueousdispersions exhibited smaller particle sizes than the poly-carbonate-based series at the same PTFPMS concentration.

Table 2 also indicates that all the PUU aqueous disper-sions studied here were stable at the ambient temperaturefor more than 6 months. The PTFPMS-modified PUU aque-ous dispersions exhibited excellent high-temperature col-loidal stability as the comparable aqueous dispersions,but even better freeze–thaw stability than the pure PUUspecimens. These features are important for an aqueousdispersion further applied in industries.

3.2. Surface properties of PUU films

The hydrophilic/hydrophobic balance on the surface ofpolymer has an important influence on its blood compatibil-ity. Table 3 lists some surface properties of the films pre-pared with the different PUU aqueous dispersions. Thesurface energy for a PUU film is difficult to measure directly,but it can be calculated indirectly through the measurement

Table 3Some physical properties of the anionic PUU films with different PTFPMS content

Sample Water absorption, 24 h (wt.%) Contact angles (�

Water Eth

T2000-FS-0 7.0 81 54T2000-FS-5 5.6 87 60T2000-FS-30 4.0 96 71C2000-FS-0 5.5 83 54C2000-FS-5 2.9 89 63C2000-FS-30 3.1 103 78

of the equilibrium contact angles of some standard liquids,e.g. water and ethylene glycol, on its surface [21]:

ð1þ cos h1Þc1 ¼ 4cd

1cds

cd1 þ cd

s

þ cp1c

ps

cp1 þ cp

s

� �ð3Þ

ð1þ cos h2Þc2 ¼ 4cd

2cds

cd2 þ cd

s

þ cp2c

ps

cp2 þ cp

s

� �ð4Þ

cs ¼ cds þ cp

s ð5Þ

where h1 and h2 are the contact angles of water and ethyleneglycol on the surface of the PUU film, respectively; cs, cd

s , andcp

s are the surface energy, dispersion component, and polarcomponent for the PUU films, respectively; c1, cd

1, and cp1

are the surface tension, dispersion component, and polarcomponent for water (cd

1 = 21.8 mN/m, cp1 = 51.0 mN/m),

respectively; c2,cd2, andcp

2 are the surface tension, dispersioncomponent, and polar component for ethylene glycol(cd

2 = 29.3 mN/m, cp2 = 19.0 mN/m) , respectively [21].

Table 3 shows a decrease in the surface energy for theboth series of PUU films with increasing PTFPMS content.The polycarbonate-based series was more hydrophobicthan the polyether-based series. Since the decrease in sur-face energy came mainly from the reduction of the polarcomponent, this phenomenon must result from the migra-tion of the hydrophobic PTFPMS segments containing boththe silicon and the fluorine groups toward the outermostsurface of PUU film. Thus, the surface composition of dif-ferent PTFPMS-containing PUU films was examined byATR-FTIR, and the spectra were shown in Fig. 1. In thespectra of these specimens, the strong absorption bandaround 1000–1100 cm�1 corresponds to the Si–O–Si asym-metric stretching vibration, which is overlapped by the C–O stretching vibration of the urethane groups or ether link-ages. The peaks at 1263 and 800 cm�1 are attributed to the

s.

) cs (mN/m) cps (mN/m) cd

s (mN/m)

ylene glycol

32.1 14.7 17.429.0 11.7 17.324.0 8.4 15.631.8 12.9 18.927.5 11.1 16.421.5 5.3 16.2

Fig. 1. ATR-FTIR spectra of the anionic PUU films with different PTFPMScontents.

Table 4Relative contents of various groups on the surfaces of the different anionicPUU films.

Sample ISi—O—Si I—CH2CH2 CF3

T2000-FS-0 0 0T2000-FS-5 9.4 2.8T2000-FS-30 12.7 3.5C2000-FS-0 0 0C2000-FS-5 10.2 3.2C2000-FS-30 14.1 4.9


symmetric bending and rocking vibrations of the Si–CH3

group, respectively, while the Si–CH2CH2CF3 group has astrong sharp absorption peak at 1209 cm�1 [15]. The signalat 1550 cm�1 corresponds to the C@O absorption peak ofDMPA units existing in the PUU macromolecular chains[3]. In terms of the C–H absorption band at around 2800–3000 cm�1 as an internal standard, the relative contentsof the –CF2CF2CF3 unit and the Si–O–Si unit on the PUUfilm surface could be estimated from the absorption peakat 1209 cm�1 and the region at 1000–1100 cm�1, respec-tively, as follows:

I—CH2CH2CF3 ¼A—CH2CH2CF3

AC—Hð6Þ

ISi—O—Si ¼ASi—O—Si

AC—Hð7Þ

where AC—H, A—CH2CH2CF3 and ASi—O—Si are the normalizedabsorbances for C–H, –CH2CH2CF3 and Si–O–Si units.

