Synthesis and Characterization of Organic/Inorganic Polyrotaxanes from Polyhedral Oligomeric Silsesquioxane and Poly(ethylene oxide)/α-Cyclodextrin Polypseudorotaxanes via Click Chemistry

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<ul><li><p>Synthesis and CharacteriInorganic Polyrotaxanes</p><p>no</p><p>Polyrotaxanes and polypseudorotaxanes are a class of</p><p>structures, these supramolecular assemblies have been</p><p>utilized as stimuli-responsive hydrogels,[9] insulating</p><p>.</p><p>-</p><p>-</p><p>Full Paper</p><p>Organic/inorganic polyrotaxanes were synthesized via Huisgen 1,3-dipolar cycloadditionbetween 3-azidapropylhepta(3,3,3-trifluoropropyl) POSS and dialkyne-terminated PEO/a-cyclodextrin polypseudorotaxanes. The organic/inorganic hybrid polyrotaxanes were charac-terized by means of 1H NMR spectroscopy andWAXRD. It was found that the nanosized POSSblocking agents significantly affected the crystalstructures of polyrotaxanes. Thermal gravimetricanalysis showed that the organic/inorganichybrid polyrotaxanes exhibited enhanced ther-mal stability compared to their parent polypseu-dorotaxanes, in terms of rate of thermaldegradation and the summation of char andceramic yields.topologically interlocked supramolecules composed of</p><p>macrocyclic compounds threaded onto linear polymer</p><p>backbones without covalent bonds linking these two</p><p>species. Since Harada et al. first reported the inclusion</p><p>complexes of a-cyclodextrin (a-CD) with poly(ethylene</p><p>glycol) (PEG) in the 1990s,[18], this class of supramolecules</p><p>wires[10,11] and polyrotaxane networks.[1214] For the</p><p>preparation of polyrotaxanes from the polypseudorotax-</p><p>anes, it is important to utilize efficient end-capping</p><p>reactions with the proper blocking agents. Harada et al[15] used 2,4-dinitrofluorobenzene to react with amino</p><p>terminated poly(ethylene oxide) (PEO)-polypseudorotax-</p><p>anes to obtain the corresponding polyrotaxanes. Kihara</p><p>et al. reported the preparation of polytetrahydrofuran-</p><p>polyrotaxanes via the reaction of 4-tritylphenyl isocyanate</p><p>with the hydroxyl terminals of the polypseudorotax-</p><p>anes.[16] Choi et al. reported the reaction of 9-anthralde-</p><p>hyde with amino-terminated poly(ethylene imine)</p><p>K. Zeng, S. ZhengCollege of Chemistry and Chemical Engineering, and State KeyLaboratory of Metal Matrix Composites, Shanghai Jiao TongUniversity, Shanghai 200240, ChinaFax: 86 21 5474 1297; E-mail: has been extensively investigated. Owing to their uniqueOligomeric Silsesquioxaoxide)/a-Cyclodextrin PClick Chemistry</p><p>Ke Zeng, Sixun Zheng*Macromol. Chem. Phys. 2009, 210, 783791</p><p> 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheimzation of Organic/from Polyhedrale and Poly(ethylenelypseudorotaxanes viaDOI: 10.1002/macp.200800605 783</p></li><li><p>polypseudorotaxanes to obtain polyrotaxanes.[17] More</p><p>recently, Gecheler et al.[18] reported that fullerene-60 was</p><p>used as an end-capping agent to obtain fullerene-</p><p>terminated polyrotaxanes.</p><p>Polyhedral oligomeric silsesquioxanes (POSS) are a class</p><p>of important nanosized cage-like molecules, derived from</p><p>hydrolysis and condensation of trifunctional organosi-</p><p>lanes. POSS molecules possess a formula of [RSiO3/2]n,</p><p>n 612, where R represents various types of organicgroups, one (ormore) of which is reactive or polymerizable.