Preparation and properties of polyhedral oligomeric silsesquioxane/epoxy hybrid resins

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<ul><li><p>Preparation and Properties of Polyhedral OligomericSilsesquioxane/Epoxy Hybrid Resins</p><p>Guojun Ding,1,2 Jifang Fu,1 Xing Dong,1 Liya Chen,1 Haisen Jia,1 Wenqi Yu,1,2 Liyi Shi11Nano-Science &amp; Technology Research Center, Shanghai University, Shanghai 200444,Peoples Republic of China</p><p>2College of Science, Shanghai University, Shanghai 200444, Peoples Republic of China</p><p>Octaaminophenyl polyhedral oligomeric silsesquioxane(OAPS) was synthesized using three-step method andused to modify o-cresol-novolac epoxy resin (ECN) forprinted circuit board. The influence of OAPS on thereactivity and the final properties of the hybrid networkswere evaluated. The intercrosslinking reaction betweenECN and OAPS was confirmed by Fourier transforminfrared spectra. The ECN/OAPS hybrids have betterimpact strength, higher electrical resistivity and thermalstability, lower water absorption than the unmodifiedECN. The volume resistivity and surface resistivity ofthe hybrids increase by an order of magnitude or morecompared to the neat epoxy. The thermal stability ofthe hybrids improves by the incorporation of OAPS; theinitial decomposition temperature and char yield showan increasing tendency up to 4 wt% loading of OAPS.The hybrids exhibit higher storage modulus and glasstransition temperature (Tg) than the neat epoxy. The Tgof the hybrids greatly improves up to 153.3C at 3 wt%content, much higher than 119.4C of the neat epoxy.POLYM. COMPOS., 34:17531760, 2013. VC 2013 Society ofPlastics Engineers</p><p>INTRODUCTION</p><p>Epoxy resin (EP) is one of the most important thermo-</p><p>setting materials due to their superior mechanical and</p><p>thermal properties and simplicity in processing, which has</p><p>been extensively used as adhesives, electronic encapsulat-</p><p>ing compounds, matrix of composites, coatings, and so</p><p>on. However, EP has many shortcomings such as brittle-</p><p>ness owing to high crosslinking densities, low stiffness</p><p>and strength, poor toughness, and so on. Therefore, it is</p><p>necessary to modify the EP to improve the comprehensive</p><p>properties of EP [14].</p><p>Meanwhile, organicinorganic hybrid nanocomposite</p><p>materials have attracted increasing attentions because</p><p>they combine the advantages of inorganic materials</p><p>with those of organic polymers in recent years. Polyhe-</p><p>dral oligomeric silsesquioxanes (POSS) with empirical</p><p>formula RSiO1.5 [5] possesses a cage-like structure</p><p>ranging in size from 1 to 3 nm [6], which includes a</p><p>rigid inorganic core made up of silicon atoms linked by</p><p>oxygen atoms (SiO1.5) and organic groups (R) posi-</p><p>tioned at the vertices of the cages [7]. Compared with</p><p>traditional inorganic fillers, POSS has the advantages</p><p>of monodispersed size, low density, high thermal stabil-</p><p>ity, and good compatibility with polymer matrix. The</p><p>incorporation of POSS into EP can improve their ther-</p><p>mal resistance, mechanical strength, dielectric proper-</p><p>ties, flame retardancy [3,8]. Nowadays, many authors</p><p>have reported that EP modified by POSS through cur-</p><p>ing process promotes an improvement in use properties</p><p>[813]. The representative work was carried out by</p><p>Chens group [6], in which the nanocomposites involv-</p><p>ing diglycidyl ether of bisphenol A and octaamino-</p><p>phenyl polyhedral oligomeric silsesquioxane (OAPS)</p><p>were prepared.</p><p>Recently, many methods have been used to improve</p><p>the thermal stability, electrical properties, water absorp-</p><p>tion, mechanical properties, and dimensional stability of</p><p>EP for printed circuit board (PCB). In our work, OAPS</p><p>was synthesized based on the previous reports [13]</p><p>and was used directly to prepare a novel network with</p><p>o-cresol-novolac epoxy resin (ECN) for PCB. The aimwas to analyze the influence of OAPS on the reactivity</p><p>and the final properties of the network.