沈燕宇, 何桂金, 郭永勝, 方文軍
(浙江大學(xué) 化學(xué)系, 浙江 杭州 310058)
超支化聚合物作為金屬納米粒子穩(wěn)定劑的研究進(jìn)展
沈燕宇, 何桂金, 郭永勝, 方文軍
(浙江大學(xué) 化學(xué)系, 浙江 杭州 310058)
在本研究中,著重介紹了用作金屬納米粒子穩(wěn)定劑的聚酰胺-胺、聚縮水甘油和聚乙烯亞胺等幾類(lèi)超支化聚合物的研究進(jìn)展。聚酰胺-胺類(lèi)超支化聚合物可用于堵水劑和化學(xué)驅(qū)油劑,用于金屬納米粒子反應(yīng)器時(shí)既作還原劑,又作分散劑,能穩(wěn)定分散金屬納米粒子,還能提高納米復(fù)合材料的循環(huán)再生性能;聚縮水甘油類(lèi)含有大量的端羥基,經(jīng)修飾可得到兩親性的納米膠囊,具有良好的生物相容性,可用作優(yōu)質(zhì)的原油破乳劑,金屬納米粒子的粒徑可通過(guò)其相對(duì)分子質(zhì)量來(lái)調(diào)控;聚乙烯亞胺-胺類(lèi)具有眾多的胺官能團(tuán),為金屬離子的配位提供了豐富的位點(diǎn),其包裹的金屬納米粒子可用于溫敏材料等。結(jié)合超支化聚合物的結(jié)構(gòu)可控性以及納米金屬優(yōu)秀的催化性能,這類(lèi)物質(zhì)在石油工程領(lǐng)域中會(huì)有較大的應(yīng)用前景。
超支化聚合物; 金屬納米粒子; 穩(wěn)定劑
超支化聚合物從一個(gè)中心核出發(fā),由支化單體ABn逐級(jí)伸展形成具有高度支化的三維球狀立體結(jié)構(gòu),并具有豐富的末端基團(tuán)(如圖1)。顯示出與相應(yīng)線型分子截然不同的性質(zhì),如低黏度、良好的溶解性以及高流變性。同時(shí),其合成相對(duì)簡(jiǎn)單、成本較低。因此,超支化聚合物具有廣闊的應(yīng)用前景,在石油工程領(lǐng)域中,已用于堵水劑[1]、化學(xué)驅(qū)油劑[2-3]、原油破乳劑[4-5]以及鉆井液處理劑[6]等。

圖1 超支化聚合物結(jié)構(gòu)示意圖Fig.1 Schematic structure of hyperbranched polymers
1.1 超支化聚合物的合成
自20世紀(jì)中期首次成功合成超支化聚合物以來(lái),其合成方法得到了極大豐富和完善。依據(jù)聚合機(jī)理,主要有以下幾類(lèi)合成方法:(1)縮聚法。由具有兩個(gè)或兩個(gè)以上官能團(tuán)的單體,通過(guò)縮聚反應(yīng)生成超支化聚合物,同時(shí)產(chǎn)生簡(jiǎn)單分子(如H2O、HX、醇等)。縮聚法可在本體或溶液中進(jìn)行,反應(yīng)簡(jiǎn)單,所合成聚合物的相對(duì)分子質(zhì)量具有多分散性。目前,通過(guò)一步縮聚法已經(jīng)成功制備了聚苯類(lèi)[7]、聚酯類(lèi)[8]、聚酰胺類(lèi)[9]和聚硅烷類(lèi)[10]等多種類(lèi)型的超支化聚合物。(2)加聚法。在引發(fā)基團(tuán)上通過(guò)烯烴加成反應(yīng)生成超支化聚合物,可賦予超支化聚合物以C—C骨架,從而使其具有比雜原子骨架更好的穩(wěn)定性。參與該合成過(guò)程的單體數(shù)較多,可以制備相對(duì)分子質(zhì)量較大的超支化聚合物。比如,F(xiàn)réchet等[11]采用自縮合乙烯基聚合法制備超支化聚合物,乙烯基單體既是引發(fā)劑也是支化點(diǎn),它在外激發(fā)作用下可被活化,產(chǎn)生多個(gè)活性自由基,形成新的反應(yīng)中心,從而引發(fā)下一步的反應(yīng),生成相對(duì)分子質(zhì)量很大的超支化聚合物。(3)開(kāi)環(huán)聚合。將具有環(huán)狀結(jié)構(gòu)的單體(如圖2)引發(fā)后,通過(guò)開(kāi)環(huán)反應(yīng)聚合成超支化聚合物。反應(yīng)過(guò)程中不需要除去小分子化合物且能得到相對(duì)分子質(zhì)量高的超支化聚合物。目前,采用開(kāi)環(huán)聚合法制備了超支化的聚胺[9]、聚酯[12]和聚醚[13]等,但與其他結(jié)構(gòu)超支化聚合物的報(bào)道相比仍較少。

