李?lèi)?ài)香, 陳復(fù)強(qiáng), 呂滋建
(山東理工大學(xué) 材料科學(xué)與工程學(xué)院,山東 淄博 255049)
嵌段共聚物刷穩(wěn)定的納米銀粒子的制備與表征
李?lèi)?ài)香, 陳復(fù)強(qiáng), 呂滋建
(山東理工大學(xué) 材料科學(xué)與工程學(xué)院,山東 淄博 255049)
摘要:制備了鏈中間含三硫代酯基團(tuán)的苯乙烯-丙烯酸丁酯嵌段共聚物刷保護(hù)的納米銀(Ag NPs)粒子.首先采用可逆加成斷裂鏈轉(zhuǎn)移(RAFT)聚合法制備苯乙烯-丙烯酸丁酯三嵌段共聚物PS-b-PBA-b-PS,然后以PS-b-PBA-b-PS為穩(wěn)定劑,硼氫化鈉(NaBH4)為還原劑,原位還原硝酸銀得到嵌段共聚物刷保護(hù)的納米銀粒子.用紅外光譜(IR)、核磁共振氫譜(1H NMR)、GPC等方法對(duì)聚合物進(jìn)行了表征,用紫外可見(jiàn)光譜(UV-Vis)、透射電子顯微鏡(TEM)等對(duì)納米銀復(fù)合粒子進(jìn)行了表征.結(jié)果表明,含三硫代酯基團(tuán)的聚合物不必經(jīng)過(guò)還原和水解成巰基,可直接作為配體制備穩(wěn)定的納米銀粒子,粒子粒徑分布均勻,分散性好.
關(guān)鍵詞:三嵌段共聚物;RAFT聚合;原位還原;聚合物刷;納米銀
收稿日期:2015-01-15
基金項(xiàng)目:國(guó)家自然科學(xué)基金項(xiàng)目(51303096); 山東理工大學(xué)青年教師發(fā)展支持計(jì)劃項(xiàng)目
作者簡(jiǎn)介:李?lèi)?ài)香,女,axl@sdut.edu.cn
文章編號(hào):1672-6197(2016)01-0046-05
中圖分類(lèi)號(hào):O631
文獻(xiàn)標(biāo)志碼:A
Abstract:Triblock copolymer of styrene and butyl acrylate PS-b-PBA-b-PS containing trithiocarbonate group was synthesized by reversible addition-fragmentation transfer (RAFT) polymerization. And silver nanoparticles (Ag NPs) were prepared by in-situ reduction method using this triblock copolymer as stabilizer, sodium borohydride as reductant. The structure of triblock polymer was characterized by FTIR,1H NMR, and the molecular weight and the distribution of the triblock copolymer and its precursor were determined by gel permeation chromatography (GPC).Ag NPs were characterized by TEM and UV-Vis spectrum. The results showed that the triblock copolymers PS-b-PBA-b-PS could be used to stabilize Ag NPs directly without reductant and hydrolysis. Ag NPs stabilized by tribolck copolymer brushes by in-situ reduction method had good stability and dispersibility.
Preparation and characterization of silver
nanoparticles stabilized by block copolymer brushes
LI Ai-xiang, CHEN Fu-qiang, LYU Zi-jian
(School of Materials Science and Engineering, Shandong University of Technology, Zibo 255049,China)
Key words: triblock copolymer; RAFT polymerization; in-situ reduction; polymer brush; silver nanoparticles
近年來(lái),金屬納米粒子,尤其是金和銀,由于在納米電子、納米光學(xué)、催化、生物和生物醫(yī)學(xué)等領(lǐng)域的潛在應(yīng)用而吸引了重大的研究興趣[1-7].含巰基聚合物刷穩(wěn)定的金屬納米粒子由于組成多樣和聚合物優(yōu)異的加工性能尤其吸引人的關(guān)注.
