Living Radical Polymerization of Styrene: RuCl2(PPh

Chapter 12

Living Radical Polymerization of Styrene: RuCl (PPh ) and Alkyl Iodide-Based Initiating Systems 2

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Yuzo Kotani, Masami Kamigaito, and Mitsuo Sawamoto

Department of Polymer Chemistry, Graduate School of Engineering, Kyoto University, Kyoto 606-8501, Japan A series of 1-phenylethyl halides [CH CH(Ph)X: X = I, Br, and Cl] were employed as initiators for living radical polymerization of styrene with ruthenium(II) dichlorotris(triphenylphosphine) [RuCl (PPh ) ] in the presence of Al(Oi-Pr) in toluene at 100 °C. With X = I, the number-average molecular weights (M ) were controlled by the feed ratio of the monomer to the initiator, and the molecular weight distributions (MWDs) were relatively narrow (M /M ~ 1.5). In contrast, the MWDs were broader with X = Br, while the M was controlled. With X = C l , the M was much higher than the calculated values. End-group analysis by H N M R supported that the polymerization proceeds via reversible activation of the terminal C-I bond derived from CH CH(Ph)I as the initiator. In addition, F(CF ) I and C H I were effective for the styrene living polymerization. Ti(Oi-Pr) was also effective as additives, which induced faster polymerization than that did Al(Oi-Pr) at 60 °C. The resulting polystyrene with Al(Oi-Pr) and Ti(Oi-Pr) showed narrow MWDs (M /M ~ 1.2).

Downloaded by FUDAN UNIV on January 9, 2017 | http://pubs.acs.org Publication Date: August 15, 2000 | doi: 10.1021/bk-2000-0768.ch012

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Introduction The last several years have witnessed remarkable developments in control of radical polymerization, among which transition metal complexes had led up to novel living radical polymerization systems (/). The initiating systems that permit precision control of molecular weights and distributions generally consist of alkyl halides as initiators and group 7-11 transition metal complexes as catalysts. Thus far, various kinds of metal complexes, such as Ru(II) (2-6), Cu(I) (7-/2), Fe(II) (13, 14% Ni(II) (75-77), Ni(0) (18, 79), Rh(I) (20, 21), Pd(II) (22), and Re(V) (23) with suitable ligands, have been employed for expanding the scope of the living radical polymerization. Design and use of a suitable metal complex for a certain monomer seems necessary to achieve the living radical polymerization that involves reversible Corresponding author.

168

© 2000 American Chemical Society

Matyjaszewski; Controlled/Living Radical Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 2000.

169 and homolytic cleavage of carbon-halogen ( C - X ) terminal via single-electron redox reaction of the metal center [ — C - X + M(n) ^ C» X-M(n+1)] (ig lh). We have developed Ru(H)-based initiating systems for methyl methacrylate ( M M A ) living radical polymerization, which consist of RuCl (PPh ) , various alkyl chlorides or bromides ( R - X ) , and aluminum alkoxides (2-5). As indicated in Scheme 1, for the Ru(II)-mediated system, the homolytic cleavage of the C - X bond in the initiator ( R - X ) occurs via a single electron oxidation reaction of Ru(II), followed by the addition of R« to the monomer, and the generated Ru(III) species is reduced to the original Ru(II) to give an adduct of R - X and the monomer that possesses a terminal C - X bond. The polymerization proceeds via a similar repetitive addition of monomer to the radical species, reversibly generated from the covalent species with a C - X terminal and Ru(II). The RuCl (PPh ) -based initiating systems, initially developed for M M A , have been also applied for acrylates (24), styrenes (25), and acrylamides (26). Styrene was indeed polymerized by CCl /RuCl (PPh ) /Al(0/'-Pr) in toluene at 60 °C but to give polymers with broad molecular weight distributions (MWDs) (MJM = 3-4), in contrast to the narrow MWDs (MJM = 1.2-1.3) of P M M A obtained under similar conditions. t

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R-

R—X (Ru":

XRu

111

-R-CH -CH2

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R-CH -CH-X

-CH -ÇH-

2

2

Al(0/-Pr)

-Ru"

ό

RuCI (PPh ) ) 2

XRu'III

X R u.III "

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Living Polymer Ru"

Rww^c- XRu Dormant (Covalent)

m

Active (Radical)

Scheme 1. Living radical polymerization of styrene with Ru(ll) complex.

