polymers Communication
Hedgehog Buckyball: A High-Symmetry Complete Polyhedral Oligomeric Silsesquioxane (POSS) Yu Hu 1, *, You Wang 1, *, Hong You 2 and Di Wang 3 1 2 3
*
School of Materials Science and Engineering, Harbin Institute of Technology, Harbin 150001, China State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150001, China;
[email protected] Material Science and Engineering College, Northeast Forestry University, Harbin 150040, China;
[email protected] Correspondence:
[email protected] (Y.H.);
[email protected] (Y.W.); Tel.: +86-451-8641-2679 (Y.H.); +86-451-8641-2516 (Y.W.)
Academic Editor: Ping Xu Received: 19 July 2016; Accepted: 16 August 2016; Published: 22 August 2016
Abstract: In this study, we report UV-MALDI-TOF MS evidence of a fullerene-like silsesquioxane, a high-symmetry polyhedral oligomeric silsesquioxane (POSS or SSO) formulated as R60 -Si60 O90 or T60 (T = RSiO1.5 ). The T60 preparation can be performed using a normal hydrolytic condensation of [(3-methacryloxy)propyl]trimethoxysilane (MPMS) as an example. Theoretically, four 3sp3 hybrid orbitals (each containing an unpaired electron) of a Si atom are generated before the bond formation. Then it bonds to another four atom electrons using the four generated hybrid orbitals which produced a stable configuration. This fullerene-like silsesquioxane should exhibit much more functionality, activity and selectivity and is easier to assemble than the double bonds in a fullerene. Keywords: polyhedral oligomeric silsesquioxane (POSS); high-symmetry; fullerene-like silsesquioxane; synthesis and characterization
The fullerene buckyball (FBB), C60 , was named “Molecule of the Year” for 1991 by Science [1]. Since the discovery of the C60 buckyball, fullerene science has continued to accelerate, investigating both the basic science and its potential applications [2,3]. One investigation involves a major focus on its analogue, the Si60 cluster [4,5]. For Si60 clusters, the cages should not be very stable due to the use of three (3sp3 ) orbitals to bond to other Si atoms. Thus, the cages need some other atoms for the fourth bond whereas the C60 fullerene uses the second period sp2 orbitals along with a π bond to bond exclusively with other C atoms. Most investigations focus on endohedral Si60 isomers (using the fourth bond of the 3sp3 orbital) which are unstable [6]. To produce a stable Si60 configuration, Wang and Yang conducted ab initio calculations based on density functional theory on a Si60 fullerene-like cage passivated with F or Cl atoms [7]; however, this research is limited by a complex experimental synthesis. In this study, we report UV-MALDI-TOF MS evidence of a fullerene-like silsesquioxane, a high-symmetry polyhedral oligomeric silsesquioxane (POSS or SSO) formulated as R60 -Si60 O90 or T60 (T = RSiO1.5 ) [8]. Theoretically, four 3sp3 hybrid orbitals (each containing an unpaired electron) of a Si atom are generated before the bond formation. Then it bonds to another four atom electrons using the four generated hybrid orbitals which produced a stable configuration. A significant difference between a FBB and T60 POSS is that the cage in the former is the four-bond (three 2sp2 hybrid orbits and one original 2p orbital) connection of each C atom on the FBB surface, while it is the three-bond (three of four 3sp3 hybrid orbits) connection of each Si atom on the POSS surface. The remaining bond to each silicon connects to a pendant organic group adorning the surface of the T60 cage, showing a hedgehog buckyball (HBB, see Figure 1). These organic groups exhibit much more functionality, activity and
Polymers 2016, 8, 315; doi:10.3390/polym8080315
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showing a hedgehog buckyball (HBB, see Figure 1). These organic groups exhibit much more functionality, activity and selectivity and are easier to assemble than the double bonds in a fullerene, selectivity and are easier to assemble than the double bonds in a fullerene, which facilitates the synthesis which facilitates the synthesis of POSS-based materials possessing unique properties and the ability of POSS-based materials possessing unique properties and the ability to set up applications [9–14]. to set up applications [9–14].
