A Homotelechelic bis-terpyridine macroligand: One-step synthesis and its metallo-supramolecular self-assembly

Article abstract of DOI:10.1002/pola.26586

A homotelechelic macroligand bearing two 2,2′:6′,2″- terpyridin-4′-yl units, as chain ends, is used as building block for the preparation of a linear metallo-supramolecular chain-extended polymer. The macroligand has been prepared by nitroxide-mediated po

Full text of DOI:10.1002/pola.26586

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
A Homotelechelic Bis-terpyridine Macroligand: One-Step Synthesis and
its Metallo-Supramolecular Self-Assembly
Ulrich Mansfeld,1,2,3 Andreas Winter,1,2,3 Martin D. Hager,1,2,3 Wolfgang Gu¨ nther,1
Esra Altuntasꢀ,1,2 Ulrich S. Schubert1,2,3
1
L
a
b
o
r
a
t
o
r
y
f
o
r
O
r
g
a
n
i
c
a
n
d
M
a
c
r
o
m
o
l
e
c
u
l
a
r
C
h
e
m
i
s
t
r
y
7
(
I
O
M
C
)
,
F
r
i
e
d
r
i
c
h
-
S
c
h
i
l
l
e
r
-
U
n
i
v
e
r
s
i
t
y
J
e
n
a
,
H
u
m
b
o
l
d
t
s
t
r
.
1
0
,
0
7
7
4
3
J
e
n
a
,
G
e
r
m
a
n
y
2
J
e
n
a
C
e
n
t
e
r
f
o
r
S
o
f
t
M
a
t
t
e
r
(
J
C
S
M
)
,
P
h
i
l
o
s
o
p
h
e
n
0
w
e
g
,
0
7
7
4
3
J
e
n
a
,
G
e
r
m
a
n
y
3
D
u
t
c
h
P
o
l
y
m
e
r
I
n
s
t
i
t
u
t
e
(
D
S
P
I
)
,
P
.
O
.
B
o
x
9
0
2
,
5
6
0
A
X
E
i
n
d
h
o
v
e
n
,
T
h
e
N
e
t
h
e
r
l
a
n
d
s
C
o
r
r
e
s
p
o
n
d
e
n
c
e
t
o
:
U
.
S
.
c
h
u
b
e
r
t
(
E
-
m
a
i
l
:
u
l
r
i
c
h
.
s
c
h
u
b
e
r
t
@
u
n
i
-
j
e
n
a
.
d
e
)
R
e
c
e
i
v
e
d
6
N
o
v
e
m
b
e
r
2
0
1
2
;
r
e
v
i
s
e
d
2
3
D
e
c
e
m
b
e
r
2
0
1
2
;
a
c
c
e
p
t
e
d
8
J
a
n
u
a
r
y
2
0
1
3
;
p
u
b
l
i
s
h
e
d
o
n
l
i
n
e
DOI: 10.1002/pola.26586
ABSTRACT:
20 60 200
A
h
o
m
o
t
e
l
e
c
h
e
l
i
c
m
a
c
r
o
l
i
g
a
n
d
b
e
a
r
i
n
g
t
w
o
i
n
t
o
t
h
e
c
h
a
i
n
-
e
x
t
e
n
d
e
d
m
e
t
a
l
l
o
p
o
l
y
m
e
r
a
n
d
t
h
e
d
i
s
a
s
s
e
m
b
l
y
2
,
:
,
-
t
e
r
p
r
y
r
i
d
i
n
-
4 0
-
y
l
u
n
i
t
s
,
a
s
c
h
a
i
n
e
n
d
s
,
i
s
u
s
e
d
a
s
b
u
i
l
d
-
t
h
e
r
e
o
f
,
i
n
t
h
e
p
r
e
s
e
n
c
e
o
f
a
s
t
r
o
n
g
p
c
c
o
m
p
e
t
i
t
i
v
e
l
i
g
a
n
d
,
h
a
s
i
n
g
b
l
o
c
k
f
o
t
h
d
e
p
r
e
p
a
r
a
t
i
o
n
o
f
a
l
i
n
e
a
r
m
e
t
a
l
l
o
-
s
u
p
r
a
m
o
l
e
c
u
l
a
r
d
a
d
d
b
o
o
e
e
n
s
t
u
d
i
e
d
b
y
U
V
–
v
i
s
a
b
s
o
r
p
t
i
o
n
s
e
t
r
o
s
c
o
p
y
a
n
d
d
i
f
f
u
s
i
o
n
-
c
h
a
i
n
-
e
x
t
e
n
d
e
p
o
l
y
m
e
r
.
T
h
e
m
a
c
r
o
l
i
g
a
n
d
h
a
s
b
e
e
n
p
r
e
p
a
r
e
r
f
d
e
r
e
d
N
M
R
s
p
e
c
t
r
o
s
c
o
p
y
.
T
h
e
r
e
v
e
r
s
i
b
i
l
i
t
y
o
f
t
h
e
f
o
r
m
a
t
i
o
n
b
y
n
i
t
r
o
x
i
d
e
-
m
e
d
i
a
t
e
d
p
o
l
y
m
e
r
i
z
a
t
i
o
n
(
N
M
P
)
o
f
s
t
y
r
e
n
e
u
s
i
n
g
t
h
e
m
e
t
a
l
l
o
-
s
u
p
r
a
m
o
l
e
c
u
l
a
r
m
a
t
e
C
V
r
i
a
l
,
w
h
e
n
a
d
d
r
e
s
s
e
d
b
y
bis
-
t
e
a
a
r
p
y
r
i
d
i
n
e
-
f
u
n
c
t
i
o
n
a
l
i
z
e
d
N
h
M
P
i
n
i
t
i
a
t
o
r
.
T
h
e
c
o
n
t
r
o
l
l
e
e
e
x
t
e
r
n
a
l
s
t
i
m
u
l
i
,
c
o
u
l
d
b
e
p
r
o
v
e
n
.
2
0
1
3
W
i
l
e
y
P
e
r
i
o
d
i
c
a
l
s
,
c
c
h
h
a
a
r
r
c
c
t
e
e
r
o
f
t
h
e
N
M
P
p
r
o
c
e
s
s
a
s
y
s
b
e
e
n
c
o
n
f
i
r
m
e
d
b
y
d
e
t
a
i
l
I
n
c
.
J
P
o
l
y
m
S
c
i
P
a
r
t
A
:
P
o
l
y
m
C
h
e
m
0
0
0
:
0
0
0
–
0
0
0
,
2
0
1
3
t
r
i
z
a
t
i
o
n
o
f
t
h
e
p
o
l
y
m
e
r
b
e
s
i
z
e
-
e
x
c
l
u
s
i
o
n
c
h
r
o
m
a
t
o
g
r
a
-
s
s
p
h
y
,
n
u
c
l
e
a
r
m
a
g
n
e
t
i
c
r
e
s
o
n
a
n
c
p
e
c
t
r
o
s
c
o
p
y
a
s
w
e
l
l
a
s
m
a
s
KEYWORDS:
m
e
t
a
l
-
p
o
l
y
m
e
r
c
o
m
p
l
e
x
e
s
;
n
i
t
r
o
x
i
d
e
-
m
e
d
i
a
t
e
d
p
o
-
I
I
s
p
e
c
t
r
o
m
e
t
r
y
.
S
u
b
s
e
q
u
e
n
t
l
y
,
t
h
e
s
e
l
f
-
a
s
s
e
m
b
l
y
w
i
t
h
F
e
i
o
n
l
y
m
e
r
i
z
a
t
i
o
n
;
s
u
p
r
a
m
o
l
e
c
u
l
a
r
s
t
r
u
c
t
u
r
e
s
;
t
e
l
e
c
h
e
l
i
c
INTRODUCTION The design of functional materials with
tailor-made chemical and physical properties meeting the
needs of various technology areas is one of the key chal-
lenges in today’s polymer and material science. In particular,
polymers precisely functionalized at their chain ends play an
important role in view of potential applications, for example,
in the synthesis of block copolymers, thermoplastic elasto-
mers, polymer networks, surfactants, or as macromonomers.1
Telechelic polymers are defined as polymeric molecules fea-
turing reactive end-groups that have the capacity to enter
into further polymerizations or other reactions.2 Telechelics
can be classified as mono-/semi-, di-, tri-, and multifunc-
tional telechelics (i.e., polytelechelics).3 In polymer science,
the term ‘‘telechelic’’ typically refers to a linear polymer hav-
ing the same functionality at both chain ends (‘‘homotele-
chelic’’); when the polymer chain possesses two different
functional groups at its ends, it is called ‘‘heterotelechelic.’’4
Thereby, the end-groups originate either from the initiator or
the terminating agent (or the chain-transfer agents) in the
case of polymers prepared by chain-growth reactions. In con-
trast, the functional groups could originate from monomer(s)
in typical polycondensation and polyaddition reactions,
respectively.5 The end-group modification may also take
place in appropriate post-polymerization reactions. Starting
from Bayer’s and Uraneck’s pioneering work6,7 this class of
polymeric materials has attracted considerable interest in
current research.4
The precise control of the polymerization process is crucial
for the preparation of well-defined telechelics and other end-
functionalized macromolecules.8 Traditionally, control over
the degree-of-functionality, the molar mass as well as the
uniformity (i.e., polydispersity) was accomplished using liv-
ing ionic polymerization techniques.9 As a drawback, the
ionic processes suffer from stringent synthetic requirements
and, in some cases, are sensitive to the functional groups to
be incorporated. In contrast, free radical polymerization is
flexible and less sensitive to the polymerization conditions
and tolerates a large variety of functional groups. However,
free radical polymerization reactions suffer from poor con-
trol over the molar mass and degree-of-functionalization
(due to competing coupling, disproportionation reactions
A
d
d
i
t
i
o
n
a
l
S
u
p
p
o
r
t
i
n
g
I
n
f
o
r
m
a
t
i
o
n
m
a
y
b
e
f
o
u
n
d
i
n
t
h
e
o
n
l
i
n
e
v
e
r
s
i
o
n
o
f
t
h
i
s
a
r
t
i
c
l
e
.