</p><p>Correspondence to: Fu Jifang; e-mail:, or Shi Liyi; e-mail:</p><p>Contract grant sponsor: Key Project of Chinese Ministry of Education;</p><p>contract grant number: 208182; contract grant sponsor: Shanghai Lead-</p><p>ing Academic Discipline Project; contract grant number: S30107; Con-</p><p>tract grant sponsor: Shanghai University Development Foundation;</p><p>contract grant number: A.10-0407-11-002; Contract grant sponsor: Pro-</p><p>gram for Professor of Special Appointment (Eastern Scholar) at Shang-</p><p>hai Institutions of Higher Learning; contract grant number: B.39-0411-</p><p>10-001; Contract grant sponsor: Education and Research for the Teacher</p><p>Professional Development Project; contract grant number: B.60-B407-</p><p>11-002; Contract grant sponsor: Key Subject of Shanghai Municipal</p><p>Education Commission; contract grant number: J50102.</p><p>DOI 10.1002/pc.22579</p><p>Published online in Wiley Online Library (</p><p>VC 2013 Society of Plastics Engineers</p><p>POLYMER COMPOSITES2013</p></li><li><p>EXPERIMENTAL</p><p>Materials</p><p>ECN was received from Shengyi Technology, China.</p><p>Phenyltrichlorosilane (PhSiCl3, 99%) was purchasedfrom Guangtuo Chemicals, Shanghai, China. Methyl hex-</p><p>ahydrophthalic anhydride (MeHHPA, 99%) was pur-chased from Huicheng Electronic Material, Puyang,</p><p>Henan, China. Tetrahydrofuran (THF), acetone, ethyl ace-</p><p>tate, hydrazine, benzene were all analytically pure grade</p><p>and were supplied by Shanghai Reagent, China.</p><p>Synthesis of OAPS</p><p>According to the literature [13], OAPS was synthe-</p><p>sized following a three-step mechanism as described in</p><p>Scheme 1.</p><p>Synthesis of Octaphenyl Polyhedral OligomericSilsesquioxane (Ph8Si8O12)</p><p>PhSiCl3 (32 g, 0.154 mol) and benzene (120 mL) were</p><p>put into a three-necked flask (500 mL), equipped with a</p><p>magnetic stirrer, thermometer, and a dropping funnel. Then</p><p>the deionized water (225 mL) was added slowly into the</p><p>system at 10C or lower. The hydrolysis was carried out atroom temperature for 2 days. Thereafter, the benzene layer</p><p>was isolated and washed for three times with deionized</p><p>water to remove the hydrochloric acid. The above benzene</p><p>solution and 10 mL of methanol solution of benzyltrime-</p><p>thylammonium hydroxide (50 wt%) were charged to a</p><p>flask equipped with a mechanical stirrer. The mixture was</p><p>refluxed for 48 h to ensure complete rearrangement reac-</p><p>tion. After that, the mixture was cooled to room tempera-</p><p>ture, and then white powder was obtained (14.17 g, 71.2</p><p>wt%). The product was extracted using benzene to remove</p><p>the soluble resin and further dried in vacuum.</p><p>Synthesis of Octanitrophenyl Polyhedral OligomericSilsesquioxane</p><p>The Ph8Si8O12 was nitrified using fuming nitric acid to</p><p>prepare octanitrophenyl polyhedral oligomeric silsesquioxane</p><p>(OnpPOSS). About 150 mL of fuming nitric acid was put</p><p>into a three-neck flask equipped with a magnetic stirrer, and</p><p>25 g of Ph8Si8O12 was added slowly within 30 min with stir-</p><p>ring at 0C and followed by stirring at room temperature for20 h. After that, the solution was poured into 250 g of ice.</p><p>A faintly yellow powder was collected by filtration. The pre-</p><p>cipitate was washed with saturated NaHCO3 aqueous solu-</p><p>tion and water, respectively, until the pH value is 7. The</p><p>obtained product was dried in a vacuum oven at 50C for 24h. Exhaustive extraction of solid with benzene afforded a</p><p>white microcrystalline powder (32.4 g, 89.7 wt%).</p><p>Synthesis of OAPS</p><p>OAPS was prepared by reducing OnpPOSS. 