Figure molecular structures: (a)(a) FBB, thethe C atom on on thethe FBBFBB surface connects the the other three C Figure1.1.The The molecular structures: FBB, C atom surface connects other three surface and atoms; (b) (b) HBB, thethe Si atom connects thethe bridged three OO atoms ononthe C atoms; HBB, Si atom connects bridged three atoms theT60 T60 surface andone oneorganic organic group groupRRoutside outsidethe theHBB HBBsurface. surface.
The TheHBB HBB TT6060preparation preparationcan canbebeperformed performedusing usinga anormal normalhydrolytic hydrolyticcondensation condensationofof [(3-methacryloxy)propyl]trimethoxysilane [(3-methacryloxy)propyl]trimethoxysilane(MPMS) (MPMS)that thatwe wehave haveused usedtotoprepare preparesilsesquioxane silsesquioxane coatings [15,16]. Hydrolysis and condensation normally give rise to smaller oligomers withaadozen dozenor coatings [15,16]. Hydrolysis and condensation normally give rise to smaller oligomers with orfewer fewermonomers monomersinterconnected interconnectedinto intorings rings[17]. [17].By Byextending extendingthe thecondensation condensationtime timewe weare areable ableto toproduce produce more viscous products (M-POSS or MSSO) with molecular the range more viscous products (M-POSS or MSSO) with molecular weights inweights the rangeincalculated for calculated for methacryloxypropy-T 60 (10,755 Daltons). methacryloxypropy-T60 (10,755 Daltons). 13C Generally groups andand the the location of theofgroups are determined by FTIRby and NMR (1H,NMR Generallythe the groups location the groups are determined FTIR and 29 and Si); then29all structures structures are established by the molecular weights assigned (1 H, 13 C and Si);possible then allpredicted possible predicted are established by the molecular weights from the peaks of UVMALDI-TOF MS and the general formula [8,18,19]. Figure S1 schemes the assigned from the peaks of UVMALDI-TOF MS and the general formula [8,18,19]. Figure S1 schemes 1 13 structural formula of MSSO, facilitating analysis andand assignment of of FTIR C-NMR 1 H-and the structural formula of MSSO, facilitating analysis assignment FTIRand and Hand 13 C-NMR −1 spectra. The typical FTIR MSSO spectrum (Figure S2b) bands at 417–478 and 1122–1129 cm spectra. The typical FTIR MSSO spectrum (Figure S2b) bands at 417–478 and 1122–1129 cm−1are are primarily of O–Si–O O–Si–Oand andSi–O–Si; Si–O–Si;the theobvious obviousbands bands about 1298, 1410 primarilyascribed ascribedto to the the stretching stretching of at at about 1298, 1410 and −1 derive from stretches of CH=CH2 and C=O groups in methacrylate chains; a decrease and 1724 1 derive 1724 cm−cm from stretches of CH=CH2 and C=O groups in methacrylate chains; a decrease in the −1 is observed relative to the lower molecular