This paper deals with new haloalkyl initiators ( R - X ; X = C l , Br, I) for the RuCl (PPh ) -mediated living radical polymerization of styrene (Scheme 2). The halide initiators should be carefully selected so that the C - X bond is reactive enough to generate radical species [C» XRu(III)] at a considerable rate via interaction with RuCl (PPh ) . For this, the choice of both the alkyl group (R) and the halogen (X) in R - X is important. Especially, the halogen in R - X , which will be transferred to the growing polymer terminal (R C - X ) , is crucial for the control of the polymerization, because it affects the rate of interconversion between the dormant and the active species as well as the stability of the growing terminal. The reactivity of C - X bonds in Kharasch addition reactions via peroxy and related free radicals is in the following 2

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170 order; C - I > C - B r > C-CI (27), which agrees with their bond dissociation energy (28). Because of this, iodo-compounds have often been employed for free radical addition reactions (29). In addition, the C - X bond activation with an iridium(I) complex via single electron transfer is significantly slower for CC1 than for C B r or C I (30). 4

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Initiators (R-l): CH H C-Ç—1 3

CH —CH—X 3


[A]

(X:CI,Br,l)

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3 3

Additives: 3

Ti(OJ-Pr)

Πιι»

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AI(Oi-Pr)

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|^HU^.....pp

Ph P^

CHI

?=° OEt

Ruthenium(ll) Complex: RuCI (PPh )

C

F(CF ) I

3

h 3

\ \

Scheme 2. Ru(II)-Based initiating systems for living radical polymerization of styrene.

The use of alkyl iodides for controlled radical polymerization was first reported by Tatemoto (31), where fluorinated monomers such as C F C F were polymerized by K S 0 in the presence of fluoroalkyl iodides such as F(CF ) I. Similar systems were also applied for styrene (32-35), acrylates (33, 34), and vinyl acetate (36) to give polymers with controlled molecular weights, although the control seems inferior to that with the metal catalyzed systems. However, alkyl iodides have rarely been employed in metal-mediated radical additions, where usually chlorides or bromides are preferentially employed. There were only a few examples coupled with zerovalent metals like Cu and A g for the radical addition reactions (37) and just a preliminary report for styrene polymerization (38). With these backgrounds, we employed three 1-phenylethyl halides [CH CH(Ph)X: X = CI, Br, and I], unimer models of polystyrene with a C - X terminal, as initiators for the Ru(II)-mediated living radical polymerization of styrene. Among the three halogens, iodine proved very effective for this purpose. 2

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Results and Discussion Effects of Initiator-Halogens The three phenylethyl halides were employed as initiators for the polymerization of styrene to be coupled with RuCl (PPh ) in the presence of Al(0/-Pr) in toluene at 2

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171 100 °C. A l l three systems induced polymerization without an induction phase, and monomer conversion reached over 90% within 10-14 h (Figure 1). The polymerization with CH CH(Ph)I proceeded faster than that with CH CH(Ph)Br or CH CH(Ph)Cl. Without Al(0/-Pr) , almost no polymerization proceeded. 3

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100

ι

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(MfSl Ο: Cl Ο: Br I

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I

10

15

Time, h Figure 1. Polymerization of styrene with CH CH(Ph)X (X = CI, Br, and I)/ RuC^fPPh^j/AlfOi-PrJj in toluene at 100 °C: [styrene] = 6.0 M; [CH CH(Ph)X] = 60 mM; [RuCl (PPh^] = 30 mM; [Al(Oi-Pr) ] = 100 mM. 3

