活性自由基聚合RAFT

1、基于可逆加成-碎裂型鏈轉(zhuǎn)移劑的活性自由基聚合Living radical polymerization in the presence of reversible addition-fragmentation chain transfer RAFT, 1998123調(diào)聚反應(yīng)！456基于可逆加成-碎裂型鏈轉(zhuǎn)移劑的活性自由基聚合CSIRO，澳大利亞聯(lián)邦科學(xué)與工業(yè)研究組織( Commonwealth Scientific and Industrial Research Organisation ) In the early 1980s a CSIRO team led by David Solomo

2、n and Ezio Rizzardo devised a radical-trapping technique. During the next decade the team introduced catalytic chain transfer agents, macromonomers, addition-fragmentation chemistry and pioneered a form of living radical polymerisation mediated by nitroxides. The patent for this last invention Nitro

3、xide-mediated living radical polymerisation (NMP) has been in the top 10 of the worlds most cited patents since 1999 (CAS Science Spotlight). The novelty and the potential industrial utility of their science was recognised by DuPont in 1990 and a Strategic Research Alliance with CSIRO formed. 7In 19

4、86, CSIRO in Australia reported the use of PMMA macromonomers as chain transfer agents (CTAs) in radical polymerization. They called the process addition-fragmentation chain transfer (AFCT): 891988-1996年間irreversible addition-fragmentation chain transfer agent,分子量調(diào)節(jié)劑，末端官能化試劑（引入雙鍵等）10烯丙基硫化物鏈轉(zhuǎn)移劑的分子結(jié)構(gòu)式

5、硫代羰基化合物類鏈轉(zhuǎn)移劑的分子結(jié)構(gòu)式irreversible addition-fragmentation chain transfer agent,分子量調(diào)節(jié)劑，末端官能化試劑11reversible addition-fragmentation chain transfer (RAFT) agent加成-斷裂均為高活性，大分子的加成斷裂也為高活性！1213Main equilibriumPreequilibrium14Macromolecules 1998, 31, 5559-55621516RAFT聚合機(jī)理和動力學(xué)： A steady state concentration of rad

6、icals is established via initiation and termination processes as in conventional RP. The deactivation-activation equilibria are chain-transfer reactions.Radicalradical termination is not directly suppressed by the RAFT process.穩(wěn)態(tài)與平衡，與ITP相同：17穩(wěn)態(tài)與平衡：18RAFT Polymerization SchematicInitiator/RAFT 多為5/1,

7、 更寬的范圍為20:1-3:1 191. The initial RAFT agents 1 and the polymer RAFT agent 3 should have a reactive C=S double bond (high kadd).2. The intermediate radicals 2 and 4 should fragment rapidly (high k, weak SR bond) and give no side reactions.3. The intermediate 2 should partition in favour of products (

8、k kadd).4. The expelled radicals (R) must efficiently re-initiate the polymerization (ki kp).For an efficient RAFT polymerization:20Moad, G.; Rizzardo, E.; Thang, S. H. Acc. Chem. Res. 2008, 41, 1133-1142. Typical molecular weight distributions for a conventional and a RAFT polymerization of styrene

9、 under similar experimental conditions. In an ideal RAFT process, the RAFT agent should behave as a transfer agent. Retention of the thiocarbonylthio groups in the polymeric product is responsible for the living character of RAFT polymerization and renders the process suitable for synthesizing block

10、 copolymers and end functional polymers. 21 =當(dāng)鏈較長后為0.5Preequilibriummainequilibrium22d is the number of chains produced in a radicalradical termination event (d 1.67 for MMA polymerization and 1.0 for styrene polymerization) and f is the initiator efficiency.（5）忽略引發(fā)劑產(chǎn)生的鏈原因：MMA歧化終止為主，St幾乎都為偶合終止！2324（

11、7）The fraction of living chains (L)In an ideal RAFT process，L=1.0A negative deviation from the line predicted by equation indicates that other sources of polymer chains are significant (e.g. the initiator, chain transfer to solvent, monomer). A positive deviation from the line predicted by equation

