Polyurethane Networks Modified with Octa(propylglycidyl ether) Polyhedral Oligomeric Silsesquioxane

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<ul><li><p>Polyurethane Networks Modified with</p><p>1842 DOI: 10.1002/macp.200600241 Full PaperOcta(propylglycidyl ether) Polyhedral</p><p>Oligomeric Silsesquioxane</p><p>Yonghong Liu, Yong Ni, Sixun Zheng*control polyurethane. In terms of TGA, the nanocompositesdisplayed improved thermal stability. Tensile tests indicatethat the organic-inorganic hybrid networks were signifi-cantly reinforced with the inclusion of POSS. Contact anglemeasurements show that the organic-inorganic nanocompo-sites displayed a significant enhancement in surface hydro-phobicity as well as a reduction in the surface free energy.The improvement in surface properties was ascribed to thepresence of the POSS moiety in place of the polar com-ponent of polyurethane. XPS shows enrichment with Si-containing moieties on the surfaces.</p><p>Organic-Inorganic Hybrid PU Networks.Summary:OpePOSS was incorporated into polyurethane tomake organic-inorganic hybrid composites and nano-com-posites containing up to 20 wt.-% POSS were prepared. Theformation of the hybrid polyurethane networks is ascribed totwo principal cross-linking reactions: i) the cross-linkingreaction between MOCA and the polyurethane prepolymerand ii) the inter-component reaction between the PU net-works and OpePOSS. The latter was confirmed by modelcompound reactions. TEM indicates that the POSS washomogeneously dispersed in the polymer matrix at the nano-meter scale. DSC showed that the nanocomposites displayedincreased glass transition temperatures compared to theDepartment of Polymer Science and Engineering, Shanghai JiaoShanghai 200240, ChinaFax: 86 21 5474 1297; E-mail: szheng@sjtu.edu.cn</p><p>Received: May 16, 2006; Revised: July 12, 2006; Accepted: Au</p><p>Keywords: morphology and properties; polyhedral oligomeric silse</p><p>Introduction</p><p>The purpose of incorporating inorganic or organometallic</p><p>segments into organic polymers is to afford improved</p><p>material properties via the synergism of the inorganic and</p><p>organic components.[16] During the past years, organic-</p><p>inorganic nanocomposites have been prepared via the sol-</p><p>gel process:[711] intercalation and exfoliation of layered</p><p>silicates by organic polymers.[1216] Polyhedral oligomeric</p><p>silsesquioxane (POSS) macromers and POSS-containing</p><p>polymers are emerging as a new technology for accessing</p><p>Macromol. Chem. Phys. 2006, 207, 18421851Tong University, 800 Dongchuan Road,</p><p>gust 16, 2006; DOI: 10.1002/macp.200600241</p><p>squioxane; polyurethanes</p><p>organic-inorganic nanocomposites.[1729] POSS molecules</p><p>possess nano-sized cage-like structures, derived from</p><p>hydrolysis and condensation of trifunctional organosilanes</p><p>with a formula of [RSiO3/2]n, with n in the range from 6 to</p><p>approximately 12, and where R are various types of organic</p><p>groups, one or more of which is reactive or polymeriz-</p><p>able. With the reactive R groups, POSS molecules can be</p><p>introduced onto the backbones of polymer chains via the</p><p>formation of covalent bonds between the POSS cages and</p><p>the polymer matrices.[1729] During the past years, there</p><p>has been extensive work reported in the literature on</p><p> 2006 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim</p></li><li><p>lation over CaH2 under reduced pressure.</p><p>Equimolar amounts of DEC (2.66 g, 0.01 mmol) and</p><p>Polyurethane Networks Modified with Octa(propylglycidyl ether) Polyhedral Oligomeric Silsesquioxane 1843organic-inorganic hybrid thermoplastic (or thermoset)</p><p>nanocomposites containing POSS. However, the modifica-</p><p>tion of elastomeric materials via POSS remains largely</p><p>unexplored.</p><p>Polyurethanes (PU) are a class of important elastomers,</p><p>and their wide spread applications drive efforts to prepare</p><p>materials with improved properties. Several authors have</p><p>reported the modification of polyurethanes via POSS. Fu</p><p>et al.