圖2 常見(jiàn)開(kāi)環(huán)聚合的單體Fig.2 Common monomers of ring opening polymerization
1.2 超支化聚合物的應(yīng)用
超支化聚合物具有較低的黏度和良好的流變性能,通過(guò)結(jié)構(gòu)改造或修飾,還具有兩親性和一定的反應(yīng)活性,在石油化工、涂料、油墨等領(lǐng)域已有應(yīng)用[14-16]。He等[17]發(fā)現(xiàn),超支化聚縮水甘油改性物在碳?xì)淙剂仙郎剡^(guò)程中能發(fā)揮“自由基倉(cāng)庫(kù)”的作用,從而促進(jìn)碳?xì)淙剂系牧呀猓籅ruchmann等[18]通過(guò)調(diào)控超支化聚酯的親水性和親油性,得到了一種高效的油溶性破乳劑;Zhang等[19]用3-(丙烯酰氧乙基)磷酸酯(TAEP)和哌嗪通過(guò)邁克爾加成反應(yīng)制備了超支化多聚磷酸鹽丙烯酸酯(HPPAs),可以用于紫外光固化涂料。超支化聚合物還可用于主-客體封裝,制備有機(jī)-無(wú)機(jī)雜化材料,甚至可以在反應(yīng)中直接用作納米反應(yīng)器。超支化聚合物也能用于形狀記憶材料[20-22]、自我修復(fù)材料[23]、CO2捕集材料[24]、多微孔材料[25]、彈性體[26]、黏合劑[27]和催化劑[28]等等。
納米粒子是尺寸為1~100 nm的超細(xì)粒子,由幾十到幾百個(gè)原子或分子構(gòu)成。納米粒子具有獨(dú)特的物理、化學(xué)和生物學(xué)特性[29],目前已被廣泛用于石油化工、醫(yī)藥、電子工業(yè)及農(nóng)業(yè)生產(chǎn)等領(lǐng)域[30]。尤其是金屬納米粒子具有良好的光學(xué)、電學(xué)、磁學(xué)以及催化特性,在石油開(kāi)采、催化、光學(xué)器件、生物傳感等領(lǐng)域中呈現(xiàn)出廣闊的應(yīng)用前景[31]。納米金屬粒子作為催化劑和助燃劑已成功地應(yīng)用到碳?xì)淙剂系拇呋呀夂腿紵衃32];還可以摻雜到高能密度材料(如炸藥)中,作為引爆劑使用。金屬納米粒子的特殊性質(zhì)和潛在應(yīng)用價(jià)值均與它的納米級(jí)尺寸和形貌密切相關(guān)。因此,建立一個(gè)可以對(duì)金屬納米粒子尺寸和形貌有效調(diào)控的制備方法尤為重要,也是納米材料領(lǐng)域的關(guān)鍵技術(shù)。迄今為止,人們已經(jīng)深入研究和發(fā)展了多種可控合成納米金屬粒子的物理或化學(xué)方法,包括相轉(zhuǎn)移法、光照還原法、激光燒蝕法、綠色生物學(xué)法等[33-34]。
2.1 相轉(zhuǎn)移法
相轉(zhuǎn)移法主要用于制備貴金屬(如Au、Ag等)納米粒子。常用的方法是在相轉(zhuǎn)移劑的作用下,將金屬鹽從水溶液中萃取到含有穩(wěn)定劑(如硫醇等)的非極性有機(jī)溶劑中,然后緩慢加入還原試劑(如NaBH4等),在有機(jī)相中還原制備具有一定納米尺度的金屬粒子。相轉(zhuǎn)移法的關(guān)鍵在于選擇恰當(dāng)?shù)南噢D(zhuǎn)移劑或穩(wěn)定劑,使納米金屬粒子能夠高效轉(zhuǎn)移并且穩(wěn)定存在。常用的相轉(zhuǎn)移試劑有烷基銨類(lèi)表面活性劑、氨基化合物、硫醇、油酸、檸檬酸和聚合物等。超支化聚合物作為相轉(zhuǎn)移劑時(shí)分為兩類(lèi):一類(lèi)是需要外加還原劑(如NaBH4等);另一類(lèi)是不需要外加還原劑,利用自身所帶官能團(tuán)還原金屬離子,原位生成金屬納米粒子。
