A Designed Surface Modification to Disperse SilicaPowder into PolyurethaneLianying Liu,1Hideo Watanabe,2Takashi Shirai,2Ma...
make the grafting of PU on particle surface more com-plex in comparison with the grafting of homopoly-mers such as polysty...
of PEG400 (3 Â 10À3mol), MDI (3 Â 10À3mol) andDMAc. 0.05 mL or 0.5mL of the as-produced disper-sion was coated on a piece ...
dM improved along with increase of modifieramount, confirming the successful incorporation ofNCO-groups on particle surfac...
observations were presented after repeated reactionwith PEG and MDI in cycles (Figure 2, curves a5and a6). The above descr...
and soft segment content in grafted PU chains, onecould find that the content ratio of hard and soft seg-ment was close to...
weight loss %) were more favorable for preparing atransparent hybrid film. Using a piece of quartzglass as reference, the ...
11. Radhakrishnan, B.; Ranjan, R.; Brittain, W. J. Soft Matter 2006,2, 386.12. Frankamp, B. L.; Boal, A. K.; Tuominen, M. ...
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A designed surface modification to disperse silica powder into polyurethane

  1. 1. A Designed Surface Modification to Disperse SilicaPowder into PolyurethaneLianying Liu,1Hideo Watanabe,2Takashi Shirai,2Masayoshi Fuji,2Minoru Takahashi21Key Laboratory of Carbon Fiber and Functional Polymers, College of Materials Science and Engineering,Beijing University of Chemical Technology, Beijing 100029, China2Ceramics Research Laboratory, Nagoya Institute of Technology, Tajimi, Gifu 507-0033, JapanReceived 13 September 2011; accepted 25 December 2011DOI 10.1002/app.36734Published online 12 June 2012 in Wiley Online Library (wileyonlinelibrary.com).ABSTRACT: Nanoparticles of silica powder were modi-fied by grafting polyurethane (PU) short chains or oligom-ers using surface-started condensation reactions of variousdi- or tri-ols and di-isocyanates in step-by-step. Surfacedensity of NCO-groups, introduced by an autoclavemethod and ready for starting of subsequent reactions,was adjusted by amount of 3-isocyanatepropyltriethoxysi-lane (ICPTES). Length of grafted oligomers was deter-mined by reaction steps. TG/DTA measurementsdemonstrated a gradual increase of NCO-groups densitywith the amount of modifier input. FTIR spectra and ther-mal weight loss analyses confirmed the occurrence of reac-tion in each step and the growth of grafted oligomer. SEMimages of particles dispersed in N, N-dimethylacetamideor in prepolymer of PU indicated an improved dispersion.Moreover, when as-modified particles were incorporatedin PU prepolymer, the resultant hybrid films displayed anenhanced optical property, thermal stability, and Vicker’shardness, suggesting a better dispersion of modified par-ticles. VC 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 126:E522–E529, 2012Key words: silica nanoparticle; surface modification;dispersion; polyurethaneINTRODUCTIONPolymer/silica nanocomposite materials haveattracted both academic and industrial interest forseveral decades because of their unique synergisticproperties, advantages of availability and inexpen-siveness, and potential applications in variousfields.1–9However, a well-defined dispersion ofsilica powder nanoparticles (NPs) in polymer matri-ces is still a pursuing issue, as the enough stronginteractions at interface between polymer matricesand inorganic NPs is intrinsically hard to achieve.10Up to now, extensive research works have beendone to mitigate the self-aggregation of inorganic NPsderived from Vander Waals attractions, and thus toimprove the compatibility of inorganic NPs with anorganic phase.11–13Among them, surface initiated con-trol/living radical polymerizations10,14–16are consid-ered to be effective techniques to firmly control pa-rameters including graft density, molecular