Controlled/living polymerization of methyl methacrylate using new sterically hindered imidazoline nitroxides prepared via intramolecular 1,3-dipolar cycloaddition reaction

Article abstract of DOI:10.1002/pola.27071

A series of imidazoline nitroxides with bulky spirocyclic moieties at the positions 2 or 5 of imidazole ring were synthesized using intramolecular 1,3-dipolar cycloaddition in 2H-imidazole 1-oxides or 4H-imidazole 3-oxides with pent-4-enyl groups followed by isoxazolidine ring opening and oxidation. Capability of the nitroxides to control radical polymerization of methyl methacrylate (MMA) and styrene was investigated. For that purpose, alkoxyamines were synthesized from the aforementioned nitroxides and tert-butyl α-bromoisobutyrate. Homolysis rate constants of the alkoxyamines were measured and possible contributions of side reactions were quantified. Nitroxide-mediated polymerization of styrene and MMA was studied using the alkoxyamines as initiators. MMA polymerization was found to proceed in controlled regime up to 55% of monomer conversion and the polymer obtained was able to reinitiate the polymerization of styrene. Quota of living chains estimated to reach 90%.

Full text of DOI:10.1002/pola.27071

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Controlled/Living Polymerization of Methyl Methacrylate Using New
Sterically Hindered Imidazoline Nitroxides Prepared via Intramolecular
1,3-Dipolar Cycloaddition Reaction
Mariya V. Edeleva,1 Dmitriy A. Parkhomenko,1,2 Denis A. Morozov,2,3 Sergey A. Dobrynin,2,3
Dmitry G. Trofimov,3 Beket Kanagatov,1,2 Igor A. Kirilyuk,3 Elena G. Bagryanskaya1,3
1International Tomography Center SB RAS, Institutskaya 3A, Novosibirsk 630090, Russia
2Novosibirsk State University, Pirogova 2, Novosibirsk 630090, Russia
3N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Pr. Lavrentjeva 9, Novosibirsk 630090, Russia
Correspondence to: M. V. Edeleva (E-mail: masha@tomo.nsc.ru)
Received 5 August 2013; accepted 10 December 2013; published online 27 December 2013
DOI: 10.1002/pola.27071
ABSTRACT: A series of imidazoline nitroxides with bulky spirocy-
clic moieties at the positions 2 or 5 of imidazole ring were syn-
thesized using intramolecular 1,3-dipolar cycloaddition in 2H-
imidazole 1-oxides or 4H-imidazole 3-oxides with pent-4-enyl
groups followed by isoxazolidine ring opening and oxidation.
Capability of the nitroxides to control radical polymerization of
methyl methacrylate (MMA) and styrene was investigated. For
that purpose, alkoxyamines were synthesized from the afore-
mentioned nitroxides and tert-butyl a-bromoisobutyrate. Homol-
ysis rate constants of the alkoxyamines were measured and
possible contributions of side reactions were quantified.
Nitroxide-mediated polymerization of styrene and MMA was
studied using the alkoxyamines as initiators. MMA polymeriza-
tion was found to proceed in controlled regime up to 55% of
monomer conversion and the polymer obtained was able to
reinitiate the polymerization of styrene. Quota of “living” chains
C
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estimated to reach 90%. 2013 Wiley Periodicals, Inc. J. Polym.
Sci., Part A: Polym. Chem. 2014, 52, 929–943
KEYWORDS: block copolymers; kinetics (polym.); living radical
polymerization (LRP); methyl methacrylate; NMR
ogy for bulk production of high quality polymer of this type
is of current importance. The best results on NMP of methyl
methacrylate (MMA) were achieved when 2,2-diphenyl-3-
phenylimino-2,3-dihydroindol-1-yloxyl nitroxide (DPAIO) was
used as mediator for polymerization control.26 No H-transfer
reaction was detected for this nitroxide.27 Polymerization of
MMA using DPAIO as a mediator allowed to reach 60% of
monomer conversion in bulk at 100 ꢀC. However, DPAIO is
not suitable for the controlled polymerization of styrene
(Sty) due to extremely high activation energy of homolysis of
corresponding alkoxyamine. Therefore, preparation of
pMMA-b-pSty copolymers is hardly achievable using this
nitroxide. Moreover, the polymer formed in NMP controlled
by DPAIO nitroxide was not able to reinitiate polymerization
due to side reaction of NAO bound fragmentation in corre-
sponding alkoxyamine.16,26 Other approach that permits
NMP of MMA has been proposed by Charleux et al.28,29 It
implies addition of small amount of styrene or acrylonitrile,
which allows controlled NMP of MMA with N-tert-butyl-N-[1-
diethylphosphono-(2,2-dimethylpropyl)] nitroxide (SG1) as
mediator. In this case, polymerization can be conducted at
INTRODUCTION Nitroxide-mediated polymerization (NMP) is
a powerful technique for preparation of low polydispersity,
end-functionalized polymeric materials.1–5 The technique
was first successfully applied for styrene polymerization
using commercially available nitroxide 2,2,6,6-tetramethylpi-
peridine N-oxide (TEMPO).6,7 Since that many new nitroxides
have been designed for the application as control agents in
NMP-enabling controlled polymerization of styrenic and
acrylic monomers and preparation of well-defined block
copolymers.8,9 There are a number of methods in NMP that
allow for the controlled polymerization of a broad range of
monomers. They include the variation of polymerization con-
ditions, for example, temperature, pressure, solvents, or
polarity of the medium.10–14 The latter leads to protonation/
deprotonation of functional substituents in alkoxyamines and
nitroxides, which affects either on the initiation or polymer-
ization rate. Methacrylates is one of monomer families which
are hard to polymerize via NMP due to the side reactions of
b-hydrogen atom transfer via intramolecular or radical path-
way.15–19 It should be noted that pMMA-b-pSty copolymers
possess valuable functional properties,20–25 so the technol-
Additional Supporting Information may be found in the online version of this article.
C
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CHART 1 The structures of nitroxides, alkoxyamines, and their decomposition products.
78 ꢀC in controlled regime up to 60% of monomer conver-
sion with formation of perfectly “living” polymer. This
approach has the only drawback that it does not allow for
the preparation of pure p-MMA. Even small amount of como-
nomer can alter properties of the polymer formed as exem-
plified by the change in properties of block-like
copolymers.30 Thereby, an efficient mediator of NMP of MMA
is not found yet.
EXPERIMENTAL
General
5-Bromo-1-pentene was purchased from ABC; copper (II) tri-
fluoromethane sulfonate was obtained from Alfa Aesar; and
all other chemicals were purchased from Aldrich and used as
received. Monomers were distilled before use. The 2H-imidaz-
ole 1-oxides 4a-c38 and 4,4-dimethyl-5-phenyl-4H-imidazole
3-oxide39 were prepared according to literature protocols.
Imidazoline nitroxides are known to be efficient mediators
of styrene polymerization.31–35 Recently, we reported synthe-
sis of a series of sterically hindered imidazoline nitroxides
and corresponding alkoxyamines. Studies of their thermal
decomposition revealed very low rates of H-transfer reac-
tion.17 One of these alkoxyamines (1, Chart 1) has been even
successfully applied for NMP of MMA although polymer
formed was not “living” due to thermal degradation of the
corresponding nitroxide. Mechanism of the nitroxide decom-
position was shown to imply homolytic detachment of tert-
butyl group from the a-carbon of nitroxyl group. One could
expect that replacement of tert-butyl group with spirocyclic
moiety may increase in thermal stability retaining high
degree of sterical hindrance.
1H NMR spectra were recorded at 300 or 400 MHz, and 13C
NMR spectra were recorded at 75 or 100 MHz.1H and 13C
chemical shifts (d) were internally referenced to the residual
solvent peak. IR spectra were acquired on FTIR spectrometer
in KBr and are reported in wave numbers (cm21). Reactions
were monitored by TLC using UV light (254 nm) and/or
aqueous permanganate for visualization. Column chromatog-
raphy was performed on silica gel 60 (702230 mesh).
Synthesis
See Scheme 1.
Pent-4-enyl Nitrones 5a–d (General Procedure)
A solution of pent-4-enylmagnesium bromide was prepared via
slow addition of a 5-bromopentene-1 (2.38 g, 16 mmol) and dry
Et2O (20 mL) mixture to a suspension of Mg chips (0.49 g, 20.4
mmol) in dry Et2O (20 mL). Then a solution of nitrone 4a–d
(13.3 mmol) in a mixture of dry Et2O (20 mL) and dry benzene
(20 mL) was added dropwise. The reaction mixture was stirred
for 325 h, quenched with water (15 mL). Organic layer was sep-
arated and manganese dioxide (10 g, 115 mmol) was added. The
mixture was stirred for 2 h, the oxidant was filtered off, the solu-
tion was concentrated in vacuum, and the residue was separated
using column chromatography on silica gel using hexane-diethyl
ether mixture 1:1 as an eluent to give the alkenyl nitrones 5a–d.
We have recently demonstrated that intramolecular 1,3-dipo-
lar cycloaddition may be successfully applied to nitroxides
synthesis.36,37 Due to relatively low sensitivity of intramolec-
ular 1,3-dipolar cycloaddition reactions to sterical hindrance,
this method may help in construction of strained spiro-cyclic
moieties adjacent to nitrogen atom, allowing for the synthe-
sis of highly sterically hindered nitroxides. This approach
was successfully used for preparation of nitroxides 2a–d
(Chart ) from 2H-imidazole 1-oxide and 4H-imidazole 3-
oxide derivatives. The nitroxides were converted to corre-
sponding alkoxyamines 3a–d. The thermal homolysis/refor-
mation of the later was studied using NMR to evaluate the
applicability of the nitroxides 2a–d as mediators for NMP.
The nitroxides 2a–d were found to be efficient mediators of
NMP of styrene and MMA.
