張　良，于方麗，劉　方

(鹽城工學(xué)院 材料工程學(xué)院，江蘇 鹽城　224051)

?

由4-氰基芐溴引發(fā)的苯乙烯電子活化再生原子轉(zhuǎn)移自由基聚合

張良，于方麗，劉方

(鹽城工學(xué)院 材料工程學(xué)院，江蘇 鹽城224051)

摘要：以4-氰基芐溴(CBB)為引發(fā)劑、FeCl3·6H2O/PPh3絡(luò)合體系為催化劑、VC為還原劑實現(xiàn)了對苯乙烯(St)的電子活化再生原子轉(zhuǎn)移自由基聚合(AGET ATRP)。研究表明，聚合過程中單體轉(zhuǎn)化隨反應(yīng)時間增加而線性增長、數(shù)均分子量隨單體轉(zhuǎn)化率提高而線性增長、得到的聚合物分子量分布指數(shù)(PDI)在1.07～1.31之間。為進(jìn)一步研究取代基團(tuán)對聚合的影響，選用了4-甲基芐溴(MBB)為引發(fā)劑作了對比研究，所得聚合物的結(jié)構(gòu)用核磁氫譜進(jìn)行了驗證。

關(guān)鍵詞：電子活化再生原子轉(zhuǎn)移自由基聚合；苯乙烯；4-氰基芐溴；引發(fā)劑

原子轉(zhuǎn)移自由基聚合(ATRP)方法是1995年Matyjaszewski[1]和Sawamoto[2]課題組幾乎同時發(fā)現(xiàn)的。這種聚合方法是以可逆的鹵原子轉(zhuǎn)移為基礎(chǔ)，通過氧化還原反應(yīng)，鹵原子從有活性的烷基鹵化物轉(zhuǎn)移到低價的過渡金屬化合物，形成烷基自由基和高價態(tài)的金屬絡(luò)合物。反應(yīng)電烷基自由基先與單體發(fā)生加成反應(yīng)，生成中間體，再從高價態(tài)的金屬絡(luò)合物中奪取鹵素，通過自由基活性種與大分子有機鹵化物休眠種之間的可逆動態(tài)平衡，實現(xiàn)對聚合反應(yīng)的有效控制。ATRP技術(shù)為合成結(jié)構(gòu)規(guī)整、分子量分布窄的指定分子量的聚合物提供了很好的方法。然而，普通ATRP因為使用相對不夠穩(wěn)定的低價態(tài)的金屬離子絡(luò)合物作催化劑使得這種方法存在一些缺陷，如需去除氧或氧化物等[3-8]。近些年有研究者通過電子活化再生改進(jìn)原子轉(zhuǎn)移自由基聚合(AGET ATRP)[9-14]，有效克服了普通ATRP的一些缺陷。在典型的AGET ATRP體系中，烷基鹵用作引發(fā)劑，高價態(tài)的金屬離子絡(luò)合物(Cu(II)絡(luò)合物)作催化劑，低價態(tài)的催化劑活性中心(Cu(I)絡(luò)合物)通過還原劑(如辛酸亞錫、維生素C等)原位生成[10-14]。正因為AGET ATRP使用高氧化態(tài)的金屬氧化物作催化劑，大大降低鹵化物失活引起反應(yīng)失敗的幾率,使得合成均聚物或嵌段共聚物過程控制性更好，而且聚合過程中對氧氣不是特別敏感,催化劑更易于制備、存儲和使用[9]。在ATRP過程中，引發(fā)劑在決定增長聚合物鏈的數(shù)目上起著重要作用,芐鹵結(jié)構(gòu)由于與苯乙烯結(jié)構(gòu)的相似性，經(jīng)常用作苯乙烯的引發(fā)劑[15]。含不同取代結(jié)構(gòu)的芐鹵已成功用于普通ATRP聚合[16-32],然而，根據(jù)現(xiàn)有文獻(xiàn)，尚沒有芐鹵衍生物用于苯乙烯的AGET ATRP報道，盡管引發(fā)劑的結(jié)構(gòu)對聚合速率、活性會產(chǎn)生重要影響[33]。在本研究中，使用4-氰基芐溴(CBB)作為引發(fā)劑，F(xiàn)eCl3·6H2O/PPh3/VC作為催化體系(該體系具有低毒、來源豐富、生物相容性好的優(yōu)點)[34-37]，進(jìn)行苯乙烯的本體AGET ATRP,得到了結(jié)構(gòu)規(guī)整且分子量分布窄的聚合物。