Grafting-from和Grafting-onto方法已經(jīng)被廣泛應(yīng)用在制備聚合物刷保護(hù)的金屬納米粒子上.Grafting from方法首先在納米粒子的表面引入可以引發(fā)聚合的官能團(tuán),然后采用適合的聚合方法引發(fā)單體聚合,可得到聚合物刷保護(hù)的納米粒子.例如Ohno等[8]首先在含二硫鍵和溴官能團(tuán)的化合物存在下,用硼氫化鈉還原HAuCl4制備了含多個(gè)Br原子的納米金粒子(Au NPs),然后用此Au NPs為引發(fā)劑,引發(fā)MMA進(jìn)行原子轉(zhuǎn)移自由基聚合(ATRP),得到了高密度聚合物刷保護(hù)的Au NPs.而Dong等[9]采用相似的方法,制備了高熱穩(wěn)定性聚丙烯酸丁酯保護(hù)的Au NPs. Grafting-from法制備聚合物刷保護(hù)的金屬納米粒子雖然非常有效,但是僅限于低溫聚合,因?yàn)锳u-S和Ag-S鍵在高溫下不穩(wěn)定,容易斷裂,造成納米粒子的聚集,因而限制了其應(yīng)用和發(fā)展.
Grafting-onto法可事先制備含巰基的聚合物,然后再在聚合物存在下原位還原金屬鹽制備納米粒子.例如,Muriel等[10]用grafting-onto的方法,用巰基封端的聚苯乙烯(PS)和聚乙二醇(PEG)作配體,合成了一系列高密度聚合物刷保護(hù)的Au NPs.Greiner等[11]首先用陰離子聚合法制備了含巰基的PS,然后用grafting-onto法,以三乙基硼氫化鋰為還原劑,在四氫呋喃(THF)中原位還原三氟醋酸銀,得到高濃度穩(wěn)定的銀納米粒子(Ag NPs),此納米粒子可在PS基體中均勻分散.眾所周知,用可逆加成-裂解鏈轉(zhuǎn)移(RAFT)聚合法可直接制備含二硫代酯或者三硫代碳酸酯基團(tuán)的聚合物[12-17],經(jīng)還原和水解可得到含巰基的聚合物,可被用作配體制備金屬納米粒子.例如,Bae等[18]用二芐基三硫碳酸酯(DBTTC)為鏈轉(zhuǎn)移劑(CTA)通過(guò)RAFT聚合苯乙烯制備了含三硫代酯基團(tuán)的PS,然后經(jīng)還原和水解產(chǎn)生了巰基封端的PS.用此聚合物為穩(wěn)定劑,用兩相法還原HAuCl4,得到了平均粒徑在3~5nm的Au NPs,并用含有Au NPs的PS薄膜制備了有機(jī)記憶器件,表現(xiàn)出較好的開(kāi)關(guān)行為.
然而,已經(jīng)被證明,含二硫代酯基團(tuán)的聚合物可以不必經(jīng)過(guò)水解成巰基,直接用來(lái)作穩(wěn)定劑制備金屬納米粒子,因?yàn)樵诮饘偌{米粒子的制備過(guò)程中,還原劑可直接將二硫代酯還原為巰基[19-21].而用含三硫代酯基團(tuán)的聚合物為穩(wěn)定劑直接制備金屬納米粒子的研究較少被報(bào)道.
本文報(bào)道了用含三硫代酯基團(tuán)的苯乙烯-丙烯酸丁酯三嵌段共聚物PS-b-PBA-b-PS為穩(wěn)定劑,直接原位還原制備銀納米粒子.該方法直接簡(jiǎn)便,避免了還原和水解等過(guò)程,合成的納米粒子粒徑均勻,分散性和穩(wěn)定性好.
1實(shí)驗(yàn)部分
苯乙烯(St)和丙烯酸丁酯(BA)從上海國(guó)藥集團(tuán)購(gòu)買(mǎi),用之前過(guò)堿性三氧化二鋁柱子除去阻聚劑,-18℃保存?zhèn)溆?;二芐基三硫代碳酸酯(DBTTC)從Sigma-Aldrich公司購(gòu)買(mǎi).偶氮二異丁腈(AIBN)用無(wú)水乙醇重結(jié)晶.其它試劑未做進(jìn)一步純化.