2,2-Diethyl-5-(pent-4-enyl)-4-phenyl-2H-imidazole 1-oxide
(5a)
Yield: 70%, oil. UV (EtOH) kmax(log e), nm: 231 (3.29), 275
(3.39); IR (neat) m, cm21: 698.2, 771.5, 914.2, 1008.7,
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SCHEME 1 Synthesis of the nitroxides 2a–d and alkoxyamines 3a–d: (i) CH2@CH(CH2)3MgBr; (ii) PbO2; (iii) 110 ꢀC; (iv) Zn/AcOH
(Method A) or Ti(O-iPr)4/EtMgBr (Method B); (v) MCPBA; (vi) BrCMe2COOtBu, Cu, Cu(OTf)2.
1197.8, 1278.8, 1305.8, 1350.1, 1384.9, 1448.5, 1516.0,
1564.2, 1589.3, 1641.4, 2858.4, 2879.6, 2929.8, 2974.1. 1H
NMR (400 MHz, CDCl3): d 5 0.47 (t, J 5 7, 6H) and 1.84–2.13
(m, 4H), (23Et), 1.49–1.61 (m, 2H, 6CH2), 1.84–2.13 (m, 2H,
1211.2, 1384.8, 1448.4, 1481.2, 1515.9, 1562.2, 2871.7,
2957.6, 3062.7; 1H NMR (400 MHz, CDCl3): d 5 1.60–1.69
(m, 2H, 6CH2), 1.96–2.11 (m, 8H) and 2.18–2.27 (m, 2H)
(53CH2), 2.69–2.75 (m, 2H, 4CH2), 4.90–4.98 (m, 2H, 8CH2);
5.71 (tdd, Jt 5 6.7, Jd1 5 10.2, Jd2 5 17, 1H, 7CH), 7.43–7.50
(m, 3H) and 7.67–7.72 (m, 2H) (Ph); 13C NMR (100 MHz,
CDCl3): d 5 23.25 and 23.97 (5CH2, 6CH2), 25.85 and 36.92
(spiro-cyclopentane), 32.91 (4CH2), 107.20 (1C), 115.10
(8CH2), 136.88 (7CH), 139.45 (3C), 127.13 (Co, Ph), 128.40
(Cm, Ph), 130.32 (Cp, Ph), 139.45 (Ci, Ph); 165.69 (C@N);
Anal. Calcd for C18H22N2O: C, 76.56; H, 7.85; N, 9.92. Found:
C, 76.49; H, 7.53; N 10.08.
5CH2), 2.58–2.66 (m, 2H, CH2), 4.79–4.89 (m, 2H, CH2), 5.61
(tdd, Jt 5 6.7, Jd1 5 10.4, Jd2 5 17, 1H, 7CH), 7.32–7.41 (m, 3H)
and 7.58–7.64 (m, 2H) (Ph); 13C NMR (100 MHz, CDCl3):
d 5 6.10 (CH3, Et), 29.45 (CH2, Et), 22.94 and 24.05 (5CH2,
6CH2), 33.07 (4CH2), 103.59 (1C), 115.19 (8CH2), 127.04(Co,
Ph), 128.45 (Cm, Ph), 130.47 (Cp, Ph), 132.02 (Ci, Ph), 136.76
(7CH), 141.64 (3C), 168.09 (C@N); Anal. Calcd for C18H24N2O:
C, 76.02; H, 8.51; N, 9.85. Found: C, 76.12; H, 8.86; N 9.92.
4
8
2-(Pent-4-enyl)-3-phenyl-1,4-diazaspiro[4.4]nona-1,3-diene
1-oxide (5b)
Yield: 75%, oil; UV (EtOH) kmax(log e), nm: 218 (3.15), 269
(3.40); IR (neat) m, cm21: 696.2, 773.4, 923.8, 992.3, 1023.1,
2-(Pent-4-enyl)-3-phenyl-1,4-diazaspiro[4.5]deca-1,3-diene
1-oxide (5c)
ꢀ
Yield: 77%, m.p. 37 C (hexane); UV (EtOH) kmax(log e), nm:
230 (3.18), 262 (3.35); IR (KBr) m, cm21: 701, 779, 912,
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1014, 1168.8, 1384.8, 1445.5, 1513.0, 1564.1, 1583.4,
1640.3, 2859.2, 2935.4, 3073.3; 1H NMR (400 MHz, CDCl3):
d 5 1.31–1.47 (m, 3H), 1.80–1.94 (m, 5H), 2.00–2.08 (m, 2H)
and 2.10–2.20 (m, 2H) (63CH2); 1.58–1.68 (m, 2H, 6CH2),
Calcd for C18H24N2O: C, 76.02; H, 8.51; N, 9.85. Found: C,
76.10; H, 8.86; N 10.02.
1-Phenyl-6a,7,8,9-tetrahydro-6H-
4
8
spiro[cyclopenta[c]imidazo[1,5-b]isoxazole-3,1’-
cyclopentane] (6b)
2.70–2.76 (m, 2H, CH2), 4.89–4.98 (m, 2H, CH2), 5.71 (tdd,
7
Jt 5 6.8, Jd1 5 10.2, Jd2 5 17, 1H, CH), 7.43–7.51 (m, 3H), and
Yield: 81%; 121–122 ꢀC (hexane15% CHCl3); UV (EtOH)
7.68–7.75 (m, 2H) (Ph); 13C NMR (100 MHz, CDCl3):
d 5 23.36 (CH2), 24.38 (CH2), 24.67 (CH2), 23.08 (CH2),
34.90 (CH2), 33.20 (4CH2), 101.50 (1C), 115.39 (8CH2),
127.53(Co, Ph), 128.46 (Cm, Ph), 130.55 (Cp, Ph), 132.83 (Ci,
Ph), 137.23 (7CH), 139.34 (3C), 166.61 (C@N); Anal. Calcd
for C19H24N2O: C, 76.99; H, 8.16; N, 9.45. Found: C, 76.85; H,
8.05; N 9.32.
k
max(log e), nm: 248 (2.63); IR (KBr) m, cm21: 694.4, 771.5,
1001.0, 1037.7, 1203.5, 1290.3, 1446.6, 1571.9, 1606.7,
1
2852.6, 2869.9, 2960.1; H NMR (400 MHz, CDCl3): d 5 1.70–
2.20 (m, 12H, 63CH2), 1.60–1.69 (m, 1H, 4CH2), 2.36–2.43 (m,
1H, 4CH2), 3.28–3.37 (m, 1H, 7CH), 3.42 (t J 5 8.5, 1H) and
4.07 (t J 5 8.5, 1H) (8CH2), 7.34–7.44 (m, 3H) and 7.85–7.90
(m, 2H) (Ph); 13C NMR (100 MHz, CDCl3): d 5 24.62 (CH2),
24.73 (CH2), 25.15 (CH2), 29.73 (CH2), 33.74 (CH2), 35.63
(CH2), 39.90 (4CH2), 52.08 (7CH), 71.58 (8CH2), 92.34 (3C),
102.79 (1C), 128.10 (Co, Ph), 128.28 (Cm, Ph), 130.23 (Cp, Ph),
131.62 (Ci, Ph), 167.99 (C@N); Anal. Calcd for C18H22N2O: C,
76.56; H, 7.85; N, 9.92. Found: C, 76.79; H, 7.82; N 9.98.
4,4-Dimethyl-2-(pent-4-enyl)-5-phenyl-4H-imidazole
3-oxide (5d)
Yield: 80%; oil; UV (EtOH) kmax(log e), nm: 232 (3.10), 265
(3.39), 361 (3.82); IR (neat) m, cm21: 991.4, 1105.2, 1238.3,
1382.9, 1463.9, 1647.2, 2875.8, 2935.6, 2979.9; 1H NMR
(400 MHz, CDCl3): d 5 1.62 (s, 6H, 23CH3), 1.86 (quintet
J 5 7.4, 2H, 5CH2); 2.14 (q J 5 7, 2H, 4CH2), 2.78 (t J 5 7.5,
2H, 6CH2), 4.94 (dbr, J 5 10.3, 1H) and 5.02 (dd, Jvic 5 1.4,
1’-Phenyl-6a’,7’,8’,9’-tetrahydro-6’H-spiro[cyclohexane-1,3’-
cyclopenta[c]imidazo[1,5-b]isoxazole] (6c)
Yield: 75%; m.p. 110–111 ꢀC (hexane15% CHCl3); UV
(EtOH) kmax(log e), nm: 248 (2.61); IR (KBr) m, cm21: 694.3,
771.5, 986.5, 1038.6, 1106.1, 1447.4, 1492.8, 1572.8, 1609.4,
2855.3, 2864.9, 2943.1; 1H NMR (400 MHz, CDCl3):
d 5 1.48–2.20 (m, 16H, 83CH2), 3.21–3.31 (m, 1H, 7CH),
3.42 (t J 5 8, 1H) and 4.03 (t J 5 8, 1H) (8CH2), 7.35–7.46
(m, 3H) and 7.85–7.92 (m, 2H) (Ph); 13C NMR (100 MHz,
CDCl3): d 5 23.32 (CH2), 23.62 (CH2), 25.21 (CH2), 25.56
(CH2), 29.47 (CH2), 31.81(CH2), 37.11 (CH2), 38.51 (CH2),
52.53 (7CH), 71.12 (8CH2), 91.71 (3C), 95.26 (1C), 128.15 (Co,
Ph), 128.32 (Cm, Ph), 130.18 (Cp, Ph), 131.95 (Ci, Ph), 168.65
(C@N); Anal. Calcd for C19H24N2O: C, 76.99; H, 8.16; N, 9.45.
Found: C, 76.96; H, 8.03; N 9.76.