1實驗部分

1.1　原料與試劑

苯乙烯(國藥集團(tuán)化學(xué)試劑有限公司，純度≥99%)：經(jīng)5%NaOH溶液洗滌3次，去離子水洗滌3次，加無水硫酸鎂干燥過夜，減壓蒸餾保存在-18 ℃冰箱環(huán)境中；FeCl3·6H2O(>99%)、 PPh3(>99%)、 VC(>99.7%)皆購于國藥集團(tuán)化學(xué)試劑有限公司，未經(jīng)提純直接使用；4-氰基芐溴(CBB，純度>98%)和4-甲基芐溴(MBB，純度>98%)皆從百靈威集團(tuán)有限公司購買，未經(jīng)提純直接使用；四氫呋喃(THF)及其它試劑皆從國藥集團(tuán)化學(xué)試劑有限公司購買并直接使用。

1.2　聚合與純化

按配比將FeCl3·6H2O、PPh3、St、CBB、VC加入干燥圓底燒瓶并攪拌，用氬氣鼓泡20 min以除去溶液中的氧氣。燒瓶封口后置于油浴中在設(shè)定的溫度下攪拌反應(yīng)，到預(yù)定的反應(yīng)時間后，通過冰水冷卻，反應(yīng)物用THF稀釋后倒入大量甲醇中析出聚合物(Vmethanol/VTHF=100/1)。經(jīng)過濾并真空干燥后作為分析測試之用。

1.3　分析與測試

轉(zhuǎn)化率用稱重法測定；聚合物分子量分布用Waters公司1515型GPC測定，流動相為四氫呋喃，柱溫30 ℃，PMMA標(biāo)樣校正；1H NMR用INOVA 300 MHz NMR核磁共振儀，CDCl3為溶劑測定。

2結(jié)果與討論

2.1　苯乙烯的AGET ATRP本體聚合

圖1表示的是在110 ℃苯乙烯的AGET ATRP動力學(xué)點ln([M]0/[M])和反應(yīng)時間的關(guān)系(聚合條件為[St]0∶[I]0∶[FeCl3·6H2O]0∶[PPh3]0∶/[VC]0= 200∶1∶1∶3∶1；St=3 mL)。由圖1看出反應(yīng)呈一階線性關(guān)系，表明聚合過程中增長自由基濃度恒定；由圖1還可看出，在聚合初始有大約2 h的誘導(dǎo)期，這與以前報道中以三價鐵離子為催化中心的催化體系中觀察到的現(xiàn)象一致[36-37]。根據(jù)3價鐵離子催化的AGET ATRP反應(yīng)機理，還原劑使催化中心原位生成，接下來的反應(yīng)機理同ATRP，即引發(fā)劑與催化劑反應(yīng)生成自由基，可以引發(fā)聚合[38]，在聚合初期，如果原位生成的催化中心數(shù)量不足，而存在大量氧化態(tài)的鐵離子絡(luò)合物，反應(yīng)平衡會向左移，導(dǎo)致自由基濃度不足，從而產(chǎn)生誘導(dǎo)期。

圖1　110 ℃苯乙烯本體AGRT ATRP反應(yīng)速率及單體轉(zhuǎn)化率與聚合時間的關(guān)系Fig.1　ln([M]0/[M]) and conversion as a function of time for the AGET ATRP of St at 110 ℃ in bulk