10 g of</p><p>OnpPOSS was dissolved in 80 mL of THF in a 250 mL</p><p>three-neck flask equipped with a water-cooled condenser</p><p>and a magnetic stirrer. Then, 1.22 g of Pd/C catalyst, 0.4</p><p>SCH. 1. The synthesis route of OAPS. [Color figure can be viewed in the online issue, which is available</p><p>at]</p><p>1754 POLYMER COMPOSITES2013 DOI 10.1002/pc</p><p></p></li><li><p>g of FeCl36H2O were put into the flask. The mixturewas heated to 54C and hydrazine hydrate was slowlydropped and then the mixture was reflexed for 5 h. After</p><p>that, the Pd/C catalyst was removed by filtration under</p><p>reduced pressure to obtain an orange solution and then</p><p>washed for several times using about 60 mL of ethyl ace-</p><p>tate. In the next step, the extracted organic solution was</p><p>washed using deionized water until it became almost col-</p><p>orless. Then the residual water in the colorless solution</p><p>was removed by reacting with magnesium sulfate</p><p>(MgSO4). Finally, the solution was precipitated with 1200</p><p>mL of petroleum ether. The pale powder was collected by</p><p>filtration under reduced pressure and further dried in vac-</p><p>uum at 50C for 24 h. Yield: 6.2 g. Fourier transforminfrared (FTIR) spectra (cm21) with KBr powder: 3378</p><p>(NAH), 1120 (SiAOASi). 1H NMR (DMSO-d6): 7.78.8(4H), 4.04.7 (2H).</p><p>Preparation of ECN/MHHPA/OAPS Nanocomposites</p><p>Various amounts of OAPS were previously dissolved</p><p>in THF and added into the desired quantity of ECN, and</p><p>then the mixture was kept stirring for 2 h at room temper-</p><p>ature. After that, a stoichiometric amount of MeHHPA</p><p>was added to the above mixture at room temperature, and</p><p>then the mixture of the three substances was stirred until</p><p>the mixture became homogenous. According to Table 1,</p><p>the contents of OAPS in the nanocomposites were con-</p><p>trolled to 1, 2, 3, 4, and 5 wt%, respectively.</p><p>The mixtures were degassed under vacuum at 80C toremove the solvent and gas. After that, the mixture was</p><p>poured into a preheated (80C) aluminum mold (80 mm310 mm 3 5 mm) and then cured and postcured followingthe procedures of 90C/1 h 1 100C/1 h 1 110C/1 h 1120C/12 h 1 160C/6 h successively [14,15]. The result-ing hybrids were transparent in each case. The reacting pro-</p><p>cess between ECN and OAPS is shown in Scheme 2:</p><p>CHARACTERIZATION</p><p>FTIR spectra were recorded between 400 and 4000</p><p>cm21 with a resolution of 4 cm21 on Avatar 370 spec-</p><p>trometer. The sample was pressed into a pellet with KBr.</p><p>Impact strength tests were performed using a JJ-20</p><p>impact tester according to China National Standard</p><p>GB1043-79. The three-dimension of specimen size was</p><p>80 mm 3 10 mm 3 4 mm. The flex strength was meas-</p><p>ured on an Instron Model 1185 test machine according to</p><p>ASTM D790-2010. The specimen size was also 80 mm</p><p>3 10 mm 3 4 mm. All of the mechanical propertieswere obtained by averaging at least three measurements.</p><p>A JSM-6700F scanning electron microscope (SEM)</p><p>was used to study the morphology of the impact fracture</p><p>surface of EP containing POSS. The samples were coated</p><p>with a thin gold layer using a sputter coater prior to the</p><p>SEM observation to get a clear image of facture surface.</p><p>The resistivity was performed on an Angilent 4339B</p><p>megger at room temperature according to ASTM D257-</p><p>2007. The water absorption of the networks was tested</p><p>according to GB/T 1462-2005. Thermogravimetric analy-</p><p>ses (TGA) were also performed using TA Q500 HiRes</p><p>analyzer at a heating rate of 10C/min in flowing nitrogenfrom 25 to 700C.</p><p>The dynamic mechanical tests were carried out on a</p><p>dynamic mechanical thermal analyzer (DMA, Q800, TA</p><p>Instrument Company) with the temperature range from 20</p><p>to 300C. The frequency used is 1.0 Hz. The specimendimension was 35 mm 3 10 mm 3 2 mm.</p><p>RESULTS AND DISCUSSION</p><p>FTIR Spectral Analysis</p><p>Fig. 1 shows FTIR spectra of different contents of</p><p>OAPS-reinforced ECN/MeHHPA nanocomposites. The</p><p>disappearance of new peak at 1617 cm21 corresponding</p><p>to NAH bending included in OAPS demonstrated thecrosslinking reaction between the epoxy and OAPS. At</p><p>the same time, the SiAOASi peak at 1101 cm21 stillappeared after curing, which confirms that the cage struc-</p><p>ture made up of SiAOASi bond was very stable. In addi-tion, OAH stretching of ECN was found at 3469 cm21</p><p>due to the reaction between ECN and OAPS [11].