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The M and M W D of the obtained polystyrene depended on the initiator halogens, more than polymerization rate did, as shown in Figure 2. With CH CH(Ph)I or CH CH(Ph)Br, the M increased with monomer conversion and almost agreed with the calculated values based on the assumption that one molecule of the initiator generates one living polymer chain. Furthermore with the iodide, the polydispersity ratios remained narrow (MJM ~ 1.5) throughout the polymerization. CH CH(Ph)Cl gave polymers with broad M W D s (MJM ~ 2) and much higher M (M - 2 χ 10 ), independent of conversion. This is due to the greater bond strength of C - C l , which in turn leads to a slow initiation from the chloride and to a slow interconversion between the dormant and the active species (cf. Scheme 1). In contrast, with the bromide- and the iodide-based initiating systems, the initiation occurs enough fast to control the molecular weights. However, the MWDs with the bromide were still broad probably due to slow exchange reaction. Among the halides, the CH CH(Ph)I-based initiating system proved the best for the living radical polymerization of styrene mediated by RuCl (PPh ) . Thus, the following section will discuss the details on this CH CH(Ph)I-based initiating system. n

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172

Figure 2. M,„ MJM , and SEC curves of polystyrene obtained with CH CH(Ph)X (X = CI, Br, and l)/RuCl (PPh ) /Al(Oi-Pr) in toluene at 100 °C: [styrene] = 6.0 M; [CH CH(Ph)X] = 60 mM; [RuCl (PPh ) ] = 30 mM; [Al(Oi-Pr) ] = 100 mM. n

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C H C H ( P h ) I Initiating System 3

Effects of Monomer Concentration A series o f styrene polymerizations were carried out using C H C H ( P h ) l / R u C l ( P P h ) / A l ( 0 / - P r ) system in toluene at 100 °C at varying initial monomer concentrations ( [ M ] ) , while the initial ratio o f the styrene to the initiator, 3

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Time, h Figure 3. First-order plots for the polymerization of styrene with CH CH(Ph)l/ RuCl (PPh )/Al(Oi-Pr) in toluene at 100 °C: [styreneMCH CH(Ph)lJo/ [RuCl (PPh ) MAl(Oi-Pr) ] = 6000/60/30/100 mM (Θ); 4000/40/20/80 mM (A); 2000/20/10/40 mM (O). 3

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173 [M] /[CH CH(Ph)I]o, was fixed at 100 (Figure 3). At any [M] , styrene polymerization occurred without induction phase. The lower [M] , the slower the polymerization; for example, time for 50% monomer conversion was 3, 5, and 19 h at [M] = 6.0, 4.0, and 2.0 M , respectively. As shown in Figure 3, the logarithmic conversion data, ln([M] /[M]) plotted against time t, gave straight line at [M] = 6.0 M over 90%, which shows constant concentrations of growing species during the polymerization. However, at lower [ M ] (4.0 M or 2.0 M), the plots shows downward curvatures, and then the polymerization ceased around 80-85% monomer conversion. Figure 4 shows the M , MJM and MWDs of polystyrene obtained under the same conditions indicated for Figure 3. The M of the polystyrene obtained with [ M ] = 6.0 M increased in direct proportion to monomer conversion over 90%. The M also increased even at the lower [M] , although the polymerization was not quantitative. This showed no chain transfer and no recombination but primary termination reaction like elimination of hydrogen iodide from the polymer terminal during the polymerization at lower [M] (4.0 M and 2.0 M). The MWDs obtained at [M] = 4.0 and 6.0 M were relatively narrow and almost constant (MJM = 1.4-1.5) throughout the reaction whereas the MWDs at lower [ M ] (2.0 M) were became broader with conversion. This suggests the existence of dead polymer chain. 0

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Figure 4. M„, MJM and SEC curves of polystyrene obtained with CH CH(Ph)l/ RuCl (PPh^Al(Oi-Pr) in toluene at 100 °C: [styreneMCH CH(Ph)I]o/ [RuO/PPhJJo/fAliOi-PrJJo = 6000/60/30/100 mM (Φ, A); 4000/40/20/80 mM (Θ, A); 2000/20/10/40 mM (O, A). m