2.2 光照還原法
光照還原法是利用光照將金屬離子還原成零價(jià)金屬的方法,可以通過(guò)控制光照時(shí)間來(lái)控制金屬粒子的尺寸、形貌等[35]。Rodriguez等[36]在紫外光照射下,用肝素鈉還原HAuCl4合成了金納米粒子,通過(guò)改變肝素鈉的濃度和光照時(shí)間等可以得到粒徑為20~300 nm的各向異性的納米金,如橢圓形、三角形、六邊形以及棒狀納米粒子等。Prakash等[37]用絡(luò)氨酸為光還原劑,不需要添加額外的穩(wěn)定劑,在水相中通過(guò)光照合成了粒徑分布窄的銀納米粒子。
2.3 激光燒蝕法
激光燒蝕法是利用脈沖激光束將靶材瞬間(<10 ms)加熱到氣化溫度以上,產(chǎn)生由靶材原子、離子和原子簇組成的蒸氣,在飛行過(guò)程中與環(huán)境氣體原子碰撞減速而形成納米顆粒。Smalley等[38]用激光照射銅靶,在超聲速氣體的作用下獲得了銅納米粒子,這是利用激光燒蝕法首次制得的納米材料。Mohamed等[39]報(bào)道了一種在聚乙烯醇(PVA)水溶液中用激光燒蝕法制備銀納米粒子的方法,其中PVA既作為還原劑,又能通過(guò)分子骨架保護(hù)金納米粒子。在質(zhì)量分?jǐn)?shù)為1%、3%和4% 的PVA水溶液中,所得到的納米金粒徑可分別控制為6.13 nm、6.86 nm和3.99 nm。
2.4 綠色生物學(xué)法
近年來(lái),很多生物學(xué)模板被用于合成金屬納米粒子,比如植物[40]、藻類(lèi)、真菌[41]、細(xì)菌以及病毒[42]等。Kuber等[43]通過(guò)培養(yǎng)真菌的方法來(lái)合成銀納米粒子。Richa等[44]用了18種碳酸鈣不動(dòng)桿菌做研究,發(fā)現(xiàn)鮑曼-醋酸鈣不動(dòng)桿菌LRVP54可以在70℃條件下還原AgNO3,生成粒徑為8~12 nm單分散的球形納米銀。
在金屬納米粒子的各種合成方法中,相轉(zhuǎn)移法是最為簡(jiǎn)便、應(yīng)用最多的方法。由于金屬納米粒子在相轉(zhuǎn)移過(guò)程中容易發(fā)生聚集[45],因此,在制備過(guò)程中需用穩(wěn)定劑來(lái)輔助分散[46]。樹(shù)枝狀聚合物和超支化聚合物是典型的穩(wěn)定劑,樹(shù)枝狀大分子可作為金屬納米粒子的反應(yīng)器,金屬離子首先與聚合物配位富集,然后再在還原劑的作用下被原位還原成穩(wěn)定的納米粒子[47]。然而,樹(shù)枝狀大分子由于結(jié)構(gòu)完美,合成條件比較復(fù)雜,成本相對(duì)較高。相比之下,超支化聚合物合成方法簡(jiǎn)單,成本低廉,且化學(xué)、物理性質(zhì)與樹(shù)枝狀大分子非常接近。因此,近年來(lái)超支化聚合物作為金屬納米粒子穩(wěn)定劑的研究受到重視[48-50],已有3類(lèi)超支化聚合物較多用于金屬納米粒子的穩(wěn)定劑,下面分別闡述。
3.1 聚酰胺-胺類(lèi)超支化聚合物
聚酰胺-胺大分子主鏈重復(fù)單元中含有酰胺-胺基團(tuán),端基以胺基為多(如圖3)。胺基或酰胺的孤對(duì)電子能與金屬離子配位,起到捕集、固定金屬離子的作用;它還具有還原性,在一定條件下可將金屬離子還原成金屬,達(dá)到原位還原的目的,減少金屬離子在還原過(guò)程中聚集。這類(lèi)超支化聚合物既作還原劑,又作分散劑,克服了納米金屬溶膠制備工藝復(fù)雜、適用性差的缺點(diǎn)[51]。因此,越來(lái)越多的聚酰胺-胺類(lèi)聚合物用作金屬納米粒子反應(yīng)器[52-54]。