在一個(gè)典型的聚合過(guò)程中,將24mL(0.21mol)苯乙烯,0.21g(1.28 mmol)AIBN,0.33 mL (1.16mmol) DBTTC和20 mL甲苯放入100 mL Schlenk瓶中,經(jīng)過(guò)三次冷凍-抽真空-暖化-通高純氬氣,密封反應(yīng)瓶.將反應(yīng)瓶浸入80℃油浴中,磁力攪拌反應(yīng)24 h.冰浴冷卻20 min終止反應(yīng).將聚合物溶液滴加到100 mL甲醇中沉淀,過(guò)濾,將固體聚合物再用THF/甲醇溶解沉淀兩次,除去未反應(yīng)的單體和引發(fā)劑.所得固體大分子鏈轉(zhuǎn)移劑PS-CTA在50℃真空干燥24 h.
取1g PS-CTA,8mg AIBN,2mL BA和6mL甲苯置于100mL Schlenk瓶中,經(jīng)過(guò)三次冷凍-抽真空-暖化-通高純氬氣,密封反應(yīng)瓶.將反應(yīng)瓶浸入80℃油浴中,磁力攪拌反應(yīng)24 h.冰浴冷卻20 min終止反應(yīng).將聚合物溶液滴加到100mL甲醇中沉淀,過(guò)濾,將固體聚合物再用THF/甲醇溶解沉淀兩次,除去未反應(yīng)的單體和引發(fā)劑.所得聚合物在50℃真空干燥24 h.
17 mg AgNO3和50 mg的PS-b-PBA-b-PS置于錐形瓶中,加入10 mL DMF,超聲溶解,冰浴冷卻20 min.取4.2 mg NaBH4溶解于3mL DMF中.劇烈攪拌下,將NaBH4溶液滴加到AgNO3中,繼續(xù)反應(yīng)3h.
嵌段共聚物的傅里葉變換紅外光譜(FTIR)采用溴化鉀壓片法,使用島津8400S型傅立葉紅外光譜儀測(cè)定.嵌段共聚物的1H NMR譜在Bruck 400 Hz型核磁共振儀上進(jìn)行測(cè)定,CDCl3為溶劑.嵌段共聚物及其前體的分子量及其分布用Waters 1414型凝膠滲透色譜(GPC)儀測(cè)試,兩根PS色譜柱(styrogel HR 4, 5),折光指數(shù)檢測(cè)器,THF為淋洗劑,流速為1 mL/min,線(xiàn)形PS為標(biāo)準(zhǔn)樣品,溫度為40℃.紫外可見(jiàn)光譜(UV-Vis)用Scinco S-3150型紫外光譜儀記錄,DMF為參比.Ag NPs的尺寸和分散性和用JEOL JEM- 1011型透射電子顯微鏡(TEM)觀察,加速電壓100KV.將Ag NPs膠體溶液直接滴在純碳膜上,在空氣中自然晾干觀察.
2結(jié)果與討論
首先,用DBTTC為鏈轉(zhuǎn)移劑用RAFT聚合法聚合苯乙烯制備聚苯乙烯大分子鏈轉(zhuǎn)移劑(PS-CTA),三硫代酯基團(tuán)位于高分子鏈中間;然后以PS-CTA為鏈轉(zhuǎn)移劑聚合丙烯酸丁酯制備PS-b-PBA-b-PS三嵌段共聚物;最后,利用三硫代酯基團(tuán)上的S原子和Ag的較強(qiáng)的絡(luò)合作用,原位還原硝酸銀制備聚合物刷保護(hù)的Ag NPs.合成路線(xiàn)如圖1所示.
圖1 苯乙烯-丙烯酸丁酯三嵌段共聚物PBA-b-PS-b-PBA的合成及聚合物刷保護(hù)的Ag NPs的制備
參照文獻(xiàn)[14],采用DBTTC為鏈轉(zhuǎn)移劑,先溶液聚合苯乙烯,制備大分子鏈轉(zhuǎn)移劑PS-CTA,然后再聚合丙烯酸丁酯合成鏈中間含有三硫代酯基團(tuán)的三嵌段共聚物PS-b-PBA-b-PS.圖2為PS-b-PBA-b-PS及其前體PS-CTA的GPC譜圖.我們可以看到,對(duì)應(yīng)于PS-CTA的峰為一尖銳單峰,分子量分布窄,GPC測(cè)得的數(shù)均分子量為6300,分子量分布指數(shù)為1.27.與PS-CTA的峰相比,嵌段共聚物PS-b-PBA-b-PS的峰明顯向高分子量方向移動(dòng),峰形仍然為尖銳單峰,表明成功合成了嵌段共聚物.GPC測(cè)得的數(shù)均分子量為8020,分子量分布指數(shù)為1.29.因?yàn)镚PC測(cè)試時(shí)使用PS做標(biāo)準(zhǔn)樣品,所以測(cè)得的嵌段共聚物的分子量是不準(zhǔn)確的.