However, as discussed previously, the absorption regionat 1000–1100 cm�1 is the combination of the Si–O–Si asym-metric stretching vibration and the C–O stretching vibrationof the urethane groups or ether linkages. Therefore, the peakarea belonging to the C–O vibration must be deducted to ob-tain the pure peak area of the Si–O–Si vibration. In the ATR-FTIR spectra of PUU, the absorption peak corresponding tothe carbonyl group in the urethane and/or carbonate link-ages is located at approximately 1700 � 1760 cm�1

[13,27]. Since the Si–O–Si contains no carbonyl group, theabsorption band at 1700 � 1760 cm�1 can be used hereinas a normalizing factor. The following equation isestablished:

AFS0C—O

AFS0C@O¼ A0modified

C—O

AmodifiedC@O

ð8Þ

where AFS0C—O and A0modified

C—O are the normalized absorbancesfor the C–O stretching vibration in the unmodified speci-men (T2000-FS-0 or C2000-FS-0) and in the PTFPMS-mod-ified specimens, respectively; AFS0

C@O and AmodifiedC@O are the

normalized absorbances for the C@O vibrations in the

unmodified specimen and the PTFPMS-modified speci-mens, respectively. With the value of A0modified

C—O obtainedfrom Eq. (8), the absorbance corresponding to the Si–O–Si vibration can be calculated as follows:

ASi—O—Si ¼ AmodifiedC—O � A0modified

C—O ð9Þ

where AmodifiedC—O is the measured absorbance at 1000–

1100 cm�1 for the PTFPMS-modified PUU specimens.Table 4 lists the values of I—CH2CH2CF3 and ISi—O—Si for dif-

ferent PUU specimens. For both the modified PUU series,the values of I—CH2CH2CF3 and ISi—O—Si increased with increas-ing PTFPMS content, indicating the enrichment of thehydrophobic PTFPMS segments on the film surface. Forthe polycarbonate-based series, the values of I—CH2CH2CF3

and ISi—O—Si were both higher than those for the poly-ether-based series, and this implied that the migration ofPTFPMS segments to the surfaces of polycarbonate-basedPUUs was easier than to those of polyether-based PUUs.Therefore, the C2000-FS-30 film exhibited the lowest sur-face energy, as shown in Table 3.

AFM technique was used to study the microdomains ofPUUs lying underneath the uppermost surface layer. Fig. 2shows the topographic and phase images of T2000-FS-0,T2000-FS-5, C2000-FS-0 and C2000-FS-5 samples at moder-ate tapping mode with a scan area of 1 lm � 1 lm. Thephase data for the hard blocks are bright and the soft blocksare dark. It should be pointed out that the surfaces of T2000-FS-30 and C2000-FS-30 appeared to be rather ‘‘tacky”. Thatis, the silicon tip tended to stick onto the surfaces of thesetwo PUU samples during the imaging procedure, althoughmoderate or heavier tapping force was employed. Revenkoand coworkers [22] reported similar phenomenon whenthey tried to visualize the surface morphology of pure poly-carbonate by AFM. This phenomenon could be ascribed tothe relatively high contents of soft PTFPMS segments en-riched on the surfaces of T2000-FS-30 and C2000-FS-30films compared with other samples. Therefore, attempts toimage these two samples by AFM did not succeed. For thepolyether-based series, T2000-FS-0 showed a typical twophase morphology with the spherule-like hard microdo-mains dispersed in the soft segment-rich phase. Upon theintroduction of 5 wt.% PTFPMS segments, the domain sizeincreased and the boundary between the two phases blurredfor the T2000-FS-5 system. This result showed directly thatthe phase mixing on the surface of PTFPMS-containing poly-ether-based PUU was enhanced with incorporating a smallnumber of PTFPMS segments, which will be discussed later.For the polycarbonate-based series, the morphology chan-ged from the spherule-like domains of C2000-FS-0 to the

Fig. 2. AFM tapping mode topographic and phase images of T2000-FS-0, T2000-FS-5, C2000-FS-0, and C2000-FS-5. The scan area is 1 lm � 1 lm, and theheight scale and phase scale are 0–20 nm and 0–20�, respectively.