</p><p>A typical POSS molecule possesses the structure of a cube-</p><p>octameric framework, represented by the formula</p><p>(R8Si8O12), with an inorganic silica-like core (Si8O12)</p><p>K. Zeng, S. Zheng</p><p>784(0.53 nm in diameter) surrounded by eight organiccorner groups, one or more of which is reactive; the</p><p>distance between two adjacent organic groups is about</p><p>11.5 nm, depending on the length of the organic group</p><p>(Scheme 1).[1921] It is noted that POSS macromers have</p><p>been recently incorporated into polypseudorotaxanes.[2224]</p><p>Chang et al. [22] and He et al. [23] have investigated</p><p>supramolecular inclusion complexes of octa-armed star-</p><p>shaped poly(e-caprolactone) (PCL) and PEOwith a-CD. Theyfound that the efficiencies of inclusion complexation for</p><p>the organic/inorganic star-shaped polymers were lower</p><p>than those of their linear counterparts with CDs.</p><p>Furthermore, the presence of bulky POSS cages constituted</p><p>a steric hindrance to the formation of inclusion complexes</p><p>(ICs).[22,23] We recently examined the effect of the POSS</p><p>macromer at one end of the PCL chain on the efficiency of</p><p>inclusion complexation.[24] To the best of our knowledge,</p><p>there has been no previous report on organic/inorganic</p><p>polyrotaxanes with POSS macromers as the end-capping</p><p>agents. In this work, we explore the synthesis of the</p><p>organic/inorganic polyrotaxanes involving dialkyne-</p><p>terminated PEO/a-CD polypseudorotaxanes and POSS.</p><p>The utilization of POSS as the end-capping agent in this</p><p>work is based on the following considerations: i) POSS is a</p><p>nanosized molecule, which allows investigation of the</p><p>effect of the nanosized capping agent on the structures of</p><p>polyrotaxanes; and, ii) the end-capping agent used in thisScheme 1. Structure of POSS.</p><p>Macromol. Chem. Phys. 2009, 210, 783791</p><p> 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, WeinheimSynthesis of 3-Bromopropylhepta(3,3,3-</p><p>trifluoropropyl) POSS</p><p>Firstly, hepta(3,3,3-trifluoropropyl)tricycloheptasiloxane triso-</p><p>dium silanolate [Na3O12Si7(C3H4F3)7] was synthesized by follow-</p><p>ing themethod reported by Fukuda et al.[7] In a typical experiment,</p><p>(3,3,3-trifluoropropyl)trimethoxysilane (50.0 g, 0.23 mol), THF</p><p>(250mL), deionized water (5.25 g, 0.29mol) and sodium hydroxide</p><p>(3.95 g, 0.1mol) were charged to a flask equippedwith a condenser</p><p>and a magnetic stirrer. After refluxed for 5 h, the reactive system</p><p>was cooled down to room temperature and held at this</p><p>temperature for 15 h with vigorous stirring. Then, all the solvent</p><p>and other volatile were removed by rotary evaporation, leaving a</p><p>white solids. After drying at 40 8C in vacuo for 12 h, 37.3 g ofproduct were obtained at a yield of 98%. The as-prepared</p><p>hepta(3,3,3-trifluoropropyl)tricycloheptasiloxane trisodium sila-Experimental Part</p><p>Materials</p><p>3,3,3-Trifluoropropyltrimethoxysilane was obtained from Zhe-</p><p>jiang Chem-Tech Co., China. Both 3-bromopropyltrichlorosilane</p><p>and sodium azide (NaN3) were purchased from Gelest Co. USA and</p><p>used as received. Both propargyl bromide and a-CD were</p><p>purchased from Alfa Co., China. PEG with Mn 1 000, 2 000,4 000 and 6000 were purchased from Fluka Co. Germany.