[30] and Hsiao et al.[31] investigated the structure and</p><p>properties of a linear polyurethane containing POSS. In</p><p>their work, a 3-(allylbisphenol-A) propyl(dimethylsilox-</p><p>ane) POSS was used as a chain extender and POSS mole-</p><p>cules were grafted onto the macromolecular backbone</p><p>through one of the corner groups of the POSS. Devaux</p><p>et al.[32] reported that the incorporation of POSS into</p><p>polyurethane gave materials with improved flame retar-</p><p>dance. To facilitate incorporation of silsesquioxane cages</p><p>into polyurethanes, Neumann et al.[33] reported the syn-</p><p>thesis of an octa(isocyanate)-functionalized POSS macro-</p><p>mer, which can subsequently be used to prepare organic-</p><p>inorganic hybrid polyurethanes. Liu et al.[34] used</p><p>octa(aminophenyl) POSS to replace a part of the aromatic</p><p>amine, the traditional extender or cross-linker, to cross-link</p><p>the polyurethane networks and found that even the pre-</p><p>sence of a small amount of POSS can result in a significant</p><p>improvement in the thermo-mechanical properties. More</p><p>recently, Turri et al.[35,36] and Oaten et al.[37] reported</p><p>studies on the surface properties of linear polyurethanes</p><p>modified with mono-functional POSS macromers and</p><p>noted that the presence of POSS can significantly reduce</p><p>the surface free energy and thus improve surface hydro-</p><p>phobicity.</p><p>To the best of our knowledge, all previous studies were</p><p>concerned mainly with linear polyurethanes modified</p><p>with POSS, while cross-linked polyurethane networks</p><p>remain largely unexplored.[33,34] In POSS-containing</p><p>linear polyurethanes, the POSS molecules were grafted</p><p>onto polyurethane chains with one (or two) covalent</p><p>bond(s). Nonetheless, there is continuing interest in intro-</p><p>ducing octa-functionalized POSS into polyurethanes to</p><p>obtain POSS-reinforced PU networks. In this protocol of</p><p>preparation, octa-functionalized POSS molecules will act</p><p>as nano-sized cross-linking sites and thus, the thermo-</p><p>mechanical properties of materials may be further im-</p><p>proved. In the present work, we present studies on the</p><p>modification of polyurethanes using octa(propylglycidyl</p><p>ether) polyhedral oligomeric silsesquioxane (OpePOSS).</p><p>In this system, additional nano-cross-linking reactions</p><p>could be formed apart from the cross-linking reaction</p><p>between the polyurethane prepolymers and aromatic ami-</p><p>nes. The additional cross-linking reaction occurs between</p><p>the amide moiety of the polyurethane and the epoxide</p><p>groups of the OpePOSS. The goal of this work is to explore</p><p>the efficiency of this approach by investigating the pro-</p><p>perties of the resulting materials. To this end, the cross-Macromol. Chem. Phys. 2006, 207, 18421851 www.mcp-journal.deDGEBA (3.91 g, 0.01 mmol) were added to a flask equippedwith a magnetic stirrer. In a nitrogen atmosphere, the mixturewas heated up to 100 and 150 8C, and reactions were carriedout with stirring for 4 h, respectively. It was observed that theviscosity of system did not display significant changes for thereaction at 100 8C. However, the system viscosity increasedsignificantly when the reaction was carried out at 150 8C, inthe same timescale, thus polymerization occurred under theseconditions. In the final stage of the reaction, the reactants wereReaction of Model Compounds</p><p>In order to investigate the additional cross-linking reactionbetween PU and OpePOSS, 2,4-di(ethyl carbamate)toluene(DEC) was designed and synthesized via the reaction betweenTDI and ethanol. Typically, TDI (1.00 g, 5.74 mmol) wasadded to a flask equipped with a condenser and a magneticstirrer, and then ethanol (1.10 g, 0.024 mol) was added withvigorous stirring in a dry nitrogen atmosphere. The reactionwas carried out at 85 8C for 2 h. The excess ethanol waseliminated via rotary evaporation and a white solid wasobtained with a yield of 90 wt.