Living Radical Polymerization - American

Chapter 43

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Organotellurium-Mediated Living Radical Polymerization Shigeru Yamago, Kazunori Iida, and Jun-ichi Yoshida Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan

Polymer-end mimetic organotellurium compounds initiate controlled/living radical polymerization that allows accurate molecular weight control with defined end-groups. A variety of monomers including styrene, acrylate, and methacrylate derivatives are polymerized under mild thermal conditions using same initiators. AB-Diblock, A B A - and ABC-triblock copolymers composed of different families of monomers are also synthesized with highly controlled manner. Transformations of the end-groups via radical and ionic reactions provide a variety of end-group modified polymers with defined structure with various functional groups.

The synthesis of new nanostructural organic materials by controlled polymerization has attracted a great deal of attention, because these materials would lay essential foundations for nanoscience and nanotechnologies (1,2). Living radical polymerization (LRP) is becoming increasingly important for this goal because of its potential Appl.icability to different types of monomers with various polar functional groups, which do not lend themselves to ionic and metal-catalyzed polymerization conditions. While impressive developments in LRP systems have emerged such as nitroxide-mediated polymerization (NMP) (5), atom transfer radical polymerization (ATRP) (4\ and reversible additionfragmentation chain transfer (RAFT) (5), the invention of a more versatile system is clearly needed to achieve polymerization of different families of monomers with control of molecular structure and with defined polymer endgroups. We have already reported that organotellurium compounds undergo reversible carbon-tellurium bond cleavage upon thermolysis and photolysis (6),

© 2003 American Chemical Society

In Advances in Controlled/Living Radical Polymerization; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

631


632 and that the resulting carbon-centered radicals can react with a variety of radical acceptors (7,8). Since N M P also relies on reversible generation of carboncentered radicals and persistent nitroxyl radicals at the polymer end (9), we decided to investigate the use of organotellurium compounds as unimolecular radical initiators for living radical polymerization. We report here a highly versatile method for the synthesis of structurally defined polymers based on organotellurium mediated living radical polymerization (TERP). We have found that TERP is extremely general and can beAppl.icablefor the polymerization of different families of monomers, such as styrene, acrylate, and methacrylate derivatives, using the same initiators in a highly controlled manner. Furthermore, the versatility of TERP allows the synthesis of various A B - , A B A - and A B C block copolymers starting from a single monofunctional initiator (Scheme 1) (10,11).

Scheme 1. 1

3

R n

1

R R *• Rj^Xl

J^ 2 R

R—TeMe

m

2

|R» «TeMel heat

R ^k 4 *• R

1^ ^TeMe

! Ï 2

3

RVR R R

4

6

^ R

2

3

4

5

6

R.\R R. R R. .R

TeMe

OSiMe

C0 Et 2

Ph^TeR' Ph

1 a: R* = Me b: R* = Ph

ο

3

X

^TeMe 2

^

T

e

M

3

e

R j jr T e P h 4

pf^SeMe

5

Bond dissociation energies of initiators. Previous reports on the N M P indicate that the efficiency of the initiators is closely related to their bond dissociation energies (BDE) (12). Therefore, we first calculated the BDEs of the organotellurium compounds 1-5 (Table 1). Density functional theory (DFT) calculations indicated that the BDEs of 1 and 3 are 112 - 123 kJ/mol, the values of which are very similar to those of the corresponding TEMPOAnal.ogue(119 kJ/mol).


633 Table 1. Calculated bond dissociation energies of initiators." Compound la lb 2

BDE (kJ/mol) 123 112 142

Compound 3 4 5

BDE (kJ/mol) 114 25 182


"Obtained by B3LYP DFT calculations with LANL2DZ basisSci.for tellurium atom and 6-3 lG(d) basisSci.for the rest.