Table 5Hemolysis of the different PTFPMS-containing anionic PUUs.

Sample OD values at 545 nm Hemolysis (%)

Negative 0.014 ± 0.001 –Positive 0.747 ± 0.005 –T2000-FS-0 0.023 ± 0.001 1.36T2000-FS-5 0.021 ± 5.8E-4 0.95T2000-FS-30 0.019 ± 0.001 0.68C2000-FS-0 0.021 ± 0.001 0.95C2000-FS-5 0.018 ± 0.002 0.55C2000-FS-30 0.016 ± 5.8E-4 0.27


worm-like co-continuous domains of C2000-FS-5, and thedomain size decreased as the PTFPMS content increased, asshown in Fig. 2. This result gave direct evidence that the de-gree of phase separation increased on the surface of PTFPMS-containing polycarbonate-based PUU with incorporatingPTFPMS at a small amount. Furthermore, as obtained fromthe AFM topographic images using NanoScope 5.12 soft-ware, the values of RMS roughness for C2000-FS-0 andC2000-FS-5 were 1.23 and 0.84 nm, respectively; whereas,those for T2000-FS-0 and T2000-FS-5 were 1.16 and0.55 nm, respectively. These results indicated that the incor-poration of PTFPMS reduced the surface roughness of bothseries of modified PUU films, and the surfaces of the poly-ether-based series were smoother than those of the polycar-bonate-based series.

Fig. 3. (a) The dynamic clotting time curves of the different test materials. Data(b) The clotting time of the different test materials.

The hemolysis study reveals the lysis of red blood cellsresulting from contact with a material surface. The smallerthe hemolysis, the better is the hemocompatibility of thematerial. The acceptable limit of percentage of hemolysisfor a hemocompatible material is 5% [23]. With increasingPTFPMS content, the percentage of hemolysis for both ser-ies decreased, and was well within the acceptable limit, aslisted in Table 5. Therefore, these PTFPMS-containing PUUscould be considered having little hemolytic effect on thehuman red blood cells.

Fig. 3 depicts the blood clotting profiles on the surfaces ofthe different PUU films. The absorbance of hemolyzedhemoglobin solution varies with time. The higher absor-bance indicates the better antithrombogenicity. The timeat which the absorbance equals 0.1 is generally defined asclotting time. The best blood compatibility of materials canbe achieved by the longest clotting time. Fig. 3 also showsthe clotting time for the different PUU specimens. Appar-ently, the thrombogenic tendency of the PUU anionomerswithout PTFPMS was more or less lower than that of the po-sitive control and even the negative one. This result could beascribed to the anionic groups on the surfaces of T2000-FS-0and C2000-FS-0, which reduced the degree of platelet adhe-sion and activation on the PUU surfaces owing to the electro-static repulsion between the carboxylate groups andplatelet membrane [4,8]. As the PTFPMS content increased,both series of PTFPMS-containing PUU anionomers exhib-

are presented as mean ± standard deviation of three parallel experiments.

Fig. 4. Schematic representation of blood-material interaction. (a)PTFPMS-containing anionic PUU. (b) Anionic PUU without PTFPMS.


ited even better antithrombogenicity than those compara-ble specimens without PTFPMS, with their clotting time ex-tended significantly. This could be explained by that thePTFPMS segments migrating to the PUU surface and the car-boxylate groups may have a synergistic effect to reduce thethrombogenicity, as illustrated in Fig. 4. When a polymercontacts with blood, the thrombus formation on the poly-mer surface is usually initiated by protein adsorption onthe surface, then followed by platelet adhesion and activa-tion along coagulation pathways. Although Si–O–Si linkagesexhibit poor resistance to protein adsorption [24], the 3,3,3-trifluoropropyl groups bonded directly with the siliconatoms in the PTFPMS segments can provide steric protectionto the siloxane chains, which should enhance the resistanceof PTFPMS to protein and platelet adhesion. The coexistenceof the negatively-charged carboxylate groups and thePTFPMS segments enriched on the surface of PUU wouldbe favorable for further reducing the protein and plateletdeposition onto the surface, thereby leading to the markedlyenhanced antithrombogenicity of PUU. It is worth noting

Fig. 5. FTIR spectra of the anionic PUUs with different PTFPMS conte

that, the polyether-based PUU series exhibited superiorthromboresistance to the polycarbonate-based series,although more PTFPMS segments were resident on the sur-faces of C2000-FS-X series. Hayama et al. [25] found thatsmooth surfaces helped to decrease the platelet adhesionand activation. Hence, this observation may be attributedto the smoother surfaces of the polyether-based series thanthose of the polycarbonate-based series, as characterized byAFM measurement. All these experimental results indicatedthat the hemocompatibility of the anionic waterborne PUUwas enhanced upon the incorporation of PTFPMS.