C
V
2
0
1
3
W
i
l
e
y
P
e
r
i
o
d
i
c
a
l
s
,
I
n
c
.
W
W
W
.
M
A
T
E
R
I
A
L
S
V
I
E
W
S
.
C
O
M
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0
1

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
and uncontrolled chain transfer). The vast developments in
controlled radical polymerization (CRP) nowadays provide
access to well-defined telechelic polymers with controlled
functionality.10 In this respect, the atom-transfer radical poly-
merization,11,12 the nitroxide-mediated polymerization
(NMP),13 the reversible addition-fragmentation chain-transfer
polymerization14 and others15–18 have been used for the
preparation of telechelic polymers.4,19 For the most common
CRP methods, two main strategies for synthesizing telechelic
polymers can be pointed out:20,21 functionalities can be
incorporated onto the initiating and/or the terminating frag-
ment of initiators providing a,x-difunctionalized, a-function-
alized and x-functionalized telechelic polymers, respectively.
Moreover, one type or two different types of functionalities
can be attached to yield homotelechelic and heterotelechelic
polymers, respectively. Alternatively, the functionalization of
the chain ends can be achieved by appropriate post-polymer-
ization reactions. However, the former approach has a wider
scope by means of construction flexibility compared to a
postmodification approach for telechelic polymers, as the
chain length and composition between the functionalities can
be varied in less reaction steps and purification can be sim-
ply performed by precipitation.
(Merck). Styrene was freshly purified prior to use by filtration
over neutral aluminum oxide 90 (Merck). 1D (1H, 13C) and 2D
(1HA1H COSY, DOSY) nuclear magnetic resonance (NMR)
experiments were conducted on a Bruker 400 MHz spectrom-
eter at 298 K. Chemical shifts are reported in parts per million
(ppm) downfield from tetramethylsilane and were calibrated
to the residual solvent peaks. Deuterated solvents for NMR
spectroscopy were obtained from Cambridge Isotope Labora-
tories as well as Eurisotop. For size-exclusion chromatography
(SEC) an Agilent system equipped with a PSS Degasser, a
G1310A Pump, a G1329A AS, a G1362A RID detector and a
PSS GRAM guard/1000/30 column was used. Dimethylaceta-
mide (DMA) containing 0.21% LiCl was used as eluent with a
ꢀ
flow rate of 1 mL/min at 40 C. Linear polystyrene was used
as the calibration standard. Gas chromatographic (GC) meas-
urements were performed on an Interscience Trace GC with a
Trace Column RTX-5 connected to a PAL autosampler. UV–vis
absorption spectra were recorded in diluted chloroform solu-
tions on a Perkin-Elmer Lamda-45 UV-vis spectrophotometer
at room temperature (1-cm cuvettes). GC mass spectrometry
was conducted on a Shimadzu GC17A connected to a mass
spectrometer. Infrared spectra were recorded on a Bruker
IFS55 FT-IR spectrometer. Matrix-assisted laser desorption/
ionization time-of-flight mass spectrometry (MALDI-TOF MS)
was performed on a Voyager-DETM PRO BiospectrometryTM
Workstation (Applied Biosystems) time-of-flight mass spec-
trometer using linear and reflector mode for operation. Dithra-
nol or 2-[(2E)-3-(4-tert-butylphenyl)-2-methylprop-2-enylide-
ne]malononitrile (DCTB) were used as matrices and NaI as
additive. The spectra were recorded in the positive ion mode
and ionization was performed with a 337 nm pulsed nitrogen
laser. The MALDI-TOF mass spectra of polymers were also
measured on a Bruker UltraflexTM III TOF/TOF spectrometer.
Electrospray ionization time-of-flight (ESI-TOF) mass spectro-
metric measurements were performed in the positive ion
mode with a micrOTOF (Bruker Daltonics) mass spectrometer
equipped with an automatic syringe pump which is supplied
from KD Scientific for sample injection. The standard ESI
source was used to generate the ions. For polymer samples, a
concentration of 10 lg mLꢁ1 was used (solvent: chloroform/
acetonitrile mixtures) and injected at a constant flow of the
sample solution (3 lL minꢁ1). No salt or acid addition prior
to analysis was required, ionization occurred readily from the
sodium content that is naturally present in the glass or in the
polymer sample. The ESI-Q-TOF MS instrument was calibrated
in the m/z range of 50 to 3000 using a calibration standard
which is supplied from Agilent (Tunemix solution). All data
were processed via Bruker’s data analysis software version 4.0.
The ESI mass spectra were deconvoluted to obtain singly charged
species, from the deconvoluted spectrum the Mn value of the
polymer was calculated. The following compounds were
prepared according to literature procedures: N-(Tert-butyl)-O-(1-
(4-(chloromethyl)phenyl)ethyl)-N-(2-methyl-1-(4-(((tetrahydro-
2H-pyran-2-yl)oxy)methyl)phenyl)propyl)hydroxylamine (1),28
2,20:60,200-terpyridin-40 (10H)-one (2),34 O-(1-(4-((2,20:60,200-ter-
pyridin-40-yloxy)methyl)phenyl)ethyl)-N-(tert-butyl)-N-(2-methyl-
1-(4-(((tetrahydro-2H-pyran-2-yl)-oxy)methyl)phenyl)propyl)hy-
droxylamine (3)28 and (4-(1-((1-(4-((2,20:60,200-terpyridin-40-
In this study, a homodifunctional alkoxyamine based on the
TIPNO nitroxide was utilized for the synthesis of a homotele-
chelic polymer via NMP. Functionalized TIPNO derivatives
were initially reported by Hawker and coworkers22,23 as uni-
versal initiators for NMP featuring a high end-group fidelity
and a high tolerance toward a broad range of functional
groups
(TIPNO:
2,2,5-trimethyl-4-phenyl-3-azahexane-3-
nitroxide). Schubert and co-workers expanded the scope of
functional TIPNOs to the field of terpyridine chemistry by
using tpy-TIPNO, as initiator, for the synthesis of terpyridine-
functionalized semi-telechelic block copolymers via
NMP.24–27 Later, the utilization of a heterodifunctional TIPNO
initiator featuring one terpyridine (tpy) and one 2-ureido-
4H-pyrimidone (UPy) moiety, as orthogonal supramolecular
binding sites, for the NMP of styrenes was reported.28,29 The
heterotelechelic polymers were self-assembled into supramo-
lecular chain-extended polymers exhibiting stimuli-respon-
sive behavior based on the orthogonality of the non-covalent
interactions. The homodifunctional initiator bearing two tpy
moieties would be a versatile building block for the prepara-
tion of metallo-supramolecular chain-extended polymers
based on in-chain metal-to-ligand coordinative bonds.24,30–33
Herein, the synthesis of the initiator, its application in the
NMP of styrene and the subsequent reversible formation of a
chain-extended polymer via metal-ion complexes is reported.
EXPERIMENTAL
All chemicals were received from Aldrich, Fluka and Acros;
solvents were purchased from Biosolve. Unless otherwise
stated, the chemicals and solvents were used without further
purifications. DMF was dried over molsieves (pore size of
4 Å). THF and toluene were dried using a PureSolv-ENTM sol-
vent purification system. Column chromatography was carried
out on silica gel 60 and standardized aluminum oxide 90
2
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
yloxy)methyl)phenyl)ethoxy)(tert-butyl)amino)-2-methylpropyl)-
phenyl)methanol (4).28
4H), 6.34–7.54 (m, 550H), 7.90 (m, 4H), 8.11–8.26 (m, 4H),
8.62–8.76 (m, 8H) ppm. SEC (CHCl3, RI): Mn
10,000 g molꢁ1, PDI ¼ 1.17.