J
hem 5 17, 1H) (8CH2), 5.79 (tdd, Jt 5 6.7, Jd1 5 10.3, Jd2 5 17,
1H, CH); 7.38–7.49 (m, 3H) and 7.90–7.97 (m, 2H) (Ph); 13C
NMR (100 MHz, CDCl3): d 5 23.73 (23CH3); 24.31 and 24.93
(5CH2 and 6CH2), 33.18 (4CH2), 78.98 (1C), 115.13 (8CH2),
126.90 (Co, Ph), 128.82 (Cm, Ph), 131.53 (Cp, Ph), 130.31 (Ci,
Ph), 137.50 (7CH), 151.31 (3C), 176.80 (C@N); Anal. Calcd
for C16H20N2O: C, 74.97; H, 7.86; N, 10.93. Found: C, 74.81;
H, 7.98; N 11.01.
7
Intramolecular 1,3-Dipolar Cycloaddition of Nitrones
5a–d (General Procedure)
A solution of 5a–d (0.3 mmol) in toluene (2 mL) was stirred
ꢀ
at 1110 C during 50–70 h or heating in microwave oven at
3,3-Dimethyl-2-phenyl-6a,7,8,9-tetrahydro-3H,6H-
cyclopenta[c]imidazo[1,2-b]isoxazole (6d)
ꢀ
1170 C for 30–60 min. Progress of the reaction was moni-
tored by TLC (silica gel, Et2O/C6H14 1:1, developing with 1%
aq KMnO4). The solution was concentrated in vacuum and
residue was separated by column chromatography (silica gel
60, Et2O/C6H14 1:1) to give 6a–d, respectively. The yield was
not dependent on the method of heating.
Yield: 70%; oil; UV (EtOH) kmax(log e), nm: 243 (2.58); IR
(neat) m, cm21: 698.2, 775.4, 866.0, 966.3, 1031.9, 1172.7,
1191.9, 1224.8, 1292.3, 1365.6, 1384.9, 1446.6, 1463.9,
1494.8, 1573.9, 1608.6, 2850.7, 2866.1, 2949.1, 2968.4; 1H
NMR (400 MHz, CDCl3): d 5 1.47 (s, 3H, CH3), 1.54 (s, 3H,
CH3), 1.57–1.62 (m, 1H, 6CH2), 1.88–1.94 (m, 1H, 6CH2);
5
4
3,3-Diethyl-1-phenyl-6a,7,8,9-tetrahydro-3H,6H-
1.88–1.94 (m, 2H, CH2), 1.95–1.99 (m, 2H, CH2), 3.02–3.08
(m, 1H, 7CH), 3.39 (t J 5 8.5, 1H) and 4.02 (t J 5 8.5, 1H)
(8CH2), 7.32–7.40 (m, 3H) and 7.68–7.72 (m, 2H) (Ph); 13C
NMR (100 MHz, CDCl3): d 5 20.52 and 28.20 (23CH3), 25.68
(5CH2), 28.96 (6CH2), 36.93 (4CH2), 54.04 (7CH), 70.61
(8CH2), 75.61 (1C), 109.25 (3C), 127.97 (Co, Ph), 128.17 (Cm,
Ph), 129.84 (Cp, Ph), 132.75 (Ci, Ph), 173.27 (C@N); Anal.
Calcd for C16H20N2O: C, 74.97; H, 7.86; N, 10.93. Found: C,
74.88; H, 8.18; N 11.09.
cyclopenta[c]imidazo[1,5ꢀ-b]isoxazole (6a)
Yield: 90%; m.p. 99–101 C (hexane); UV (EtOH) kmax(log e),
nm: 246 (2.55); IR (KBr) m, cm21: 694.5, 771.5, 985.6,
1037.7, 1164.9, 1294.2, 1446.6, 1454.3, 1494.8, 1573.9,
1610.5, 2854.6, 2945.2, 2964.5, 2985.7; 1H NMR (400 MHz,
CDCl3): d 5 1.03 (t J 5 7.5, 3H) and 1.14 (t J 5 7.5, 3H)
(23CH3); 1.50–1.80 (m, 4H, 23CH2) 1.89–2.12 (m, 4H,
23CH2), 1.89–2.12 (m, 2H, 4CH2), 3.17–3.28 (m, 2H, 7CH),
8
3.41 (t J 5 8, 1H), 3.97 (t J 5 8, 1H, CH2), 7.32–7.43 (m, 3H)
and 7.81–7.89 (m, 2H) (Ph); 13C NMR (100 MHz, CDCl3):
d 5 8.52 (Me), 9.28 (Me), 24.02, 25.26, 29.49 and 30.92
(23CH2Me, 5CH2, 6CH2), 37.05 (4CH2), 52.68 (7CH), 71.20
(8CH2), 91.84 (3C), 98.85 (1C), 128.09(Co, Ph), 128.26 (Cm,
Ph), 130.07(Cp, Ph), 132.00 (Ci, Ph), 168.49 (C@N); Anal.
General Procedure for Isoxazolidine Ring Opening
(Synthesis of 7a–d)
Method A
Zn powder (650 mg, 10 mmol) was added in one portion to
a warm (60 ꢀC) stirred solution containing isoxazolidines
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5a–d (1 mmol), EtOH (3 mL), AcOH (60%, 6 mL) and
EDTAꢁdisodium salt (2 g). The reaction mixture was stirred at
24 h. Organic layer was separated, solvent was evaporated in
vacuum, and the residue was purified using column chroma-
tography (silica gel, EtOAc) to give 7c.
ꢀ
60 C for 3 h, and then cooled down to r.t. The mixture was
basified to pH 10 with 30% NH4OH solution and extracted
with CHCl3. The CHCl3 extract was dried with Na2CO3 and con-
centrated in vacuum. The residue was purified by column
chromatography (silica gel, Et2O) to give amines 7a–d.
Yield: 75% (Method A), 71% (Method B); oil; IR (neat) m,
cm21: 698.2, 769.6, 950.9, 1028.0, 1105.2, 1269.1, 1315.4,
1446.6, 1573.9, 1612.4, 2856.5, 2933.6, 3281.1; 1H NMR
(400 MHz, CDCl3): d 5 1.39–1.90 (m, 14H, 73CH2), 1.98–
2.08 (m, 1H) and 2.12–2.19 (m, 1H) (4CH2), 2.50–2.59 (m,
1H, 7CH), 3.58 (dd, J1 5 4, J2 5 11.8, 1H) and 3.79 (dd,
J1 5 2J2 5 11.8, 1H) (8CH2), 7.33–7.42 (m, 3H) and 7.59–7.64
(m, 2H) (Ph); 13C NMR (100 MHz, CDCl3): d 5 23.05, 23.18,
23.42, 25.09, 26.14, 39.75 and 39.99 (5CH2, 6CH2 and
53(CH2)spiro-cyclohexane), 42.73 (4CH2), 46.45 (7CH), 61.36
(8CH2), 81.70 (3C), 89.25 (1C), 127.93 (Co, Ph), 128.25 (Cm,
Ph), 129.60 (Cp, Ph), 133.39 (Ci, Ph), 170.88 (C@N); Anal.
Calcd for C19H26N2O: C, 76.47; H, 8.78; N, 9.39. Found: C,
76.65; H, 8.59; N 9.25.
(2,2-Diethyl-4-phenyl-1,3-diazaspiro[4.4]non-3-en-6-yl)
methanol (7a)
Yield: 72%; m.p. 98–99 ꢀC (hexane-ethyl acetate 5:1); IR
(KBr) m, cm21: 697.2, 767.6, 950.8, 1027.9, 1107.1, 1171.7,
1243.9, 1316.3, 1376.1, 1445.5, 1458.1, 1574.8, 1614.3,
1736.8, 2938.3, 2964.4; 1H NMR (400 MHz, CDCl3): d 5 0.91
(t J 5 7.5, 3H, CH3), 1.01 (t J 5 7.5, 3H, CH3), 1.68–1.85 (m, 6H,
33CH2), 1.62 and 1.90 (each qAB, Jq 5 7.5 JAB 5 14.8, 2H,
CH2Me), 1.94–2.04 and 2.10–2.20 (each m, 2H, 4CH2), 2.49–
7
2.59 (m, 1H, CH), 3.60 (ddJ1 5 4J2 5 11.7, 1H) and 3.80 (dd,
J1 5 2J2 5 11.7, 1H) (8CH2), 7.30–7.41 (m, 3H) and 7.56–7.63
(m, 2H) (Ph); 13C NMR (100 MHz, CDCl3): d 5 8.29 and 8.31
(23Me), 31.21 and 33.65 (23CH2Me), 22.93 and 26.31 (5CH2
and6CH2), 41.89 (4CH2), 46.38 (7CH), 61.17 (8CH2), 81.68 (3C),
92.54 (1C), 127.59 (Co, Ph), 127.96(Cm, Ph), 129.26(Cp, Ph),
133.16 (Ci, Ph), 171.19 (C@N); Anal. Calcd for C18H26N2O: C,
75.48; H, 9.15; N, 9.78. Found: C, 75.22; H, 8.88; N 9.45.
(3,3-Dimethyl-2-phenyl-1,4-diazaspiro[4.4]non-1-en-6-yl)
methanol (7d)
Yield: 78%; m.p. 119–120 ꢀC (CHCl3); IR (KBr) m, cm21
:
700.1, 783.1, 846.7, 954.7, 1012.6, 1114.8, 1153.4, 1188.1,
1215.1, 1371.4, 1444.6, 1467.8, 1570.0, 1604.7, 1643.3,
2869.9, 2906.6, 2962.6, 2981.9, 3271.2; 1H NMR (400 MHz,
CDCl3): d 5 1.50 (s, 3H, CH3), 1.55 (s, 3H, CH3), 1.67–2.00
(m, 5H, 23CH2 and1/2 4CH2); 2.03–2.12 (m, 2H, 1/24CH2
and7CH), 3.58 (dd, J1 5 3J2 5 11.5, 1H) and 3.65 (dd,
J1 5 8J2 5 11.5, 1H) (8CH2), 7.34–7.43 (m, 3H) and 7.69–7.76
(m, 2H) (Ph); 13C NMR (100 MHz, CDCl3): d 5 21.77 and
26.90 (5CH2and 6CH2), 28.70 and 28.76 (23CH3), 39.65
(4CH2), 48.36 (7CH), 64.30 (8CH2), 69.42 (1C), 99.05 (3C),
128.26 (Co, Ph), 128.65 (Cm, Ph), 130.17 (Cp, Ph), 133.18 (Ci,
Ph), 173.25 (C@N); Anal. Calcd for C16H22N2O: C, 74.38; H,
8.58; N, 10.84. Found: C, 74.31; H, 8.26; N 10.75.