inintensity the intensity the Si–OCH 3 group band at 2938 cmobserved −1 is of theofSi–OCH relative to the lower molecular weight 3 group band at 2938 cm weight MSSO, evidenced together with the generation of a broad band cm−1, assigned to – MSSO, evidenced together with the generation of a broad band at 3423 cmat−13423 , assigned to –OH groups −1 OH groups from Si–OH. Exceptatfor bands 2938 3423 cm these data are in goodwith agreement −1 , these from Si–OH. Except for bands 2938 and at 3423 cmand data,are in good agreement those of with those of the MPMS spectrum in Figure S2a and give complementary information for theof the MPMS spectrum in Figure S2a and give complementary information for the characterization characterization the structure. of the structure. 1H-NMR spectrum (Figure S3) were assigned: 0.698 ppm (1); 1.784 The in in thethe 1 H-NMR spectrum (Figure S3) were assigned: 0.698 ppm (1); Thefollowing followingpeaks peaks ppm (2); 1.925 ppm (7); 3.520, 3.580 ppm3.580 (CH3ppm –OH,(CH Si–OH); 4.111, 4.103 ppm (3); 5.545, 6.091 ppm 1.784 ppm (2); 1.925 ppm (7); 3.520, 3 –OH, Si–OH); 4.111, 4.103 ppm (3); 5.545, (5, 6); ppm 7.280(5, ppm (CHCl 3); 8.004, 8.049 ppm (HCOOCH3, HCOOH). The following peaks in the 6.091 6); 7.280 ppm (CHCl3 ); 8.004, 8.049 ppm (HCOOCH3 , HCOOH). The following peaks in 13C-NMR spectrum (Figure S4) were assigned: 8.534 ppm (1); 17.865 ppm (7); 21.954 ppm (2); 66.121, 13 the C-NMR spectrum (Figure S4) were assigned: 8.534 ppm (1); 17.865 ppm (7); 21.954 ppm (2); 66.121, 65.894 77.319 ppm ppm (CHCl (CHCl3,, CH CH3-OH, -OH,Si–OH); Si–OH);125.006 125.006ppm ppm(5); (5);135.983 135.983 ppm 65.894ppm ppm(3); (3);76.674, 76.674, 77.000, 77.000, 77.319 ppm (6); 3 3 1 13 (6); 162.785 ppm (HCOOH); 167.019ppm ppm(4,(4,HCOOCH HCOOCH). 3). Besides 1H- and 13 162.785 ppm (HCOOH); 167.019 Besides H- and C-NMR C-NMRspectroscopy, spectroscopy, 3 29Si NMR spectroscopy permits quantitative measurement of the degree of condensation by the 29 Si NMR spectroscopy permits quantitative measurement of the degree of condensation by the 3 relative nuclei, Si–(O–Si) 3 [20–23]: −65.681 ppm is characteristic of the T3 3 silicon relativeabundance abundanceofofthe theT Tsilicon nuclei, Si–(O–Si) 3 [20–23]: −65.681 ppm is characteristic of the 2 species, and and –56.577 ppm cancan be be assigned to toT T2structures, 2(OH), from incompletely T3 species, –56.577 ppm assigned structures,Si–(O–Si) Si–(O–Si) 2 (OH), from incompletely 0 or T1 structures were present in the 29Si-NMR condensed species in the product mixture; no T condensed species in the product mixture; no T0 or T1 structures were present in the 29 Si-NMR spectrum spectrumwhich whichisisconsistent consistentwith withhigher highermolecular molecularweight weightand andcyclic cyclicMSSO. MSSO.