圖3 聚酰胺-胺的結(jié)構(gòu)Fig.3 Schematic structure of poly(amidoamine)
Nelly等[55]用具有超支化結(jié)構(gòu)的聚酰胺-胺(HYPAM)(如圖4)及其葡萄糖胺衍生物(如圖5)合成了水溶性金納米粒子。納米粒子在水溶液中的穩(wěn)定性主要受聚合物相對(duì)分子質(zhì)量以及溶液pH值的影響。聚合物相對(duì)分子質(zhì)量越大,納米粒子的穩(wěn)定性越好,而聚合物相對(duì)分子質(zhì)量可以通過(guò)改變聚合條件來(lái)調(diào)控。HYPAM的葡萄糖胺功能化可進(jìn)一步阻止金納米粒子的聚集,對(duì)金納米粒子穩(wěn)定性的影響要大于聚合物尺寸效應(yīng)帶來(lái)的影響。

圖4 HYPAM超支化聚合物的結(jié)構(gòu)Fig.4 Schematic structure of HYPAM

圖5 葡萄糖胺功能化的HYPAM超支化聚合物Fig.5 Functionalization of HYPAM with gluconolactone
Nitul等[56]用聚丙烯酰胺(PA)和超支化聚胺/聚丙烯酰胺混雜體(HB-PA)來(lái)合成銀納米粒子,用HB-PA合成的銀納米粒子比用PA合成的銀納米粒子要穩(wěn)定。以HB-PA為母體時(shí),銀納米粒子的粒徑為8.5 nm;以PA為母體時(shí),銀納米粒子的粒徑為9.9 nm。HB-PA包裹的銀納米粒子對(duì)枯草芽孢桿菌的抗菌性要高于用PA合成的銀納米粒子。
Roozbe等[57]用超支化聚酰胺(PAMAM)在聚乙烯胺功能化的介孔氧化硅(PVAm/SBA-15)表面發(fā)生聚合,生成雜化材料。通過(guò)PAMAM和金屬離子的配位作用誘捕水溶性的金屬離子(如Ni2+等),然后再用NaBH4將金屬離子還原得到由這種雜化材料包裹的鎳納米粒子。所得到的納米復(fù)合材料可作為擬均相催化劑催化NaBH4還原芳硝基物的反應(yīng),且具有良好的循環(huán)再生性能,經(jīng)循環(huán)10次后其催化活性仍未明顯下降。
3.2 聚縮水甘油改性物