weight,and chemical composition of graft and matrix poly-mers, etc.17–19to enhance the dispersion of inorganicNPs.19Usually, dense and long grafted chains wereprerequisite to achieve complete isolation of NPs inhomo- or block-polymer matrices19to take full advant-age of large specific surface/interface area of NPs.Sometimes, particles grafted with relative sparse andshort chains also brought about an effective disper-sion, and their self-assembly into highly anisotropicstructures led to a pronounced enhancements in me-chanical property of resultant nanocomposites.10,17,19In addition, condensation reactions initiated froma solid surface provide an alternative to covalentlyimmobilize linear or branched functional copolymerchains on particles, and hence to facilitate the disper-sion of inorganic NPs. Some of investigations on sur-face-started condensation polymerization have beenperformed to create highly advanced organic/inor-ganic nanocomposites,20for example, Chen et al.21prepared polyurethane (PU)/silica hybrid nanocom-posites by incorporation of inorganic nanosizedsilica building blocks into PU matrix via a two stepfunctionalized reaction including encapsulation of 3-aminopropyltriethoxysilane (APTS) and tether of PUshell on silica surface. In previous works, elaboratecontrol of grafting of PU chains onto silica powderparticles, such as manipulation of surface density,grafted chain length, and structure, by condensationreactions started from particle surface, was seldominvolved in, and a better dispersion of silica powderin matrix of PU is still needed.It is known that PU can be manufactured by con-densation polymerization of di-isocyanates and di- ortri- hydroxyl compounds (di-ols or tri-ols). Theemployment of multifunctional monomers wouldCorrespondence to: M. Fuji (fuji@nitech.ac.jp).Journal of Applied Polymer Science, Vol. 126, E522–E529 (2012)VC 2012 Wiley Periodicals, Inc.
  2. 2. make the grafting of PU on particle surface more com-plex in comparison with the grafting of homopoly-mers such as polystyrene (PSt), or poly(methyl meth-acrylate) (PMMA) by free radical polymerizations.Especially, when surface condensation reactions startfrom large aggregated silica particles, rather than fromindividual NPs dispersed homogeneously in a goodsolvent or media, it is not easy to achieve dense andlong linear grafted chains because of high reactivity ofmultifunctional monomers. Furthermore, the dispers-ing behavior of as-grafted NPs in PU is supposed to bedissimilar to that of silica NPs attached homopolymerin analogous matrices of homopolymer, block copoly-mer16or miscible blends of polymers19Accordingly,further investigations on the grafting of PU on particlesurface by condensation reaction to disassociate silicapower in PU are demanded.In our group, surface designed reactions were pro-posed to shield silica particle surface with denselygrafted functional polymers to achieve a good disper-sion in polyimide (PI) or in slurry.22,23Herein, withthe aim to improve the dispersibility of silica powderin PU matrix, oligomer, or short-chain of PU wasdevised to incorporate onto particles by an autoclavemethod under supercritical hexane using 3-isocyana-tepropyltriethoxysilane (ICPTES) as a modifier agent,and followed by graft condensation reactions of sur-face-coupled isocyanate groups (NCOA) with di-, tri-ols, and di-isocyanate, as shown in Scheme 1. Surfacedensity of initial functional groups (NCOA), whichindicated the surface grafting density of oligomers onsilica particles, was adjusted by modifier agent inputand evaluated by TG/DTA measurements. Graftchain length of PU oligomers, demonstrated by FTIRspectra analysis, and TG/DTA measurements, wasthought to be manipulated by further grafting reac-tions of di- or tri-ols, and di-isocyanate in step