¼
N-(1-(4-((2,20:60,200-Terpyridin-40-yloxy)methyl)phenyl)-2-methyl
propyl)-O-(1-(4-((2,20:60,200-terpyridin-40-yloxy)methyl)pheny-
l)ethyl)-N-(tert-butyl)hydroxylamine (tpy-TIPNO-tpy, 5). Tri-
phenylphosphine (100 mg, 0.38 mmol), 3 (70 mg, 0.11
mmol) and 2,20:60,200-terpyridin-40 (10H)-one (35 mg, 0.14
mmol) were dissolved in dry THF (1.5 mL). Diisopropyl azo-
dicarboxylate (DIAD, 77 mg, 0.38 mmol) was added drop-
wise to the solution. Subsequently, the reaction mixture was
stirred overnight at room temperature. The solution was
concentrated and subjected to a precolumn (Al2O3, eluent:
heptane-to-chloroform gradient) to remove instable, gas-gen-
erating byproducts. The concentrated oil was subsequently
purified by column chromatography (Al2O3; eluent: diethyl
ether/pentane, 4:1 ratio) and preparative SEC (BioRad beads
S-X8; eluent: dichloromethane) to yield 5 as a colorless
amorphous solid (69 mg, 70%, mixture of diastereomers).
UV-Vis Titration Experiments
The macroligand (6b 0.85 mg) was dissolved in chloroform
(20 mL) and FeCl2 (0.913 mg, 0.0072 mmol) was dissolved
in methanol (10 mL). The methanol solution was subse-
quently added to the polymer solution in steps of 10 lL
while the formation of the FeII bis-complex was monitored
by UV–vis absorption spectroscopy after each addition. The
point-of-equivalence and the Mn value of the macroligand
were obtained by plotting the UV–vis absorption intensity at
the LC (319 nm) and the absorption band at 559 nm [mainly
ascribed to the metal-to-ligand charge-transfer (MLCT)] as a
function of added FeII ions.
Metallo-Polymerization of 6b
A solution of FeCl2 ꢂ 4H2O (0.015 mmol) and SnCl2 ꢂ 2H2O
(0.015 mmol) in methanol (300 lL) was added to a solution
of 6b (0.010 mmol) in chloroform (1.2 mL). The resultant
clear solution was stirred under an argon atmosphere at 40 ꢀC
for 24 h. After cooling to room temperature and adding an
excess of NH4PF6 (ca., 15 eq.) the reaction mixture was parti-
tioned between water and dichloromethane. The organic phase
was washed three times with water, dried over Na2SO4 and
concentrated in vacuo to result the chain-extended polymer.
1H NMR (400 MHz, CD2Cl2, d, diastereomers aþb): 0.20 (d, J
¼ 6.5 Hz, 3H, a), 0.58 (d, J ¼ 6.4 Hz, 3H, b), 0.83 (s, 9H, b),
0.95 (d, J ¼ 6.2 Hz, 3H, a), 1.09 (s, 9H, a), 1.35 (d, J ¼ 6.3 Hz,
3H, b), 1.38–1.51 (m, 1H, a), 1.59 (d, J ¼ 6.5 Hz, 3H, a), 1.68
(d, J ¼ 5.3 Hz, 3H, b), 2.28–2.49 (m, 1H, b), 3.39 (d, J ¼ 10.8
Hz, 1H, a), 3.52 (d, J ¼ 10.6 Hz, 1H, b), 4.99 (q, J ¼ 6.5 Hz,
2H, aþb), 5.27 (s, 2H, a/b), 5.32 (s, 2H, b), 5.34 (s, 2H, a/b),
5.37 (s, 2H, a), 7.27–7.66 (m, 16H, aþb), 7.27–7.40 (m, 8H,
aþb), 7.82–7.94 (m, 8H, aþb), 8.11–8.20 (m, 8H, aþb), 8.58–
8.77 (m, 16H, aþb); 13C NMR (100 MHz, CD2Cl2, d, diaster-
eomers aþb): 20.6, 20.8, 21.7, 21.8, 22.7, 24.4, 28.0, 28.2,
31.7, 32.0, 53.4, 60.4, 60.5, 69.9, 70.0, 70.1, 70.1, 71.7, 71.8,
82.5, 83.3, 107.4, 107.5, 121.1, 123.9, 126.5, 126.7, 127.4,
127.4, 127.6, 131.2, 131.3, 134.0, 134.3, 134.6, 135.4, 136.7,
142.3, 142.6, 144.9, 145.8, 149.1, 155.9, 156.0, 157.2, 167.0,
167.0, and 167.1; MALDI-TOF MS (m/z, matrix: DCTB):
870.46 [(MþNa)þ]; High resolution ESI-MS: anal. calcd. for
[C54H53N7O3Na]þ m/z ¼ 870.4102, found: m/z ¼ 870.4103.
{[Fe(6b)2](PF6)2}n. 1H NMR (400 MHz, CD2Cl2): d ¼ 0.46–
2.67 (set of multiplets), 3.24–3.51 (m, 1H), 4.12–4.30 (m,
1H), 5.61–5.81 (m, 4H), 6.35–7.48 (m, 570H), 7.50–7.71 (m,
4H) 7.80–7.94 (m, 4H), 8.28–8.54 (m, 8H) ppm.
DOSY NMR Experiments of {[Fe(6b)2](PF6)2}n
For the DOSY experiment 30 mg of the supra-polymer
{[Fe(6b)2](PF6)2}n were dissolved in 1 mL dichloromethane-
d2/methanol-d4 (4:1) and measured at 298 K. For the inves-
tigation of the responsiveness, 50 lL of an aqueous solution
(35%) of HEEDTA was added into the NMR tube and after
10 min the DOSY was measured again.
General Procedure for the Polymerization of Styrene
Styrene was freshly purified by filtration over Al2O3 prior to
use to remove the inhibitor. Solvents were used as supplied.
To a clear solution of the initiator 5 in anisole, freshly puri-
fied styrene was added to the polymerization vessel. After
applying three freeze-pump-thaw-cycles to remove the oxy-
gen, argon was added and the vessel was immersed in an oil
RESULTS AND DISCUSSION
The synthesis of the homodifunctional initiator tpy-TIPNO-
tpy (5) was carried out via stepwise functionalization of the
nitroxide derivative
1 (Scheme 1). As reported previ-
ously,28,29 the terpyridine-containing initiator 4, as key build-
ing block, was obtained by nucleophilic substitution reaction
of the heterodifunctional alkoxyamine 1 with 2,20:60,200-ter-
pyridin-40(10H)-one (2) and subsequent cleavage of the THP-
protecting group from the intermediate 3 (THP: tetrahydro-
pyrane). Finally, the homodifunctional system 5 could be
ꢀ
bath at 123 C for a certain period of time. To remove resid-
ual monomer the reaction mixture was precipitated from
chloroform into cold methanol. The conversion was deter-
mined by GC measurements, the molar masses (Mn, Mw) and
the polydispersity index (PDI) were determined by SEC,
whereas 1H NMR spectroscopy was used for the calculation
of the end-group functionality (by integration and compari-
son of the corresponding end-group signals) and Mn values
(by the integration of the polymer backbone to the terpyri-
dine signals).
prepared in high yield via Mitsunobu coupling of
4
with 2.35,36
The telechelic initiator was characterized by NMR spectros-
copy and mass spectrometry. The central TIPNO moiety has
two stereogenic centers. Thus, 5 was obtained as a mixture
of two diastereomers. Consequently, two main sets of signals
tpy-PS-TIPNO-tpy (6b)
1H NMR (400 MHz, CD2Cl2): d ¼ 0.05–2.64 (set of multip-
lets), 3.15–3.41 (m, 1H), 4.03–4.25 (m, 1H), 5.22–5.41 (m,
(in a ca. 1:1 ratio) could be observed in the H and (partially)
1
also in the 13C NMR spectrum (see Fig. 1 and Supporting
W
W
W
.
M
A
T
E
R
I
A
L
S
V
I
E
W
S
.
C
O
M
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0
3

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 1
S
c
h
e
m
a
t
i
c
r
e
p
r
e
s
e
n
t
a
t
i
o
n
o
f
t
h
e
s
y
n
t
h
e
s
i
s
o
f
t
e
l
e
c
h
e
l
i
c
5
v
i
a
s
t
e
p
w
i
s
e
f
u
n
c
t
i
o
n
a
l
i
z
a
t
i
o
n
.
Information Fig. S1). The attachment of the second terpyri-
dine entity was characterized in the 1H NMR spectrum by a
quantitative shift of the signals for the benzyl group com-
pared to alkoxyamine 4, that is, for the methylene group 9
(4.5 ppm to 5.4 ppm) and the aromatic protons b (7.2–7.5
ppm; Fig. 1). The full assignment of these signals could be
carried out unambiguously by 2D NMR experiments. Admit-
tedly, additional signals could be observed in the 1H NMR
spectra, which are still present after repeated column chro-
matography as well as preparative SEC purifications of the
product. After careful analysis of these signals in the 2D NMR
spectra, they show a similar cross peak pattern as the desired
structure 5 and, thus, the presence of the analogous meta-
substituted isomer can be concluded (commercially available
4-chloromethylstyrene, used for the synthesis of 1, consists
of a mixture of para- and meta-isomers in a about 9:1 ratio,
see Supporting Information Fig. S2). In this vein, MALDI-TOF
mass spectrometric analysis of 5 showed only the expected
[MþH]þ adduct at m/z ¼ 870.46, the experimental isotopic
pattern was in good agreement with the calculated value of
m/z ¼ 870.41 (Fig. 2). All additional peaks at lower m/z val-
ues could be assigned to fragments of 5, as supported by the
parent ion peaks from the spectrum in the LIFT mode. The
main peaks at m/z ¼ 389 and 504 are ascribed to the Naþ-
adducts of fragments pointing to a fragmentation at the ther-
mally labile NOAC bond of the alkoxyamine entity under the
measurement conditions. Alkoxyamine 5 was further con-
firmed by high resolution ESI-TOF MS measurements, where
also the Naþ adduct could be experimentally found (m/z ¼
870.4103), deviated by only m/z ¼ 0.0001 from the calcu-
lated value (m/z ¼ 870.4102; see the isotopic pattern in the
Supporting Information Fig. S3).
