活性自由基聚合RAFT

1、基于可逆加成-碎裂型链转移剂的活性自由基聚合Living radical polymerization in the presence of reversible addition-fragmentation chain transfer RAFT, 1998123调聚反应！456基于可逆加成-碎裂型链转移剂的活性自由基聚合CSIRO，澳大利亚联邦科学与工业研究组织( 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年间irreversible addition-fragmentation chain transfer agent,分子量调节剂，末端官能化试剂（引入双键等）10烯丙基硫化物链转移剂的分子结构式

5、硫代羰基化合物类链转移剂的分子结构式irreversible addition-fragmentation chain transfer agent,分子量调节剂，末端官能化试剂11reversible addition-fragmentation chain transfer (RAFT) agent加成-断裂均为高活性，大分子的加成断裂也为高活性！1213Main equilibriumPreequilibrium14Macromolecules 1998, 31, 5559-55621516RAFT聚合机理和动力学： 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.稳态与平衡，与ITP相同：17稳态与平衡：18RAFT Polymerization SchematicInitiator/RAFT 多为5/1,

7、 更宽的范围为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 =当链较长后为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）忽略引发剂产生的链原因：MMA歧化终止为主，St几乎都为偶合终止！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测定： =忽略引发和双基终止产生的链传统自由基聚合测链转移常数：29测定： 不忽略引发和双基终止产生的链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黄原酸酯二硫代氨基甲酸酯。（最后两种基本不可控）Z基团的影响：34最后两种：Z基团给电子性，降低C=S的反应活性？3536当富电子原子（O/N)上有吸电子取代基，特别是可与O/N原子中孤对电子发生离域作用的取代基取代后，可以显著提高其转移常数。37R基团的影响：R基团对自由基与RAFT试剂的反应没有太大影响，但它决定反应中形成的自由基中间体的分解方向，而分解形成的自由基R的立体位阻、极化性能和稳定性等决定了一个RAFT试剂链转移常数的大小。R的离去能力和再引发能力要平衡！38不同R基团有如下递减规律: -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，只有当 R=-C(Me)2Ph和-C(Me)2CN时才能得到可控的MMA聚合物。但所有这些不同结构的RAFT都能有效控制St和MA的聚合3940注意： R基团为-C(Me)2COOEt不能得到可控的MMA聚合物。这与ATRP、SFRP中的规律不同。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当使用黄原酸酯作为RAFT试剂时聚合过程也被称MADIX (Momolecular Design via the Interchange of xanthates)42“more-activated” monomers (MAMs) ：styrene, methyl acrylate (MA), and methyl methacrylate(MMA) “less activated”monomers (LAMs）：vinyl acetate (VAc), N-vinylpyrrolidone (NVP

17、), and N-vinylcarbazole (NVC).单体与RAFT的匹配：43RAFT 聚合对官能团不敏感，官能化的St, MA，MMA, AA, MAA, HEA, HEMA, AM等单体均能实现可控聚合。4445说明： 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 可实现VAc的可控聚合，与VC一样，是重大突破。Xanthate ：Z 基团为烷氧基团,使黄原酸酯自由基中心电荷密度增加, 加成自由基的断裂速率加快。RAFT: Xanthate dithiocarbamateMacromol. Rapid Commun. 2001,

19、 22: 1497Macromol. Rapid Commun. , 2000, 21: 1035Macromol. Symp. , 2000, 150: 23 难点： VAc作为R, 是难离去基团； VAc 的自由基异常活泼，易发生转移等反应。55注意R基：缺电子基团，应能保证快引发，个人认为是实现可控的另一个重要因素。56按RAFT聚合机理，只要能快速发生加成一一断裂反应，形成的中间体2和4的寿命较短，且没有其他副反应，那么RAFT试剂的加入不应该显著影响聚合反应速率，因为RAFT试剂不会影响增长自由基浓度，增长自由基的浓度应由引发一一终止平衡反应所控制。RAFT process does

20、 not rely on a PRE, 因此应该没有retardation。RAFT聚合中的阻滞现象：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聚合中的阻滞原因：Factors responsible for retardation：59其他的阻滞原因：加成自由基的副反应：60其他的阻滞原因：加成自由基的副反应：Some decrease polymerization rate is clearly

22、attributable to a mitigation of gel ( or Trommfsdorf) effect.61RAFT聚合中的诱导期（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温下不明显或观测不到62RAFT 试剂的合成：63RAFT 试剂的合成：部分已经商品化！64嵌段聚合物的制备：大致顺序：甲基丙烯酸酯基苯乙烯基， 丙烯酸酯基。656667星形聚合物的制备：686970聚合物RAFT 端基的脱除与转换：71聚合物RAFT 端基的脱除与转换：With an

23、excess of radicals 表明RAFT聚合中可控性要好引发剂用量一定要尽可能少72聚合物RAFT 端基的脱除与转换：73聚合物RAFT 端基的脱除与转换：74Switchable RAFT AGENT: 适用高活性和低活性单体！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的工业化：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的工业化：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