bystep. Furthermore, hybrid thin films with modifiedsilica particles dispersed in PU were prepared by acontrolled roller coating and thermal curing, and theiroptical properties, thermal, and mechanical propertieswere examined.EXPERIMENTALMaterialsSilica powder (Aerosil OX 50, average particle sizeof 40 nm, specific surface area 50 m2/g, supplied byNippon Aerosil) was dried at 130C in a vacuumoven for at least 48 h and stored at room tempera-ture (RT) with a relative humidity (RH) of 34%.Modifier agent ICPTES (Shin-Etsu Silicone, KBE9007, 99.7%, purchased from Shin-Etsu Chemical),poly-ols including polyethylene glycol (PEG, MW ¼400, 2000, 99%), triethylene glycol (TEG, MW ¼150.17, 99.8%), diethanolamine (DEOA, MW ¼105.14, 99.8%), tris-(hydroxymethyl)aminomethane(TOAM, MW ¼ 121.14, 99.8%), and 4,4-Diphenylme-thane diisocyanate (MDI, 99.7%), etc., from Shin-Etsu Chemical, were used without further purifica-tion. Solvents such as N, N-dimethylacetamide(DMAc) and acetone, etc., were used as received.Modification of silica particles with ICPTESThe chemical reaction of ICPTES with hydroxylgroups of silica (density of OHA groups: 2.8/nm2)was carried out using an autoclave method asdescribed previously.22The amount of modifierapplied was referred to mole ratio of NCO-group tosilanol groups (NCOA/OH in moles) on silica sur-face. The surface density of modifier, noted as sur-face density of NCO-groups (dM, NCOA nm2) onparticles, was determined with weight loss datafrom TG/DTA analysis and calculated according tothe following equation23:dMðNCOÀ=nm2Þ ¼ðDWCH À DWOHÞNAMWSN2where DWCH is the weight loss ratio of modifiedsilica particle, DWOH is that of pristine one, NA is theAvogadro number, MW is the molecular weight ofmodified group (84), and SN2 is the specific surfacearea of silica powder used (50 m2/g).Surface grafting by condensation reactionsIn a 100 mL, 4-neck bottom flask equipped with con-denser, thermometer and N2 inlet, the modified par-ticles (SiANCO) were suspended into DMAc withaids of a magnetic stirrer, and then di- or tri-ols, orMDI was introduced into the suspension in step bystep. The condensation reaction was performed usu-ally under a small N2 flow at 25C for 3 h.After cycles of reaction of diisocyanate and poly-ols, particle surface was coated with oligomers ofPU. Sample produced in each step was isolated bycentrifugation, washed with DMAc, and acetone forat least 3 cycles, and then dried under vacuum.Preparation of hybrid filmsPristine or surface-modified silica particles (5 wt %)were ultrasonically dispersed in 2 mL of a mixtureScheme 1 Representation of surface modification of silicaNPs with ICPTES, and further reactions with di-, tri-ol, ordi-isocyanate.DISPERSING SILCA POWDER INTO POLYURETHANE E523Journal of Applied Polymer Science DOI 10.1002/app
  3. 3. of PEG400 (3 Â 10À3mol), MDI (3 Â 10À3mol) andDMAc. 0.05 mL or 0.5mL of the as-produced disper-sion was coated on a piece of quartz or pyrex glassusing a K101 Control Coater (RK Print Coat Instru-ment, UK), and then cured at 70C for 12 h to get athin or thick film.CharacterizationWeight loss data: determined on a Thermo PlusTG8120 analyzer (Rigaku, Japan) under O2 atmos-phere with a flow rate of 500 mL/min, heating rateof 10C/min, from room temperature to 700C.Grafted chains analysis: done on a FTIR 6200 spec-trometer (Jasco, Japan) using KBr pellets.Morphology of particles: observed on a JSM-7000FScanning Electron Microscope (SEM, Jeol, Japan),under an accelerating voltage of 10 kV. Sampleswere prepared by dropping suspension of silica par-ticles in DMAc on a small piece of cover glass andevaporating at room temperature, or by spin-coatingthe mixture of silica particles, PEG, MDI, and DMAcon a glass and then drying under vacuum at 70Cfor 8 h. Before SEM observation, samples werecoated with