In view of homotelechelic polymers featuring terpyridine
moieties at both chain ends, the NMP initiated by 5 has to
meet several criteria: the polymerization has to be of con-
trolled nature (a) and exhibit a high end-group fidelity (b),
that is, the functional groups at both chain ends must not be
cleaved in course of the polymerization.4,37
As a model reaction, the NMP of styrene, initiated by 5, was
investigated (Scheme 2, Table 1): The polymerization process
is controlled and oligomers and polymers (up to Mn
¼
10,000 g molꢁ1) with PDI values below 1.2 were obtained
(6a,b). In the 1H NMR spectrum of 6b (Supporting Informa-
tion Fig. S4) a high field shift for the protons next to the
nitroxide at the position 12 (5.0 ppm to 4.2 ppm) and 1 (3.5
ppm to 3.3 ppm; Fig. 1) could be observed pointing to the
insertion of the styrene between the initiating and the medi-
ating fragment. The Mn values calculated from NMR seem to
overestimate the molar mass that was theoretical expected,
while the Mn values obtained from the SEC are in the same
range (Table1). Since low polydispersity index values (PDI)
alone are not a stringent evidence for a controlled progress
of a polymerization reaction, kinetics investigations were
also performed. For this purpose, different reaction vessels
were equipped with 5 and styrene (solvent: anisole); after
the removal of oxygen, the vessels were subjected to an oil
bath (temperature: 123 ꢀC) and the reactions were stopped
after certain periods of time (up to 5 h).
With increasing polymerization time, the SEC traces of tpy-
PS-TIPNO-tpy (6c–e) were shifted to shorter elution times
corresponding to an increase of the molar mass. For all sam-
ples taken narrow, unimodal curves could be observed indi-
cating control over the polymerization (Fig. 3). The kinetic
4
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
1
FIGURE 1
H
N
M
R
s
p
e
c
t
r
u
m
o
f
5
(
4
0
0
M
H
z
,
C
D
C
S
l
,
2
9
8
K
)
.
T
h
e
s
i
g
n
a
l
s
a
r
i
s
i
n
g
f
r
o
m
t
h
e
m
e
t
a
-
s
u
b
s
t
i
t
u
t
e
d
r
e
g
i
o
i
s
o
m
e
r
a
r
e
m
a
r
k
e
d
2
2
1
1
w
i
t
h
a
s
t
e
r
i
s
k
s
(
s
e
e
2
D
H
-
H
C
O
S
Y
e
v
a
l
u
a
t
i
o
n
i
n
u
p
p
o
r
t
i
n
g
I
n
f
o
r
m
a
t
i
o
n
F
i
g
.
S
2
)
.
plots, that is, the semilogarithmic plot for the polymerization
index as a function of time (ln([M0]/[M]) vs. t) and the plot
for the molar mass vs. conversion revealed a linear depend-
ency [Fig. 4(a,b)].
version of 40%. In contrast to the heterotelechelic initiator
bearing one tpy as well as one UPy moiety no persistent rad-
ical effect was observed under the same conditions for the
polymerization of styrene.29
The observed Mn values were in good agreement with the
theoretical ones showing narrow polydispersity index values
(PDI < 1.2) (Table 1, Fig. 4). Thus, the homodifunctional ini-
tiator 5 enables the polymerization of styrene under the
used conditions in a controlled fashion at least up to a con-
The purified polymer 6a was characterized by mass spec-
trometry, in particular with respect to end-group analysis.
However, MALDI-TOF MS was found to be ineligible in this
case due to a distinct fragmentation behavior (Supporting In-
formation Fig. S5). As known from literature, the characteri-
zation of nitroxide-functionalized polymers by mass spec-
trometry is often difficult due to the complex fragmentation
during the MALDI-process.38,39 One major distribution, show-
ing peak-to-peak distances of m/z ¼ 104 as it is typical for
polystyrene, could be observed; however, the peaks could
neither be correlated to the expected telechelic materials nor
to reasonable fragmentations, that were found for parent
heterotelechelic polystyrenes29—independent from the na-
ture of the applied matrix (dithranol, DCTB) or the ionic
additive (e.g., NaI, AgI). In contrast, the ESI-TOF MS using a
milder ionization method exhibited in the mass spectrum
two main distributions for 6a corresponding to doubly and
triply charged polystyrene species, respectively (Fig. 5). After
careful analysis, the main distribution could be assigned to a
PS series, where one of the terpyridine units was cleaved off
during the ESI-TOF measurement leaving the central TIPNO
moiety still intact. The predetermined breaking point is
ascribed to the benzylic bond of the terpyridine entity. Due
to the assigned fragmentation, only one terpyridine can here
directly be proven as end-group. Nonetheless, the main frag-
mentation promotes the assumption that also the second tpy
FIGURE 2
M
n
A
L
D
I
-
T
O
F
m
a
s
s
s
p
e
c
t
r
u
a
m
o
f
5
;
t
h
e
i
n
s
e
t
s
h
o
w
o
s
t
h
e
c
o
m
p
a
r
i
s
o
o
f
t
h
e
e
x
p
e
r
i
m
e
n
t
a
l
n
d
t
h
e
c
a
l
c
u
l
a
t
e
d
i
s
t
o
p
i
c
þ
p
a
t
t
e
r
n
f
o
r
t
h
e
[
C
H
N
O
þ
N
a
]
p
e
a
k
.
A
f
r
a
g
m
e
n
t
a
t
i
o
n
o
f
5
5
4
5
3
7
3
d
u
e
t
o
t
h
e
l
a
b
i
l
e
a
l
k
o
x
y
a
m
i
n
e
5
N
A
O
b
o
n
d
g
i
v
e
r
i
s
e
t
o
t
h
e
a
d
d
i
-
t
i
o
n
a
l
s
i
g
n
a
l
s
m
/
z
¼
3
8
9
a
n
d
0
4
(
m
a
t
r
i
x
:
D
C
T
B
)
.
W
W
W
.
M
A
T
E
R
I
A
L
S
V
I
E
W
S
.
C
O
M
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0
5

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
SCHEME 2
S
c
h
e
m
a
t
i
c
r
e
p
r
e
s
e
n
t
a
t
i
o
n
o
f
t
h
e
p
o
l
y
m
e
r
i
z
a
t
i
o
n
o
f
s
t
y
r
e
n
e
u
s
i
n
g
5
a
s
i
n
i
t
i
a
t
o
r
.
is incorporated into the polymer, since this unusual degrada-
tion is most likely caused by the ESI-process and not by
thermal degradation during polymerization.
analytic as well as a synthetic point of view. From an analyti-
cal point of view, UV–vis titration experiments with FeII ions
were carried out to determine the number-averaged molar
mass of 6b via one further independent method. For this
purpose, the evolution of the ligand-centered and the MLCT
at related absorptions at 318 and 559 nm, respectively, were
plotted as a function of added FeII ions (Fig. 6). The point-of-
equivalence indicates the full consumption of free tpy sites
by complexation at a 1:1 ratio of the macroligands and FeII
ions (i.e., formation of [Fe(tpy)2]2þ complexes). The Mn value
of 7500 g molꢁ1, as calculated from this experiment, was
roughly in the same range as the values derived from the
other analytical methods (Table 1) while showing an under-
estimation as it is reported for the heterotelechelic tpy func-
tionalized PS bearing the 2-ureido-4H-pyrimidone (UPy) moi-
ety on the other end.29
However, the intact telechelic PS bearing both tpy units
could be assigned to a sub distribution (Supporting Informa-
tion Fig. S6). The isotopic pattern as obtained from high-re-
solution ESI measurements was in good agreement with the
calculated one: The calculated pattern for the triply charged
species [C54H53N7O3(C8H8)63þ3H]3þ deviated by only m/z ¼
0.0004 from the experimental found value (Supporting Infor-
mation Fig. S6) which confirms the incorporation of both tpy
units into the polystyrene. The Mn value of 8500 g molꢁ1 for
6a was derived from the deconvoluted mass spectrum of the
singly charged species. The number-averaged molar mass
obtained from ESI measurements is in agreement with the
one derived from SEC (Mn ¼ 7200 g molꢁ1).
From a synthetic point of view, the complexation of divalent
metal ions is in the present case important, since the com-
plexation with the telechelic polystyrene is the strongest
supramolecular driving force that can be used to engineer
defined suprapolymeric structures.