Polymerization of vinyl monomers. Bulk polymerization of styrene (X = H) was initially examined at 105 °C for 16-18 h, and the results are shown in Table 2 (entries 1-8). The polymer-end mimetic initiator l a (R' = Me) initiated the polymerization efficiently, and afforded polystyrene with the predicted molecular weight and low polydispersity (M = 9200, PD = 1.17) in 96% yield (Table 1, entry 1). The initiator l b (R' = Ph) also promoted polymerization, but the control of the molecular weight was less efficient. Benzyl telluride 2 also initiated polymerization with acceptable polydispersity. The result is in sharp contrast to the NMP polymerization, in which benzyl derivatives are far less efficient than the 1-phenylethyl derivatives (cf. l a vs. 2).The ester 3 also initiated polymerization efficiently with low polydispersity. The ability to initiate polymerization of 4 and 5 was found to be unsatisfactory. These results may suggest that both the BDEs and the reactivity of the initiating radicals toward styrene are important factors in controlling the polymerization process. It is also worth mentioning that, while the first-generation initiators for N M P required high temperature and long reaction times, e.g., 130 °C for 72 h, the initiators l a and 3 promoted polymerization under much milder conditions. Molecular weight increased linearly with the increase of the amount of styrene, and the products were obtained with low polydispersity (entries 7 and 8). The observed linearlity as well as low polydispersity (PD < 1.3) strongly suggested the living character of the current polymerization (see below). Because TERP proceeds under neutral conditions, styrenes possessing a variety of functional groups, such as chloro- and methoxy groups, could also be polymerized using l a as the initiator (entries 9 and 10). It is worth noting thatpmethoxy-substituted styrene, which is a poor monomer for ATRP (13% was successfully polymerized by this method. To understand the generality of TERP, we next examined the polymerization of acrylates by heating at 100 °C for 24 h with the initiators l a or 3, which are excellent initiators for the polymerization of styrenes. We found that both l a and 3 worked efficiently and afforded polyMA with predictable molecular weight and low polydispersity (entries 11 and 12). The initiators also polymerized a variety of acrylate derivatives efficiently (entries 13 - 17). It is worth noting that all the monomers gave the desired polymers with low polydispersity (PD < 1.23) and in high yield. The successful polymerization of n


634 Table 2. TERP of styrene, acrylate and methacrylate derivatives. Entry 1 2 3 4 5 6 Downloaded by STANFORD UNIV GREEN LIBR on August 8, 2012 | http://pubs.acs.org Publication Date: June 26, 2003 | doi: 10.1021/bk-2003-0854.ch043

Τ

8" 9 10 11 12 13 14 15 16

e

IT

18 20^ 21 22 * 23** 24^ 25^ /β

e

Initiator la lb 2 3 4 5 la la la la la 3 la 3 la la la 3 3 la la la la la 3

Monomer" St St St St St St St St

cist MeOSt MA MA nBA tBA DMAEA DMA AN MMA MMA MMA MMA MMA MMA EMA HEMA

Condns (°C/h) Yield (%) 96 105/17 91 105/17 105/16 89 79 105/20 76 105/16 83 105/18 78 105/27 84 105/29 88 100/17 94 100/36 86 100/24 70 100/24 89 100/24 100/24 85 81 100/96 100 105/23 100/24 53 67 80/15 84 80/13 92 80/13 83 80/19 79 80/18 80/24 83 97 105/2 97 80/17

PD* 1.17 1.45 1.46 1.15 1.80 1.58 1.21 1.30 1.41 1.17 1.12 1.11 1.13 1.18 1.23 1.22 1.07 1.77 1.16 1.18 1.14 1.18 1.14 1.12 1.18

M" a

9200 15900 9000 9000 50700 25400 35700 62600 8800 10900 8800 6400 10300 9800 12000 10100 20800 11800 8200 9700 16200 36300 79400 10600 22300

e

St: styrene, CISt: /?-chlorostyrene, MeOSt: /?-methoxystyrene, MA: methyl acrylate, nBA: n-butyl acrylate, tBA: /-butyl acrylate, DMAEA: 2-dimethylaminoethyl acrylate, DMA: N N-dimethylacrylamide, AN: acrylonitrile, MMA: methyl methacrylate, EMA: ethyl methacrylate, HEMA: 2-hydroxyethyl methacrylate. ^Molecular weight (A/ ) and polydispersity (PD) were determined by size exclusion chromatography calibrated by poly St or polyMMA standards. 500 Equiv of monomer was used. 1000 Equiv of monomer was used. *Τηβ reaction was carried out in DMF. ^ne equiv of dimethyl ditelluridc was added. *200 Equiv of monomer was used. Two equiv of dimethyl ditelluride were added. 9

n

c

A

2-dimethylaminoethyl acrylate (DMAEA), Ν,Ν-dimethyl acrylamide (DMA), and acrylonitrile (AN) is particularly noteworthy, since the polar functional groups of these monomers often disturb the precise control of the polymerization using other methods. We next examined the polymerization of methyl methacrylate (MMA, 100 equiv) with initiator 3, but initial attempts revealed that the control of the reaction was insufficient (PD = 1.77, entry 18). The result could be attributed to the high reactivity of M M A toward the polymer-end radicals, and we anticipated that the addition of an agent to cap the radical species would