圖2　110 ℃本體聚合數(shù)均分子量和分子量分布指數(shù)與轉(zhuǎn)化率的關(guān)系Fig.2　Number-average molecular weight (Mn,GPC) and molecular weight distribution versus the conversion for the AGET ATRP of St at 110 ℃ in bulk

圖2表示的是110 ℃本體聚合數(shù)均分子量和分子量分布指數(shù)與轉(zhuǎn)化率的關(guān)系。由圖2看出，聚合物數(shù)均分子量隨單體轉(zhuǎn)化而線性增長，分子量分布指數(shù)比較窄(1.07~1.17)。圖2還標(biāo)出了數(shù)均分子量的理論值，這些理論值都要低于實驗值，表明引發(fā)效率相對較低。通常高活性的引發(fā)劑在聚合初期會產(chǎn)生大量自由基，自由基相互耦合會終止而不是用于引發(fā)聚合，導(dǎo)致引發(fā)效率降低[15]。

2.2　反應(yīng)溫度對聚合的影響

圖3　本體聚合不同溫度下AGRT ATRP反應(yīng)速率與聚合時間的關(guān)系Fig.3　Kinetic plot for St polymerization in bulk at different temperatures

2.3　引發(fā)劑用量對聚合的影響

在苯乙烯的AGRT ATRP中，熱聚影響不可忽視[37]，表1為10 ℃本體聚合反應(yīng)12 h引發(fā)劑用量對聚合的影響。由第1組反應(yīng)1看出，不加引發(fā)劑單體轉(zhuǎn)化率為6.5%，數(shù)均分子量為3 200。引發(fā)的不充分會導(dǎo)致數(shù)均分子量的提高，而增加引發(fā)劑的用量會導(dǎo)致單體轉(zhuǎn)化率的提高。根據(jù)表1，[St]0∶[I]0∶[FeCl3·6H2O]0∶[PPh3]0∶[VC]0的最佳比率為200∶2∶1∶3∶1。

表1　110 ℃本體聚合反應(yīng)12 h引發(fā)

注：①R=[St]0∶[I]0∶[FeCl3·6H2O]0∶[PPh3]0∶[VC]0

②Mn,th=([St]0/[I]0)×Mw,St×轉(zhuǎn)化率%

2.4　取代基團(tuán)對聚合的影響

為了進(jìn)一步研究取代基團(tuán)對聚合的影響，還選用MBB作為引發(fā)劑進(jìn)行了苯乙烯的AGET ATRP聚合(反應(yīng)條件為[St]0∶[I]0∶[FeCl3·6H2O]0∶[PPh3]0∶[VC]0= 200∶1∶1∶3∶1)，結(jié)果見表2。根據(jù)表2，使用MBB作為引發(fā)劑，聚合物數(shù)均分子量及分布指數(shù)都顯著增加，產(chǎn)生這樣現(xiàn)象可以解釋為供電子基團(tuán)的電子效應(yīng)使得碳-溴鍵難于斷裂，導(dǎo)致引發(fā)劑的活性降低[33]。

表2　110 ℃本體AGET ATRP引發(fā)劑

注：①Mn,th=200×Mw,St×轉(zhuǎn)化率%

②CBB作為引發(fā)劑

③MBB作為引發(fā)劑

2.5　聚合物結(jié)構(gòu)表征

根據(jù)AGET ATRP機理，在得到的聚合物中引發(fā)劑基團(tuán)留在聚合物鏈的α端，而ω端為鹵素封端，這可以通過本實驗所得聚苯乙烯的核磁氫譜(圖4~圖5)驗證。圖4中(7.60~6.20)×10-6(a)的出峰信號對應(yīng)CBB上的苯環(huán)質(zhì)子氫，而(2.60~1.20)×10-6(b)處的出峰為聚苯乙烯主鏈上亞甲基、次甲基的質(zhì)子氫信號，(4.75~4.25)×10-6(c)處的出峰為聚苯乙烯ω端-C(Ph)H-Br結(jié)構(gòu)的質(zhì)子氫信號，這表明在實驗聚合體系中引發(fā)劑的溴原子確已引入聚合物的ω端。