More important, 2D (1HA1H) DOSY experiments were carried
out to confirm that the terpyridine units (representing small
molecules) were attached to polystyrene chains (representing
in comparison rather large molecules), which could be recog-
nized by similar relative diffusion coefficients (similar to Fig. 9
right). However, the presence of small amounts of mono- or
non-functionalized polystyrene, for example, formed by auto-
polymerization of styrene, could not be excluded by this
method (this point will be addressed below).
The incorporation of 6, as ditopic macroligand, into a
metallo-supramolecular chain-extended polymer can be
achieved by complexation with divalent transition metal ions
via formation of bis-terpyridine complexes of (distorted)
octahedral geometry.24 According to the theory of polyaddi-
tion reactions, polymers of maximum molar masses are
The complexation of the terpyridine sites, in particular by
divalent transition metal ions, is of importance—from an
TABLE 1
O
v
e
r
v
i
e
w
o
f
t
h
e
S
y
n
t
h
e
s
i
z
e
d
T
d
e
l
e
c
h
e
l
i
c
P
o
l
y
s
t
y
r
e
n
e
s
u
s
i
n
g
A
l
k
o
x
y
a
m
i
n
e
5
a
s
I
n
i
t
i
a
t
o
r
a
]
t
(
1
2
5
8
C
w
i
t
h
a
(
1
M
o
n
o
m
e
r
t
o
I
n
i
t
i
a
t
o
r
R
a
t
i
o
o
f
2
0
0
:
1
a
n
a
M
o
n
o
m
e
r
C
o
n
c
e
n
t
r
a
t
i
o
n
o
f
3
m
o
l
1
a
1
1
1
b
,
c
T
i
m
e
[
m
i
n
]
C
o
n
v
.
[
%
]
(
G
C
)
Mn
[
g
m
o
lꢁ
]
(
t
h
e
o
.
)
Mn
[
g
m
o
lꢁ
]
(
H
N
M
R
)
Mn
[
g
m
o
lꢁ
S
E
C
)
P
D
I
S
E
C
)
6a
6b
6c
6d
6e
a
3
3
1
2
3
2
0
–
–
9
,
5
0
0
7
,
2
0
0
1
.
.
.
.
.
1
8
80
05
45
35
4
0
5
3
9
9
,
,
,
3
4
1
0
5
5
0
1
2
,
1
0
0
1
0
,
1
0
0
1
1
1
1
1
7
5
8
6
1
2
3
4
6
0
0
–
–
–
4
,5
,0
,9
0
0
1
1
1
6
0
0
0
1
0
,
1
0
0
9
0
Mn
(
t
h
e
o
.
)
r
e
p
r
e
s
e
n
t
s
t
h
e
t
a
r
g
e
t
e
d
M
w
i
t
h
r
e
s
p
e
c
t
t
o
t
h
e
c
o
n
v
e
r
s
i
o
n
(
G
C
)
.
n
b
c
A
A
f
t
e
r
p
r
e
c
i
p
i
t
a
t
i
o
n
o
f
t
h
e
p
o
l
y
m
e
r
i
n
t
o
m
e
t
h
a
n
o
l
.
l
i
n
e
a
r
p
o
l
y
s
t
y
r
e
n
e
c
a
l
i
b
r
a
t
i
o
n
w
i
t
h
D
M
A
a
s
e
l
u
e
n
t
w
a
s
u
s
e
d
.
6
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Another disadvantage of using nickel(II) ions for the prepa-
ration of responsive polymers is the inert character of the
complex against external stimuli as it can be also seen for
ruthenium(II) and cobalt(III) bis-terpyridine complexes. In
contrast the zinc(II) and cadmium(II) bis-complexes are suffi-
ciently labile but the formation is weak and for zinc weaker
than the formation of the mono-complexes,41 which would
hinder the formation of linear high molar mass coordination
polymers.
Following optimized reaction conditions described by Schu-
bert and coworkers,45–47 the metallopolymer {[Fe(6b)2]
(PF6)2}n (Fig. 7) was obtained as a purple powder (the color
was arising from the MLCT absorption of the FeII bis-terpyri-
dine complex related to the absorption at 559 nm, see Sup-
porting Information Fig. S7). An excess of the metal ion was
used to ensure the quantitative coordination of the macroli-
gand 6b as the bis-complex is believed to be insensitive
against exceeding the metal-to-ligand ratio of 1:1 also in an
organic solvent. Moreover, the excess of metal ions suppress
the formation of rings, as a ring-chain equilibrium has to be
assumed for the flexible polymeric spacer.48 To prevent oxi-
dation of the FeII ions prior to coordination, stannous chlo-
ride was added as reducing agent in stoichiometric amounts.
Utilizing PFꢁ6 as counterions, the solubility of the supramo-
lecular polymer in organic solvents could be enhanced. The
formation of the chain-extended polymer was also confirmed
by 1H NMR spectroscopy: upon complexation by the FeII
ions, the signals of the terpyridine protons were significantly
shifted as it was reported for FeII bis-terpyridine com-
plexes—in small molecules as well as in macromolecular
species [Fig. 8(a,b)].24,46 In addition, the methylene protons
in the benzylic positions of the end-groups are quantitatively
low-field shifted upon complexation pointing also to a com-
plete complexation within the sensitivity limits of NMR
spectroscopy.
FIGURE 3
S
E
C
t
r
a
c
e
s
o
f
6
c
–
e
a
f
t
e
r
d
i
f
f
e
r
e
n
t
p
o
l
y
m
e
r
i
z
a
t
i
o
n
t
(
i
m
e
s
f
o
r
t
h
e
N
M
P
o
f
s
t
y
r
e
n
e
u
s
i
n
g
a
l
k
o
x
y
a
m
i
n
e
5
a
s
i
n
i
t
i
a
t
o
r
e
l
u
e
n
t
:
D
M
A
)
.
formed at an ideal 1:1 ratio of ditopic macroligand and the
corresponding metal ions.40 Among the common used metal
ions for bis-terpyridine complexes, the iron(II) was chosen
as the model ion for the formation of a responsive coordina-
tion polymer, since the iron(II) ion shows the tendency of
forming bis-terpyridine complexes characterized by a high
binding constant (logK2 ¼ 13.8 in water), while the mono-
terpyridine complex shows a relative low binding constant
(logK1 ¼ 7.1 in water).41 Despite the high complex stability
constants the Fe(II) complexes are considered as labile.42
These two facts ensure the formation of high molar mass
coordination polymers and the insensitivity against exceed-
ing the metal-to-ligand ratio of 1:1, which can happen by
using macroligands with averaged masses.43,44 In this vein,
the corresponding nickel(II) or cobalt(II) bis-complexes are
in fact also very stable in water (logK2 ꢃ 10 in water),41 but
since the mono-complexes show proximate binding con-
stants, the formation of high molar mass polymers is sensi-
tive against metal-to-ligand ratios exceeding 1:1.44
Moreover, 2D DOSY measurements of {[Fe(6b)2](PF6)2}n
were carried out. These measurements revealed that all sig-
nals (i.e., terpyridine, polystyrene and TIPNO protons)
FIGURE 4
K
e
i
n
e
t
i
c
p
)
l
o
t
s
f
o
r
t
h
e
N
M
P
o
f
s
t
y
r
e
n
e
u
s
i
n
g
a
l
k
o
x
y
a
m
i
n
e
5
:
(
a
)
s
e
m
i
l
o
g
a
r
i
t
h
m
i
c
p
l
o
t
o
f
m
o
n
o
m
e
r
c
o
n
v
e
r
s
i
o
n
v
s
.
p
o
l
y
m
e
r
-
i
z
a
t
i
o
n
t
i
m
a
n
d
(
b
m
o
l
a
r
m
a
s
s
v
s
.
c
o
n
v
e
r
s
i
o
n
.
W
W
W
.
M
A
T
E
R
I
A
L
S
V
I
E
W
S
.
C
O
M
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0
7

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
arising from one macromolecular species, due to the same
relative diffusion coefficients of all moieties (Fig. 9, left). It
can be concluded within the sensitivity limits of 1H NMR
spectroscopy that both endgroups are attached to the poly-
mer chain and the presence of nonfunctionalized polystyrene
or monofunctional tpy-PS can be excluded, as such com-
pounds would reveal a different diffusion coefficient range
for the terpyridine and polystyrene signals. To prove the re-
versibility of the metal-to-ligand coordination, the metallo-
polymer was treated in situ with Na3(HEEDTA), as strong
competitive ligand (HEEDTA: hydroxy-2-ethylenediaminetri-
acetic acid). The disassembly of the metallopolymer was
monitored by 2D DOSY measurements (Fig. 9, right).