635 enhance controllability. Because ditellurides are excellent radical capturing reagents (11,14% we thought that they would serve as capping reagents for polymer-end radicals. Indeed, polyMMA with low polydispersity was obtained by the addition of one equiv of dimethyl ditelluride (PD = 1.16, entry 19). Initiator l a also polymerized M M A with highly controlled manner in the presence of one equiv of dimethyl ditelluride (PD = 1.18, entry 20). The molecular weight increased predictably with the amount of M M A used, and high molecular-weight polyMMA formed with precise molecular weight control by the addition of one or two equiv of dimethyl ditelluride (entries 21 - 23). The polymerization completed within 2 h by earring out the reaction at 105 °C with ethyl methacrylate (EMA), and the desired polymer formed with low polydispersity (entry 24). 2-Hydroxyethyl methacrylate (HEMA) could also be polymerized in the presence of dimethyl ditelluride in a highly controlled manner (entry 25).

Confirmation of living character. The "living" character of the current polymerization was ascertained by several control experiments. First, the molecular weight (M ) increased linearly with an increase in the amount of styrene or M M A used as shown above (entries 7, 8 and 21 - 23). Secondly, the molecular weight also increased linearly with an increase of the conversion of styrene (Figure 1). The same experiments with M A and M M A also showed excellent linear relation between the molecular weight and the conversion. Finally, the existence of active carbon-tellurium bond in the polymer end was confirmed by labeling experiments. Thus, treatment of the polymer block 6 prepared from l a and 30 equiv of styrene with either tributyltin hydride or tributyltin deuteride afforded 8 or 8-di quantitatively through the radical n

Conv(%) Figure L Molecular weight (M ) of polySt obtained by the bulk polymerization of styrene (100 equiv) with l a as a function of the conversion of styrene. n


636 intermediate 7 (Scheme 2) (8a). Selective incorporation of the deuterium atom in the polymer was ascertained by the MALDI-TOF mass spectroscopy by observing an increase of one mass numbers in 8-di compared to those in 8 (Figure 2). The H N M R of 8-di further supported the selective incorporation of deuterium at the benzylic position (δ = 2.36 ppm, broad singlet). The results clearly revealed the existence of organotellurium group at the polymer end, 2


Scheme 2.

6 7 ΆΙΒΝ (0.1 equiv), Bu SnH(D) (3 equiv), C H CF , 80 °C, 1 h. 3

6

5

8

3

2600.20 • 2704.36 2808.57

M = 2900 PD=1.08 N

ι

1000

2000

3000 -2601.26 • 2705.54 2809.72

8-di

M = 2800 PD=1.08 N

Mil!

ULULUUUUJJ

1000

2000

mi 3000

JLLLJUL

4000

5000 m/e

Figure 2. The MALDI-TOF mass spectra of protonated- and deuterated polySt 8and8-d].


637


which was reduced by tributyltin hydride (or deuteride). It is also worth mentioning that the differences of each mass peaks in the major series of peaks are 104, which corresponds to the molecular mass of styrene, and that there are essentially no peaks derived from impurities in between the major series of peaks. The results must be attributed to the highly controlled character of TERP, in which the polymerization is initiated by the definite initiating radical generated from l a and proceeds with least unfavorable side reactions. The same deuterium labeling experiments with polyMMA, which was prepared from l a with 30 equiv of M M A , resulted in the virturally same results.