12、indicates incomplete usage of transfer agent。（8）In a well-designed RAFT polymerization, L will be 0.95。2526The proportion of dead chains Dc：2728測定： =忽略引發(fā)和雙基終止產(chǎn)生的鏈傳統(tǒng)自由基聚合測鏈轉(zhuǎn)移常數(shù)：29測定： 不忽略引發(fā)和雙基終止產(chǎn)生的鏈Ctr = 0, and for less active RAFT agents at low monomer conversion,Xn(calc) is the expected number-avera

13、ge degree of polymerization assuming complete consumption of transfer agent.30The transfer constants of various RAFT agents have been measured in the range of 0.01 to above 1000 depending on the nature of Z, R, and type of monomer. It has been reported that to obtain narrow polydispersity polymers (

14、Mw=Mn 三硫代碳酸酯脂肪二硫代羧酸酯黃原酸酯二硫代氨基甲酸酯。（最后兩種基本不可控）Z基團(tuán)的影響：34最后兩種：Z基團(tuán)給電子性，降低C=S的反應(yīng)活性？3536當(dāng)富電子原子（O/N)上有吸電子取代基，特別是可與O/N原子中孤對電子發(fā)生離域作用的取代基取代后，可以顯著提高其轉(zhuǎn)移常數(shù)。37R基團(tuán)的影響：R基團(tuán)對自由基與RAFT試劑的反應(yīng)沒有太大影響，但它決定反應(yīng)中形成的自由基中間體的分解方向，而分解形成的自由基R的立體位阻、極化性能和穩(wěn)定性等決定了一個RAFT試劑鏈轉(zhuǎn)移常數(shù)的大小。R的離去能力和再引發(fā)能力要平衡！38不同R基團(tuán)有如下遞減規(guī)律: -C(alkyl)2CN,-C(Me)2Ar -C(

15、Me)2(C=O)O(alkyl) -C(Me)2(C=O)NH(alkyl) -C(Me)2CH2C(Me)3 -C(Me)HPh -C(Me)3, -CH2ph，只有當(dāng) R=-C(Me)2Ph和-C(Me)2CN時才能得到可控的MMA聚合物。但所有這些不同結(jié)構(gòu)的RAFT都能有效控制St和MA的聚合3940注意： R基團(tuán)為-C(Me)2COOEt不能得到可控的MMA聚合物。這與ATRP、SFRP中的規(guī)律不同。原因： R radical is a poor leaving group with respect to the PMMA propagating radical (n2）。This

16、difference is attributed to steric factors 。41當(dāng)使用黃原酸酯作為RAFT試劑時聚合過程也被稱MADIX (Momolecular Design via the Interchange of xanthates)42“more-activated” monomers (MAMs) ：styrene, methyl acrylate (MA), and methyl methacrylate(MMA) “l(fā)ess activated”monomers (LAMs）：vinyl acetate (VAc), N-vinylpyrrolidone (NVP

17、), and N-vinylcarbazole (NVC).單體與RAFT的匹配：43RAFT 聚合對官能團(tuán)不敏感，官能化的St, MA，MMA, AA, MAA, HEA, HEMA, AM等單體均能實現(xiàn)可控聚合。4445說明： 得到可控聚合物的分子量有上限。464748可控性差！49505152Figure . Molecular weight distributions for PMMA formed by high conversion RAFT polymerization of MMA (6.55 M in benzene) with 1,1-azobis(1-cyclohexan

18、ecarbonitrile) (0.0018 M) as initiator and various concentrations of RAFT agent （S-dodecyl S-(2-cyano-4-carboxy)but- 2-yl trithiocarbonate ）for 6 h at 90 C. 5354RAFT 可實現(xiàn)VAc的可控聚合，與VC一樣，是重大突破。Xanthate ：Z 基團(tuán)為烷氧基團(tuán),使黃原酸酯自由基中心電荷密度增加, 加成自由基的斷裂速率加快。RAFT: Xanthate dithiocarbamateMacromol. Rapid Commun. 2001,