The tremendous decrease in molar mass due to the decom-
plexation of {[Fe(6b)2](PF6)2}n toward 6b could be con-
cluded from the significant differences in the relative diffu-
sion behavior for the tpy and the PS signals of both
materials (Fig. 9). This points within the sensitivity of 1H
NMR spectroscopy to the absence of monomeric or low
molar mass coordination polymers of 6b and, thus, to the
predominant formation of the iron(II) bis-complex within
{[Fe(6b)2](PF6)2}n before the decomplexation. However, no
FIGURE 5
E
S
I
-
T
O
F
m
a
s
s
s
p
e
c
t
r
u
m
o
f
6
a
r
e
v
e
a
l
s
d
i
f
f
e
r
e
n
t
c
h
a
r
g
e
d
d
i
s
t
r
i
b
u
t
i
o
n
s
.
reasonable
estimation
for
the
molar
mass
of
{[Fe(6b)2](PF6)2}n could be concluded via the Stokes–Ein-
stein equation. A correlation between diffusion coefficient
and molar mass that is valid for the polymeric monomer and
for the supramolecular polymer is unknown, since the back-
bone of the supramolecular polymer is different in nature
(as partially ionic) due to the metal complexes giving a dif-
ferent correlation between molar mass and hydrodynamic
radius. To the best of our knowledge no example is
reported up to now where an estimation of the molar mass
for a metallopolymer via DOSY NMR is given. In addition,
since the iron(II) bis-terpyridine complex is not stable
under the SEC conditions used for polystyrenes, the molar
FIGURE 6
U
V
–
v
i
s
a
b
s
o
r
p
t
i
o
n
t
i
t
r
a
t
i
o
n
e
x
p
e
r
i
m
e
n
t
s
o
f
6
b
w
i
t
h
I
I
F
e
i
o
n
s
.
T
h
e
e
v
o
l
u
t
i
o
n
o
f
t
h
e
a
b
s
o
r
p
t
i
o
n
b
a
n
d
s
a
s
t
3
1
8
a
n
d
5
5
9
I
I
n
m
,
r
e
s
p
e
c
t
i
v
e
l
y
,
a
s
a
f
u
n
c
t
i
o
n
o
f
a
d
d
e
d
F
e
i
o
n
s
i
a
l
s
o
s
h
o
w
n
.
FIGURE 7
S
c
h
e
m
a
t
i
c
r
e
p
r
e
s
e
n
t
a
t
i
o
n
o
f
t
h
e
s
y
n
t
h
e
s
i
s
o
f
s
u
p
r
a
m
o
l
e
c
u
l
a
r
c
h
a
i
n
-
e
x
t
e
n
d
e
d
p
o
l
y
m
e
r
s
{
[
(
6
b
)
M
(
6
b
)
]
(
P
F
6
) } b
2 n
y
m
e
t
a
l
-
t
o
-
I
I
l
i
g
a
n
d
c
o
o
r
d
i
n
a
t
i
o
n
(
S
n
C
l
w
a
s
a
d
d
e
d
t
o
t
h
e
r
e
a
c
t
i
o
n
m
i
x
t
u
r
e
t
o
p
r
e
v
e
n
t
o
x
i
d
a
t
i
o
n
o
f
t
h
e
F
e
i
o
n
)
.
2
8
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
chemical shift for the tpy signals can be explained by the
change of the NMR solvent from pure dichloromethane to a
mixture of methanol and dichloromethane. Thus, metal-free
6b could be regenerated quantitatively by addressing the
metallopolymer with an external stimulus, that is, a strong
competitor for the FeII ions—a similar behavior is expected
for significant changes in the pH value or when applying re-
dox chemistry, that is, oxidizing the metal ions to a þIII state
which will be investigated in future work.
CONCLUSIONS
In the present contribution a bis-terpyridine functionalized
initiator for NMP was synthesized to access a,x-difunctional-
ized polymers in one-step retaining the terpyridines as end-
groups. The polymerization of styrene was proven to be a
controlled process, while tpy as substituent of the initiating
as well as of the mediating fragment of the alkoxyamine did
not disturb the performance of the initiator. This approach
has a wider scope by means of construction flexibility com-
pared to a postmodification approach, as the chain length
and composition between the supramolecular binding sites
can be varied in less reaction steps and purification can be
simply done by precipitation. The self-assembly of the pre-
pared building blocks via iron-ion complexation toward lin-
ear supramolecular polymers was investigated by UV–vis
spectroscopy and DOSY. The reassembly and responsiveness
of the system against a competing ligand to the tpy was pro-
ven by NMR techniques.
1
FIGURE 8
Z
o
o
m
i
n
t
o
t
h
e
l
o
w
-
f
i
e
l
d
r
e
g
i
o
n
o
)
f
t
h
e
H
N
M
R
s
p
e
c
-
r
r
t
{
t
r
a
o
f
(
a
)
t
e
l
e
c
h
e
l
i
c
p
d
o
l
y
s
t
y
r
e
n
e
6b
,
(
b
t
h
e
s
u
p
r
a
p
o
l
y
m
e
e
[
(
6
b
)
F
e
(
6
b
)
]
(
P
F
)
6
}
2 n
a
n
t
h
e
s
t
e
l
e
c
h
e
l
i
c
p
o
l
y
s
t
y
r
e
n
e
6
b
(
c
)
a
f
t
h
e
a
d
d
i
t
i
o
n
o
f
H
E
E
D
T
A
a
c
o
m
p
e
t
i
n
g
l
i
g
a
a
n
d
.
F
o
r
a
/
l
l
s
p
e
c
t
r
a
:
4
0
0
M
H
z
,
2
9
8
K
(
w
i
t
h
C
D
C
l
f
o
r
(
a
)
,
(
b
)
,
n
f
d
C
D
C
2
l
M
e
O
D
f
o
}
r
2
2
2
(
c
)
a
s
s
o
l
v
e
n
t
s
s
e
e
t
h
e
w
h
o
l
e
s
p
e
c
t
r
u
m
o
{
[
(
6
b
)
F
e
(
6
b
)
]
(
P
F
)
6
2
n
i
n
t
h
e
S
u
p
p
o
r
t
i
n
g
I
n
f
o
r
m
a
t
i
o
n
F
i
g
.
S
8
)
.
mass can also not be determined by this method.46 A theo-
retical estimation of the average molar mass of the coordi-
nation polymer in solution suggests Mn ꢃ 106 g molꢁ1
,
which is based on a ring-chain equilibrium model and bind-
ing constants in organic solvents with distinct assumptions
(a critical consideration is provided in the supporting infor-
mation).48–50
The presented work provides a promising strategy for the
construction of metallo-supramolecular architectures in a
minimum of steps, which makes it appealing for studying
the influence of the polymeric spacer within more reversible
architectures (using, for example, zinc complexes) or more
complex structure (using, for example, heteroleptic com-
plexes) with respect to the progress of efficient stimuli-re-
sponsive and self-healing materials.
The related 1H NMR spectrum shows quantitative backshifts
of the tpy signals as well as for the benzylic methylene
groups of both end-groups which are similar with that of the
initial macroligand 6b [Fig. 8(a,c)]. The slight difference in
1
1
FIGURE 9
L
e
f
t
:
2
D
H
A
H
D
O
S
Y
s
p
e
c
t
r
u
m
o
f
{
[
(
6
b
)
F
e
(
6
b
)
]
(
P
F
)
} d
2 n
e
m
o
n
h
s
t
r
a
t
i
n
g
t
h
e
s
a
m
e
d
i
f
f
u
s
i
o
n
c
o
e
f
f
i
c
i
e
n
t
s
f
o
r
s
i
g
n
a
l
s
o
f
t
p
y
6
1
1
c
o
m
p
l
e
x
a
n
d
p
o
l
y
s
t
y
r
e
n
e
.
R
i
g
h
t
:
2
D
H
A
H
D
O
S
Y
s
p
e
c
t
r
u
m
o
f
6
b
a
f
t
e
r
t
e
a
d
d
i
t
i
o
n
o
f
H
E
E
D
T
A
d
e
m
o
n
s
t
r
a
t
i
n
g
t
h
e
d
e
c
o
m
p
l
e
x
a
t
i
o
n
(
d
i
f
f
u
s
i
o
n
c
o
e
f
f
i
c
i
e
n
t
o
f
d
i
c
h
l
o
r
o
m
e
t
h
a
n
e
w
a
s
t
a
k
e
n
a
s
r
e
f
e
r
e
n
c
e
)
.
W
W
W
.
M
A
T
E
R
I
A
L
S
V
I
E
W
S
.
C
O
M
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0
9

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
23
M
.
R
o
d
l
e
r
t
,
E
.
H
a
r
t
h
,
I
.
R
e
e
,
s
4
,
7
C
.
J
.
7
H
a
.
w
k
k
e
r
,
J
.
P
o
l
y
m
.
S
c
i
.
,
ACKNOWLEDGMENTS
Part A: Polym. Chem. 2000, 38
4
9
–
4
6
3
The authors kindly acknowledge financial support from the
Dutch Polymer Institute (DPI, technology area HTE), the Fonds
der Chemischen Industrie and the Thuringian Ministry for Edu-
cation, Science and Culture (grant #B514-09049, PhotoMic).
24
U
.
S
.
S
c
h
u
b
e
r
t
,
A
e
.
W
i
H
n
t
e
r
W
,
e
G
n
.
h
R
.