</p><p>Pentamethyldiethylenetriamine (PMDETA) was purchased from</p><p>Aldrich Co., USA and used as received. Unless specifically</p><p>indicated, other reagents such as sodium, calcium hydride</p><p>(CaH2), sodium hydroxide and copper(I) bromide (CuBr) were of</p><p>chemically pure grade and obtained from Shanghai Reagent Co.,</p><p>China. Organic solvents, such as N,N0-dimethylformamide (DMF),tetrahydrofuran (THF), dichloromethane triethylamine (TEA) and</p><p>petroleum ether (distillation range: 6090 8C) were of chemicallypure grade, obtained from commercial sources. Before use, THF</p><p>was refluxed above sodium and then distilled and over a</p><p>molecular sieve of size 4 A. Triethylamine was refluxed over</p><p>calcium hydride and then purified with p-toluenesulfonyl</p><p>chloride, followed by is a 3-azidopropylhepta(3,3,3-trifluoropropyl) POSS </p><p>the semifluorinated ligands of the POSS possess fluor-</p><p>ophobic properties and, thus, endow the polyrotaxanes</p><p>with amphiphilicity.</p><p>In this communication, we report the synthesis of</p><p>organic/inorganic polyrotaxanes. The end-capping reac-</p><p>tion is the Huisgen 1,3-dipolar cycloaddition between 3-</p><p>azidapropylhepta(3,3,3-trifluoropropyl) POSS and dia-</p><p>lkyne-terminated PEO/a-CD polypseudorotaxane under</p><p>benign conditions, that is, click chemistry.[2528] The effect</p><p>of the nanometer size of the terminal POSS groups on the</p><p>crystalline structures and thermal stability of polyrotax-</p><p>anes will be addressed on the basis of wide-angle X-ray</p><p>diffraction and thermal gravimetric analysis.nolate [Na3O12Si7(C3H4F3)7] (10.0 g, 8.8 mmol) and triethylamine</p><p>DOI: 10.1002/macp.200800605</p></li><li><p>14.0H, SiCH2CH2CF3), 0.96 (t, 2.0H, CH2CH2CH2Br).29Si NMR (acetone-d6): d65.8, 66.8, 67.0.</p><p>14.0H, SiCH2CH2CF3), 1.76 (m, 2.0H, CH2CH2N3), 1.03 (m,14.0H, SiCH2CH2CF3), 0.86 (t, 2.0H, CH2CH2CH2N3).</p><p>Preparation of Polypseudorotaxanes</p><p>PMDETA (10 mL) was added to the system using a syringe. The</p><p>reaction was carried out at room temperature for 24 h and then</p><p>Techniques and Measurement</p><p>Synthesis and Characterization of Organic/Inorganic Polyrotaxanes from . . .Synthesis of Dialkyne-Terminated PEO</p><p>Dialkyne-terminated PEO was prepared via the reaction between</p><p>propargyl bromide and PEG in the presence of sodium hydride</p><p>(NaH). Prior to use, the PEG samples (Mn 1000, 2 000, 4 000 and6000) were dried via azeotropic distillation with toluene. In a</p><p>typical experiment, to a 500 mL round bottom flask, NaH (0.96 g,</p><p>40 mmol) and anhydrous THF (50 mL), PEG (Mn 4 000) (20.0 g)dissolved in 150mL anhydrous THFwas slowly added dropwise to</p><p>the system within 30 min. The mixture was maintained at this</p><p>temperature for 3 h and then propargyl bromide (4.76 g, 40 mmol)</p><p>dissolved in 50 mL anhydrous THF was added dropwise. The</p><p>reaction was carried out for a further 20 h with vigorous stirring,</p><p>to reach completion. The salt (i.e., NaBr) and the unreacted NaH</p><p>were removed by filtration. The filtrate was concentrated and</p><p>precipitated in