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End Group Analysis In order to clarify these results, the terminal structure of the obtained polystyrene was investigated by H N M R spectroscopy. Figure 5 shows the Ή N M R spectra (4.0-6.4 ppm) of the polystyrenes obtained with CH CH(Ph)I/RuCl (PPh ) /Al(0/Pr) in toluene at 100 °C. The absorption around 4.6 ppm (peak a) is attributed to the l

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174 methine proton adjacent to the terminal iodine, and peak b (the small absorption near peak a) is from the - C - C l terminal generated through the halogen-exchange reaction between the - C - I ω-end and the R u C l complex (4, 39, 40). At an early stage of polymerization (conversion ~ 40%), the peak a could be observed in both spectra for [M] = 6.0 M and 2.0 M ( A l and B l in Figure 5, respectively), and the numberaverage end functionality (F ) for the whole halogen end (a + b) was 0.78 and 0.62, respectively. After the polymerization proceeded, however, peak a became small [F (a+b) = 0.36], then new peaks c and d appeared around 6.1 ppm at [ M ] = 2.0 M (B2). The new peaks c and d are attributed to the olefin proton of the dead polymer chain produced via β-Η elimination from the ω-end (denoted in Figure 5). On the other hand, almost no olefin-related peak was observed and peak a still remained in the spectrum (A2) for [ M ] = 6.0 M [F (a+b) = 0.71]. These results prove that the C-I growing terminal is maintained throughout the polymerization even at 100 °C at high monomer concentrations, though some of them are replaced with chlorine. The propagation reaction is considered to compete with the /3-H elimination and the former is faster at a higher monomer concentration. However, at the later stage of the polymerization at [ M ] = 2.0 M , the monomer concentration decreases so that the 2

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ÇH-CH -CH—I

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Figure 5. H NMR spectra of polymers obtained with CH CH(Ph)I/RuCl (PPhj)/ Al(Oi-Pr) in toluene at Î00 °C: [styrene]^[CH CH(Ph)l]J[RuCl (PPh^JJ[Al(OiPr)jJ = 6000/60/30/100 mM(Al andA2); 2000/20/10/40 mM (Bl andB2). 3

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175 iodide terminal is converted to the olefinic terminal via j3-H elimination. analytical data are consistent with the results shown in Figures 3 and 4.

These

Molecular Weight Control with CH CH(Ph)l To confirm the living nature of the polymerization at [ M ] = 6.0 M , the monomer-addition experiment was carried out (Figure 6); thus styrene (100 equiv to the initiator) was polymerized with the CH CH(Ph)I/RuCI (PPh )3/Al(0/-Pr)3 system in toluene at 100 °C, and a fresh feed of styrene (100 eq) was added to the reaction mixture when the initial charge had almost been consumed. The M of the polystyrene further increased in direct proportion to monomer conversion after monomer addition and agreed with the calculated values based on the monomer/initiator ratio. Furthermore, the polymer MWDs showed no shoulder and remained narrow in the second-phase. These results demonstrate that living polymerization of styrene was achieved with CH CH(Ph)I. High molecular weight polystyrenes were also synthesized with the same initiating system; thus, styrene, 400 eq to the initiator, was polymerized with the same system in bulk at 100 °C (Figure 7). The polymerization proceeded faster than that in toluene to reach 90% in 48 h. The SEC curves were unimodal and shifted to high molecular weight as the polymerization proceeded. The M increased linearly up to ~ 5 χ 10 with conversion, and the MWDs were narrow (MJM = 1.3-1.4). 3

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Figure 6. M M /M„, and SEC curves of polystyrene obtained in a monomer-addition experiment with CH CH(Ph)I/RuCl (PPh )/Al(Oi-Pr) in toluene at 100 °C: fstyreneJo = [styrene] = 6,0. M; [CH CH(Ph)l] = 60 mM; [RuCl (PPh^ ] = 30 mM; [Al(Oi-Pr) J = W0 mM. The diagonal solid line indicates the calculated M„ assuming the formation of one living polymer per CH CH(Ph)I molecule. tp