(13-Phenyl-6,12-diazadispiro[4.1.4.2]tridec-12-en-1-yl)
methanol (7b)
Yield: 65%; oil; IR (neat) m, cm21: 698.2, 769.6, 945.1, 1010.7,
1026.1, 1105.2, 1298.1, 1332.8, 1444.7, 1573.9, 1610.5,
1
2871.9, 2956.8, 3298.2; H NMR (400 MHz, CDCl3): d 5 1.56–
2.10 (m, 13H, 63CH2, and 1/24CH2), 2.14–2.21 (m, 1H, 4CH2),
7
2.45–2.55 (m, 1H, CH), 3.58 (dd, J1 5 4.3, J2 5 11.7, 1H) and
3.78 (dd, J1 5 2 J25 11.7, 1H) (8CH2), 7.32–7.40 (m, 3H) and
7.59–7.65 (m, 2H) (Ph); 13C NMR (100 MHz, CDCl3):
d 5 23.28, 24.01, 24.12, and 26.38 (5CH2, 6CH2 and
23CH2spiro-cyclopentane), 41.29, 41.69, 41.93 (4CH2,
23CH2spiro-cyclopentane), 46.46 (7CH), 61.38 (8CH2), 81.92
(3C), 97.40 (1C), 127.93 (Co, Ph), 128.27 (Cm, Ph), 129.57 (Cp,
Ph), 133.26 (Ci, Ph), 170.79 (C@N); Anal. Calcd for C18H24N2O:
C, 76.02; H, 8.51; N, 9.85. Found: C, 75.82; H, 8.78; N 9.65.
Nitroxides 2a–d (General Procedure)
A solution of 7a–d ꢀ(145 mg, 0.38 mmol) in CHCl3 (4 mL)
was cooled to 210 C and MCPBA (65 mg, 0.38 mmol) was
added in one portion. The mixture was stirred at 0 ꢀC until
the reaction was complete (control by TLC analysis, silica gel
Et2O – hexane 1:1).The solution was concentrated in vacuum,
and the residue was separated by column chromatography
(silica gel 60, Et2O – hexane 1:1).
(14-Phenyl-6,13-diazadispiro[4.1.5.2]tetradec-13-en-1-yl)
methanol (7c)
Method B
2,2-Diethyl-6-(hydroxymethyl)24-phenyl-1,3-
Titanium (IV) iso-propoxide (Ti(O-iPr)4, 3.01 g, 10.58 mmol)
was injected with a syringe into a flask with dry Et2O (5 mL)
under a stream of argon. Then 2 M solution of EtMgBr in Et2O
(5.5 mL, 11 mmol) was added dropwise within 2 min upon
vigorous stirring. The solution turned black over the course of
EtMgBr addition. The reaction mixture was stirred under
argon for 15 min at rt and then for 15 min under reflux. A
solution of 6c (1 g, 3.4 mmol) in Et2O (5 mL) was added drop-
wise, and the resulting solution was stirred under reflux for
325 h until consumption of the starting material occurred.
Progress of the reaction was monitored by TLC (silica gel,
EtOAc, developed with 1% aq KMnO4). The reaction mixture
was quenched with H2O (3 mL) and stirred under reflux for
diazaspiro[4.4]non-3-en-1-oxyl (2a)
Yield: 69%; m.p. 95–99 ꢀC (hexane); UV (EtOH) kmax(log e),
nm: 245 (4.03); IR (KBr) m, cm21: 695.3, 766.6, 1037.6,
1123.4, 1184.2, 1302.8, 1417.6, 1445.5, 1573.8, 1612.4,
2879.5, 2938.3, 2969.2; Anal. Calcd for C18H25N2O2: C, 71.73;
H, 8.36; N, 9.29. Found: C, 71.58; H, 7.98; N 9.31.
1-(Hydroxymethyl)-13-phenyl-6,12-
diazadispiro[4.1.4.2]tridec-12-en-6-oxyl (2b)
Yield: 75%, m.p. 77–78 ꢀC (hexane); UV (EtOH) kmax(log e),
nm: 246 (4.10); IR (KBr) m, cm21: 650.0, 696.3, 771.5,
1006.8, 1029.9, 1176.5, 1209.3, 1313.5, 1338.6, 1446.6,
1467.8, 1494.8, 1570.0, 1598.9, 2871.9, 2958.7; Anal. Calcd
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t
for C18H23N2O2: C, 72.21; H, 7.74; N, 9.36. Found: C, 72.50;
H, 7.57; N 9.37.
MHz, CDCl3): d 5 1.44 (s, 3H, CH3), 1.46 (s, 9H, Bu), 1.49 (s,
3H, CH3), 1.45–1.57 (m, 2H), 1.63–1.81 (m, 5H), 1.83–1.96 (m,
2H); 2.00–2.09 (m, 2H), 2.21–2.29 (m, 1H), 2.39–2.48 (m, 1H)
7
1-(Hydroxymethyl)-14-phenyl-6,13-
and 2.64–2.74 (m, 1H) (73CH2), 3.29–3.39 (m, 1H, CH), 3.62
(dd, J1 5 4J2 5 12, 1H) and 3.78 (dd, J1 5 8 J2 5 12, 1H, CH2),
8
diazadispiro[4.1.5.2]tetradec-13-en 6-oxyl (2c)
Yield: 71%, oil; UV (EtOH) kmax(log e), nm: 244 (4.06); IR
(neat) m, cm21: 650.0, 696.3, 771.5, 906.5, 1037.7, 1112.9,
1176.5, 1284.6, 1446.6, 1494.8, 1571.9, 1600.9, 2858.4,
2935.6; Anal. Calcd for C19H25N2O2: C, 72.81; H, 8.04; N,
8.94. Found: C, 72.50; H, 7.91; N 8.75
7.29–7.36 (m, 3H) and 7.45–7.50 (m, 2H) (Ph); 13C NMR (100
MHz, CDCl3): d 5 22.41, 23.13, 23.28, 27.99, 29.64 and 33.94
(53CH2); 24.52, 24.97 and 27.73 (23CH3 andtBu), 38.07
(4CH2), 49.20 (7CH), 63.28 (8CH2), 81.33, 82.20 and 87.28 (3C,
CMe3 andCMe2), 104.28 (1C), 127.75 (Co, Ph), 128.09 (Cm, Ph),
128.94 (Cp, Ph), 135.19 (Ci, Ph), 170.97 (C@N), 171.88 (C@O);
Microanalysis: Anal. Calcd for C26H38N2O4: C, 70.56; H, 8.65; N,
6.33. Found: C, 70.65; H, 8.49; N 6.59.
6-(Hydroxymethyl)-2,2-dimethyl-3-phenyl-1,4-
diazaspiro[4.4]non-3-en-1 oxyl (2d)
Yield: 79%; m.p. 86–87 ꢀC (hexane); UV (EtOH) kmax(log e),
nm: 246 (4.16); IR (KBr) m, cm21: 702.1, 785.2, 1043.5,
1122.5, 1161.1, 1203.5, 1247.9, 1307.7, 1328.9, 1377.1,
1446.6, 1460.1, 1571.9, 1602.8, 2870.0, 1933.6, 2966.4;
Anal. Calcd for C16H21N2O2: C, 70.30; H, 7.74; N, 10.25.
Found: C, 70.15; H, 7.42; N 9.93.
tert-Butyl 2-{[1-(hydroxymethyl)-14-phenyl-6,13-
diazadispiro[4.1.5.2]tetradec-13-en-6-yl]oxy}-2-
methylpropanoate (3c)
Yield: 54%; m.p. 117–120 ꢀC; UV (EtOH) kmax(log e), nm:
231 (3.84); IR (KBr) m, cm21: 702.1, 1136.0, 1280.7, 1367.5,
1444.6, 1452.4, 1600.9, 1641.4, 1732.0, 2869.9, 2923.9,
2964.5; 1H NMR (400 MHz, CDCl3): d 5 1.47 (s, 3H, CH3),
Synthesis of Alkoxyamines 3a–d (General Procedure)
The alkoxyamines were prepared using method developed
by Matyjaszewski et al.40 A mixture of the nitroxide 2a–d
(2.2mmol), 2-bromo-2-methylpropionic acid tert-butyl ester
(0.5 g, 2.25 mmol), Cu powder (140 mg, 2.25 mmol), 4,40-di-
tert-butyl-2,20-bipyridine (24 mg, 0.09 mmol), Cu(OTf)2 (8
mg, 0.023 mmol), and benzene (5 mL) was placed to a
Schlenk flask and degassed by three freeze-pump-thaw
cycles. The solution was stirred for 24 h at 50 ꢀC. Benzene
was removed in. vacuum and the residue was separated by
column chromatography (silica gel, EtOAc–hexane 3:7)
t
1.49 (s, 9H, Bu), 1.53 (s, 3H, CH3), 1.20–1.28 (m, 2H), 1.41–
1.55 (m, 1H), 1.57–1.93 (m, 10H), 1.97–2.06 (m, 1H), 2.30–
2.39 (m, 1H) and 2.07–2.16 (m, 1H) (73CH2), 2.87 (ddd,
J1 5 6J2 5 7.5, J3 5 9.5, 1H 7CH), 3.65 (dd, J1 5 6J1 5 12, 1H)
and 3.80 (dd, J1 5 7.5J1 5 12, 1H) (8CH2), 7.33–7.38 (m, 3H)
and 7.51–7.55 (m, 2H) (Ph); 13C NMR (100 MHz, CDCl3):
t
d 5 24.60, 25.27 and 27.82 (23CH3 and Bu); 22.91, 23.46,
23.98, 25.64 and 28.21 (5CH2, 6CH2 and 33CH2 spiro-cyclo-
hexane), 30.11 and 33.97 (23CH2 spiro-cyclohexane), 37.94
(4CH2), 49.73 (7CH), 63.04 (8CH2), 81.23, 82.27 and 85.79
(3C, CMe3 and CMe2); 95.24 (1C), 127.91 (Co, Ph), 128.03
(Cm, Ph), 128.99 (Cp, Ph), 135.36 (Ci, Ph), 172.61 and 172.83
(C@O and C@N); Anal. Calcd for C27H40N2O4: C, 71.02; H,
8.83; N, 6.13. Found: C, 71.16; H, 8.56; N 6.33.