圖2 PS-b-PBA-b-PS 及其前體PS-CTA的GPC譜圖
圖3為PS-b-PBA-b-PS的1H NMR譜圖.化學(xué)位移δ=4.1×10-6附近的峰歸屬于PBA鏈段上與酯基相連的碳上的兩個(gè)質(zhì)子峰,而化學(xué)位移δ=6.0~7.2×10-6的峰歸屬于PS鏈段上苯環(huán)上的峰,通過(guò)比較這兩個(gè)峰的峰面積,可計(jì)算出嵌段共聚物的分子量為15540.嵌段共聚物的組成為PBA36-b-PS29-b-PBA36.嵌段共聚物及其前體的分子量及其分布表征如表1所示.
圖3 嵌段共聚物PS-b-PBA-b-PS的1H NMR
表1嵌段共聚物PS-b-PBA-b-PS及其前體的分子表征
PolymerMn/g·mol-1GPC1HNMR Mw/g·mol-1PDIPS CTA6300—80001.27PS b PBA b PS802015540103401.29
圖4為PS-b-PBA-b-PS的FTIR光譜圖.1490cm-1處為苯環(huán)上的峰,1730cm-1處的峰歸屬于PBA鏈段的酯基,也表明成功得到了嵌段共聚物PS-b-PBA-b-PS.
圖4 嵌段共聚物PS-b-PBA-b-PS的FTIR譜圖
在PS-b-PBA-b-PS的存在下,用NaBH4作還原劑,在DMF中原位還原硝酸銀制備Ag NPs.溶液顏色由無(wú)色很快變?yōu)闇\黃色,至深褐色,表明生成了Ag NPs.溶膠放置數(shù)月無(wú)任何聚集,表明無(wú)需將聚合物還原和水解,三硫代酯基團(tuán)也對(duì)Ag NPs有很好的保護(hù)和穩(wěn)定作用.圖5為得到的Ag NPs的UV-Vis譜圖.可以看出,Ag NPs在DMF中表現(xiàn)出明顯的等離子體共振吸收峰,最大吸收波長(zhǎng)在414nm.峰形為單峰,對(duì)稱(chēng)性較好,表明Ag NPs為球形,粒徑分布窄.
圖6a和圖b為Ag NPs的TEM圖和粒徑分布柱形圖.可以看出,Ag NPs為球形,無(wú)任何聚集,粒子平均粒徑為5.6 nm.
圖5 Ag NPs的UV-Vis譜圖
3結(jié)論
圖6 Ag NPs的TEM圖(a)和粒徑分布柱形圖(b)
用RAFT聚合法先聚合苯乙烯,再聚合丙烯酸丁酯,制備了含三硫代酯基團(tuán)的苯乙烯-丙烯酸丁酯三嵌段共聚物,并以此共聚物為穩(wěn)定劑,制備了嵌段共聚物刷保護(hù)的納米銀粒子,粒子粒徑分布均勻,穩(wěn)定性好.該方法簡(jiǎn)單易行,具有普適性.若將第二單體換成可交聯(lián)的單體,如乙烯基芐基氯,4-乙烯基吡啶等,得到嵌段聚合物穩(wěn)定的納米銀粒子以后可進(jìn)一步交聯(lián),得到高熱穩(wěn)定性交聯(lián)殼和聚合物刷保護(hù)的復(fù)合粒子.
參考文獻(xiàn)
[1]Brust M, Bethell D, Kiely C J,etal. Self-assembled gold nanoparticle thin films with nonmetallic optical and electronic properties [J]. Langmuir, 1998, 14: 5425-5429.
[2] Liu S Q, Tang Z Y. Nanoparticle assemblies for biological and chemical sensing [J]. J Mater Chem, 2010, 20: 24-35.
[3]Brett D M, Jake F, ZhengW,etal. Generation of fluorescent silver nanoscale particles in reverse micelles using gamma irradiation [J]. Chem Commun, 2012, 48: 10657-10659.