Block copolymer synthesis. The results presented above suggest that the TERP would be suitable for a tailored synthesis of block copolymers composed of different families of monomers using macroinitiators, because the same initiators can control the polymerization of different types of monomers under similar thermal conditions (75). To clarify this point, we next examined the synthesis of AB-block copolymers with all possible combinations of styrene, M M A , and tBA starting from l a as an initiator. We were pleased to find that TERP could synthesize the desired AB-diblock copolymers regardless of the order of first and second monomers (Table 2, entries 1-6). Thus, the A B diblock copolymer of styrene and M M A could be efficiently prepared starting from either the polystyrene block (prepared by l a and styrene) or the polyMMA block (prepared by l a and M M A ) with M M A or styrene, respectively (entries 1 and 3). The AB-diblock copolymers of styrene and tBA, and of M M A and tBA were also synthesized regardless of the order of the added monomers (entries 2 and 4-6) (16). The desired diblock copolymers were obtained in all cases with predictable molecular weight with low polydispersity. Due to the stronger carbon-tellurium bond in poly(tBA) compared with the one in polystyrene and polyMMA, the controllability of the diblock copolymers initiated by the poly(tBA) macroinitiator was slightly less efficient (entries 5 and 6), but is still at an acceptable level (PD < 1.35). Because the order of monomer addition is less important in TERP compared to that of other LRP systems, A B A and A B C triblock copolymers could also be prepared starting from diblock macroinitiators (entries 7-11). Thus, successive treatment of l a with M M A and styrene afforded poly-MMA-Z>polySt macroinitiator, which was further treated with M M A to give the desired poly-MMA-6-polySt-è-polyMMA triblock copolymer with narrow molecular weight distribution (entry 7).The GPC trace of the each block polymers clearly indicates the increase in the molecular weight as the progress of the reaction (Figure 3). A B A triblock copolymer of M M A and tBA could be also prepared by the successive polymerization of M M A , tBA followed by M M A starting from l a (entry 8). The ABC-triblock copolymer of styrene, M M A , and tBA, of M M A , styrene, and tBA, and of M M A , tBA, and styrene could be also synthesized by successive addition of each monomers starting from l a (entries 9


638


Table 3. Synthesis of A B di- and A B A tri- and A B C triblock copolymers using macroinitiators. Entry Macroinitiator (M/PD)' AB Diblock copolymer 1 PolySt (9000/1.15) 2 PolySt (9000/1.15) 3 PolyMMA (8500/1.12/ 4 PolyMMA (8500/1.12/ 5 Poly(tBA) (9600/1.10/ 6 Poly(tBA) (8200/1.19/ ABA Triblock copolymer 7 PolyMMA-6-polySt (18700/1.18) 8 PolyMMA-6-poly(tBA) (11000/1.11) ABC Triblock copolymer PolyST-o-polyMMA 9 (12600/1.30) 1CI PolyMMA-^-polySt (19000/1.13) PolyMMA-Z>-poly(tBA) 11 (11500/1.09)

Monomer MMA tBA St tBA St MMA

C

C

Yield (%)

b

M

n

85 50 85 57 77 88

13900 11300 18800 17100 19200 19500

PD* 1.25 1.18 1.13 1.11 1.32 1.35

MMA

C

65

28100 1.22

MMA

C

83

18600 1.30

tBA

32

16100 1.27

tBA

45

21800 1.18

St

69

21600 1.27

"The macroinitiator was prepared from la and the corresponding monomer according to the conditions shown in Table 1. 100 equiv and 200 equiv of monomers were used for the diblock and triblock copolymer synthesis, respectively. ^Molecular weight (M ) and polydispersity (PD) were determined by size exclusion chromatography calibrated by polySt standards for crude samples. One equiv of dimethyl ditelluride was added. ^Calibrated using polyMMA standards. n

PolyMMA-b-polySt-6-polyMMA

^ PolyMMA-b-polySt PolyMMA

1

10

12

14

16

18

20 (min)

Figure 5. Comparison of GPC traces of the polyMMA, polyMMA-&-polySt, and poryMMA-2>-polySt-ft-polyMMA block copolymers.


639 - 11). These triblock copolymers were obtained in all cases in a highly controlled manner.