tert-Butyl 2-(2,2-diethyl-6-(hydroxymethyl)-4-phenyl-1,3-
diazaspiro[4.4]non-3-en-1-yloxy)-2-methylpropanoate
(3a)
ꢀ
Yield: 60%; m.p. 113–121 C; UV (EtOH) kmax(log e), nm: 234
(3.85); IR (KBr) m, cm21: 700.1, 771.5, 842.9, 943.2, 970.2,
1024.2, 1130.3, 1157.2, 1290.3, 1369.4, 1448.5, 1573.9,
1618.2, 1724.3, 2873.9, 2943.3, 2972.2; 1H NMR (400 MHz,
CDCl3): d 5 0.93 (t J 5 7.5, 3H, CH3), 0.97 (t J 5 7.5, 3H,
CH3),1.46 (s, 3H, OCCH3); 1.49 (s, 9H, tBu), 1.52 (s, 3H,
OCCH3), 1.56–1.65 (m, 2H), 1.70–1.82 (m, 2H), 1.96–2.17 (m,
tert-Butyl 2-(6-(hydroxymethyl)-2,2-dimethyl-3-phenyl-
1,4-diazaspiro[4.4]non-3-en-1-yloxy)-2-methylpropanoate
(3d)
Yield: 63%; oil; UV (EtOH) kmax (log e), nm: 234 (3.83); IR
(neat) m, cm21: 698.2, 1033.8, 1134.1, 1292.3, 1367.5, 1444.1,
1462.0, 1627.9, 1728.2, 2871.9, 2935.6, 2978.3; 1H NMR (400
7
5H) and 2.34–2.42 (m, 1H)(53CH2), 2.98–3.07 (m; 1H, CH),
t
MHz, CDCl3): d 5 1.46 (s, 9H, Bu), 1.41 (s, 3H), 1.42 (s, 3H),
3.76 (dd, J1 5 7J2 5 11, 1H) and 3.87 (dd, J1 5 6J2 5 11, 1H)
(8CH2), 7.36–7.39 (m, 3H) and 7.55–7.59 (m, 2H) (Ph); 13C
NMR (100 MHz, CDCl3): d 5 9.18 and 9.33 (23CH3CH2), 27.75
(23CH3CH2), 24.75, 25.68 and 27.87 (23CH3 and tBu), 23.38,
28.46 and 29.00 (33CH2), 50.71 (7CH), 62.23 (8CH2), 81.14,
82.44 and 84.97 (3C, CMe3 and CMe2), 97.03 (1C), 172.92 and
173.53 (C@N, C@O); 127.83 (Co, Ph), 128.08 (Cm, Ph), 129.19
(Cp, Ph), 134.97 (Ci, Ph); Anal. Calcd for C26H40N2O4: C, 70.24;
H, 9.07; N, 6.30. Found: C, 70.29; H, 8.72; N 6.76.
1.47 (s, 3H) and 1.55 (s, 3H) (43CH3), 1.72–1.79 (m, 1H),
1.90–2.15 (m, 4H) and 2.33–2.44 (m, 1H) (33CH2), 3.48 (dt,
Jd 5 4.5 Jt 5 11.2, 1H, 7CH), 3.83 (dbr, J 5 11.2, 1H) and 4.40
(dbr, J 5 10, 1H)(8CH2), 7.33–7.39 (m, 3H) and 7.54–7.59 (m,
2H) (Ph); 13C NMR (100 MHz, CDCl3): d 5 22.13, 24.32, 24.48
and 25.74 (43CH3), 27.80 (tBu), 20.63 and 26.73 (5CH2 and
6CH2), 32.32 (4CH2), 51.16 (7CH), 65.04 (8CH2), 77.67 (1C),
81.51 and 82.07 (CMe3 and CMe2), 106.86 (3C), 127.46 (Co,
Ph), 127.82 (Cm, Ph), 128.15 (Cp, Ph), 129.32 (Ci, Ph), 172.00
and 172.16 (C@N and C@O); Anal. Calcd for C24H36N2O4: C,
69.20; H, 8.71; N, 6.73. Found: C, 69.45; H, 8.51; N 6.69.
tert-Butyl 2-{[1-(hydroxymethyl)-13-phenyl-6,12-
diazadispiro[4.1.4.2]tridec-12-en-6-yl]oxy}-2-
methylpropanoate (3b)
Yield: 64%; m.p. oil; UV (EtOH) kmax (log e), nm: 232 (3.81); IR
(KBr) m, cm21: 701.7, 1134.0, 1281.3, 1368.5, 1444.1, 1450.4,
1605.9, 1639.4, 1729.0, 2867.9, 2923.1, 2963.7;1H NMR (400
Kinetic Measurements
For kinetic measurements, 20 mM solutions of alkoxyamines
(700 lL) in benzene-d6 in conventional NMR tube were
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degassed by three freeze-pump-thaw cycles, sealed under
vacuum and placed into preheated probe head of the Bruker
Avance – 200 MHz NMR spectrometer. H NMR spectra were
Integration of NMR signals of the polymer and the monomer
allowed to calculate of the monomer conversion.
1
The polymer molecular weight and PDI were determined by
gel permeation chromatography. The polymer precipitated
from a reaction mixture after dilution with methanol was fil-
tered off and dried. The resulting dry polymer (3 mg) was
dissolved in 1 mL of THF and analyzed on Agilent-1200 LC
chromatograph equipped with isocratic pump, thermostated
PL-gel Mixed C column, variable wavelength, and refractive
index detectors. THF was used as eluent at 1 mL/min flow
rate. Polymer fractions were quantified using refraction
index. Mn and PDI values were obtained after automatic inte-
gration with the help of universal calibration curve obtained
for low polydispersity polystyrene calibration standards
(Agilent).
recorded at different time intervals after the beginning of
heating. The NMR experiments gave series of NMR spectra
resolved in time. The resulting kinetics was obtained by
automatic integration of the NMR signals corresponding to
initial alkoxyamine, alkane R-H, alkene R(-H).
In separate experiments, thiophenol (200 mM) was added as
a radical scavenger. PhSH is known to suppress reformation
of alkoxyamine via irreversible quenching of the alkyl radi-
cals with large rate constants.41,42 Mechanism of PhSH reac-
tion with nitroxides is rather complicated,43 so the reaction
products were not analyzed.
Nitroxides 2a–d Thermal Stability
EPR spectra were recordered on Bruker X-band spectrome-
ter. Solutions (1024 M) of a nitroxide in chlorobenzene (300
lL) were placed into a glass tubes, degassed, and sealed.
The samples were placed into preheated to 100 ꢀC oil bath
for 24 h. EPR spectra of the samples were recorded and
compared to a spectrum of a standard solution of TEMPO.
RESULTS AND DISCUSSION
Synthesis
We have recently found a new method for sterically hindered
nitroxides construction, based on intramolecular 1,3-dipolar
cycloaddition—isoxazolidine
ring
opening—oxidation
sequence.36,37 This sequence allowed for stereospecific syn-
thesis of highly sterically hindered nitroxide from optically
active aldonitrone of pyrroline series.37 Here, we used essen-
tially the same approach to prepare few spiro-bicyclic nitro-
xides of imidazoline series. Nitroxides 2a–d and
alkoxyamines 3a–d were prepared according to Scheme 1.
Polymerization
Monomer (5 mL) was placed into round bottom two-neck
flask equipped with magnetic stirrer and backflow con-
denser. Then precalculated amount of alkoxyamine was
added. The mixture was purged with argon for 15 min to
remove oxygen from the system and the reaction vessel was
placed into a preheated oil bath. Samples of the polymeriza-
tion mixture (typically 100 lL) were taken through definite
Aldonitrones 4a–d were treated with pent-4-enylmagnesium
bromide. After quenching of the reaction mixture with water,
products were oxidized in situ and a-pent-4-enyl nitrones
5a–d were isolated with good yields. Heating of the nitrones
5a–d in toluene either under reflux or upon microwave irra-
diation afforded a single product in each case. Isolated prod-
ucts showed shift in UV absorption wavelengths to 245 nm
(typical for phenylimine absorption) from 260 to 280 nm for
5a–c and 362 nm for 5d, and absence of low-field signals
belonging to aldonitrone and terminal alkene moieties in
NMR 1H spectra, indicating an intramolecular 1,3-dipolar
cycloaddition occurrence. One could expect two regioisomers
6 and 8 formation in this reaction (Scheme 1). Low field sig-
nal of methylene group carbon at 70.6–71.6 ppm allowed to
ꢀ
periods of time and stored in a fridge at 218 C. They were
used to determine monomer conversion and molecular
weight and polydispersity index (PDI) of polymer formed.