[4] Arcadi A. Alternative synthetic methods through new developments in catalysis by gold [J]. Chem Rev, 2008, 108: 3266-325.
[5] Liu S, Han M. Synthesis, functionalization, and bioconjugation of monodisrse, silica-coated gold nanoparticles: robust bioprobes [J]. Adv Funct Mater, 2005, 15: 961-967.
[6] Nam J, Won N, Jin H,etal. pH-Induced aggregation of gold nanoparticles for photothermal cancer therapy [J]. J Am Chem Soc, 2009, 131: 13639-13645.
[7] Rycenga M, Cobley C M, Zeng J,etal. Controlling the synthesis and assembly of silver nanostructures for plasmonic applications [J]. Chem Rev, 2011, 111: 3669-3712.
[8] Ohno K, Koh K, Tsujii Y,etal. Synthesis of gold nanoparticles coated with well-defined, high-density polymer brushes by surface-initiated living radical polymerization [J]. Macromolecules, 2002, 35: 8989-8993.
[9] Dong H, Zhu M, Yoon J A,etal. One-pot synthesis of robust core/shell gold nanoparticles [J]. J Am Chem Soc, 2008, 130: 12852-12853.
[10] Corbierre M K, Cameron N S, Lennox R B. Polymer-stabilized gold nanoparticles with high grafting densities [J]. Langmuir, 2004, 20: 2867-2873.
[11] Bokern S, Getze J, Agarwal S,etal. Polymer grafted silver and copper nanoparticles with exceptional stability against aggregation by a high yield one-pot synthesis [J]. Polymer, 2011, 52: 912-920.
[12] Moad G, Rizzardo E, Thang S H. Radical addition-fragmentation chemistry in polymer synthesis [J]. Polymer, 2007, 49: 1079-1131.
[13] Zhang J, Dong A, Cao T,etal. Carbazyl RAFT agents synthesized by an improved aqueous phase method and their applications in RAFT polymerizatiol [J]. Eur Polym J, 2008, 44: 1071-1080.
[14] Chernikova E V, Terpugova P S, Garina E S,etal. Controlled radical polymerization of styrene and n-butyl acrylate mediated by trithiocarbonates [J]. Polym Sci, Ser A, 2007, 49: 108-119.
[15] Freal-Saison S, Save M, Bui C,etal. Emulsifier-free controlled free-radical emulsion polymerization of styrene via RAFT using dibenzyltrithiocarbonate as a chain transfer agent and acrylic acid as an ionogenic comonomer: batch and spontaneous phase inversion processes [J]. Macromolecules, 2006, 39: 8632-8638.
[16] Zhou D, Zhu X, Zhu J,etal. Preparation and characterization of poly(styrene)/metal composites via reversible addition-fragmentation chain transfer (RAFT) polymerization [J]. React Funct Polym, 2009, 69: 55-61.
[17] Liu X, Chen J, Sun P,etal. Grafting modification of ramie fibers with poly(2,2,2-trifluoroethyl methacrylate) via reversible addition-fragmentation chain transfer (RAFT) polymerization in supercritical carbon dioxide [J]. React Funct Polym, 2010, 70: 972-979.
[18] Bae S K, Lee S Y, Hong S C. Thiol-terminated polystyrene through the reversible addition-fragmentation chain transfer technique for the preparation of gold nanoparticles and their application in organic memory devices [J]. React Funct Polym, 2011, 71: 187-194.
[19] Deng Y, Sun Y Y, Wang P. Nonlinear optical properties of silver colloidal solution by in situ synthesis technique [J]. Current Applied Physics, 2008, 8: 13-17.
[20] Shan J, Nuopponen M, Jiang Ha,etal. Amphiphilic gold nanoparticles grafted with poly(N-isopropylacrylamide) and polystyrene [J]. Macromolecules, 2005, 38: 2918-2926.
[21] Lowe A B, Sumerlin B S, Donovan M S,etal. Facile preparation of transition metal nanoparticles stabilized by well-defined (co)polymers synthesized via aqueous reversible addition-fragmentation chain transfer polymerization [J]. J Am Chem Soc, 2002, 124: 11562-11563.
(編輯:姚佳良)