Possible mechanisms. Detailed mechanisms of the current polymerization are not clear at the present time. One possible explanation is that tellurium radicals have sufficient lifetime to act as persistent radicals (17). However, tellurium-centered radicals are less persistent than nitroxyl radicals and usually form ditellurides. Indeed, The DFT calculated bond dissociation energy of dimethyl ditelluride is 147 kJ/mol (B3LYP density functionals with LANL2DZ basisSci.for tellurium atom and 6-31G(d) basisSci.for the rest), suggesting that the equilibrium between the methyltellanyl radical and dimethyl ditelluride completely shifts toward dimethyl ditelluride. Therefore, it is unlikely that the methyltellanyl radical acts as a persistent radical. A n alternative mechanism is the ditelluride capping mechanism, in which ditellurides serve as the capping reagent for the reactive polymer ends to give the dormant species (Scheme 3). The effect of the dimethyl ditelluride in the polymerization of M M A strongly suggests that the current polymerization proceeds via the ditelluride-capping mechanism. In this case, the high reactivity of ditellurides toward carbon-centered radicals must be responsible for the high control of the polymerization process (14). However, other possibilities involving the degenerative chain transfer could not be rigorously excluded (18). Further experimental as well as theoretical investigations are required to clarify the mechanism.

Scheme 3.

[•TeMe]

R—TeMe 1

) heat

L

1/2 (TeMe)

2

^ TeMe

[ [•TeMej (n-1)^R-

InTeMe

End-group transformations. Another characteristic advantage of TERP is the versatility of the end-group transformations (Scheme 4), because organotellurium compounds are excellent



640 precursors for carbon-centered radicals (6-8% carbanions (19), and carbocations (20,21). Thus, the radical-mediated transformation through 7 with ethyl tributylstannylmethylacrylate afforded the enoate-functionalized polymer 9 with 61% end-group functionalization (See also Scheme 2). Furthermore, the tellurium-lithium transmetallation by treatment of 6 with buthyllithium followed by trapping of the resulting lithium species 10 with carbon dioxide gave lithium carboxylate 11, which was treated with aqueous HC1 to give carboxylic acid 12. The esterification of 11 with pyrenebutanol under standard Yamaguchi conditions (22) afforded 13, U V spectra of which revealed 86% incorporation of the carboxylate residue to the polymer end. The functional groups in 9,11 and 12 would afford good foundations for the further end-group modifications. Scheme 4.

6

—1

11:R = Li >s -v 12:R = H J 13: R= 1-pyrenebutyl d

J

"AIBN (0.1 equiv), Ethyl tributylstannylmethylacrylate (4 equiv), C H CF , 80 °C, 6 h, BuLi (1.5 equiv), THF, -72 °C, 3 min, C 0 (excess), aq. HC1 (excess), '2,4,6C1 C6H C0C1 (2 equiv), Et N (2 equiv), THF, rt, 1.5 h, then 1-pyrenebutanol (4 equiv), DMAP (4 equiv), CH C1 , rt, 3h. 6

6

C

5

3

rf

2

3

2

3

2

2

Summary Organotellurium compounds initiate living radical polymerization with a variety of vinyl monomers to give structurally defined Macromolecules. A variety of A B - , A B A - , and ABC-block copolymers with defined structures are also prepared using macroinitiators. As anAnal.ogyto the successful synthesis of the block copolymers in Table 2, combined with the data in Table 1, various combinations of multiblock copolymers could possibly be synthesized. Furthermore, random copolymerization using different families of monomers could be also possible. In addition, the versatility of the end-group transformations of the polymer would be also beneficial to add new functions to the polymers. These features clearly indicate that TERP provides a powerful


641 method for the synthesis of functionalized Macromolecules with defined structures. Acknowledgement This work is partly supported by a Grant-in-Aid for Scientific Research from the Japan Society for the Promotion of Science. Experimental assistance of Mitsuru Nakajima is gratefully acknowledged.