After the polymerization experiment the reaction mixture
was diluted with cold methanol, polymer precipitate was fil-
tered off, dried, and used as initiator for a reinitiation experi-
ment. The later was performed similarly to the described
above procedure.
Determination of the “Living” Character of the
Polymerization
1
unambiguously discard structures 8. Analysis of NMR H and
The “living” nature of the polymerization was confirmed by
either reinitiation experiment (see above) or by decomposi-
tion of macroalkoxyamines in air saturated solutions. The
weighted amount of precipitated polymer was dissolved in
toluene to get 5 3 1025 to 1024 M solution. The solution
was heated at 100 ꢀC in the oil bath. ESR spectra were
recorded before and in the course of heating. Quantification
of the nitroxide formed allowed for the estimation of quota
of “living” chains.
13C spectra revealed structural similarity to intramolecular
cycloaducts formed from a-pent-4-enyl nitrones of pyrroline
series37 and allowed to assign the cyclopenta[c]imidazoisoxa-
zole-type structures 6a–d to the isolated products.
It should be noted that in no case 100% conversion was
observed and starting compound 5 was always present in
the reaction mixtures independently on conditions and reac-
tion time. Moreover, formation of 5a was observed by TLC
and NMR upon heating of the pure cycloadduct 6a in tolu-
ene. After 60 min of heating at 160 ꢀC under microwave
irradiation the ratio 5a:6a was 1:5. These observations
denote reversibility of cycloaddition reaction, which coincide
with the concept of orbital-controlled mechanism.44 The
Sample Analysis
To determine a monomer conversion, a sample of the poly-
merization mixture (50 lL) was dissolved in 650 lL of chlo-
roform-d. 1H NMR spectra were recorded for each sample.
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observable amount of aldonitrones 5a–d under conditions
close to equilibrium may result from stabilization of the
nitrone group due to conjugation with phenylimine system.
be determined before application of an alkoxyamine as an
initiator for NMP.
ꢀ
ꢁ
1=2
2kdktln 10
kckp½Iꢂ0
F5
(1)
(2)
(3)
Recently, we have suggested a new convenient method for
NAO bong cleavage in isoxazolidines by low-valence titanium
(LVT) reagent prepared from Ti(O-iPr)4 and EtMgBr.36,37
Treatment of cycloadduct 6c with the LVT reagent resulted
in the selective cleavage of isoxazolidine ring to give corre-
sponding aminoalcohol 7c in a good yield.
!
1=2
pkp3½Iꢂ0
kdkckt
½Iꢂ0
PDI 511
1
1
½Mꢂ0
ꢀ
ꢁ
3=2
1=2
ð2ln 10Þ
5
kt
t90%
3=2
3kp
K½I0ꢂ
It has been shown that Zn/HOAc system is an efficient rea-
gent for reductive isoxazolidine ring opening.45 Indeed, treat-
ment of the cycloadducts 6a–d with Zn/HOAc afforded
corresponding aminoalcohols 7a–d. A yield of 7c was only a
bit lower than that obtained using low-valence titanium
(LVT) reagent (see Experimental section).
Earlier an experimental approach that makes possible to
determine a value of homolysis rate constant kd and intra-
molecular/radical H-atom transfer reaction rate constants
kdD and kcd, respectively, was proposed. The approach is
based on analysis of products and kinetics of decomposition
of an alkoxyamine alone and in the presence of alkyl radicals
scavenger/nitroxide reducing agent.17 Reactions which may
proceed under these conditions are shown in the Supporting
Information Scheme 1.
It is known that oxidation of highly sterically hindered amines
into nitroxides with H2O2/Na2WO4 is sometimes unsuccessful
and use of peracids, for example, MCPBA, gives better result.
36,37,46
Similarly, only trace amounts of corresponding nitro-
xides were formed in the reaction of aminoalcohols 7a–d with
hydrogen peroxide in presence of Na2WO4, while oxidation
with MCPBA afforded 2a–d in 69–79% yields.
When an alkoxyamine decomposes in the presence of PhSH,
alkyl radicals are scavenged with formation of alkane RH
(see Supporting Information Scheme 1a). Formation of
alkene indicates H-atom transfer by intramolecular mecha-
nism (reaction 4 in Supporting Information Scheme 1a). Ana-
lyzing kinetics of alkoxyamine decomposition and alkene/
alkane formation one can obtain both kd and kdD values.
The nitroxides were converted into alkoxyamines 3a–d via
standard Matyjaszewski’s procedure40 with tert-butyl 2-
bromo-2-methylpropanoate. It has been shown that alkoxy-
amines prepared from imidazoline nitroxides may show dou-
ble set of signals in the NMR spectra because of formation of
two diastereomeric forms due to slow inversion at alkoxy-
amine nitrogen.12 However, single set of signals was
observed for highly sterically hindered alkoxyamines of this
series,37 presumably because bulky substituents in the asym-
metric molecule make one of the invertamers strongly favor-
able. Similar effect occurs for alkoxyamines 3a–d. Obviously,
rigidly fixed hydroxymethyl group at spirocyclopentane moi-
ety does not permit inversion at N1, leading to a single
invertamer formation.
In another experiment, an alkoxyamine is heated alone (Sup-
porting Information Scheme 1b). If no side reactions take place,
so-called persistent radical effect is observed in the course of
reversible homolysis (reactions 1, 5, 7 at Supporting Informa-
tion Scheme 1b) and kinetics of alkoxyamine decomposition is
described by eq (4).4848 For alkoxyamines with tertiary alkyl
fragment at oxygen atom, H-atom transfer with alkene forma-
tion may take place (Reaction 6). Kinetics of an alkoxyamine
decomposition is exponential according to eqs (5) and (6). If
the value of kc is known or estimated, a rate constant of H-atom
transfer can be obtained. Even though if an exact value of kc is
unknown, eq (5) allows for an estimation of factor of dispro-
portionation fD. This parameter is very important for NMP of
methacrylates. Fischer48 has shown that if fD is lower that 0.7%
H-atom transfer reaction has no effect on NMP.
Nitroxides 2a–d as Mediators for NMP
Measurements of kd and Kinetic Parameters for H-Atom
Transfer Reaction
To predict a NMP result, Fischer47 developed phase-diagram
approach based on eqs (1–3), providing both a living fraction
(0 < F < 1, F being the fraction of dead chains, eq (1)), a PDI
(eq (2)), and time of polymerization (t90% being the time for
90% monomer conversion, R 5 kd/kc, eq (3)). Monomer is
characterized with two parameters: a rate constant of propa-
gating chain radical addition to monomer double bond
(kp),and a propagating chains recombination (termination)
constant (kt).A success of the NMP experiments, that is, high
livingness (F > 0.8) and high control (PDI < 1.5), depends
primarily on kd value for dormant species. Value of kc is less
important as its variation by 10–20 times has little effect on
a position of the alkoxyamine on Fischer’s diagram. Side
reactions, for example, H-atom transfer, can alter controlled
regime of polymerization, so possible side reactions should
ꢀ
ꢁ
1=3
3kd22kt
kc2
2=3
½Aꢂ5½Aꢂ02½Aꢂ0
t1=3
(4)
½Aꢂ5½Aꢂ0 e2k f t
(5)
(6)
d
D
kcD
fD5
kc1kcD
where [A] is the alkoxyamine concentration, fD is the fraction
of disproportionation.
Experiments of these types were performed for alkoxy-
amines 3a–d. Figure 1 demonstrates 1H NMR data before
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FIGURE 1 1H NMR spectra recorded before (lower) and after (upper) the decomposition of alkoxyamine 3a alone (a) and in the
presence of 20 equiv of PhSH (b). Temperature of decomposition was 70 ꢀC, concentration of alkoxyamine was 20 mM, solvent –
C6D6. Inset: NMR signals of the vinyl protons of alkene formed during decomposition of 3a in pure solution.
and after heating of alkoxyamine 3a in the presence and in
the absence of scavenger. Noteworthily, no trace of alkene
was observed upon thermolysis of this alkoxyamine in the
presence of PhSH [Fig. 1(b)], clearly showing that intramo-
lecular H-transfer does not occur. Analysis of alkoxyamines
decomposition kinetics (Supporting Information Fig. 1) gave
rate constants kd for the alkoxyamines 3a–d presented in
Table 1. Values of activation energies of homolysis were
obtained with average vibration factor A0 5 2.4 3 1014
slow. The kinetics analysis made it possible to evaluate the
contribution of H-atom transfer into one cycle of decomposi-
tion and recombination (disproportionation factor fD) for
alkoxyamines 3a–d (see Table 1). As disproportionation fac-
tor is relatively low for alkoxymine 3a that compound can
be considered as possible initiator for NMP of MMA. Values
of kc for alkoxyamines 3a–d formation were estimated by
structure-reactivity correlations developed by Marque et al.
as 5 3 107 M21 21 52–54
s
.
s21 49–51
.
Values of fD and of kcd (Table 1) decrease in the row
2d>2b>2c>2a clearly following the pattern of overall sterical
requirements of the substituents adjacent to the nitroxide
group. This fact is in agreement with general consideration
that access of the nitroxide oxygen to a proper hydrogen atom
of C-centered radical is a rate-limiting step in intermolecular
H-transfer. Meanwhile, this row does not coincide with the
row of kd and Ea dependence on alkoxyamine structure (3d
>3c>3a>3b). The difference may arise from nonplanar geom-
etry of sp3 alkoxyamine nitrogen atom with a bulky alkoxy
group: structures with more bulky, but more flexible diethyl
(3a) and spiro-cyclohexane (3c) moieties are less strained
There are two main parameters that contribute to the value
of homolysis and H-atom transfer kinetic parameters named
sterical hindrance and polarity of nitroxyl and alkyl fragment
of alkoxyamine. For alkoxyamines 3, alkyl parts are identical,
and polarity of nitroxyl parts has close values. So that here-
after only steric parameters of the nitroxyl parts are
discussed.