osmium (OsO4).Particle size and its distribution: evaluated byZetasizer Nano Series (Malvern Instrument) in a sol-vent of DMAc.Transmittance of hybrid films: measured on aUV–VIS–NIR spectrophotometer, UV3150 (Shi-madzu, Japan) in wavelength range of 190–900 nm.Vicker hardness of hybrid film: estimated on aHMV-2T micro-hardness tester (Shimadzu, Japan),and for each sample, at least four points was meas-ured to get an average value.RESULTS AND DISCUSSIONSurface-initiated condensation reactions andstructure analysisAn autoclave method was used to allow the surfaceAOH groups react efficiently with silane couplingagent22,23due to AOH groups in silica powder arenot easy to be fully exposed on surface. Surface den-sity of NCO-groups (dM) introduced firstly onto par-ticle, approximating the graft density of PU oligomeror short chain in subsequent process, could be con-trolled by varying ICPTES input in system and eval-uated by TG/DTA analysis. As plotted in Figure 1,Figure 1 Surface density of NCO-groups on silica par-ticles modified with various ratio of NCO-/OH.Figure 2 FTIR spectra analysis of silica particles and materials, 0: pristine particles, 1: Si-NCO particles, 2,4,6 (a) particlesproduced after reaction with PEG (a) or DEOA (b), 3,5 (a) particles produced after further reaction with MDI. 7(a), 5(b):MDI, 8(a): PEG, 6(b) DEOA.E524 LIU ET AL.Journal of Applied Polymer Science DOI 10.1002/app
  4. 4. dM improved along with increase of modifieramount, confirming the successful incorporation ofNCO-groups on particle surface. When mole ratio ofNCOA/OH was increased up to 12.2, surface den-sity of about 1.14 NCO-groups/nm2was achieved,and then a slight change of coupling of NCO-groupsdisplayed at a higher mole ratio of NCOA/OH.In the present experiments, values of dM werelower than that achieved previously22,23and far lessthan theoretical one of 2.8-OH/nm2.23This casewould cause some difficulties in detecting the pres-ence of NCO-groups by FTIR analysis (Figure 2,curve 1). The aggregation of silica particles in pow-der (could be at around 600–1700 nm, evaluated bydynamic light scattering, DLS) might screen somefree AOH groups on surface and limit their reactionwith modifier of ICPTES, leading to a low couplingdegree of NCO-groups. In addition, the possiblereaction of NCO-groups of ICPTES with OH-groupson particle surface might also be negative to the cou-pling of NCO-groups.When poly-ols such as PEG or DEOA werecharged into reaction system to start condensationreaction with pristine particles, and MDI was addedin subsequent step, the obtained particles showed nodistinct FTIR absorptions and marked weigh lossdiffering from those of pristine particles. In systemcontained particle with NCO-groups coupled on sur-face in a density of 1.14/nm2, FTIR analysis indi-cated that in the first step, with poly-ols such asPEG or DEOA charged, no significant variations wasdiscerned (Figure 2, curve 2). While, with MDI seg-ments incorporated onto particle surface, characteris-tic absorption of NCO-group at 2279 cmÀ1wasobserved clearly (Figure 2, curves a3 and b3). Thisphenomenon implied that more NCO- groups couldbe combined because of the possible reaction of MDIwith surface free AOH groups freshly exposed dueto a gradually improved dispersion. The aboveresults further verified the successful introduction oforiginal NCO-groups, and revealed that it wasenough to start condensation reactions from particlessurface with NCO-groups in a low density, allowingto graft sparse and enough long polymer chains onsurface to improve the dispersion of particles.As seen in Figure 2, absorption at 1720 cmÀ1couldbe assigned to AC¼¼O group come forth with theaddition of MDI. Absorption at 1650 cmÀ1could beascribed to amide groups ACOANHA, and absorp-tions at 1705, 1632 cmÀ1could be attributed