-%.</p><p>FTIR (KBr): 3 337, 3 288 (NH in amide), 1 696 cm1 (OC&lt; in urethane moiety).</p><p>1H NMR (chloroform-d): d 1.331.28 (CH3CH2O, 6.03H, m, J 6.83 Hz); 2.2 (CH3Ph, 3.23 H, s); 4.254.18(CH3CH2O, 4.00 H, m, J 6.83 Hz); 6.38, 6.58 and 7.09(protons of aromatic ring; 1.00 H, 0.96 H and 1.08 H; s, s andd, J 7.80 Hz); 7.78 (OCONH, 2.45, s).linking reactions involved in the formation of hybrid net-</p><p>works are investigated via the reaction of model com-</p><p>pounds. The morphology and properties of the organic-</p><p>inorganic hybrid networks were investigated through</p><p>transmission electronic microscopy (TEM), thermal ana-</p><p>lyses (DSC and thermogravimetric analysis (TGA)) and</p><p>measurements of the mechanical and surface properties.</p><p>Experimental Part</p><p>Materials</p><p>Toluene-2,4-diisocyanate (TDI) and 4,40-methylenebis(2-</p><p>chloroaniline) (MOCA) were of analytical grade, purchasedfrom Shanghai Reagent Co., China. Poly(propylene oxide)glycol (PPG) was kindly supplied by the Polyurethane Divi-sion, Gaoqiao Petrochemical Co., Shanghai/China, under thetrade name GE-210. It has a quoted molecular weight ofMn1 000. Diglycidyl ether of bisphenol A (DGEBA)was suppliedby Shanghai Resin Co., China and has a quoted epoxideequivalence of 185. OpePOSS was synthesized in our labo-ratory via the hydrosilylation reaction of octahydrosilses-quioxane (H8Si8O8) with allylglycidyl ether, catalyzed withthe Karstedt catalyst, as detailed elsewhere.[38,39] All of thesolvents such as toluene, tetrahydrofuran (THF), methanol andethanol were of chemically pure grade, obtained from com-mercial sources. Prior to use, toluene was purified via distil- 2006 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim</p></li><li><p>converted into a thermoplastic product. Solubility tests showthat the resulting product is soluble in common solvents suchas THF and chloroform.</p><p>Preparation of POSS-Containing PolyurethaneNanocomposites</p><p>50.00 g PPG and 17.416 g TDI (i.e., [NCO]:[OH] 2:1) wereadded to a dried, 250 ml, three-necked flask, equipped with acondenser capped with a CaCl2 drying tube, a mechanicalstirrer and a N2 inlet. The reactants were reacted at 85 8C withvigorous stirring for 2 h under a dry nitrogen atmosphere toproduce the PU prepolymer. The desired amount of OpePOSS</p><p>out using a Soxhlet extractor for 48 h. After extraction with</p><p>1844 Y. Liu, Y. Ni, S. Zheng</p><p>15 2.0:1.0:0.36:0.529</p><p>20 2.0:1.0:0.36:0.750</p><p>a) The reactants are TDI, PPG, MOCA, and OpePOSS, respect-ively.THF as the solvent, the gel components were dried at 60 8C for4 h, followed by drying in a vacuum oven at 60 8C for another4 h to remove the residual solvent. The dried samples wereweighed to calculate the fraction of insoluble (or soluble)components.</p><p>Fourier Transform Infrared (FTIR) Spectroscopy</p><p>Infrared measurements were carried out on a Perkin-ElmerParagon 1000 Fourier transform spectrometer at roomtemperature (25 8C). The attenuated total reflection (ATR)accessories were used to measure the FTIR spectra of all the</p><p>Table 1. Compositions of organic-inorganic hybrid polyur-ethane containing POSS.</p><p>POSS content Molar ratio of reactantsa)</p><p>wt.-%</p><p>0 2.0:1.0:0.36:0.0005 2.0:1.0:0.36:0.15810 2.0:1.0:0.36:0.333was added to the PU prepolymer under vigorous stirring toattain complete dissolution, and then an amount ofMOCAwasadded to system, equimolar with respect of the quality of the NCO groups of the polyurethane prepolymers, under vigorousstirring to ensure that the MOCAwas completely dissolved inthe system. The mixtures were degassed under decreasedpressure, before the reactants were poured into a pre-heatedstainless steel mold. The samples were cured at 110 8C for 4 hand 150 8C for 4 h to access the complete cross-linking reac-tions. The compositions of organic-inorganic hybrid poly-urethanes containing POSS are summarized in Table 1.