In the absence of scavenger, quantitative formation of alkene
was observed for all the alkoxyamines indicating radical
mechanism of H-atom transfer reaction. It should be noted
that kinetics of decomposition of alkoxyamines was rather
TABLE 1 Kinetics Parameters of Decomposition of Alkoxyamines (0.02 M) Alone and in Presence of Thiophenol (0.2 M) at 70 ꢀC
Decomposition in the Presence of
Scavenger
Decomposition in the Absence of Scavenger
Alkoxyamine
kd 3 104 (s21
)
Ea (kJ/mol)
kobs 3 104 (s21
)
fD (%)
kcd 3 1026 (M21s21
)
3a
3b
3c
3d
1a
2.6 6 0.2
3.3 6 0.3
1.8 6 0.3
1.0 6 0.3
6.0
118.0
117.0
119.0
120.0
115.5
0.035 6 0.003
0.090 6 0.005
0.040 6 0.005
0.0306 0.005
0.017
1.3
2.7
2.3
3.0
0.28
0.7
1.4
1.2
1.6
0b
a
b
Data from ref. 17.
Below the detection limit of the method.
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FIGURE 2 Fischer’s diagram for (a) Sty polymerization at 120 ꢀC in bulk with initiator monomer to initiator ratio 1/350; (b) for
MMA polymerization at 80 ꢀC in bulk with initiator monomer to initiator ratio 1/400 (full line) and 1/800 (dashed line). Symbols:
position of nitroxides 2a–d.
than in 3b, where 6,12-diazadispiro[4.1.4.2]tridec-12-ene ring
system is not capable of strong conformational changes.
independent. Resulting Fischer’s diagrams for the polymer-
ization of styrene and MMA are presented in Figure 2.
Comparison of new alkoxyamines 3a–d with alkoxyamine
117 (see Table 1) reveals that the later showed better param-
eters, that is, lower Ea value and smaller fD for the corre-
sponding nitroxide compared to 2a–d. A crucial obstacle
which impedes the application of 1 in NMP is thermal insta-
bility of the nitroxide.
Application of Alkoxyamine 3a as Initiator for NMP of
MMA and Sty
According to the above data, alkoxyamine 3a showed the
smallest contribution of H-atom transfer reaction among the
alkoxyamines studied. It is thermally stable up to 100 ꢀC;
therefore, it was selected as initiator for NMP of MMA. The
conditions of polymerization were selected according to
Fischer’s diagram analysis [Fig. 2(b)] that is bulk polymeriza-
tion at 80 ꢀC with initiator to monomer ratio were 1/800
and 1/350, so that target Mn was 80 and 35 kDa, respec-
tively. Although position of alkoxyamine 2a is on the border
of “living and controlled” zone when monomer to initiator
ratio is 800 to 1, it can still be tested as initiator in afore-
mentioned conditions.
Thermal Stability
Thermal degradation of a nitroxide can alter NMP parame-
ters decreasing the quota of “living” chains, capable of reini-
tiation, in a polymer formed.17 Heating of nitroxides 2a–d
degassed solutions in chlorobenzene at 100 ꢀC for 24 h did
not lead to decay of the nitroxides EPR signals, implying that
they are sufficiently stable to be used in NMP.
Fischer’s Diagrams
The evolution of molecular mass and polydispersity versus
conversion for the polymerizations is presented in Figure 3,
and the parameters of the polymerization experiments are
summarized in Table 2. When the target Mn was 80 kDa
[Entry 1, Table 2 and Fig. 3(a)], the growth of polymer
molecular weight was linear up to 30% of monomer conver-
sion. After that, the growth of the polymer’s molecular
weight stopped. The reason for that could be poor solubility
of pMMA in its monomer. Furthermore, it is known that the
values of homolysis and recombination rate constants
depend much of the length of the polymer chain. In particu-
lar, the value of kc decreases for nitroxide and alkyl radical
with polymer residue up to 10 times, and the value of kd
increases up to 10–15 times with respect to unimolecular
alkoxyamine.60 This can also influence the controlled regime
of the polymerization. Despite nonlinear growth of the
molecular weight of the pMMA in the course of polymeriza-
tion, the polydispersity of the polymer obtained was 1.4
which is below the limit for controlled polymerization. The
polymerization was stopped at monomer conversion 45%. It
An accurate determination of kd in the above mentioned
thermolysis experiments allowed for the use of Fischers’ dia-
grams for evaluation of applicability for NMP. Applying eqs
(1–3) for different experimental conditions (i.e., polymeriza-
tion temperature, polymerization time, monomer to initiator
ratio) we predicted a character of the polymerization. Values
of kp and kt measured by Buback and coworkers were
used.55,56
It has been shown by Guillaneuf et al.57 that dependence of
kd and kc on the length of polymer chain must be taken into
account for correct calculation of NMP. For example, kd, and
kc values implemented in phase diagrams in cases of MMA58
polymerizations were corrected for the account of the penul-
timate effect on homolysis, as well as for the account of the
chain-length effect on recombination.59
In this work, we used an average value of vibration factor
A0 5 2.4 3 1014 s21 for calculation of kd values at various
temperatures. kc values were assumed to be temperature
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FIGURE 3 Evolution of Mn and PDI vs. monomer conversion for NMP of MMA initiated with alkoxyamine 3a at T 5 80 ꢀC with dif-
ferent monomers to initiator (a) 800/1, (b) 350/1.
should be noted that GPC showed formation of pMMA with
slightly nonsymmetrical molecular weight distribution [see
Fig. 4(a)]. This could be due to slow initiation as described
by Guillaneuf et al.61
parameters of homolysis/recombination of macroalkoxy-
amine with growth of polymeric chain.
Lowering the monomer to initiator ratio allowed for con-
ducting the polymerization in controlled mode up to 55% of
conversion [Entry 2, Table 2 and Fig. 3(b)]. The PDI of the
polymer obtained was as low as 1.4 that is below the theo-
retical limit for the controlled polymerization. Reinitiation
experiment was performed in the same conditions (mono-
mer to macroinitiator ratio was 40,000/1, temperature of
To evaluate the quota of “living” chains in the polymer
obtained the reinitiation experiment was performed. The
polymeric pMMA-based alkoxyamine was used to initiate the
polymerization of styrene with the following conditions: tem-
perature 90 ꢀC, bulk, monomer to initiator ration 40,000/1.
Unfortunately, pMMA is poorly soluble in Sty.62 Hence, only
large monomer to macroinitiator ratio could be examined in
the reinitiation experiment.
ꢀ
polymerization 90 C) and revealed fraction of “living” chains
exceeding 90% [Fig. 4(b)]. As the result of the chain exten-
sion experiment, pMMA-b-pSty block copolymer was
obtained. The polymer exhibited Mn 5 220 kDa and
PDI 5 1.45. The final conversion of the Sty was 10%. The
expected molar mass of the copolymer was 230 kDa. The
deviation in the molar mass of the copolymer obtained was
ꢃ10%. This allows for estimation of fraction of “living”
chains as 90%, which is in a good agreement with GPC data.
Despite the nonlinear growth of Mn with conversion during
MMA polymerization, the polymer obtained was able to
reinitiate the polymerization of styrene [Fig. 4(a)]. The inves-
tigation of the reaction mixture samples using gel permea-
tion chromatography (GPC) showed that no polystyrene
homopolymer was formed and nearly all pMMA was con-
verted to block copolymer within 2.5 h. Integration of chro-
matography peaks gave estimation of the fraction of living
chains as 80%. High percentage of “living” chains confirms
insignificant impact of H-atom transfer reaction. Thus, the
reason of the noncontrolled regime of NMP of MMA at
monomer conversion higher than 30% is changes in kinetic
To get further insight in the “living” mechanism of MMA
polymerization initiated with 3a we performed a study of
polymer chain ends by means of ESR spectroscopy. It was
found that, within 6 h, the macroalkoxyamine decomposes
completely in solution in the presence of oxygen, which is
highlighted by growth of the ESR signal of nitroxide formed.
TABLE 2 Parameters of the Polymer Obtained During Polymerization of Sty and MMA Initiated with Alkoxyamine 3a
Polymerization
Temperature (ꢀC)
Time of
a
Entries
Monomer
[M]0/[I]0
Conversion
Mn (kDa)
Mn, th (kDa)
PDI
Experiment (h)
1
2
3
4
5
MMA
MMA
MMA
Sty
80
800/1
400/1
1,900/1
350/1
800/1
0.44
0.55
0.45
0.25
0.70
25
20
30
8.7
60
35
1.40
1.44
1.35
1.27
1.43
9
80
22
6
90
66.5
9.1
58
1.2
9
120
100
Sty
45
a
According to universal calibration with PS standards.
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FIGURE 4 Reinitiation experiment: styrene polymerization initiated with poly-MMA-2 initiator (M/I ratio 40,000/1 by weight) at 90
ꢀC: (a) macroinitiator pMMA from Entry 1 in Table 2 (Mn 5 25 kDa, PDI 5 1.40, solid line), GPC trace of reaction mixture after 1.5 h
of heating (dashed line), GPC trace of reaction mixture after 2.5 h of heating (Mn 5 410 kDa, PDI51.44, dotted line) (b) macroinitia-
tor pMMA from Entry 2 in Table 2 (Mn 5 20 kDa, PDI 5 1.44, full line line), GPC trace after 3.5 h of reaction (Mn 5 220 kDa,
PDI 5 1.45, dashed line).
The quantification of the ESR signal showed that the quota
of “living” chains, for example, chains capable to decompose
with formation of nitroxide is more than 80%. The resulting
ESR spectra are presented as Supporting Information.
the course of polymerization. As a result, the polymer
obtained is not “living.”