to car-bonyl groups of urethano units (ANHCOOA).Absorptions at 1600, 1560, 1514, 1423 cmÀ1were aro-matic characteristic peaks. When reaction with PEGor DEOA occurred again, the characteristic absorp-tion of NCOA at 2279 cmÀ1was disappeared almostcompletely (Figure 2, curves a4 and b4), and absorp-tions arising from ACH2 symmetric stretching vibra-tion at 2890 cmÀ1, NAH stretching vibration at about3300 cmÀ1were detected apparently. SimilarFigure 3 (a) Typical TG curves of silica particles: pristineparticles (1), Si-NCO particles (2), modified silica particlesafter reaction with TEG (3), and then with MDI repeatedlyat 0C (4) or 25C (5) for 5 steps. (b) Condensation reactionof SiANCO particles with PEG (1) or DEOA (2), and thenwith MDI in multisteps, WSi-NCO ¼ 0.2 g, MPEG or DEOA ¼MMDI ¼ 3 Â 10À3mol, VDMAc ¼ 30 mL.TABLE IGrafting of Short Chains or Oligomers Through Condensation Reactions in MultistepsComposition ofgrafted chainsSi-NCO-TEGSi-NCO-PEG400Si-NCO-PEG2000Si-NCO-TEG-MDI-TEG-MDI-TEGSi-NCO-TOAMSi-NCO-DEOASi-NCO-DEOA-MDI-DEOAWeight loss% À3.83 À4.32 À5.15 À5.26 À4.74 À4.94 À9.15Reaction time: 6 h; temperature: 0C; WSi-NCO ¼ 0.2 g; Mols ¼ MMDI ¼ 3 Â 10À3mol; VDMAc ¼ 30 mL.DISPERSING SILCA POWDER INTO POLYURETHANE E525Journal of Applied Polymer Science DOI 10.1002/app
  5. 5. observations were presented after repeated reactionwith PEG and MDI in cycles (Figure 2, curves a5and a6). The above described FTIR analysis demon-strated the occurrence of grafting condensation reac-tion and implied the growth of grafting chains ineach step.Typical TD/DTA measurements under an O2atmosphere indicated that started from surfaceNCO-groups, condensation reactions with TEG andthen MDI repeatedly led to a gradual increase ofweight loss [Figure 3(a)], suggesting a growth ofgrafted chains. This phenomenon was further con-firmed by weight loss data against reaction steps[Figure 3(b)] with various di-ols selected as amonomer.It could be noted that from Figure 3(a), curve 4 and5, the loading amount of PU oligomers obtained atreaction temperature of 25C, was much greater thanthat achieved at 0C, and TG curve of resultant sampleappeared two distinct regions of weight loss startedfrom about 200 and 330C, respectively, analogous to atypical TG curve of PU as reported.24It is known thatPU is commonly composed of hard and soft segments.The first region was related to thermal degradation ofhard segment of grafted chains due to low thermal sta-bility of urethane groups,25while the second regionwas associated to the soft segment decomposition.26Weight losses for the first and second regions were 27and 34%, respectively. Using weight loss at each regionas an approximately quantitative indication25of hardFigure 4 SEM images of pristine (a, b) and modified (c, d, weight loss 4.5%) particles dispersed in DMAc or in prepoly-mer of PU, and pristine (e) or modified (f) particle size distribution by intensity in DMAc. [Color figure can be viewed inthe online issue, which is available at wileyonlinelibrary.com.]E526 LIU ET AL.Journal of Applied Polymer Science DOI 10.1002/app
  6. 6. and soft segment content in grafted PU chains, onecould find that the content ratio of hard and soft seg-ment was close to feed mole ratio of MDI to TEG (2/3)in reactions.Moreover, compared with reactions occurred at alower temperature, or reactions performed only oneor two steps, samples generated at a higher tempera-ture and for more than three steps displayedextremely great weight loss percents, which mightnot be reasonably attributed to the lengthened graft-ing chains. Some free oligomer might be generatedaccompanying the growth of grafted chains and re-sponsible for this exaggeration in weight losses,because of high reactivity of isocynate and its com-plexity in reaction with poly-ols.27,28To alleviate