3.3. Bulk properties of PUU films

Generally, the strong hydrogen bonding of the urethaneand urea linkages for a multiblock PUU is easily formed.The ordered structure of hard segments in PUU should berelated to the interactions of hydrogen bonding in the sys-tem and can be determined using FTIR spectrometer. Fig. 5show the FTIR spectra of the polyether-based and polycar-bonate-based PUUs with different PTFPMS contents,respectively. In the infrared spectra of these specimens,the region at 1600–1750 cm�1 corresponding to the car-bonyl stretching vibrations has been widely used to char-acterize the hydrogen bonding of PUUs. In this study, thehydrogen bonding between the urea linkages was chosenfor investigation, as the absorption peaks for urethanegroups would be affected by the carbonyl absorption peaksof the polycarbonate segment in the PUU. However, thecarbonyl absorption peak of DMPA units existing in thePUU macromolecular chains is located at 1550 cm�1,which would not influence the investigation of hydrogenbonding for urea groups [3]. Fig. 6 shows the FTIR spectraof different PUU films in the carbonyl region at 25 �C. Inthese spectra, multiple bands can be found. The iterationprocedure of damping least squares, based on a combina-tion of Lorentzian and Gaussian curve shapes, was usedto separate the absorption peaks in the carbonyl regioncorresponding to different kinds of hydrogen bonding[3,26] (Table 6), and the curve-fitting results are listed inTables 7 and 8, respectively. The degree of hydrogen bond-ing for urea groups (Xb,UA), and the percentages of orderedand disordered urea hydrogen bonds (Xo,UA and Xd,UA) aredefined as follows:

nts. (a) Polyether-based series. (b) Polycarbonate-based series.

Fig. 6. Deconvolution of carbonyl region for the anionic PUUs with different PTFPMS contents by least-square curve-fitting (solid line: original result;dashed line: curve-fitting result).

Table 6Assignment of the absorption bands in the carbonyl region of the FTIR spectra for PUUs.

Wave number (cm�1) Assignment

1747–1728 Free carbonyl stretching of urethane linkages and polycarbonate1727–1717 Disordered hydrogen-bonded carbonyl of urethane linkages and hydrogen-bonded carbonyl of polycarbonate1708–1700 Ordered hydrogen-bonded urethane carbonyl1690–1680 Free urea carbonyl1678–1650 Disordered hydrogen-bonded urea carbonyl1649–1632 Ordered hydrogen-bonded urea carbonyl


Table 7Least-square-curve-fitting FTIR spectra in the urea carbonyl region for the different polyether-based PUUs.

Sample Peak area (%) Xo,UA (%) Xd,UA (%) Xb,UA (%)

1683 (cm�1) 1669 (cm�1) 1658 (cm�1) 1645 (cm�1) 1634 (cm�1)

T2000-FS-0 �0 8.0 2.1 9.2 20.5 74.6 25.4 �100T2000-FS-5 2.0 10.1 0 8.7 23.8 72.9 22.6 95.5T2000-FS-30 10.3 4.5 3.0 5.9 28.5 65.9 14.4 80.3

Table 8Least-square-curve-fitting FTIR spectra in the urea carbonyl region for the different polycarbonate-based PUUs.