</p><p>Mechanical Properties</p><p>The effects of OAPS on impact strength of ECN/</p><p>MeHHPA are shown in Fig. 2. The incorporation of</p><p>OAPS (up to 5 wt%) into ECN/MeHHPA systems</p><p>enhanced impact strength, due to the presence of organic</p><p>groups such as phenyl, amino groups in the OAPS mole-</p><p>cule [16,17]. In the results, the impact strength reached</p><p>the highest when OAPS content was about 2 wt%, and</p><p>TABLE 1. Electrical properties of OAPS/ECN/MeHHPA hybrids.</p><p>Sample OAPS (wt%) Water absorption (%) Volume resistivity (X cm) Surface resistivity (X)</p><p>ECN/MHHPA 0 0.3491 6 0.0050 5.164 3 1016 2.459 3 1016</p><p>1 0.2194 6 0.0031 1.418 3 1017 6.899 3 1017</p><p>2 0.3380 6 0.0031 1.528 3 1017 1.886 3 1018</p><p>3 0.2328 6 0.0031 1.053 3 1017 1.839 3 1018</p><p>4 0.3195 6 0.0027 1.282 3 1017 7.094 3 1016</p><p>5 0.2587 6 0.0049 9.538 3 1016 2.569 3 1017</p><p>DOI 10.1002/pc POLYMER COMPOSITES2013 1755</p></li><li><p>the impact strength of OAPS/ECN/MeHHPA was 15.31</p><p>kJ/m2, which was 1.3 times higher than that of ECN/</p><p>MeHHPA system. However, when OAPS content was</p><p>more than 3 wt%, the tendency of impact strength was</p><p>decreasing, but it was still higher than the unmodified</p><p>system.</p><p>Fig. 3 presents the flexural properties of neat ECN sys-</p><p>tems and OAPS/ECN/MHHPA systems. The introduction</p><p>of OAPS into ECN/MeHHPA network decreased the val-</p><p>ues of flexural strength compared to those of neat epoxy</p><p>systems due to the increased chain entanglement and</p><p>enhanced free volume imparted by OAPS [18,19].</p><p>As shown in Fig. 4, the samples were visually</p><p>observed in optical clarity of ECN/OAPS composites.</p><p>EP1, EP2, EP3 were transparent like EP0; with loading</p><p>content of OAPS increasing, PH4 and PH5 became dark.</p><p>In addition, the color of composites became deeper with</p><p>the increase of POSS content. One possible explanation</p><p>was that some OAPS did not react with ECN, which</p><p>could be oxidized by oxygen in the air to the color sub-</p><p>stances and the more OAPS content in composites led to</p><p>FIG. 1. FTIR spectra of different contents of OAPS-reinforced epoxy</p><p>nanocomposites. [Color figure can be viewed in the online issue, which</p><p>is available at]</p><p>SCH. 2. The reacting process for the OAPS/ECN. [Color figure can be viewed in the online issue, which is</p><p>available at]</p><p>1756 POLYMER COMPOSITES2013 DOI 10.1002/pc</p><p></p></li><li><p>more color substances so that the color of composites</p><p>became deeper.</p><p>As shown in Fig. 5, the morphology of the cross-section</p><p>of samples after impact test was observed by SEM and was</p><p>used to analyze the influence of OAPS on the mechanical</p><p>properties of nanocomposites. Fig. 5a shows that the neat</p><p>epoxy has smooth surface [15]. Figure 5bf present that the</p><p>ECN/OAPS hybrids had rougher surface with more river-</p><p>like lines than the pure ECN. The increased surface rough-</p><p>ness means that the matrix plastic deformation is the major</p><p>fracture surface phenomenon, which absorbs surface energy.</p><p>Therefore, ECN/OAPS hybrids had higher toughness than</p><p>the pure ECN, which was in agreement with the previous</p><p>results of impact strength. It is also observed that there</p><p>were no agglomerates of nanoparticles in the ECN/OAPS</p><p>hybrids, which suggests that the OAPS exhibits good dis-</p><p>persion in the ECN matrix.</p><p>Electrical Behavior</p><p>Water absorption of samples is presented in Table 1.</p><p>At first, the test was carried out by immersing specimens</p><p>of appropriate dimension in boiling water for 30 min 6</p><p>1min. It is very important for materials used for insulation</p><p>application to have low water absorption. Generally, the</p><p>absorbed water will affect the properties of the original</p><p>materials, such as thermal, mechanical, electrical proper-</p><p>ties, and so on, Through the experiment, compared with</p><p>t...</p></li></ul>