References

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642 1992, 114, 7591. (d) Crich, D.; Chen, C.; Hwang, J.-T.; Yuan, H . ; Papadatos, Α.; Walter, R. I. J. Am. Chem. Soc. 1994, 116, 8937. (e) Engman, L . ; Gupta, V . J. Org. Chem. 1997, 62, 157. (f) Lucas, M . Α.; Schiesser, C. H. J. Org. Chem. 1996,61 , 5754. 9. Fischer, H. Chem. Rev. 2001,10 1, 3581. 10. Yamago, S.; Iida, K . ; Yoshida, J. J. Am. Chem. Soc. 2002, 124, 2874. Yamago, S.; Iida, K.; Yoshida, J. Am. Chem. Soc. 2002, 124, 13666. 11. The use of diphenyl ditelluride for the radical capturing reagent in the AIBN-initiated radical polymerization of styrene has been reported. See, Takagi, K.; Soyano, Α.; Kwon, T. S.; Kunisada, H.; Yuki, Y . Polym. Bull. 1999, 43, 143. 12. Skene, W. G.; Belt, S. T.; Connolly, T. J.; Hahn, P.; Scaiano, J. C. Macromolecules 1998, 31, 9103. Moad, G.; Rizzardo, E. Macromolecules 1995, 28, 8722. Hu, Y . ; Wang, S. Q.; Jamieson, A .M.Macromolecules 1995, 28, 1847. 13. Qiu, J.; Matyjaszewski, K. Macromolecules 1997, 30, 5643. 14. Russell, G. Α.; Tashtoush, H. J. Am. Chem. Soc. 1983,10 5, 1398. 15. (a) Hawth, E.; Bosman, Α.; Benoit, D.; Helms, B.; Fréchet, J. M . J.; Hawker, C. J. Macromol. Symp. 2001, 174, 85. Benoit, D.; Chaplinski, V.; Braslau, R.; Hawker, C. J. J. Am. Chem. Soc. 1999, 121, 3904. (b) Davis, Κ. Α.; Matyjaszewski, K. Macromolecules2000,33, 4039. Davis, Κ. Α.; Charleux, B.; Matyjaszewski, K. J. Polym. Sci., Part A: Polym. Chem. 2000, 38, 2274. Cassebras, M.; Pascual, S.; Polton, Α.; Tardi, M.; Vairon, J.-P. Macromol. Rapid. Commun. 1999, 20, 261. (c) Rizzardo, E.; Chiefari, J.; Mayadunne, R.; Moad, G.; Thang, S. Macromol. Symp. 2001, 174, 209. Chong, Y . K . ; Le, T. P. T.; Moad, G.; Rizzardo, E.; Thang, S. H . Macromolecules 1999, 32, 2071. 16. As initiators 1-3 and the macroinitiators are slightly sensitive toward oxygen, the handling of them should be carried out under inert atmosphere using standard Schlenk/Syringe techniques or in a glove box. 17. Yoshikawa, C.; Goto, Α.; Fukuda, T. Macromolecules 2002, 35, 5801. See also ref. 9. 18. Matyjaszewski, K.; Gaynor, S.; Wang, J.-S. Macromolecules 1995, 28, 2093. Goto, Α.; Ohno, K.; Fukuda, T. Macromolecules 1998, 31, 2809. See also, Oka, M . ; Tatemoto, M. In Contemporary Topics in PolymerScience;Bailey, W. J.; Tsuruta, T., Eds.; Plenum: New York, 1984; pp 763-777. 19. Kanda, T.; Kato, S.; Sugino, T.; Kambe, N.; Sonoda, N. J. Organomet. Chem. 1994, 473, 71. Hirao, T.; Kambe, N . ; Ogawa, Α.; Miyoshi, N.; Murai, S.; Sonoda, Ν. Angew. Chem. Int. Ed. Engl. 1987,26 , 1187. 20. (a) Uemura, S.; Fukuzawa, S. J. Chem. Soc. Perkin Trans. 1 1985, 471. (b) Yamago, S.; Kokubo, K.; Hara, O.; Masuda, S.; Yoshida, J. J. Org. Chem. 2002, 67, 8584. Yamago, S.; Kokubo, K.; Murakami, H . ; Mino, Y.; Hara, O.; Yoshida, J. Tetrahedron Lett. 1998, 39, 7905. Yamago, S.; Kokubo, K . ; Yoshida, J. Chem. Lett. 1997, 111. 21. Petragnani, N. Tellurium in Organic Synthesis; Academic Press: London, 1994. Comasseto, J. V . ; Barrientos-Astigarraga, R. E. Aldrichimica Acta; 2000, 33, 66. 22. Inanaga, J.; Hirata, K.; Saeki, H.; Katsuki, T.; Yamaguchi, M . Bull. Chem. Soc. Jpn. 1979, 52, 1989. In Advances in Controlled/Living Radical Polymerization; Matyjaszewski, K.; ACS Symposium Series; American Chemical Society: Washington, DC, 2003.

Living Radical Polymerization - American

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