Sample Peak area (%) Xo,UA (%) Xd,UA (%) Xb,UA (%)

1683 (cm�1) 1666 (cm�1) 1640 (cm�1)

C2000-FS-0 3.1 5.2 13.1 61.2 24.3 85.5C2000-FS-5 �0 4.6 12.0 72.3 27.7 �100C2000-FS-30 4.8 5.0 13.6 58.1 21.4 79.5


Xb;UA ¼P

AreaðbondedÞAreað1690—1680 cm�1Þ þ

PAreaðbondedÞ ð10Þ

Xo;UA ¼P

Areað1649—1632 cm�1ÞAreað1690—1680 cm�1Þ þ


Xd;UA ¼P

Areað1678—1650 cm�1ÞAreað1690—1680 cm�1Þ þ


Table 7 shows that nearly all the urea carbonyl groupsin T2000-FS-0 system were involved in hydrogen bondingwith a high value of Xo,UA. With increasing PTFPMS content,the values of both Xo,UA and Xd,UA decreased, indicating thatthe introduction of PTFPMS segments would destroy theordered structure in the hard domain and compromisethe interaction between the hard segments, so as to en-hance the phase mixing between the hard and soft seg-ments, which was in keeping with the observation by AFM.

A different result was observed for the polycarbonate-based PUUs, as shown in Table 8. It shows that the valuesof Xo,UA and Xd,UA in C2000-FS-0 were both lower thanthose in T2000-FS-0. As the PTFPMS content increasedfrom 0 to 5 wt.%, the value of Xo,UA increased significantlyand the urea carbonyl groups in C2000-FS-5 were almostcompletely hydrogen-bonded, possibly because the pres-ence of a small amount of long flexible PTFPMS would en-hance the mobility of the polycarbonate-based PUUmacromolecular chains, leading to a much orderedarrangement of hydrogen bonds. When the PTFPMS con-tent further increased to 30 wt.%, the values of Xo,UA andXd,UA decreased evidently. This phenomenon may be attrib-uted to the excess PTFPMS segments in the PUU filmdestroying the ordered hydrogen bonding arrangement inthe system.

Fig. 7 shows the DSC thermograms of the different PUUspecimens and the DSC scan results are listed in Table 9. Allthe specimens had a glass-transition temperature (Tg) ofthe soft segment, and exhibited an endothermic peak withthe melting temperature (Tm) ranging from 210.5 to221.2 �C, corresponding to the dissociation of the long-dis-tance ordering of PUU hard segments or the melting ofsome microcrystallites [3,26]. For the polyether-based ser-

ies, the Tg of T2000-FS-0 lay close to that of the pure poly-ether polyol (PolyTHF 2000), suggesting that the hard andsoft segments were hardly compatible in the system. Withincreasing PTFPMS content, the Tg was nearly unchangedwhile Tm shifted to a low temperature with decreasingmelting enthalpy (DHm). These results indicated that theintroduction of PTFPMS had little influence on the softphase, but mainly destroy the ordered structure in harddomains, so as to enhance the phase mixing between thehard and soft segments. For the polycarbonate-based ser-ies, the Tg of C2000-FS-0 shifted to a higher temperaturecompared to that of the pure polycarbonate polyol (PCDLS6002), revealing an appreciable compatibility betweenthe hard and soft segments. As the PTFPMS content in-creased, the values of Tm and DHm increased first then de-creased, while the value of Tg was nearly the same. Theseresults showed that the incorporation of PTFPMS had agreat effect on the ordering of hard domains, leading toan enhanced phase separation at low content but a phasemixing at high content of PTFPMS. All these experimentalresults are consistent with the AFM observation and thehydrogen bonding degree data characterized by FTIR, asdiscussed previously.

As shown in Table 2, the water absorption amounts ofboth the polycarbonate-based and the polyether-basedPUU films were decreased with the insertion of PTFPMSsegments. The C2000-FS-5 film showed a water absorptionamount as low as 2.9 wt.%, which should also be attributedto the significant increase in the ordered as well as the to-tal hydrogen bonding degrees in such a system (Table 7).Our previous findings showed that the ordered structureof the hard segments containing the hydrophilic DMPAunits formed from the hydrogen bonding in the polyes-ter-based PUU films is beneficial for preventing DMPAunits from attacking by water, thereby decreasing theamount of water absorption [27]. The ordered structureformed in the C2000-FS-5 film was the best with the high-est Xo,UA, thereby giving rise to the lowest water absorptionamount in this series. For the T2000-FS-0 system, the hardand soft phases were highly incompatible, which couldfacilitate the penetration of water molecules into the bulkalong the interfacial interstices. With increasing PTFPMS

Fig. 7. DSC thermograms of the different polyols and PTFPMS-containing anionic PUUs.

Table 10Mechanical properties of the anionic PUU films with different PTFPMScontents.