超支化聚縮水甘油(HPG)是一種分子內(nèi)部為醚鍵,分子周?chē)写罅苛u基的超支化聚合物[58-59](如圖6)。自Frey等[60]合成出低分散性的HPG以來(lái), 關(guān)于HPG合成與應(yīng)用的研究越來(lái)越受到重視。HPG的合成方法主要有陽(yáng)離子聚合與陰離子聚合兩種,Wang等[61]以丙三醇為核,以BF3O(C2H5)2為催化劑,對(duì)縮水甘油進(jìn)行陽(yáng)離子開(kāi)環(huán)聚合,得到了相對(duì)分子質(zhì)量為2000~3000、支化度為0.5~0.6的超支化聚縮水甘油醚。但是,陽(yáng)離子聚合反應(yīng)過(guò)程中容易出現(xiàn)環(huán)化副產(chǎn)物,反應(yīng)產(chǎn)物相對(duì)分子質(zhì)量較小且分布較寬。目前主要采用陰離子開(kāi)環(huán)聚合結(jié)合單體緩慢滴加技術(shù),以1,1,1-三羥甲基丙烷(TMP)為核,用甲醇鉀對(duì)其進(jìn)行質(zhì)子化,引發(fā)縮水甘油開(kāi)環(huán)聚合,可避免成環(huán)副反應(yīng)的發(fā)生,使產(chǎn)物的相對(duì)分子質(zhì)量分布很窄,且能得到相對(duì)分子質(zhì)量較大的聚合物。

圖6 超支化聚縮水甘油的結(jié)構(gòu)Fig.6 Schematic structure of hyperbranched polyglycerol(HPG)
HPG含有大量的端羥基,是原子轉(zhuǎn)移自由基聚合(ATRP)或者點(diǎn)擊化學(xué)來(lái)修飾HPG的活性位點(diǎn)[62],比如用長(zhǎng)鏈酰氯[63]與羥基反應(yīng)可制得油溶性的HPG(如圖7)。Slagt等[64]將HPG經(jīng)烷基酰氯部分酯化后,得到一種內(nèi)部親水、外部疏水的核-殼結(jié)構(gòu)型超支化聚合物,其親水的核能通過(guò)氫鍵作用與過(guò)渡金屬結(jié)合,從而實(shí)現(xiàn)過(guò)渡金屬催化劑的負(fù)載與富集。HPG改性物用作金屬納米粒子穩(wěn)定劑主要有以下優(yōu)勢(shì)[65]:HPG外圍是樹(shù)枝狀結(jié)構(gòu),中間含有空腔,有利于包裹金屬納米粒子;HPG的端羥基對(duì)金屬離子有一定的還原作用,所以HPG不僅可以作為穩(wěn)定劑還可以作為還原劑;包裹納米金屬后,外圍的羥基能使金屬納米粒子進(jìn)一步得到修飾,形成需要的納米復(fù)合物。