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Figure 7. Bulk polymerization of styrene with CH CH(Ph)l/RuCl (PPh ) /Al(Oi-Pr) at 100 °C. [styrene]ο = 8.0 Μ (Φ) and 2.0 M (O); [CH CH(Ph)l] = 20 mM; [RuCl (PPh ) ] = 10 mM; [Al(Oi-Pr) ] = 40 mM. 3

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IodoalkyI Initiators and Metal Alkoxide Additives Other than CH CH(Ph)l, perfluoroalkyl iodide [F(CF ) 1] and iodoform (CHI ) were employed with RuCl (PPh ) /Al(0/-Pr) in bulk at 100 °C (Figure 8). Although both iodoalkyl compounds give initiating radicals different in structure from the 3

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Figure 8. M MJM and SEC curves of polystyrene obtained with R-l/ RuCl (PPh )/Al(Oi-Pr) at 100 °C: [styrene] = 8.0 M; [R-l] = 20 mM; [RuCl/PPhJJo = 10 mM; [Al(Oi-Pr)J = 40 mM. R-l: CH CH(Ph)I (Q A); F(CF ) l(Q A);CHl (0 A). m

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177 styrene radical, they could initiate styrene polymerization at almost the same rate as with CH CH(Ph)I. The M of the polystyrene increased linearly with conversion and showed good agreement with the calculated values. With F(CF ) I, the M W D was initially very broad due to its slow initiation but narrowed as the polymerization proceeded. On the other hand, the polystyrene with CHI showed a narrow distribution throughout the polymerization, which was incomplete, however. As an additive, Ti(0/-Pr) was employed in place of Al(0/-Pr) . In the presence of these isopropoxides, styrene was polymerized with an α-haloester initiator, (CH ) C(C0 Et)I, and RuCl (PPh ) in toluene at 60 °C. It took 100 h for 90% conversion with Ti(0/-Pr) , whereas 500 h with Al(0/-Pr) . The trend is the same as for the Ru(II)-mediated polymerization of M M A (41). The M of the polystyrene with both additives increased in direct proportion to monomer conversion and well agreed with the calculated values. As shown in Figure 9, the G P C curves exhibited narrow MWDs (MJM ~ 1.2). Thus, not only Al(0/-Pr) but Ti(OZ-Pr) was proved to be efficient additives on the living radical polymerization of styrene. 3

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Figure 9. Polymerization of styrene with (CH ) C(C0 Et)l/RuCl (PPh )/Al(Oi-Pr) or Ti(Oi-Pr) in toluene at 60 °C: [styrene] = 6.0 M; [(CHj) C(CO Et)l] = 60 mM; [RuCl (PPh )J = 10 mM; [Al(Oi-Pr)J = [Ti(Oi-Pr) ] =100 mM. J 2

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Conclusions In conclusion, CH CH(Ph)I has proved to induce living radical polymerization of styrene in conjunction with RuCl (PPh ) in the presence of Al(0/-Pr) in toluene or bulk (42). The corresponding bromide [CH CH(Ph)Br] was also effective but gave broad MWDs. The chloride [CH CH(Ph)Cl] resulted in much higher molecular weight than the calculated values and broad MWDs. The end-group analysis by Ή N M R shows that the C - I growing terminal remained intact without /3-elimination 3

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178 reaction throughout the polymerization even at 100 °C under high monomer concentration. Not only CH CH(Ph)I but F(CF ) I, C H I , and (CH ) C(C0 Et)I serve as effective initiators. Also, in the presence of Ti(0/-Pr) , living polymerization proceeded faster to yield polystyrene with narrow MWDs (MJM ~ 1.2). 3