a large amount of petroleumether. The precipitatesSynthesis of 3-Azidopropylhepta(3,3,3-</p><p>trifluoropropyl) POSS</p><p>3-Azidopropylhepta(3,3,3-trifluoropropyl) POSS was synthesized</p><p>via the reaction between 3-bromopropylhepta(3,3,3-trifluoropro-</p><p>pyl) POSS and sodium azide (NaN3). In a typical experiment, 3-</p><p>bromopropylhepta(3,3,3-trifluoropropyl) POSS (3.0 g, 2.5 mmol)</p><p>and NaN3 (0.176 g, 2.75 mmol) were added to a flask equipped</p><p>with a magnetic stirrer and anhydrous DMF (10 mL) was added.</p><p>The reaction was carried out at room temperature for 24 h. Then,</p><p>the solution was concentrated and a large amount of deionized</p><p>water added to give a precipitate. The products was further dried</p><p>at 40 8C in a vacuumoven for 24 h and 2.6 g productwere obtainedat a yield of 90%.</p><p>FTIR (KBr window): n1 0901000 (SiOSi), 2 9002850(CH2), 1 120 1300 (CF3), 2 105 (N3) cm1.</p><p>1H NMR (acetone-d6): d 3.35 (t, 2.0H, CH2N3), 2.32 (m,(1.3 mL, 8.8 mmol) were charged to a flask equipped with a</p><p>magnetic stirrer and 200 mL anhydrous THF added with vigorous</p><p>stirring. The flask was immersed into an ice-water bath and</p><p>purged with high purity nitrogen for 1 h. Then, 3-bromopropyltri-</p><p>chlorosilane (2.47 g, 9.68mmol) dissolved in 20mL anhydrous THF</p><p>was slowly added, dropwise, within 30 min. The reaction was</p><p>carried out at 0 8C for 4 h and at room temperature for 20 h.Sodium chloride was filtered out and the solvent, together with</p><p>other volatiles, were eliminated via rotary evaporation to afford</p><p>white solids. The solids were washed with 50 mL methanol three</p><p>times and dried in vacuo at 40 8C for 24 h; 8.2 g product wasobtained at a yield of 76%.</p><p>FTIR (KBr window): n1 0901000 (SiOSi), 2 9002850(CH2), 1 1201300 (CF3), 624 (CBr) cm1.</p><p>1H NMR (acetone-d6): d 3.52 (t, 2.0H, CH2Br), 2.32 (m,14.0H, SiCH2CH2CF3), 1.96 (m, 2.0H, CH2CH2Br), 1.03 (m,were dissolved in THF and re-precipitated with petroleum ether.</p><p>Macromol. Chem. Phys. 2009, 210, 783791</p><p> 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, WeinheimNMR Spectroscopy</p><p>The 1H NMRmeasurements were carried out on a Varian Mercury</p><p>Plus 400 MHz NMR spectrometer. The samples were dissolved</p><p>with deuterated acetone (acetone-d6) or chloroform (CDCl3) and</p><p>the solutions were measured with tetramethylsilane (TMS) as thethe solvent was removed via rotary evaporation. The crude</p><p>products were purify by washing with water and THF several</p><p>times to remove a-CD and any unreacted 3-azidopropyl-</p><p>hepta(3,3,3-trifluoropropyl) POSS, respectively. After drying</p><p>in vacuo at 60 8C for 24 h, 1.04 g of product was obtained at ayield of 95%.</p><p>1H NMR (DMSO-d6): d7.97 (s, Hc, 2H), 5.53 (d, H7, 230H), 5.48(d, H8, 230H), 4.86 (d, H1, 230H), 4.54 (s, triazoleCH2O, 4H),4.43 (t,H9, 230H), 3.84 (t,H3, 230H), 3.783.64 (m,H6,5, 690H), 3.53</p><p>(s, CH2 of PEO, 360H), 3.44 (t, H2, 230H), 3.383.32 (m, H4, 230H),</p><p>2.26(m, CF3CH2, 28H), 0.92 (m, CF3CH2CH2, 28H).In a typical experiment, 0.2 g dialkyne-terminated PEG (Mn 4 000) was dissolved in deionized water to form a 20 wt.