Sample Tensile strength (MPa) Elongation at break (%)

T2000-FS-0 53.2 ± 2.0 1091 ± 26T2000-FS-5 46.4 ± 4.2 1236 ± 81T2000-FS-30 22.4 ± 0.9 963 ± 26C2000-FS-0 43.7 ± 2.5 610 ± 39C2000-FS-5 60.7 ± 1.9 632 ± 21C2000-FS-30 41.4 ± 2.1 541 ± 11


content, the hydrogen bonding and microphase-separationdegrees in the system decreased, as evidenced by FTIR andDSC, and this could be favorable for protecting the hydro-philic hard segments by the soft segments so as to lowerthe water absorption amount of PUU film.

The mechanical properties of all the PUU films weremeasured, as listed in Table 10. For the polyether-basedPUUs, the tensile strength decreased with increasingPTFPMS content, resulting from the decrease in hydrogenbonding and microphase-separation degrees in these sys-tems. However, it should be noted that T2000-FS-30 stillshowed a tensile strength of 22.4 MPa and an elongationat break of 963%. These tensile properties are good enoughfor this waterborne PUU to be used in soft tissue engineer-

Table 9DSC scan results for the different polyols and PTFPMS-containing anionicPUUs.

Sample Tg (�C) Tm (�C) DHm (J/g)

PolyTHF 2000 �81.8 28.2 113.0PCDL S6002 �54.2 17.0; 48.4 7.5; 51.2T2000-FS-0 �75.7 220.6 6.2T2000-FS-5 �76.7 219.8 5.6T2000-FS-30 �76.5 217.2 4.8C2000-FS-0 �36.5 210.5 2.7C2000-FS-5 �37.6 221.2 5.2C2000-FS-30 �36.8 219.1 2.4

ing scaffold [7]. For the polycarbonate-based PUUs, theC2000-FS-5 film exhibited the highest tensile strengthand breaking elongation of 60.7 MPa and 632%, respec-tively, due to the enhanced hydrogen bonding as well asthe microphase-separation in this system. Such excellentmechanical properties could be comparable with those ofsome solvent-borne poly (carbonate urethane) productsused as biomaterials, such as Bionate� and ChronoFlex�

AR [28].

4. Conclusions

Two series of novel polyether-based and polycarbonate-based anionic waterborne PUUs consisting of long PTFPMS


segments in the macromolecular chains were successfullysynthesized and characterized. The experimental resultsevidenced the migration of PTFPMS segments onto the sur-face of modified PUU, which enhanced remarkably thethromboresistance of PUU owing to the synergistic effectbetween PTFPMS segments and carboxylate anions. Allthe PTFPMS-modified PUU films possessed excellentwater-resistant and mechanical properties due to the dualeffects of the hydrogen bonding and microphase-separa-tion in the systems. Therefore, these polymers can be con-sidered good candidates for bioapplications.

Acknowledgement

This work was supported by Shanghai Leading Aca-demic Discipline Project (No. B502).

References

[1] Vermette P, Griesser HJ, Laroche G, Guidoin R. Biomedicalapplications of polyurethanes. Texas: Eurekah.com; 2001.

[2] Nanda AK, Wicks DA. The influence of the ionic concentration,concentration of the polymer, degree of neutralization and chainextension on aqueous polyurethane dispersions prepared by theacetone process. Polymer 2006;47:1805–11.

[3] Hu YS, Tao Y, Hu CP. Polyurethaneurea/vinyl polymer hybridaqueous dispersions based on renewable material.Biomacromolecules 2001;2:80–4.

[4] Chen KY, Kuo JF, Chen CY. Synthesis, characterization and plateletadhesion studies of novel ion-containing aliphatic polyurethanes.Biomaterials 2000;21:161–71.

[5] Chen H, Jiang XW, He L, Zhang T, Xu M, Yu XH. Novel biocompatiblewaterborne polyurethane using L-lysine as an extender. J Appl PolymSci 2002;84:2474–80.

[6] Yu SH, Mi FL, Shyu SS, Tsai CH, Peng CK, Lai JY. Miscibility,mechanical characteristic and platelet adhesion of 6-O-carboxymethylchitosan/polyurethane semi-IPN membranes. JMembr Sci 2006;276:68–80.

[7] Jiang X, Li JH, Ding MM, Tan H, Li QY, Zhong YP, et al. Synthesis anddegradation of nontoxic biodegradable waterborne polyurethaneselastomer with poly(e-caprolactone) and poly(ethylene glycol) assoft segment. Eur Polym J 2007;43:1838–46.