N
, 2011
e
w
o
.
m
e
,
T
e
r
p
y
r
i
d
i
n
e
-
B
a
s
e
d
M
a
t
e
r
i
a
l
s
;
W
i
l
y
-
V
C
:
i
e
i
m
25
B
.
G
.
G
.
L
o
h
m
e
i
j
e
r
,
,
U
4
.
0
S
.
S
0
c
2
h
u
b
e
r
t
, J. Polym. Sci. Part A:
, Mac-
, Chem.
Polym. Chem. 2004, 42
1
6
–
4
7
.
26
C
.
O
t
t
,
B
.
G
.
G
.
L
o
h
m
e
i
j
e
r
,
D
1
.
4
W
o
u
t
e
r
s
,
U
.
S
.
S
c
h
u
b
e
r
t
REFERENCES AND NOTES
romol. Chem. Phys. 2006, 207
27
Commun. 2009
,
3
9
–
1
4
4
9
.
J
.
-
F
.
G
o
h
y
,
C
.
O
t
–
t
,
6
S
0
.
0
H
o
e
p
p
e
n
e
r
,
U
.
S
.
S
c
h
u
b
e
r
t
1
H
a
n
d
b
o
o
k
o
f
V
i
n
y
l
P
o
l
y
m
e
.
r
s
;
M
.
K
.
M
i
s
h
r
a
,
Y
.
Y
a
g
c
i
,
E
d
s
.
;
,
6
0
3
8
4
.
C
R
C
P
r
e
s
s
:
B
o
c
a
R
a
t
o
n
,
2
0
0
9
28
U
.
M
S
a
.
n
S
s
c
f
h
e
u
l
d
b
,
e
M
.
D
.
H
a
g
e
r
,
R
.
H
o
o
g
e
n
b
,
o
3
o
3
m
,
C
.
3
O
t
.
t
,
A
.
W
i
n
-
2
m
Y
Y
.
Y
a
i
g
e
c
n
i
c
,
O
e
p
.
a
p
N
u
T
–
y
e
1
k
c
3
e
h
0
n
n
.
,
V
.
-
g
M
y
.
;
G
r
a
u
K
b
n
e
s
r
c
,
E
n
i
c
t
y
c
l
E
o
d
p
.
e
;
d
W
i
a
i
o
f
P
N
o
e
l
y
w
-
t
e
r
,
U
.
r
t
,
C
h
e
m
.
C
o
m
m
u
n
.
2
0
0
9
8
6
–
3
8
8
e
r
S
c
n
d
o
l
o
J
.
I
.
r
o
h
w
z
,
l
e
y
:
29
U
.
h
M
a
n
U
s
.
f
S
e
l
.
d
S
,
A
.
W
i
n
t
e
r
,
M
.
D
.
H
a
g
e
r
,
R
.
H
,
o
o
g
e
n
b
o
o
m
,
W
.
,
o
r
k
,
2
0
0
5
;
5
7
G
u
n
t
e
r
,
c
h
u
b
e
r
t
,
P
o
l
y
m
.
C
h
e
m
.
2
0
1
3
,
4
1
1
3
–
1
2
3
.
3
R
T
e
l
e
c
h
e
l
i
c
P
o
l
y
m
e
r
s
;
E
.
J
.
G
o
e
t
h
a
l
s
,
E
d
.
;
C
R
C
P
r
e
s
s
:
B
o
c
a
30
C
.
D
.
E
i
.
s
e
e
n
b
a
c
h
,
U
.
S
.
S
c
h
u
b
e
r
t
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
1
9
9
3
,
2
6
a
t
o
n
,
1
9
8
9
.
7
3
7
2
–
7
3
7
4
4
M
.
A
.
T
,
a
s
d
e
l
e
n
,
.
M
.
U
.
K
a
h
v
e
c
i
,
Y
.
Y
a
g
c
i
,
P
r
o
g
.
P
o
l
y
m
.
S
c
i
.
31
M
.
C
h
i
p
r
,
R
.
H
o
o
g
e
n
b
o
o
m
,
U
.
S
.
S
c
h
u
b
e
r
t
,
M
a
c
r
o
m
o
l
.
2011, 36
4
5
5
–
5
6
7
Rapid Commun. 2009, 30
32
Macromol. Chem. Phys. 2003, 204
,
5
6
5
–
5
7
8
.
5
G
K
C
.
o
J
y
m
p
e
e
s
a
n
,
,
d
J
W
i
u
.
.
m
K
o
f
P
o
e
l
c
y
,
o
m
R
m
e
.
s
r
T
S
i,
e
r
m
i
o
.
n
,
;
o
l
E
S
o
.
C
g
y
S
P
a
.
u
n
W
b
d
N
o
m
M
g:
e
n
.
C
c
l
H
m
a
t
u
r
e
;
R
T
e,
.
.
H
.
H
o
f
m
e
i
e
r
,
S
.
S
c
h
m
a
t
l
o
c
h
,
D
.
2
W
o
–
u
2
t
2
e
0
r
3
s
.
,
U
.
S
.
S
c
h
u
b
e
r
t
,
o
n
a
h
o
v
t
e
p
t
i
l
k
s
,
e ss,
b
,
1
9
7
i
t
a
a
m
V
.
M
e
t
a
n
k
E
d
s
R
l
i
s
h
i
n
a
r
i
d
g
2009
.
33
S
.
S
c
h
m
a
t
l
o
c
h
,
A
.
M
.
J
.
v
a
n
d
e
n
B
e
r
g
,
A
.
S
.
A
l
e
x
e
e
v
,
H
.
H
o
f
-
m
e
i
e
r
,
U
.
S
.
S
c
h
u
b
e
r
t
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
2
0
0
3
,
3
6
,
9
9
4
3
–
9
9
4
9
.
6
O
.
B
a
y
e
r
,
A
n
g
e
w
.
C
h
e
m
.
1
9
4
7
,
5
9
,
2
5
7
–
2
7
2
.
34
E
.
C
.
C
o
n
s
t
a
b
l
e
,
M
.
D
.
W
a
r
d
,
J
.
C
h
e
m
.
S
o
c
.
D
a
l
t
o
n
T
r
a
n
s
.
7
C
.
A
.
U
r
a
n
e
c
k
,
H
.
L
.
H
s
i
e
h
,
O
.
G
.
B
u
c
k
,
J
.
P
o
l
y
m
.
S
c
i
.
1
9
6
0
,
1990
,
1
4
0
5
–
1
4
0
9
.
46,
5
3
5
–
5
3
9
.
35
36
37
T
.
Y
H
.
-
S
.
B
u
t
,
P
.
H
.
T
o
y
,
C
h
e
m
.
A
s
i
a
n
J
.
2
0
0
7
,
2
,
1
3
4
0
–
1
3
5
5
.
8
P
b
M
a
e
c
r
E
r
t
d
o
m
o
l
A
e
p
i
c
u
p
y
l
l
a
r
a
E
n
n
:
g
s
i
;
n
e
K
e
.
r
i
M
n
g
a
:
t
P
r
s
e
z
c
e
i
w
.
s
e
s
S
y
Y
n
.
t
h
G
e
n
s
a
i
s
n
,
M
a
t
e
r
i
a
l
s
r
o
p
i
e
s
,
i
c
t
i
o
y
j
a
k
i
,
o
u
,
L
.
L
e
i
-
J
.
o
v
i
n
e
n
,
T
e
t
r
a
h
e
d
r
o
n
L
e
t
t
.
2
0
0
4
,
4
5
,
5
7
0
7
–
5
7
0
9
.
l
e
r
,
s
.
;
W
l
e
-
V
C
H
W
e
i
n
h
e
i
m
,
2
0
0
7
C
.
J
.
H
a
w
k
e
r
,
A
.
W
.
B
o
s
m
a
n
,
E
.
H
a
r
t
h
,
C
h
e
m
.
R
e
v
.
2
0
0
1
,
9
N
.
H
a
d
j
i
c
h
r
i
s
t
i
d
i
s
,
M
.
P
i
t
s
i
k
a
l
i
s
,
S
.
P
i
s
p
a
s
,
H
.
I
a
t
r
o
u
,
C
h
e
m
.
101
,
3
6
6
1
–
3
6
8
8
.
Rev. 2001, 101, 3 74 7 – 3 7 9 2 .
38
W
.
D
e
m
p
w
o
l
f
,
S
.
F
l
a
k
u
s
,
G
.
S
c
h
m
i
d
t
-
N
a
a
k
e
,
Macromol.
10
W
.
A
.
B
r
a
u
n
e
c
k
e
r
,
K
.
M
a
t
y
j
a
s
z
e
w
s
k
i
, Prog. Polym. Sci. 2007
, Chem. Rev. 2001
Chem. Rev. 2001 101
, Chem. Rev. 2001
,
,
,
,
Symp. 2007, 259
,
4
1
6
–
4
2
0
.
32, 3 9– 14 6.
39
T
.
S
c
h
u
l
t
e
,
K
.
O
.
S
i
e
g
e
n
t
h
a
l
e
,
r
,
6
H
.