the formation of free oligomer, reac-tions were carried out in low temperature for longtime, and various types of poly-ols were selected todeal with particles. As summarized in Table I, usinga diol having a high molecular weight, long chainscould be attached onto particle surface, as indicatedby the increased weight loss. Multi-step reactionscould also be favorable for the lengthening of teth-ered chains. Especially, the employment of CBn-typepoly-ols permitted the covalent incorporation ofbranched oligomer on particle surface, which wouldbe advantageous to make grafted chains spread intoa larger area as it moved away from a curved sur-face, and result in a broader grafted chain/matrixinterface and favorable grafted chain/matrix interac-tions. On the other hand, more functional groupsintroduced onto particle surface by application ofCBn-type polyols could give more possibility to inter-act with groups in PU matrix, and thus be positive tothe dispersion of particles.Dispersion of modified particlesWhen pristine silica particles were dispersed inDMAc, compact aggregate was observed from SEMimage [Figure 4(a)], even DMAc is a solvent inwhich silica particles could be eletrostatically stabi-lized.29Also, it was seen that at a low magnification,pristine silica particles could not be homogeneouslydispersed in prepolymer of PU [Figure 4(b)], and ata high magnification, great assemblies of silica parti-cle were found [Figure 4(b), inserted]. When silicaparticles were subjected to surface grafting modifica-tion, large aggregation was disappeared, only someparticles still congregated [Figure 4(c)]. At a lowmagnification, almost uniform dispersion of modi-fied particles could be observed [Figure 4(d)], andseparated particles in prepolymer of PU were pre-sented [Figure 4(d), inserted]. These observationsindicated that the grafting of polymer chains indeedimproved the dispersion of particles in DMAc andprepolymer of PU, and this effect became greater inprepolymer of PU due to stronger interactionsbetween functional groups. DLS measurement fur-ther confirmed the decrease in particle size and itsdistribution [Figure 4(e,f)].Properties of hybrid filmsWhen pristine particles were impregnated in prepol-ymer of PU, the prepared film had a transmittanceof around 35–70% in wavelength of 300–900 nmusing a piece of pyrex glass as reference (Figure 5,curve 1). When modified particles were immersed inprepolymer of PU, the hybrid film showed a trans-mittance of about 45–80% (Figure 5, curve 2), or 50–88% (Figure 5, curve 3). Silica particles immobilizedlonger oligomer on surfaces (indicated by the greaterFigure 5 Transmittance of hybrid films impregnated withpristine particle (1, 5), and modified particles (2, surfaceattached with PEG400 segment, weight loss 4.4%; 3, 4, sur-face grafted with PU oligomer composing of TEG andMDI segments, weight loss 5.6%).Figure 6 TG curves of hybrid films contained pristine (1),modified particles attached PEG400 segment (2, weightloss 4.4%) or PU oligomer composing of PEG400 and MDIsegments (3, weight loss 6.3%).DISPERSING SILCA POWDER INTO POLYURETHANE E527Journal of Applied Polymer Science DOI 10.1002/app
  7. 7. weight loss %) were more favorable for preparing atransparent hybrid film. Using a piece of quartzglass as reference, the transmittance of hybrid filmwas improved from 60–80% (Figure 5, curve 5) to58–90% (Figure 5, curve 4), closing to the transmit-tance (%80–90%, 300–900 nm) of PU film synthesizedwith PEG and MDI under similar conditions. Thisenhanced transmittance of hybrid films also evi-denced the improvement in particles dispersion.On the other hand, Figure 5 shows that in wave-length range of 190–300 nm, hybrid films appearedmarked absorptions, which could be attributed to ar-omatic and carbonyl structures of PU, and the