3結(jié)論

以芐鹵衍生物CBB為引發(fā)劑、FeCl3·6H2O/PPh3為催化劑、VC為還原劑，對苯乙烯進(jìn)行了本體聚合，聚合符合AGET ATRP機理，并具有“活性”特征。結(jié)果表明，反應(yīng)溫度、引發(fā)劑加入量、引發(fā)劑取代基的結(jié)構(gòu)均顯著影響聚合的控制性。

圖4　CBB引發(fā)的聚苯乙烯的核磁氫譜(樣品數(shù)均分子量4070，分布指數(shù)1.19)Fig.4　1H NMR spectrum of PSt initiated with CBB in bulk. Sample:Mn,GPC=4070 g/mol, PDI=1.19

圖5　MBB引發(fā)的聚苯乙烯的核磁氫譜(樣品數(shù)均分子量2860，分布指數(shù)1.21)Fig.5　1H NMR spectrum of PSt initiated with MBB in bulk. Sample:Mn,GPC=2860 g/mol, PDI=1.21

參考文獻(xiàn)：

[1]Matyjaszewski K， Wang J S. Controlled Living Radical Polymerization-Halogen Atom-Transfer Radical Polymerization Promoted by A Cu(I)/Cu(II) Redox Process[J].Macromolecules, 1995,28(23):7 901-7 910.

[2]Sawamoto M, Kato M, Higashimura T. Polymerization of Methyl Methacrylate with the Carbon Tetrachloride/Dichlorotris-(triphenylphosphine)ruthenium(II) /Methylaluminum Bis(2,6-di-tert-butylphenoxide) Initiating System:Possibility of Living Radical Polymerization[J].Macromolecules, 1995,28(5):1 721-1 723.

[3]Zhu S M, Yan D Y. Atom Transfer Radical Polymerization of Methyl Methacrylate Catalyzed by IronII Chloride/Isophthalic Acid System[J].Macromolecules, 2000,34(22):8 233-8 238.

[4]Hong S C, Matyjaszewski K. Fundamentals of Supported Catalysts for Atom Transfer Radical Polymerization (ATRP) and Application of an Immobilized/Soluble Hybrid Catalyst System to ATRP[J].Macromolecules, 2002,35(20):7 592-

7 605.

[5]Shen Y, Tang H, Ding S. Catalyst Separation in Atom Transfer Radical Polymerization[J].Prog Polym Sci, 2004,29(10):

1 053-1 078.

[6]Wang Y, Kwak Y W, Buback J, et al. Determination of ATRP Equilibrium Constants under Polymerization Conditions[J].ACS Macro Lett, 2012,1(12):1 367-1 370.

[7]汪永彬.原子轉(zhuǎn)移自由基聚合(ATRP)的研究進(jìn)展[J].化學(xué)推進(jìn)劑與高分子材料,2014,12(1):32-36.

[8]李艷明,孔娟,楊柏林,等.PS-PMMA-PBMA三嵌段聚合物的ATRP合成及表征[J].涂料工業(yè),2013,43(7):10-14.

[9]Jakubowski W, Matyjaszewski K. Activator Generated by Electron Transfer for Atom Transfer Radical Polymerization[J].Macromolecules, 2005,38(10):4 139-4 146.

[10]Pietrasik H, Dong H, Matyjaszewski K. Synthesis of High Molecular Weight Poly(styrene-co-acrylonitrile) Copolymers with Controlled Architecture[J].Macromolecules, 2006,39(19):6 384-6 390.

[11]Magenau A J, Strandwitz N C, Gennaro A, et al. Electrochemically Mediated Atom Transfer Radical Polymerization[J].Science, 2011,332(6025):81-84.

[12]Zhang Y, Wang Y, Peng C H, et al. Copper-Mediated CRP of Methyl Acrylate in the Presence of Metallic Copper: Effect of Ligand Structure on Reaction Kinetics[J].Macromolecules, 2012,45(1):78-86.