圖7 HPG的羥基功能化Fig.7 Hydroxyl functionalization of HPG
Martijn等[66]用兩親性的HPG包裹鉑螯合物,將帶有疏水烷基鏈的聚醚多元醇的羥基部分酯化,形成具有反膠束結(jié)構(gòu)的兩親性納米膠囊,這種納米膠囊能在其親水內(nèi)部包裹親水性的磺化鉑螯合物(如圖8)。這種包裹鉑螯合物的納米膠囊可作為均相催化劑用于邁克爾加成,通過(guò)透析的方式分離產(chǎn)物,催化劑的回收率高達(dá)97%。
在HPG骨架上引入巰基對(duì)納米粒子的合成十分有利。Sunny等[67]用3-巰基丙酸先與HPG發(fā)生酯化反應(yīng),再用1-溴代十二烷使外圍巰基烷基化,生成目標(biāo)超支化聚合物(如圖9),這種超支化聚合物能溶于氯仿、二氯甲烷和二甲基甲酰胺而不溶于甲醇。然后再分別與CuCl2·2H2O、AgNO3、HAuCl4配位制備Cu、Ag、Au納米粒子。Decheng等[68]用HPG做為模板合成金納米顆粒,用1-溴-3-氯丙烷使HPG的羥基烷基化,31.6%的羥基轉(zhuǎn)化成烯丙基,22.4%的羥基轉(zhuǎn)化成3-氯丙基,3-氯丙基與十二硫醇硫烷基化,形成了1個(gè)兩親性的模板分子(如圖10):親水的PG為核心、疏水的硫醚構(gòu)成外殼,合成了兩種相對(duì)分子質(zhì)量的模板分子,其包裹的金納米粒子平均尺寸分別為(3.0±1.6) nm和(5.1±2.4) nm,分散到有機(jī)溶劑(如氯仿、四氫呋喃)中形成透明膠體,可穩(wěn)定存放180 d。

圖8 兩親性HPG膠囊包裹鉑螯合物Fig.8 Encapsulation of platinum pincer complexes in the amphiphilic HPG

圖9 具有硫醚結(jié)構(gòu)的HPG及其包裹金屬納米粒子的示意圖Fig.9 Preparation of HPG with thioether shells and its encapsulation on metal NPs

圖10 含硫HPG改性物合成示意圖Fig.10 Synthesis of sulfur-bearing HPG
3.3 聚乙烯亞胺類(lèi)超支化聚合物
通過(guò)氮雜環(huán)丙烷(乙烯亞胺)的催化開(kāi)環(huán)聚合可以獲得超支化聚乙烯亞胺(HPEI)(如圖11)。胺官能團(tuán)的多功能性為金屬離子的配位提供了理想的配合位點(diǎn)。
Tang等[69]用棕櫚酰氯修飾的聚乙烯亞胺(HPEI),將檸檬酸鹽保護(hù)的金納米粒子從水相中轉(zhuǎn)移到氯仿中。研究表明,超支化聚合物作為金屬納米粒子穩(wěn)定劑,其效果要優(yōu)于線型聚合物,主要表現(xiàn)在:發(fā)生有效萃取需要的量更少;含有超支化聚合物的金納米粒子體系較少出現(xiàn)聚沉現(xiàn)象;超支化聚合物分散的金納米顆粒更均一、堆積更密集,可以干燥穩(wěn)定存放長(zhǎng)達(dá)210 d。
Liu等[70]用乙酸酐(ACAm)、丙酸酐(PRAm)、丁酸酐(BUAm)和異丁酸酐(IBAm)修飾HPEI,分別得到對(duì)應(yīng)的酰胺化產(chǎn)物HPEI-ACAm、HPEI-PRAm、HPEI-BUAm以及HPEI-IBAm(如圖12),然后分別合成金納米粒子,通過(guò)聚合物和納米金的非共價(jià)鍵作用得到了納米金復(fù)合材料,該納米金復(fù)合材料可以催化NaBH4還原4-硝基苯酚的反應(yīng)。Aymonier等[71]用帶長(zhǎng)鏈烷基的酰胺與PEI反應(yīng),用來(lái)包裹銀納米粒子(如圖13),生成了平均粒徑為5nm的具有抗菌性能的納米銀。劉訓(xùn)恿等[72]通過(guò)對(duì)不同相對(duì)分子質(zhì)量的超支化聚乙烯亞胺的端基進(jìn)行部分或完全異丁酰胺化,制備了一系列具有不同低臨界溶解溫度(LCST)的超支化溫敏聚合物。通過(guò)離子鍵或氫鍵之間的相互作用,所得超支化溫敏聚合物可以吸附于經(jīng)檸檬酸鈉還原并穩(wěn)定的金納米粒子的表面,從而得到具有溫敏性質(zhì)的金納米粒子。