[8] Poussard L, Burel F, Couvercelle JP, Merhi Y, Tabrizian M, Bunel C.Hemocompatibility of new ionic polyurethanes: influence ofcarboxylic group insertion modes. Biomaterials 2004;25:3473–83.

[9] Pizzoferrato A, Arciola CR, Cenni E, Ciapetti G, Sassi S. In vitrobiocompatibility of a polyurethane catheter after deposition offluorinated film. Biomaterials 1995;16:361–7.

[10] Chen KY, Kuo JF, Chen CY. Synthesis, characterization, and plateletadhesion studies of novel aliphatic polyurethaneurea anionomers

based on polydimethylsiloxane-polytetramethylene oxide softsegments. J Biomater Sci Polym Ed 1999;10:1183–205.

[11] Benrashid R, Nelson GL. Synthesis of new siloxane urethane blockcopolymers and their properties. J Polym Sci Part A Polym Chem1994;32:1847–65.

[12] Wang HH, Lin YT. Silicon-containing anionic water-bornepolyurethane with covalently bonded reactive dye. J Appl PolymSci 2003;90:2045–52.

[13] Tan H, Xie XY, Li JH, Zhong YP, Fu Q. Synthesis and surface mobilityof segmented polyurethanes with fluorinated side chains attached tohard blocks. Polymer 2004;45:1495–502.

[14] Su T, Wang GY, Xu XD, Hu CP. Preparation and properties ofwaterborne polyurethaneurea consisting of fluorinated siloxaneunits. J Polym Sci Part A Polym Chem 2006;44:3365–73.

[15] Su T, Wang GY, Hu CP. Preparation and properties of well-definedwaterborne polyurethaneurea with fluorinated siloxane units inhard or soft segments. J Polym Sci Part A Polym Chem2007;45:5005–16.

[16] Sutandar P, Ahn DJ, Franses EI. FTIR ATR analysis for microstructureand water uptake in poly(methyl methacrylate) spin cast andLangmuir–Blodgett thin films. Macromolecules 1994;27:7316–28.

[17] Turri S, Radice S, Canteri R, Speranza G, Anderle M. Surface study ofperfluoropolyether–urethane cross-linked polymers. Surf InterfaceAnal 2000;29:873–86.

[18] Thomas V, Kumari TV, Jayabalan M. In vitro studies on the effect ofphysical cross-linking on the biological performance of aliphaticpoly(urethane urea) for blood contact applications.Biomacromolecules 2001;2:588–96.

[19] Huang N, Yang P, Cheng X, Leng Y, Zheng X, Cai G, et al. Bloodcompatibility of amorphous titanium oxide films synthesized by ionbeam enhanced deposition. Biomaterials 1998;19:771–6.

[20] Kim BK, Lee JC. Polyurethane ionomer dispersions from poly(neopentylene phthalate) glycol and isophorone diisocyanate.Polymer 1996;37:469–75.

[21] Wu SH. Polymer interface and adhesion. New York: Marcel Dekker;1982.

[22] Revenko I, Tang Y, Santerre JP. Surface structure of polycarbonateurethanes visualized by atomic force microscopy. Surf Sci2001;491:346–54.

[23] ISO/TR 7405-1984. Biological evaluation of dental materialscontents, heamolysis test (in vitro test directly on materials).

[24] Bartzoka V, McDermott MR, Brook MA. Protein silicone interactions.Adv Mater 1999;11:257–9.

[25] Hayama M, Yamamoto K, Kohori F, Uesaka T, Ueno Y, Sugaya H, et al.Nanoscopic behavior of polyvinylpyrrolidone particles onpolysulfone/polyvinylpyrro-lidone film. Biomaterials2004;25:1019–28.

[26] Luo N, Wang DN, Ying SK. Crystallinity and hydrogen bonding ofhard segments in segmented poly(urethane urea) copolymers.Polymer 1996;37:3577–83.

[27] Yang DY, Hu CP, Ying SK. Preparation and characterization ofwaterborne poly (urethane urea) with well-defined hard segments.J Polym Sci Part A Polym Chem 2005;43:2606–14.

[28] Szycher M, Reed AM, Siciliano AA. In vivo testing of a biostablepolyurethane. J Biomater Appl 1991;6:110–30.

fluorinated siloxane-containing waterborne polyurethaneureas with excellent hemocompatibility,...

Documents