19、 22: 1497Macromol. Rapid Commun. , 2000, 21: 1035Macromol. Symp. , 2000, 150: 23 難點： VAc作為R, 是難離去基團(tuán)； VAc 的自由基異常活潑，易發(fā)生轉(zhuǎn)移等反應(yīng)。55注意R基：缺電子基團(tuán)，應(yīng)能保證快引發(fā)，個人認(rèn)為是實現(xiàn)可控的另一個重要因素。56按RAFT聚合機(jī)理，只要能快速發(fā)生加成一一斷裂反應(yīng)，形成的中間體2和4的壽命較短，且沒有其他副反應(yīng)，那么RAFT試劑的加入不應(yīng)該顯著影響聚合反應(yīng)速率，因為RAFT試劑不會影響增長自由基濃度，增長自由基的濃度應(yīng)由引發(fā)一一終止平衡反應(yīng)所控制。RAFT process does

20、 not rely on a PRE, 因此應(yīng)該沒有retardation。RAFT聚合中的阻滯現(xiàn)象：57it is common in RAFT polymerizations to observe a decreasing rate of polymerization a retardation effect when the concentration of RAFT agent is increased. This retardation effect appears to be more pronounced with the use of dithiobenzoates as op

21、posed to aliphatic dithioesters or trithiocarbonates. Macromolecules 2003, 36, 2256-2272the more stable the intermediate radical， the larger the retardation effect.58RAFT聚合中的阻滯原因：Factors responsible for retardation：59其他的阻滯原因：加成自由基的副反應(yīng)：60其他的阻滯原因：加成自由基的副反應(yīng)：Some decrease polymerization rate is clearly

22、attributable to a mitigation of gel ( or Trommfsdorf) effect.61RAFT聚合中的誘導(dǎo)期（inhibition）或初期慢聚合速率：chain-length dependent termination rate coefficient其他原因同前面分析高溫下不明顯或觀測不到62RAFT 試劑的合成：63RAFT 試劑的合成：部分已經(jīng)商品化！64嵌段聚合物的制備：大致順序：甲基丙烯酸酯基苯乙烯基， 丙烯酸酯基。656667星形聚合物的制備：686970聚合物RAFT 端基的脫除與轉(zhuǎn)換：71聚合物RAFT 端基的脫除與轉(zhuǎn)換：With an

23、excess of radicals 表明RAFT聚合中可控性要好引發(fā)劑用量一定要盡可能少72聚合物RAFT 端基的脫除與轉(zhuǎn)換：73聚合物RAFT 端基的脫除與轉(zhuǎn)換：74Switchable RAFT AGENT: 適用高活性和低活性單體！J. AM. CHEM. SOC. 2009, 131, 69146915RAFT AGENT的突破： 75Switchable RAFT AGENT: J. AM. CHEM. SOC. 2009, 131, 6914691576新的想法：Recently, it has been suggested that the control exerted by

24、 certain thioketones (X = S; A-R, Z = alkyl or aryl) over free radical polymerizations may proceed via such a mechanismChem. Commun. (Camb. U K) 2006, 835837.H. Chaffey-Millar, E. I. Izgorodina, C. Barner-Kowollik, M. L. Coote, J. Chem. Theor. Comput. 2006, 2, 16321645.T. Junkers, M. H. Stenzel, T.

25、P. Davis, C. Barner-Kowollik, Macromol. Rapid Commun. 2007, 28, 746753.7778BYK-Chemie：In 2007, BYK announced the commercialization oftwo polymer additives for coatings produced by a nondisclosed CRP process. DISPERBYK-2010 is a wetting and dispersing additive for aqueous systems.CRP的工業(yè)化：Dupont has a

26、lways been extremely active in R&D topropose and test novel CRP technologies, most of the time in collaboration with the Australian CommonwealthScientific and Research Organization (CSIRO). The company proposes a portfolio of licensable intellectual property including various addition-fragmentation

27、transfer agents and catalytic chain transfer processes.79CRP的工業(yè)化：The NMP process has gained much maturity since TEMPOwas originally used as a moderator for radical polymerization by Dupont and Xerox.Ciba has developed a number of nitroxide regulators (NORs), including special open chain NORs, piperazinone and piperidine-type NORs, and 7-ring heterocyclic NORs,One of the first commercial successes of NMP belong to Ciba (now part of BAS