-%</p><p>solution. a-CD (2.20 g) was dissolved in 15 mL deionized water to</p><p>obtain a saturated solution. The saturated aqueous solution was</p><p>added dropwise to the aqueous solution of dialkyne-terminated</p><p>PEG at room temperature. The mixtures were ultrasonically</p><p>agitated for 10 min and then allowed to stand overnight at room</p><p>temperature. The precipitates were collected by filtration and</p><p>were further washed with water three times to remove</p><p>uncomplexed PEG and a-CD. The inclusion complexes were dried</p><p>in vacuo at 60 8C for 24 h before use.</p><p>Synthesis of Polyrotaxanes</p><p>Dialkyne-terminated polypseudorotaxanes were used to react 3-</p><p>azidopropylhepta(3,3,3-trifluoropropyl) POSS; that is, click chem-</p><p>istry was carried out to afford organic/inorganic polyrotaxanes.</p><p>In a typical experiment, the inclusion complexes of PEG</p><p>(Mn 4000) with a-CD (1.0 g) and 3-azidopropylhepta(3,3,3-trifluoropropyl) POSS (0.10 g) were charged to a 25 mL flask</p><p>equipped with a magnetic stirrer. 0.10 g a-CD and 5 mL DMF were</p><p>added to the flask. The system was purged with high purity</p><p>nitrogen for 30 min and then CuBr (5 mg) was added as a catalyst.</p><p>After purging with high purity nitrogen for an additional 10 min,This procedure was repeated three times to purify the products.</p><p>The products were dried in vacuo at 30 8C for 24 h before use. Thedialkyne-terminated PEG (19.95 g) were obtained at a yield of 93%.</p><p>FTIR (KBr window): n 3243 ( CH), 2 106 (C C) cm1.1H NMR (CDCl3, PEG, Mn 4 000): d2.42 (t, 2H, HC C), 4.2</p><p>(d, 4H, C CCH2), 3.6(m, 360H, CH2CH2O).internal reference.</p><p> 785</p></li><li><p>sWide-Angle X-Ray Diffraction (WAXRD)</p><p>xanes confirmed by H NMR spectroscopy. Figure 2 shows the</p><p>K. Zeng, S. Zheng</p><p>Scheme 2. Synthesis of 3-azidopropylhepta(3,3,3-trifluoropropyl) POSS.</p><p>786Synthesis of Organic/Inorganic PolyrotaThe route of synthesis for the organic/</p><p>inorganic polyrotaxanes is depicted in</p><p>Scheme 2 and 3. The starting compound</p><p>for 3-azidopropylhepta(3,3,3-trifluoropropyl)</p><p>POSS is hepta(3,3,3-trifluoropropyl) tricy-</p><p>cloheptasiloxane trisodium silanolate</p><p>[Na3O12Si7(C3H4F3)7], which was pre-</p><p>pared via the condensation and arrange-</p><p>ment of 3,3,3-trifluoropropyltrimethoxy-</p><p>silane in the presence of sodium</p><p>hydroxide.[29] The corner-capping reac-</p><p>tion between hepta(3,3,3-trifluoropropyl)</p><p>tricycloheptasiloxane trisodium silano-</p><p>late and 3-bromopropyltrichlorosilane</p><p>was employed to obtain 3-bromopropyl-</p><p>hepta(3,3,3-trifluoropropyl) POSS. Figure 1</p><p>shows the 29Si NMR spectrum of</p><p>3-bromopropylhepta(3,3,3-trifluoropropyl)The WAXRDmeasurements were carried out on a Shimadzu XRD-</p><p>6000 X-ray diffractometer with Cu Ka (l0.154 nm) irradiation at40 kV and 30 mA with a Ni filter. Data were recorded in the</p><p>range 2u 4408 at a scanning rate and step size of 4.08 min1and 0.028, respectively.</p><p>Results and Discussion800 8C at a heating rate of 20 8C min1.The thermal degradation temperature was</p><p>taken as the onset temperature at which 5 wt.-% of weight los</p><p>occurred.Fourier-Transform Infrared (FTIR)Spectroscopy</p><p>The FTIR measurements were conducted on a</p><p>Perkin Elmer Paragon 1000 Fourier-transform</p><p>spectrometer...</p></li></ul>


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