圖11 HPEI的合成Fig.11 Synthesis of HPEI

圖12 不同氨基化合物修飾的聚乙烯亞胺(HPEI)
Anja等[73]用麥芽糖修飾的超支化聚乙烯亞胺合成金納米粒子,在金納米粒子形成的過(guò)程中,超支化聚合物既作為還原劑又作為穩(wěn)定劑。在PEI核的區(qū)域,Au3+被還原形成緊密堆積的金核,同時(shí)聚合物外圍的分子鏈發(fā)生塌陷,金納米粒子和聚合物的分子鏈結(jié)合形成新的殼-核結(jié)構(gòu)。通過(guò)調(diào)控PEI的相對(duì)分子質(zhì)量,合成出了粒徑為3.6 nm的金納米粒子。
3.4 其它超支化聚合物
除了以上3類(lèi)超支化聚合物,還有超支化聚酯、超支化聚苯乙烯、超支化聚醚胺等也可以用作金屬納米粒子穩(wěn)定劑。
超支化聚酯(HBPE)高度支化的結(jié)構(gòu)和大量的端基官能團(tuán)使它容易被接枝改性,HBPE 可有效地解決熱固性樹(shù)脂因其高度交聯(lián)結(jié)構(gòu)而產(chǎn)生的韌性差的問(wèn)題,還能改善納米粒子的團(tuán)聚現(xiàn)象,促進(jìn)納米粒子在樹(shù)脂中的分散。Zhu等[74]采用光照還原法,用端基含羥基和羧基的超支化聚酯合成了粒徑為3~19 nm的銀納米粒子。Joshua等[75]將水黃皮油(PO)羥基化形成POH,再與亞麻酸發(fā)生酯化反應(yīng),生成超支化聚酯,然后與苯乙烯共聚形成共聚物,用于合成銀納米粒子的穩(wěn)定劑。

圖13 PEI酰胺化及包裹銀納米粒子Fig.13 Silver NPs encapsulated by amidated PEI
Gao等[76]用超支化聚苯乙烯的氨鹽(HPS-NR3+Cl-)穩(wěn)定過(guò)渡金屬(M)納米粒子(如圖14)。研究表明,1~3 nm的釕、銠、銥、鉑和鈀納米粒子能穩(wěn)定分散于聚合物基體中形成M@HPS-NR3+Cl-,其 分散性可以通過(guò)改變R基團(tuán)來(lái)調(diào)控,M@HPS-NR3+Cl-對(duì)烯烴和芳香烴的加氫反應(yīng)具有良好的催化作用。Keisuke等[77]用親-疏水性可調(diào)的超支化聚苯乙烯合成鉑納米粒子,用外圍帶—Cl的超支化聚苯乙烯(HPS-Cl)合成HPS-NR3+Cl-。HPS-NR3+Cl-的一部分覆蓋在鉑納米粒子上,其帶有C12H25或者(CH2CH2O)2Me鏈的氨基可以通過(guò)靜電作用穩(wěn)定鉑納米粒子,形成多個(gè)HPS-NR3+Cl-分子包裹1個(gè)鉑納米粒子的結(jié)構(gòu)(如圖15),并且能通過(guò)改變R基團(tuán)來(lái)調(diào)節(jié)其溶解性能。
Yu等[78]用超支化聚醚胺(HPEA)自組裝合成了邊緣長(zhǎng)度為1~2 μm、厚度為4~5 nm的超支化聚醚胺的納米片(HPEA-NSs),以籠狀倍半硅氧烷(POSS)和蒽(AN)為封端劑,合成了金納米粒子(如圖16)。金的前驅(qū)體通過(guò)金原子與氨基配位吸附在HPEA-NSs的親水表面上,通過(guò)氨基的還原作用,轉(zhuǎn)變成金納米粒子。