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Figure222shows showsthe theUV-MALDI-TOF UV-MALDI-TOFMS MSin inthe them/z m/z == 0–11,000 0–11,000 Da Da range range corresponding corresponding to to MSSO MSSO Figure Figure shows the UV-MALDI-TOF MS in the m/z molecules. Three high-symmetry complete MSSOs, T 8 , T 20 and T 60 (see Figure 3), were assigned (see molecules. Three high-symmetry complete MSSOs, T , T and T (see Figure 3), were assigned molecules. Three high-symmetry complete MSSOs, T8, 8T20 and T60 (see 20 60 Figure 3), were assigned (see Table 1). These predicted structures have a compliance between the experimental measurement (see Table 1). These predicted structures havea acompliance compliancebetween between the the experimental measurement Table 1). These predicted structures have measurement + or M + + Na value and and the the calculated molecular weight according to ion ionion adducts (Mww(M H or M w+ K++)) ++ or value thecalculated calculatedmolecular molecularweight weight according to adducts Mw +M Na w++ value according to adducts (M ++ H orHMwwor + Na w ++ or K [24], however, there are are still still few few differences, probablyprobably from ion ion from adducts selected, selected, solvent used used for M K+ ) [24], however, there aredifferences, still few differences, ion selected, adducts solvent w +however, [24], there probably from adducts solvent for the measurement measurement operation, calculations and and so on. on. T60 60,,Tone one ofofthree three high-symmetry complete used for the measurement operation, calculations so on. , one threehigh-symmetry high-symmetry complete the operation, calculations and so T of 60 MSSOs, is a fullerene-like HBB and is denoted as MP-HBB as shown in Figure 3c. The difference MSSOs, is a fullerene-like HBB and is denoted as MP-HBB as shown in Figure 3c. The difference MSSOs, a fullerene-like HBB and is denoted as MP-HBB as shown in Figure 3c. The difference betweenHBB HBBand andFBB FBB(as (asmentioned mentioned above) provides an ideal vehicle for exciting exciting research which between above) provides an an ideal vehicle for exciting research which will between HBB and FBB (as mentioned above) provides ideal vehicle for research which will be timely, timely, rapidly evolving, multidisciplinary and even even appealing on an aesthetic aesthetic level. be timely, rapidly evolving, multidisciplinary and even appealing on anon aesthetic level.level. will be rapidly evolving, multidisciplinary and appealing an
Figure 2. 2. The The UV-MALDI-TOF MSMS in in thethe m/zm/z 500–11,000 Da range range correspond to the the to MSSO Figure TheUV-MALDI-TOF UV-MALDI-TOF = 500–11,000 Da range correspond the Figure 2. MS in the m/z == 500–11,000 Da correspond to MSSO MSSO oligomers. oligomers. oligomers.
Figure3.3. 3.Structures Structuresof ofthree threehigh-symmetry high-symmetrycomplete completeMSSOs: MSSOs:(a) (a)TT T (b)TT T2020 20 and and (c) (c) T T60 60. Figure 88;8;;(b) Figure Structures of three high-symmetry complete MSSOs: (a) (b) and (c) T 60.
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Table 1. Three high-symmetry complete MSSOs assigned by the mass spectrum (m/z = 0–11,000 Da).
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Experiment (m/z) Assigned structure Calculation (m/z) (+H+, K+) Symmetry + 1,472.73 R8Si8O12 (+K ) 1,472.98 Oh +) Table 1. Three high-symmetry Rcomplete MSSOs assigned by the3,585.96 mass spectrum (m/z = 0–11,000 Da). 3,579.23 20Si20O30 (+H Ih 10,763.81 R60Si60O90 (+H+) 10,755.88 Ih Experiment (m/z) Assigned structure Calculation (m/z) (+H+ , K+ ) Symmetry + ) proposed cyclic Additional corroborating evidence structures can be observed in the gel 1,472.73 R8 Si8 O12for (+Kthe 1,472.98 Oh + 3,579.23 R20 Sichromatograms permeation chromatography (GPC) obtained3,585.96 for the MSSO samples. IFigure 4 shows 20 O30 (+H ) h +) 10,763.81of the MSSOs R60 Simeasured 10,755.88 Ih index data. 60 O90 (+H by the mass distribution a GPC device which provides refractive The distribution profiles indicate that the oligomers are formed in three successive groups with average molecular weights of evidence 1413.8, 4538.8 andproposed 16,260.0 cyclic (see Figure 4b3, b2 b1, respectively) Additional corroborating