[13]張良,劉方.由NBS引發(fā)的MMA的室溫電子活化再生原子轉(zhuǎn)移自由基聚合(AGET ATRP)[J].鹽城工學(xué)院學(xué)報：自然科學(xué)版,2014,27(3):13-17.

[14]錢濤,汪娟娟,張慶華,等.ARGET ATRP制備甲基丙烯酸短全氟酯共聚物及其性能[J].浙江大學(xué)學(xué)報,2013,47(8):1 470-1 474.

[15]Matyjaszewski K. Atom Transfer Radical Polymerization (ATRP)-Current Status and Future Perspectives[J].Macromolecules, 2012,45(10):4 015-4 039.

[16]Lu J M, Xia X W, Guo X, et al. Synthesis, characterization, and property of end-functionalized telechelic PSt via ATRP[J].J Appl Polym Sci, 2008,108(5):3 430-3 434.

[17]Lu J M, Xu Q F, Yuan X, et al. Synthesis, characterization, and fluorescence of end-functionalized polystyrene initiated by 4-chloromethyl benzoic acid and ethyl 4-chloromethyl benzenecarboxylate via ATRP[J].J Appl Polym Sci, 2007,104(1):75-80.

[18]Xu Q F, Lu J M, Yang Z, et al. Synthesis and fluorescent properties of end-functional PSt initiated by 5-chloromethyl-2-methoxy-benzaldehyde via ATRP[J].Polym J, 2007,39(3):213-219.

[19]Zhang L, Xu Q F, Li N J, et al. First example of polystyrene end-functionalized with excited state intramolecular proton transfer (ESIPT) fluorophore by ATRP method[J].E-Polymers, 2008,8(1):1 845-1 854.

[20]Narrainen A P, Hutchings L R, Ansari I, et al. Multi-end-functionalized polymers: additives to modify polymer properties at surfaces and interfaces[J].Macromolecules, 2007,40(6):1 969-1 980.

[21]Kopping J T, Tolstyka Z P, Maynard H D. Telechelic aminooxy polystyrene synthesized by ATRP and ATR coupling[J].Macromolecules, 2007,40(24):8 593-8 599.

[22]Broyer R M, Quaker G M, Maynard H D. Designed amino acid ATRP initiators for the synthesis of biohybrid materials[J].J AmChem Soc, 2008,130(3):1 041-1 047.

[23]Colak D G, Cianga I, Muftuoglu A E, et al. Synthesis and characterization of mid- and end-chain functional telechelics by controlled polymerization methods and coupling processes[J].J Polym Sci A Polym Chem, 2006,44(2):727-743.

[24]Colak D G, Cianga I, Yagci Y, et al. Novel poly(phenylene vinylenes) with well-defined poly(epsiloncaprolactone) or polystyrene as lateral substituents: synthesis and characterization[J].Macromolecules, 2007,40(15):5 301-5 310.

[25]Kiskan B, Gacal B, Tasdelen M A, et al. Design and synthesis of thermally curable polymers with benzoxazine functionalities[J].Macromol Symp, 2006,245(1):27-33.

[26]Sahin E, Camurlu P, Toppare L, et al. Conducting copolymers of thiophene functionalized polystyrenes with thiophene[J].J Electroanal Chem, 2005,579(2):189-197.

[27]Yurteri S, Cianga A, Demirel A L, et al. New polyphenyleneg-polystyrene and polyphenylene-g-polystyrene/poly(epsiloncaprolactone) copolymers by combined controlled polymerization and cross-coupling processes[J].J Polym Sci A Polym Chem, 2005,43(4):879-896.

[28]Yurteri S, Cianga I, Yagci Y. Synthesis and characterization of poly(epsilon-caprolactone)-b-polystyrene macromonomer by combined ring-opening and atom transfer radical polymerizations and its use for the preparation of grafted polyphenylenes by Suzuki polycondensation[J].Des Monomers Polym, 2005,8(1):61-74.