圖14 M@HPS-NR3+Cl-的形成示意圖Fig.14 Schematic diagram for the formation of M@HPS-NR3+Cl-
(1) 具有特殊表面界面效應(yīng)、小尺寸效應(yīng)的納米粒子與具有密度小、耐腐蝕、易加工等優(yōu)良特性的超支化聚合物結(jié)合后,呈現(xiàn)出不同于常規(guī)聚合物復(fù)合材料的性能。

圖15 HPS-NR3+Cl-包裹鉑納米粒子示意圖Fig.15 Schematic diagram for stabilization of a Pt nanoparticle by HPS-N(C12H25)3+Cl-

圖16 以POSS/AN為封端劑的HPEA-NSs結(jié)構(gòu)與HPEA-NSs負(fù)載金屬納米粒子的機(jī)理Fig.16 Structure of POSS/AN ended hyperbranched poly(ether amine) and the proposed mechanism of metal nanoparticle decoration on HPEA-NSs(a) HPEA-POSS/AN(HPA); (b) HPEA-NSs
(2) 超支化聚合物具有超支化分子拓?fù)浜汀昂藲ぁ苯Y(jié)構(gòu),可作為納米材料的模板,產(chǎn)生精致的納米粒子復(fù)制品。
(3) 納米粒子一般通過(guò)配位鍵或者分子間相互作用被封裝在超支化聚合物中,通過(guò)調(diào)控聚合物分子表面的基團(tuán)可控制納米復(fù)合材料的聚集-分散行為,超支化聚合物修飾的納米粒子可穩(wěn)定地分散在介質(zhì)中,不易聚沉。
(4) 通過(guò)對(duì)超支化聚合物結(jié)構(gòu)的控制,調(diào)整其兩親性、溶解性和黏度等,有望在原油開(kāi)采、破乳、降凝輸送、油田污水處理和燃油加工等方面發(fā)揮作用。
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The Progress of Hyperbranched Polymers as Stabilizers for Metal Nanoparticles
SHEN Yanyu, HE Guijin, GUO Yongsheng, FANG Wenjun
(DepartmentofChemistry,ZhejiangUniversity,Hangzhou310058,China)
Several kinds of hyperbranched polymers including hyperbranched poly(amido-amine) (HPAM), hyperbranched polyglycerol (HPG), and hyperbranched polyethylene imine (HPEI), as metal nanoparticle stabilizers are summarized in this work. HPAM is a good candidate as a plugging agent and a chemical oil displacement agent. It can serve as both reductant and dispersant, which can not only stabilize the dispersion of metal nanoparticles but also improve the reproducibility of nanocomposites. With a large amount of hydroxyl groups, HPG can be modified to be amphiphilic nanocapsules, which has good biocompatibility and can be used as high-quality crude oil demulsifier. Furthermore, the size of metal nanoparticles can be controlled by the relative molecular mass of HPG.HPEI owns a large number of amine functional groups, which provides the ideal coordination sites for metal ions. As an example, the HPEI-coated metal nanoparticles have been found as potential thermo-sensitive materials. With the combination of the structural controllability of hyperbranched polymer and excellent catalytic activity of metal nanoparticles, metalized hyperbranched polymers show great promises in the petrochemical industry.
hyperbranched polymer; metal nanoparticle; stabilizer
2016-12-30
國(guó)家自然科學(xué)基金項(xiàng)目(91441109)資助
沈燕宇,女,碩士研究生,從事航空航天推進(jìn)劑化學(xué)研究;E-mail:mlhkdzxsyy@163.com
方文軍,教授,博士,主要從事航空航天推進(jìn)劑化學(xué)研究;E-mail:fwjun@zju.edu.cn
1001-8719(2017)04-0605-14
O63
A
10.3969/j.issn.1001-8719.2017.04.002