活性自由基聚合,TEMPO

3. NMP聚合速率的提高
TEMPO体系的聚合速率慢,主要是由于聚合体系中链增长 自由基浓度太低。 平衡常数Keq=[P.][T.]/[PT],其中P.为链增长自由基,T· 为TEMPO, PT为形成的休眠种。 Keq仅为10-11mol.L-1,而实验发现体系中的TEMPO的浓度约为初 始浓度的0.1%(约为10-3mol.L-1).因此体系中P· -8mol.L-1，因 为10 此提高链增长自由基的浓度有利于聚合速率的提高。 He等在TEMPO的存在下,连续加入少量的自由基引发剂(AIBN) 进行苯乙烯的活性聚合, 发现连续加入引发剂体系的聚合速率 比一次性加入自由基引发剂分体系的聚合速率快了近3倍。
J. Am. Chem. Soc. 2000, 122, 5929-5939
2.4 副反应
苯乙烯中的 热引发：
说明双基终止 的存在?
热引发对苯乙烯的 聚合十分有利！ 双基终止的程度：严 重影响速率，对分子 量和分布影响很小！ 因自由基浓度:约为10-8M，大分子浓度为10-2M!
2.4 副反应
烷氧胺的分解或提氢副反应：
[P.]：利用转化率和时间的函数 Kd的测定： Macromolecules 1996, 29, 6393-6398
2.3 动力学参数
K=[P.][T.]/[PT]
Macromolecules 1996, 29, 6393-6398
N-tert-butyl-N-[1-diethylphosphono-(2,2dimethylpropyl)] nitroxide (DEPN).
Polymerization Systen: Monomer: Styrene Initiator: BPO Additive: TEMPO Conditions: Initial heating at 95oC for 3.5h, followed by heating at 123oC for 69h. Results: Narrow molecular weight polystyrene with polydispersity of 1.26. The number-average molecular weight increased linearly with with monomer conversion.
2. NMP的聚合机理 2.1 平衡的建立： persistent radical effect
2.1 平衡的建立： persistent radical effect
The stable radical (6) is capable of reaction with either (2) or (4) but not itself. Due to the fact that irreversible termination will occur between active radicals the concentration of the stable radical present will increase. Due to the build up in concentration of (6), very little coupling products between active radicals (2)-(2), (2)-(4), or (4)-(4) are formed, as the active radicals react almost exclusively with the stable or persistent radical (6) .
1. NMP的发现及历史：
分子量与转化率间线性关系！ TEMPO/BPO比例对聚合的影响！
1.பைடு நூலகம்NMP的发现及历史：
Many subsequent studies have confirmed Georges findings and have also shown that increasing the molar ratio of nitroxide to initiator result in slower reactions, lower PDIs, and lower molecular weight polymers. As a comparison, Georges performed a suspension copolymerization of styrene and butadiene with (a) and without (b) TEMPO. The PDI of the polymer with TEMPO was 1.36 while the PDI of the polymer without TEMPO was 4.61.
单分子体系(Unimolecular) ：
单分子体系可控效果 优于双分子体系！
2. NMP的聚合机理

Typically these propagating carbon centered radicals are transient species , tend to disappear by self-termination, which is typically a diffusion controlled process. This raises the question, why do we only see minor amounts of irreversible termination in NMP?
2. NMP的聚合机理 2.1 平衡的建立： persistent radical effect
R·Y· , 活泼自由基，则产物有三种, 1:2:1。 R· 活泼自由基，Y· persistent radical, 产物只有一种
2. NMP的聚合机理 2.1 平衡的建立： persistent radical effect
crossover experiments concluded nitroxides could freely diffuse.
2.3 动力学与动力学参数
Negligible fraction of dead chains, neglect d[P•]/dt as compared with d[X•]/dt
2. NMP的聚合机理
2.1 平衡的建立： persistent radical effect
Radicals (2) and (4) are present at very low concentrations (approx. 10-8 M) but the persistent radical (6) is at a concentration around 10-3 M. It is critical to note that the PRE is a very important concept, which is at the heart of both NMP and ATRP. it is possible to enhance the PRE by the addition of stable radicals at the beginning of the polymerization. The Persistent Radical Effect: A Principle for Selective Radical Reactions and Living Radical Polymerizations Hanns Fischer Chem. Rev. 2001, 101, 3581-3610
Nitroxide-Mediated Free Radical Polymerization (NMP，NMRP) Stable Free Radical Polymerization (SFRP)
基于氮氧稳定自由基的活性自由基
聚合
1. NMP的发现及历史：
Georges M K, et al. (Xerox Research Center of Canada) Macromolecules, 1993,36,2987-2988
Experimental results that quasi-equilibrium exists and the time needed to reach quasi-equilibrium is much less than 1 second, typically 1 – 100 ms. Ri > 0
2.4 副反应
烷氧胺的分解或提氢副反应：
These results help to explain the differences in the polymerization of styrenics and methacrylates under the same NMP conditions. Due to the extra β hydrogen's on the methacrylates, there is a much greater amount of H transfer and therefore lack of control. This has been observed experimentally with significant amounts of “ene” terminated polymer chains detected by MALDI-MS and NMR and UV-vis studies. Acrylates : much greater amount of H transfer
J. Am. Chem. SOC. 1994,116, 11185-11186
SOLOMON八十年代的工作：
用稳定自由基封端研究St、 MMA关于引发和终止的结构
SOLOMON八十年代的工作：
SOLOMON八十年代的工作：
1. NMP的发现及历史：
Rizzardo等与TEMPO/SFRP失之交臂？温度低，分布宽
the term living, controlled and step growth were used.
N O N O
polystyrene
CH 2
CH
polystyrene
CH 2
CH
Polymerization Systen: Monomer: Styrene 双分子体系 Initiator: BPO BPO:TEMPO=1:1.3 Additive: TEMPO Conditions: Initial heating at 95oC for 3.5h, followed by heating at 123oC for 69h. Poorly defined nature of the initiating species Results: Narrow molecular weight polystyrene with polydispersity of 1.26. The number-average molecular weight increased linearly
1. NMP的发现及历史：
2,2,4,4-四甲基派啶氮氧稳定自由基 (2,2,4,4-tetramethyl-1-piperidinyloxy, TEMPO)
H3C H3C N O
CH3 CH3
相对TD，其活性更低 ，不能引发聚合，且与 苯乙烯增长链末端结合 的键更弱。
自由基捕获剂、阻聚剂、抗老化剂、热降解抑制剂和热稳定剂等。
Steady-state
X• depends on the reversible reaction as well as the initiation/termination parameters.
Steady-state
Ri =0 Ri = 0
此式常用来测平衡常数
2.3 动力学参数
K=[P.][T.]/[PT] [T.]：ESR测定
2.2 关于自由基的性质：
does the radical pair exist as a caged pair or are they free to diffuse through the reaction?
2.2 关于自由基的性质：
radical: a caged pair or free to diffuse through the reaction?