[29]Cianga I, Mercore V M, Grigoras M, et al. Synthesis and characteristics of polymacromonomers composed of alternating binaphthalene-phenylene main chain and polystyrene side chains[J].Polymer, 2007,48(22):6 501-6 509.

[30]Tarkuc S, Sahin E, Toppare L, et al. Synthesis characterization and electrochromic properties of a conducting copolymer of pyrrole functionalized polystyrene with pyrrole[J].Polymer, 2006,47(6):2 001-2 009.

[31]Sahin E, Camurlu P, Toppare L, et al. Synthesis and characterization of thiophene functionalized polystyrene copolymers and their electrochemical properties[J].Polym Int, 2005,54(12):1 599-1 605.

[32]Cianga I, Mercore V M, Grigoras M, et al. Poly(thienylphenylene)s with macromolecular side chains by oxidative polymerization of well-defined macromonomers[J].J Polym Sci A Polym Chem, 2007,45(5):848-865.

[33]Tang W, Kwak Y, Braunecker W, et al. Understanding atom transfer radical polymerization: effect of ligand and initiator structures on the equilibrium constants[J].J Am Chem Soc, 2008,130(32):10 702-10 713.

[34]Luo R, Sen A. Electron-transfer-induced iron-based atom transfer radical polymerization of styrene derivatives and copolymerization of styrene and methyl methacrylate[J].Macromolecules, 2008,41(12):4 514-4 518.

[35]Zhang L F, Cheng Z P, Shi S P, et al. AGET ATRP of methyl methacrylate catalyzed by FeCl3/iminodiacetic acid in the presence of air[J].Polymer, 2008,49(13-14):3 054-3 059.

[36]Zhang L F, Cheng Z P, Tang F, et al. Iron(III)-mediated atom transfer radical polymerization of methyl methacrylate using activators generated by electron transfer[J].Macromol Chem Phys, 2008,209(16):1 705-1 713.

[37]Zhang L F, Cheng Z P, Zhang Z B, et al. Fe(III)-catalyzed AGET ATRP of styrene using triphenyl phosphine as ligand[J].Polym Bull, 2010,64(3):233-244.

[38]Min K, Gao H F, Matyjaszewski K. Preparation of homopolymers and block copolymers in miniemulsion by ATRP using activators generated by electron transfer (AGET)[J].J Am Chem Soc, 2005,127(11):3 825-3 830.

(責(zé)任編輯：李華云)

AGET ATRP of Styrene Using 4-Cyanobenzyl

Bromide as the Initiator

ZHANG Liang, YU Fangli, LIU Fang

(School of Materials Engineering, Yancheng Institute of Technology, Yancheng Jiangsu224051, China)

Abstract：4-Cyanobenzyl bromide was used as the initiator for the atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of styrene in a FeCl3·6H2O/PPh3/VC catalytic system. Factors that can affect the AGET ATRP system, such as the reaction temperature and amount of initiator, were discussed. The rates of polymerization exhibited first-order kinetics with respect to the monomer. A linear increase in the number-average molecular weight with increased monomer conversion was observed in the initiation systems. The polydispersity indices of the polymer were relatively low (1.07~1.31). To study further the effect of the substituent group of the initiator on polymerization, 4-methylbenzyl bromide was also used as an initiator for the polymerization system. The structures of the polymers were characterized by proton nuclear magnetic resonance spectroscopy.

Keywords：AGET ATRP; Styrene (St); 4-Cyanobenzyl bromide (CBB); Initiator

作者簡介：張良(1977-)，男，江蘇建湖人，講師，博士，主要研究方向為可控/活性自由基聚合。

收稿日期：2014-12-08

中圖分類號：TQ316.32

文獻(xiàn)標(biāo)識碼：A

文章編號：1671-5322(2015)02-0009-06

doi:10.16018/j.cnki.cn32-1650/n.201502002