for the structures canand be observed in the corresponding to fractions containing the T 60 , T 20 and T 8 cyclic compounds [25]. gel permeation chromatography (GPC) chromatograms obtained for the MSSO samples. Figure 4 will ofbethe conducted on this by MP-HBB to separate it from multiple showsFurther the massresearch distribution MSSOs measured a GPC device which provides refractive MSSO index structures using a gel profiles permeation column. Theoligomers intensity of MP-Tin 60 present can be determined by data. The distribution indicate that the arethe formed three successive groups with GPC or size exclusion chromatography (SEC), and the mass of the elutant is again measured by average molecular weights of 1413.8, 4538.8 and 16,260.0 (see Figure 4b3, b2 and b1, respectively)a mass spectrometer [25,26].containing the T60 , T20 and T8 cyclic compounds [25]. corresponding to fractions
Figure Figure4.4.The Themass massdistribution distributionof ofthe theMSSO MSSOoligomers oligomersmeasured measured by byaaGPC GPCdevice devicewhich whichprovides provides ◦ ◦ refractive reaction under 70 70 C for (b) reaction under 35 C for average refractiveindex indexdata: data:(a)(a) reaction under °C 12 fordays; 12 days; (b) reaction under 3520 °Cdays, for 20 days, molecular weights ofweights oligomers formed in formed three successive groups with (b1) 16,260.0, (b2) 4538.8 and average molecular of oligomers in three successive groups with (b1) 16,260.0, (b2) (b3) 1413.8, corresponding to fractions containing T60 , T20 and compounds. T20 and T8 cyclic compounds. 4538.8 and (b3) 1413.8, corresponding to fractionsthe containing the TT608, cyclic
Supplementary Materials: following are onlinetoatseparate www.mdpi.com/2073-4360/8/8/315/s1, Figure Further research will The be conducted on available this MP-HBB it from multiple MSSO structures S1: Structural formula of MSSO (numbers correspond to the assignment of 1H- and 13C-NMR peaks), Figure S2: using a gel permeation column. The intensity of the MP-T60 present can be determined by GPC FTIR spectrum of MSSO: (a) Original material, MPMS; (b) The hydrolytic condensation of MPMS for 10 days or size exclusion 1chromatography (SEC), and the mass of the elutant 13is again measured by a mass (40 °C), Figure S3: H-NMR spectrum (DMSO-d6, 25 °C) of MSSO, Figure S4: C-NMR spectrum (DMSO-d6, 25 spectrometer °C) of MSSO. [25,26]. Acknowledgments: The financial support from The Aerospace Fund (GN: 2012-HT-HGD-11), The Supplementary Materials: The following are available onlineSupporting at www.mdpi.com/2073-4360/8/8/315/s1, Figure S1: Structural of MSSO (numbers correspond the assignment of 1 H- Funds and 13 C-NMR Heilongjiang Youth formula Science Fund (GN: QC2012C027), The to Fundamental Research for the peaks), Central Figure S2: FTIR spectrum of MSSO: (a) Original material, MPMS; (b) The hydrolytic condensation of MPMS Universities (GN: DL11BB01), and The Fundamental Research Funds for the Central Universities (GN: 1 H-NMR spectrum (DMSO-d , 25 ◦ C) of MSSO, Figure S4: 13 C-NMR spectrum for 10 days (40 ◦ C),China, Figureis S3: 6 2572014EB02-02), gratefully acknowledged. (DMSO-d6 , 25 ◦ C) of MSSO. Author Contributions: You Wang and Hong You conceived and designed the project and experiments; Di Acknowledgments: The financial support from The Aerospace Supporting Fund (GN: 2012-HT-HGD-11), Wang and Yu Hu performed the calculation, experiments and paper The Heilongjiang Youth Science Fund (GN: QC2012C027), The writing. Fundamental Research Funds for the Central Universities (GN: DL11BB01), and The Fundamental Research Funds for the Central Universities Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the (GN: 2572014EB02-02), China, is gratefully acknowledged. design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and Author Contributions: Youthe Wang and Hong You conceived and designed the project and experiments; Di Wang in the decision to publish results. and Yu Hu performed the calculation, experiments and paper writing. Conflicts of Interest: The authors declare no conflict of interest. The founding sponsors had no role in the design References of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.
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