The applicability of alkoxyamine 3a for initiation of Sty poly-
merization was tested as well. The conditions were selected
according to the Fischer’s diagram (see above).The polymer-
ization was performed at 120 ꢀC with monomer to initiator
ratio 350 to 1. It should be noted that typically NMP of sty-
rene proceeds at elevated temperatures; however, recently
new nitroxide families allowed for considerable decrease in
polymerization temperatures.63
To study the temperature effect, the polymerization of MMA
initiated with 3a was performed at 90 ꢀC. The details are
summarized in Table 2, Entry 3. The resulting polymeriza-
tion kinetics is presented as Supporting Information. It
should be mentioned that the polymerization was controlled
up to about 30% of monomer conversion. The polymer
obtained was able to reinitiate polymerization of Sty (see
Supporting Information for details). The quota of “living”
chains was estimated as 50%. It should be noted that at 90
ꢀC the impact of H-atom transfer reaction increases. This
leads to higher fraction of irreversible termination events in
The evolution of Mn and PDI versus conversion for NMP of
Sty initiated with alkoxyamine 3a is presented in Figure
5(a), the parameters of experiment and characteristics of the
polymer obtained are summarized in Table 2 (Entries 4 and
FIGURE 5 (a) Evolution of Mn and PDI versus monomer conversion for NMP of Sty initiated with alkoxyamine 3a at T 5 120 ꢀC,
[M]/[I] 5 350/1. w, PDI; ᭿, Mn; dashed line, theoretical molecular weight; (b) GPC traces of poly-Sty sample in abovementioned
polymerization experiment obtained at 25% of monomer conversion (Mn 5 8.7 kDa, PDI 5 1.27, solid line) and pSty-b-pMMA sam-
ple obtained in reinitiation experiment (Mn 5 9.2 kDa, PDI 5 1.30, dashed line) after 1 h of reaction.
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TABLE 3 Results of the Chain Extension/Reinitiation Experiments
Monomer to
Resulting
Polymer
Resulting
Macroinitiator
Initiator
Monomer Ratio
Temperature Duration
Polymer,
a
Entries Mn (kDa) PDI
(ꢀC)
(h)
Conversion Mn (kDa) PDI Mn,th (kDa) Fb
1
2
3
4
5
pMMA 25 1.40 Sty
pMMA 20 1.44 Sty
40,000/1
22,000/1
13,000/1
15,000/1
9,000/1
90
2.5
3.5
1
0.1
410 1.44
220 1.45
13,5 1.20
9.2 1.30
390 1.93
430
210
–
0.8
0.9
0.9
0.9
0.9
90
0.1
pSty 7.0 1.25
pSty 8.7 1.27
pSty 21 1.17
Sty
120
100
100
>0.01
>0.01
0.44
MMA
MMA
1
–
15
417
a
b
Molecular weight calculated on the base of monomer to initiator ratio
Fraction of “living” chains.
and monomer conversion.
5). Owing to relatively low temperatꢀure, the polymerization
proceeded rather slowly. At T 5 120 C only 25% of conver-
sion was achieved after 9 h. The polymerization was con-
trolled which is highlighted by linear growth of polymer
molecular weight with conversion and the resulting polymer
had Mn 5 8.7 kDa and PDI 5 1.27 [Fig. 5(a)]. The obtained
polymer had high percentage of “living” chains, which was
proved by chain extension experiments. Polymer obtained at
conversion 24% after about 4 h of heating was precipitated
with cold methanol and filtered (Mn 5 7.0 kDa and
PDI 5 1.25). The obtained polymer (5 mg) was added to 1
(Mn 5 21 kDa, PDI 5 1.17). The precipitated pSty was added
to MMA monomer (1/9000 initiator to monomer ratio) and
the mixture was heated in the cavity of the NMR spectrome-
ter at 80 ꢀC. The results are presented as Supporting Infor-
mation and summarized in Table 3. The GPC analysis
showed the increase of molecular weight of the resulting
polymer. The resulting block copolymer had higher PDI
(Table 3, Entry 5), presumably because the polymerization
was carried out without stirring.
CONCLUSIONS
ꢀ
mL of styrene and the mixture was heated at 130 C. In the
In this article, we demonstrated high synthetic potential of a
new methodology of sterically hindered nitroxides construc-
tion via intramolecular cycloaddition—isoxazolidine ring
opening—oxidation sequence. Series of new sterically hin-
dered imidazoline nitroxides have been prepared starting
from aldonitrones of 2H-imidazol 1-oxide and 4H-imidazole
3-oxide. To study their applicability for initiation of NMP of
different monomers, the values of the homolysis rate con-
stants were determined for corresponding alkoxyamines and
possible side reactions were monitored and quantified.
According to Fischer’s diagrams, it was found that alkoxy-
amines under investigation are suitable for initiation of NMP
of styrene and MMA. Moreover, high steric hindrance
decreases an impact of H-atom transfer reaction for this
nitroxides making them potentially effective mediators of
NMP of methacrylic monomers.
chain extension experiment performed with styrene, one
could observe the growth of molecular weight (Table 3,
Entry 3). Owing to high polymerization temperature and
small amount of macroinitiator, the contribution of styrene
self-initiation process was not negligible; however, this did
not prevent formation of high molecular weight polystyrene
with relatively low PDI.
It should be noted that application of 3a in Sty homopolyme-
rization allows for the achievement of high monomer conver-
sions. This was verified in polymerization experiment
performed in the cavity of NMR spectrometer: the sample of
700 lL of Sty and 3 mg of 3a (monomer to initiator ratio is
800/1) was degassed and placed into the preheated NMR
ꢀ
cavity (T 5 100 C). After 45 h of heating, the monomer con-
version reached 70% affording pSty with Mn 5 60 kDa,
PDI 5 1.43 (Table 2, Entry 5).
Application of alkoxyamine 3a allows for controlled polymer-
ization of Sty and MMA up to moderate conversions with
formation of polymer with low polydispersity and high quota
of “living” chains. Application of 3a as initiator for NMP is
beneficial. First of all, when 3a is employed as initiator, con-
trolled regime of two different monomers (Sty and MMA)
could be achieved. As a result, block-copolymer preparation
is facilitated. It should be noted that such MMA mediators as
DPAIO-nitroxide26 or N-phenyl nitroxides65,66 are not suita-
ble for NMP of Sty. Furthermore, NMP of MMA initiated by
3a proceeds at lower temperature in comparison with DPAIO
and N-phenylalkoxyamines and it allows for preparation of
polymers with close values of Mn and PDI. Lowering poly-
merization temperature increases the energy efficiency of
the process. In contrast to MMA polymerizations using SG1-
It is known that sometimes the block copolymer cannot be
obtained when using NMP technique with pSty macroinitia-
tor.64 The pSty obtained in the styrene homopolymerization
initiated with 3a (Mn 5 8.7 kDa and PDI 5 1.27) was also
able to reinitiate the polymerization of MMA with formation
of block copolymer of Mn 5 9.2 kDa and PDI 5 1.30 [Fig. 5(b)
and Table 3, Entry 5]. The reaction was carried out for 1 h
to prevent thickening of the reaction mixture. Owing to short
reaction time, the increase of the Mn in reinitiation experi-
ment was not large (only 0.5 kDa).
To prove once again the formation of block copolymer, the
reinitiation experiment was conducted with the pSty sample
obtained at 40% of conversion during NMR experiment
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based initiator, no addition of Sty16 or acrylonitrile67 or 9-(4-
vinylbenzyl)29H-carbazole68 is required to reach controlled
regime of polymerization when 3a is used as initiator, so
that block copolymer with pure blocks could be prepared.
15 D. Zubenko, I. Kirilyuk, G. Roshchupkina, I. Zhurko, V.
Reznikov, S. R. A. Marque, E. Bagryanskaya, Helv. Chim. Acta
2006, 89, 2341–2353.
16 M. Edeleva, S. R. A. Marque, D. Bertin, D. Gigmes, Y.
Guillaneuf, S. Morozov, E. Bagryanskaya, J. Polym. Sci. Part A:
Polym. Chem. 2008, 46, 6828–6842.
Thus, applicability of investigated nitroxides for mediation of
NMP of MMA and styrene was demonstrated. Controlled
polymerization for both monomers was conducted in mild
reaction conditions. The polymer formed contained high frac-
tion of “living” chains and was able to reinitiate the polymer-
ization making preparation of block copolymer possible.
17 M. Edeleva, I. Kirilyuk, D. Zubenko, I. Zhurko, S. R. A.
Marque, D. Gigmes, Y. Guillaneuf, E. Bagryanskaya, J. Polym.
Sci. Part A: Polym. Chem. 2009, 47, 6579–6595.
18 M. Edeleva, S. R. Marque, K. Kabytaev, Y. Guillaneuf, D.
Gigmes, E. Bagryanskaya, J. Polym. Sci. Part A: Polym. Chem.
2013, 51, 1323–1336.
19 G. Gryn’ova, Ch. Y. Lina, M. L. Coote, Polym. Chem. 2013, 4,
3744–3754.
ACKNOWLEDGMENTS
20 D. H. Kim, K. H. A. Lau, W. Joo, J. Peng, U. Jeong, C. J.
Hawker, J. K. Kim, T. P. Russell, W. Knoll, J. Phys. Chem. B
2006, 110, 15381–15388.
This work was partly supported by the Russian Foundation for
Basic Research (Grants No. 12-03-1042a, 12-03-00737a and
12-03-33010), by Russian President’s foundation (program
ŒR-1654.2013.3) and by the Ministry of Education and Sci-
ence of the Russian Federation (projects 8436 and 8456). The
Center of Collective utilization of NIOC SB RAS is acknowledged
for the recording of NMR spectra for this work.
21 H. Yulmaz, M. Degirmenci, H. I. Unal, J. Colloid Interface
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