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Experimental


Materials Styrene (Wako Chemicals; purity > 99%) was dried overnight over calcium chloride and distilled twice over calcium hydride under reduced pressure before use. RuCl (PPh ) (Merck; purity > 99%), Al(0/-Pr) (Aldrich; purity > 99.99%), and Ti(OZ-Pr) (Kanto Chemicals; purity > 97%) were used as received and handled in a glove box ( M . Braun) under dry (< 1.0 ppm) and oxygen-free (< 1.0 ppm) argon. Toluene (solvent) and tetralin (internal standards for gas chromatographic analysis of styrene and M M A ) were dried overnight over calcium chloride, distilled twice over calcium hydride, and bubbled with dry nitrogen for more than 15 min immediately before use. 2

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Initiators CH CH(Ph)Br and CH CH(Ph)Cl (both Tokyo Kasei; purity > 99%) were dried overnight over calcium chloride and distilled twice over calcium hydride under reduced pressure before use. CH CH(Ph)I was prepared by adding solution of 1.04 M HI solution (in /î-hexane, 0.5 mL) into styrene (250 m M in toluene, 1.58 mL) at -20 °C. C H I (Wako; purity > 97%) and F(CF ) I iodide (Tokyo Kasei; purity > 98%) were used as received. Ethyl 2-iodoisobutyrate ( C H ) C ( C 0 C H ) I was prepared by the method of Curran et al. (29); bp 50 °C/9 torr; identified by 500 M H z H N M R . Anal. Calcd for C H 0 I : C, 29.8, H , 4.58, I, 52.4. Found: C, 29.7, H 4.59, I, 52.3. 3

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Polymerization Procedures Polymerization was carried out by the syringe technique under dry nitrogen in sealed glass tubes. A typical example for polymerization of styrene with CH CH(Ph)I/RuCl (PPh ) /Al(0/-Pr) is given below. Al(0/-Pr) (0.1916 g) was dissolved with styrene (6.46 mL) and tetralin (1.35 mL). Then this aluminum solution (6.81 mL) and a toluene solution of CH CH(Ph)I (0.960 mL) were added into RuCl (PPh ) (0.2301 g), sequentially in this order. Immediately after mixing, the solution was placed in an oil bath at 100 °C. The polymerization was terminated by cooling the reaction mixtures to -78 °C. Monomer conversion was determined from the concentration of residual monomer measured by gas chromatography with tetralin as internal standards for styrene. The quenched reaction solutions were diluted with toluene (-20 mL) and rigorously shaken with an absorbent [Kyowaad-2000G-7 ( M g A l 0 , ) ; Kyowa Chemical] (~5 g) to remove the metal-containing residues. 3

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179 After the absorbent was separated by filtration (Whatman 113V), the filtrate was washed with water and evaporated to dryness to give the products, which were subsequently dried overnight. Measurements The M W D , M , and MJM ratios of the polymers were measured by sizeexclusion chromatography (SEC) in chloroform at room temperature on three polystyrene gel columns (Shodex K-805L x 3) that were connected to a Jasco PU-980 precision pump, a Jasco 930-RI refractive index and 970-UV ultraviolet detectors. The columns were calibrated against 11 standard polystyrene samples (Polymer Laboratories; M = 580-1547000; MJM < 1.1) as well as the monomer. H N M R spectra were recorded in CDC1 at 40 °C on a JEOL JNM-LA500 spectrometer, operating at 500.16 M H z . Polymers for H N M R analysis were fractionated by preparative SEC (column: Shodex K-2002). n

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Acknowledgments With appreciation M.S. and M . K . acknowledge the support from the New Energy and Industrial Technology Development Organization (NEDO) under the Ministry of International Trade and Industry (MITI), Japan, through the grant for "Precision Catalytic Polymerization" in the Project "Technology for Novel High-Functional Materials" (fiscal 1996-2000). Y . K . is grateful to the Japan Society for the Promotion of Sciences (JSPS) for the JSPS Research Fellowships for Young Scientists and also to the Ministry of Education, Science, Culture, and Sports, Japan for the partial support of this work by the Grant-in-Aid for Scientific Research (No. 3370).