3
L
u
8
f
t
4
m
a
n
n
,
M
.
L
e
t
z
e
l
,
A
.
11
101
M
.
K
a
9
m
i
7
g
4
a
6
i
t
o
,
T
.
A
n
d
o
,
M
.
S
a
w
a
m
o
t
o
S
t
u
d
e
r
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
2
0
0
5
,
3
8
8
3
–
6
0
.
,
3
6
8
–
3
.
40
A
.
W
i
n
t
e
r
,
M
.
D
.
H
a
e
s
g
f
e
e
r
r
,
U
.
e
S
;
.
S
M
c
h
u
b
e
r
t
,
r
I
n
P
.
o
M
l
y
m
e
y
r
S
s
c
z
i
e
e
w
n
c
e
:
,
12
K
.
M
a
t
y
j
a
s
z
e
w
s
k
i
,
J
.
-
H
.
X
i
a
,
,
€
o
A
C
o
m
p
r
e
h
e
n
s
i
v
e
A
R
r
e
n
c
.
M
l
l
e
,
,
K
p
a
t
j
a
s
k
i
2
9
2
1
–
2
9
9
0
.
E
d
s
.
;
E
l
s
e
v
i
e
r
B
V
:
m
t
e
d
a
m
,
2
0
1
2
;
V
o
l
.
5
p
2
6
9
–
3
1
0
.
13
101
14
C
.
J
.
H
a
w
8
k
8
e
.
r
,
A
.
W
.
B
o
s
m
a
n
,
E
.
H
a
r
t
h
41
R
.
H
.
H
o
l
y
e
r
,
C
.
D
.
H
u
b
b
a
r
d
,
S
.
F
.
A
.
K
e
t
t
l
e
,
R
.
G
.
W
i
l
k
i
n
s
,
,
3
6
6
1
–
3
6
Inorg. Chem. 1966, 5, 6 22 – 6 25 .
J
.
C
h
i
e
f
a
r
i
,
.
.
Y
A
.
.
.
-
K
.
a
h
B
y
a
.
C
h
o
n
g
,
,
F
.
.
E
F
r
.
c
o
l
e
,
j
J
.
C
K
.
r
L
s
.
t
i
M
n
a
o
,
J
.
J
e
f
f
r
e
y
,
T
d
.
,
42
R
.
H
o
g
g
,
R
.
G
.
W
i
l
k
i
n
s
,
J
.
C
h
e
m
.
S
o
c
.
1
9
6
2
,
3
4
1
–
3
5
0
.
P
E
.
.
-
T
.
L
e
,
R
.
T
,
M
a
d
u
n
n
e
G
M
e
i
s
,
a
d
,
G
.
M
o
a
43
R
.
D
o
b
r
a
w
a
,
F
.
W
1
u
r
t
h
5
n
e
r
,
J
.
P
o
l
y
m
.
S
c
i
.
P
a
r
t
A
:
P
o
l
y
m
.
¨
R
i
z
z
a
r
d
o
S
-
H
T
n
g
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
1
9
9
8
,
3
1
,
5
5
5
9
–
5
5
6
2
.
Chem. 2005, 43
44
,
4
9
8
–
4
9
9
.
15
T
.
O
t
s
u
,
J
.
P
o
l
y
m
.
S
c
i
.
,
P
a
r
t
A
:
P
o
l
y
m
.
C
h
e
m
.
2
0
0
0
,
3
8
,
B
.
G
.
G
.
L
o
h
m
e
9
i
j
e
6
r
8
,
P
h
D
-
t
h
e
s
i
s
,
E
i
n
d
h
b
o
v
e
n
U
n
i
v
e
r
s
i
t
y
o
f
2
1
2
1
–
2
1
3
6
.
T
e
c
h
n
o
l
o
g
y
,
2
0
0
4
,
1
–
.
16
G
.
D
a
v
i
d
,
o
C
u
.
B
i
o
n
y
e
r
,
J
.
T
o
n
n
a
r
,
B
.
A
m
e
d
u
r
i
,
P
.
L
a
c
r
o
i
x
-
D
e
s
-
45
M
.
C
h
i
p
e
r
,
M
.
A
.
R
.
M
e
i
e
r
,
J
.
M
.
K
r
a
n
e
n
u
r
g
,
U
.
S
.
S
c
h
u
b
e
r
t
,
m
a
z
e
s
,
B
.
B
t
e
v
,
C
h
e
m
.
R
e
v
.
2
0
0
6
,
1
0
6
,
3
9
3
6
–
3
9
6
2
.
Macromol. Chem. Phys. 2007, 208
,
6
7
9
–
6
8
9
.
ꢀ
e
ꢀ
Je r oˆ
17
A
.
D
e
b
u
i
g
n
e
,
R
.
P
o
l
i
,
C
.
,
J
2
r
o
ˆ
m
e
,
R
.
m
e
,
C
.
D
e
t
r
e
m
b
l
e
u
r
,
46
M
.
C
h
i
p
e
r
,
M
.
A
.
U
R
.
M
e
i
e
r
h
,
D
b
.
e
W
r
o
u
t
e
r
s
,
S
.
H
o
e
p
p
e
n
e
r
,
C
.
-
A
.
Prog. Polym. Sci. 2009, 34
1
1
–
2
3
9
.
F
2
u
s
1
t
i
–
n
2
,
J
7 77 .
.
-
F
.
G
o
h
y
,
.
S
.
S
c
u
t
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
2
0
0
8
,
4
1
,
18
19
S
.
Y
a
m
a
g
o
,
C
h
e
m
.
R
e
v
.
2
0
0
9
,
1
0
9
,
5
0
5
1
–
5
0
6
8
.
7
7
U
.
M
a
n
s
f
e
l
d
,
C
.
P
i
e
t
s
c
h
,
R
.
H
o
o
g
e
n
b
o
o
m
,
C
.
R
.
B
e
c
e
r
,
U
.
S
.
47
H
.
H
o
f
m
e
i
e
r
,
R
.
H
o
o
g
e
n
b
o
o
m
,
M
.
E
.
L
.
W
o
u
t
e
r
s
,
U
.
S
.
S
c
h
u
-
S
c
h
u
b
e
r
t
,
P
o
l
y
m
.
C
h
e
m
.
2
0
1
0
,
1
,
1
5
6
0
–
1
5
9
8
.
b
e
r
t
,
J
.
A
m
.
C
h
e
m
.
S
o
c
.
2
0
0
5
,
1
2
7
,
2
9
1
3
–
2
9
2
1
.
20
H
a
,
n
E
d
d
b
s
o
.
o
;
k
W
o
f
e
R
a
d
t
i
e
c
a
l
P
o
n
l
y
c
m
e
H
r
i
o
z
a
b
t
o
i
o
n
n
;
K
.
M
a
.
t
y
j
a
s
z
e
w
s
k
i
,
T
.
P
.
48
T
.
,
V
N
e
.
r
A
m
.
o
M
n
d
.
e
B
n
e
,
J
.
e
v
a
n
n
g
d
e
.
r
G
u
R
c
.
h
t
S
,
P
.
d
e
l
W
a
a
G
r
.
d
,
J
A
.
.
F
T . M . M ar
l ee r , M . A .
-
D
a
v
i
s
i
l
y
-
I
n
r
s
c
i
e
e
:
k
e
,
2
0
0
2
€
c
e
l
i
s
s
s
l
i
,
E
J
.
u
d
h
o
t
e
r
,
C
o
h
e
n
S
t
u
a
r
t
,
M
a
c
r
o
m
o
l
e
c
u
l
e
s
2
0
0
3
,
3
6
,
7
0
3
5
–
7
0
4
4
.
21
V
.
C
o
e
s
s
e
n
s
,
T
.
P
i
n
t
a
u
e
r
,
K
.
M
a
t
y
j
a
s
z
e
w
s
k
i
, Prog. Polym.
, J. Am.
Sci. 2001, 26
22
Chem. Soc. 2001, 121
,
3
3
7
–
3
7
7
.
49
romol. Rapid Commun. 2010, 31
50
R
.
S
h
u
n
m
u
g
a
m
,
G
.
J
.
G
a
b
r
i
e
l
,
K
.
A
.
A
a
m
e
r
,
G
.
N
.
T
e
w
,
M
a
c
-
,
7
8
4
–
7
9
3
.
D
.
B
e
n
o
i
t
,
V
.
C
h
a
p
l
i
n
s
k
i
,
R
.
B
r
a
s
l
a
u
,
C
.
J
.
H
a
w
k
e
r
,
3
9
0
4
–
3
9
2
0
.
D
.
G
.
K
u
r
t
h
,
S
c
i
.
T
e
c
h
n
o
l
.
A
d
v
.
M
a
t
e
r
.
2
0
0
8
,
9
,
0
1
4
1
0
3
.
10
J
O
U
R
N
A
L
O
F
P
O
L
Y
M
E
R
S
C
I
E
N
C
E
,
P
A
R
T
A
:
P
O
L
Y
M
E
R
C
H
E
M
I
S
T
R
Y
2
0
1
3
,
0
0
0
,
0
0
0
–
0
0
0