</p><p>Measurement and Techniques</p><p>Solubility Analysis</p><p>The organic-inorganic hybrid composites were subjected tosolubility tests using common solvents such as chloroform,acetone and THF. The extraction experiments were carriedMacromol. Chem. Phys. 2006, 207, 18421851 www.mcp-journal.despecimens on fresh surfaces. In all cases, 64 scans at aresolution of 2 cm1 were used to record the spectra.</p><p>Nuclear Magnetic Resonance (NMR) Spectroscopy</p><p>NMR measurements were carried out on a Varian MercuryPlus 400 MHz NMR spectrometer at 25 8C. The samples weredissolved in deuterated chloroform and tetramethylsilane(TMS) was used as the internal reference.</p><p>TEM</p><p>TEM was performed on a JEM 2010 high-resolution TEM atan accelerating voltage of 200 kV. The samples were trimmedusing an ultra-thin microtome and the specimen sections of 70nm approximate thickness were placed in 200-mesh coppergrids for observation.</p><p>DSC</p><p>Calorimetric measurements were performed on a PerkinElmer Pyris-1 DSC in a dry nitrogen atmosphere. The instru-ment was calibrated with standard indium. All the samples(about 10 mg) were heated from 20 to 200 8C and the DSCcurves were recorded at a heating rate of 20 8C min1. Theglass transition temperature (Tg) was taken as the midpoint ofthe curve at the change in heat capacity.</p><p>TGA</p><p>A Perkin-Elmer thermal gravimetric analyzer (TGA-7) wasused to investigate the thermal stability of the hybrid elasto-mers. Under an air atmosphere, the samples (about 10 mg)were heated from ambient temperature to 800 8C at a heatingrate of 20 8C min1. The initial thermal degradation tem-perature was taken as the onset temperature at which a massloss of 5 wt.-% occurs.</p><p>Tensile Mechanical Tests</p><p>Tensile mechanical tests were carried out according to rele-vant ASTM standards. Tensile strengths were measured usinga tensile testing machine (Instron 4465, United Kingdom) at astrain rate of 0.5% at room temperature. All the reportedresults are an average of at least five successful measurementsfor the tensile determinations.</p><p>Contact Angle Measurements</p><p>The static contact angle measurements with ultra-pure waterand diiodomethane were carried out using a JC2000A contactangle measurement instrument (Powereach Digital Instru-ments Ltd., Shanghai, China) at room temperature. Thespecimens were dried in a vacuum oven for 12 h prior tomeasurement.</p><p>X-Ray Photoelectron Spectroscopy (XPS)</p><p>XPS experiments were carried out on an RBD upgradedPHI-5000C ESCA system (Perkin Elmer Co.) with Mg and Alanode radiations. The X-ray anode was run at 250 W and thehigh voltage was kept at 14.0 kV with a detection angle at 548.The pass energy was fixed at 93.90 eV to ensure sufficientresolution and sensitivity. The base pressure of the analyzerchamber was about 108 Torr. The sample was directly 2006 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim</p></li><li><p>pressed to a self-supported disk (10 10 mm2), mounted on asample holder and then transferred into the analyzer chamber.The whole spectra (0 to 1 200 eV), and the narrow spectra ofall the elements with much higher resolution, were bothrecorded by using an RBD 147 interface (RBD Enterprises,USA) and using the AugerScan 3.21 software. The bindingenergies were calibrated by using the containment carbon(C1s 284.6 eV). The data was analyzed using the RBDAugerScan 3.21 software.</p><p>Results and Discussion</p><p>Preparation of Inorganic-OrganicNanocomposites</p><p>The synthesis of organic-inorganic hybrid polyurethanes</p><p>containing POSS is illustrated in Scheme 1. For the control</p><p>PU networks, the reaction between PPG and TDI was set</p><p>at the molar ratio of isocyanate to epoxide groups of 2:1 to</p><p>produce the PU prepolymer terminated by isocyanate</p><p>groups. The PU prepolymer was further reacted with</p><p>the MOCA amino groups to form elastomeric networks</p><p>bearing a great number of amide mo...</p></li></ul>


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