References and Notes 1.

For recent reviews on living radical polymerizations, see: (a) Georges, M . K.; Veregin, R. P. N.; Kazmaier, P. M.; Hamer, G. K . Trends Polym. Sci. 1994, 2, 66. (b) Davis, T. P.; Kukulj, D.; Haddleton, D. M . ; Maloney, D. R. Trends Polym. Sci. 1995, 3, 365. (c) Malmstöm, Ε. E.; Hawker, C. J. Macromol. Chem. Phys. 1998, 199, 823. (d) Sawamoto, M.; Kamigaito, M. Trends Polym. Sci. 1996, 4, 371. (e) Colombani, D. Prog. Polym. Sci. 1997, 22, 1649. (f) Controlled Radical Polymerization; Matyjaszewski, K. Ed.; A C S Symposium Series 685; American Chemical Society: Washington DC, 1998. (g) Sawamoto, M . ; Kamigaito, M. In Synthesis of Polymers (Materials Science and Technology Series), Schluter, A . D., Ed.; Wiley-VCH, Weinheim, Germany, Chapter 6, 1999. (h) Sawamoto, M . ; Kamigaito, M . CHEMTECH 1999, 29 (6), 30. (i) Patten, T. E.; Matyjaszewski, K. Adv. Mat. 1998, 10, 901. (j) Matyjaszewski, K . Chem. Eur. J. 1999, 5, 3095. (k) Patten, T. E.; Matyjaszewski, K. Acc. Chem. Res. 1999, 32, 895.


180 2. 3.


4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31.

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181 32. Kato, M . ; Kamigaito, M.; Sawamoto, M.; Higashimura, T. Polym. Prepr. Jpn. 1994, 43 (2), 255. 33. Matyjaszewski, K.; Gaynor, S. G.; Wang, J. -S. Macromolecules 1995, 28, 2093. 34. Gaynor, S. G.; Wang, J. -S.; Matyjaszewski, K . Macromolecules 1995, 28, 8051. 35. Lansalot, M . ; Farcet, C.; Charleux, B.; Vairon, J.-P.; Pirri, R. Macromolecules 1999, 32, 7354. 36. (a) Ueda, N.; Kamigaito, M.; Sawamoto, M . Polym. Prepr. Jpn. 1996, 45, 1267; 1997, 46, 149; 1998, 47, 134. (b) Ueda, N.; Kamigaito, M.; Sawamoto, M . M A C R O 98 Preprints, p 237. 37. Metzger, J. O.; Mahler, R. Angew. Chem. Int. Ed. Engl. 1995, 34, 902. 38. Devis, Κ.; O'Malley, J.; Paik, H.-J.; Matyjaszewski, K. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 1997, 38 (1), 687. 39. Matyjaszewski, K.; Shipp, D. Α.; Wang, J.-L.; Grimaud, T.; Patten, T. E. Macromolecules 1998, 31, 6836. 40. Haddleton, D. M . ; Heming, A . M.; Kukulj, D.; Jackson, S. G . J. Chem. Soc. Chem. Commun. 1998, 1719. 41. Hamasaki, S.; Kamigaito, M . ; Sawamoto, M . Polym. Prepr. Jpn. 1998, 47 (8), 1582. 42. The contribution of the iodine-transfer polymerization (31) may be clarified by the method of Fukuda (43). However, we do not estimate it significant, mainly due to the following reasons. In this Ru(II)-mediated system, the obtained M increased linearly with conversion from the initial stage, whereas the conversionM profile usually shows a downward curvature in the iodine-transfer systems (32-34). Second, the MWDs (Figure 9) were narrower than those in the iodinetransfer polymerization. Third, the occurrence of halogen-exchange reactions (Figure 5) apparently shows the radical formation process assisted by Ru(II). 43. Ohno, K.; Goto, Α.; Fukuda, T.; Xia, J.; Matyjaszewski, K. Macromolecules 1998, 31, 2699. n

n


Living Radical Polymerization of Styrene: RuCl2(PPh

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