pres-ence of particle attached PU oligomer seemed tostrengthen this UV absorption. This phenomenonmight be reasonable because of stronger interactionof modified particles with PU prepolymer, whichmight afford stretched grafted oligomers into matrixand hence make a contribution to UV absorption.TG/DTA measurements on hybrid films indicatedthat with modified particles (presenting greaterweight loss) dispersed in matrix of PU prepolymer,the as-prepared hybrid films exhibited a higher start-ing thermal decomposition temperature (Td) (Figure6, curve 3), while film contained particles providinglower weight loss showed no significant divergencein Td with that one impregnated pristine particles(Figure 6, curves 2 and 1). The end residue of hybridfilm after a TG/DTA run (Figure 6, curve 3) seemedto be somewhat greater than silica content (5 wt %),which might be ascribed to the trapping of polymermoiety in inorganic matrix.30The aforementionedthermal behaviors suggested an improvement ofthermal stability through incorporation of modifiedparticles. The covalently anchored functional groupson particle would cause more surface binding siteswith matrix, thus enhancing interfacial interactionwith matrix and compatibility with organic phase,and resulting in a greater thermal stability.Vicker’s hardness of prepared hybrid films meas-ured by a micro-controlled tester further proved thecompatibility enhancement derived from good disper-sion of modified particles. As shown in Table II, withparticles giving greater weight loss, the resultanthybrid film demonstrated an extremely high hardness.As reported by Smith and Bedrov,17dense andlong polymer brushes were not always necessary forachievement of well-defined dispersion and profoundimprovement of properties of composite containinginorganic NPs. Here, our results provided anotherexample to confirm this point by introducing sparseand long grafted chains to particles surface. Probablereactions of functional groups and stronger interactionsbetween the grafted oligomer and prepolymer of PUcould contribute to the dispersion.CONCLUSIONSUsing surface-emanated condensation reactions ofdi- or tri-ols with di-isocyanates in steps, dispersionof silica powder in PU was improved greatly, whichwas demonstrated by SEM observations, DLS meas-urements and improvements in properties of hybridfilms. As for the modification of silica particles, thegraft density could be controlled by amount ofmodifier agent used in planting NCO-groups ontosurface, and composition, length of grafted chainscould be devised by selecting types of di- or tri-olsand reaction steps.Reactions occurred between functional groups onparticles surface and matrix of PU, and strong inter-actions between modified particles and matrix couldbe advantageous to the improvement of dispersionof particles and properties of hybrid films, in despiteof that the density and length of grafted chains werenot so high.References1. Ueno, K.; Inaba, A.; Kondoh, M.; Watanabe, M. Langmuir2008, 24, 5253.2. Liu, Y. L.; Hsu, C. Y.; Hsu, K. Y. Polymer 2005, 46, 1851.3. Kohut, A.; Ranjan, S.; Voronov, A.; Peukert, W.; Tokarev, V.;Bednarska, O.; Gevus, O.; Voronov, S. Langmuir 2006, 22,6498.4. Elodie, B-L.; Lang. J. Macromol Symp 2000, 151, 377.5. Chalaye, S.; Elodie, B-L.; Putaux, J-L.; Lang J. Macromol.Symp. 2001, 169, 89.6. 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Nat Mater 2009, 8, 354.TABLE IIVicker’s Hardness of Hybrid FilmsSi NPs PristineSi-NCO-PEG400Si-NCO-PEG400-MDI -PEG400-MDI-PEG400Weightloss%– À4.3 À6.5Averagehardness(loading)24 (98.07 mN) 71 (245.2 mN) 554 (1.961 N)aFormulation of hybrid film: Si NPs: 5 wt %, Mols, MMDI:3 Â 10À3mol, V: 2 mL.aTime: 10 s.E528 LIU ET AL.Journal of Applied Polymer Science DOI 10.1002/app
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