Macromolecules, Vol. 38, No. 6, 2005
Alkyne-Functional Polymers 2117
(Knauer), a K-3800 Basic autosampler (Marathon), a set of
two PLgel 5 µm Mixed-D columns (300 × 7.5 mm, rated for
linear separations for polymer molecular weights from 200 to
400 000 g/mol, Polymer Laboratories), and a PL-ELS 1000
evaporative light scattering detector (Polymer Laboratories).
Data were acquired through a PL Datastream unit (Polymer
Laboratories) and analyzed with Cirrus GPC software (Poly-
mer Laboratories) based upon a calibration curve built upon
polystyrene standards with peak molecular weights ranging
from 580 to 400 000 g/mol (EasiCal PS-2, Polymer Laborato-
ries). The composition of the block copolymers was ascertained
by means of NMR (Varian Unity 500; CDCl3) and IR (Perkin-
Elmer 1600) spectroscopies. Thermal analysis was carried out
on a Q100 differential scanning calorimeter (TA Instruments)
under nitrogen calibrated with an indium reference standard.
Samples were analyzed with a heat/cool/heat cycle between
40 and 180 °C at a heating/cooling rate of 10 °C/min. Glass
transition temperatures (half-∆Cp) were recorded during the
second heating cycle. Elemental analysis was carried out by
Schwartzkopf Microanalytical (Woodside, NY). TEM images
were obtained using a JEOL 2000FX analytical electron
microscope operating at 80 or 100 kV. Copolymer TEM
samples were prepared by ultramicrotomy (Sorvall MT-1) at
room temperature of epoxy-embedded bulk samples. Cobalt-
alkyne domains appear darker due to the higher electron
density afforded by the metal atoms.
Scheme 1
chromatography (SiO2, 5:1 hexanes/EtOAc, mixed fractions
further purified with 8:1 hexanes/EtOAc or 4:1 hexanes/EtOAc)
to give a mixture of products identified by 1H NMR, including
styrene (23 mg, 4.8%), PhEt-TEMPO (548 mg, 46%), diphen-
ylacetylene (631 mg, 77%), 1,2-diphenyl-2-(2,2,6,6-tetrameth-
ylpiperidin-1-yloxy)-ethanone (2)20 (129 mg, 8.9%), benzil
(CAUTION: strong irritant!) (39 mg, 4.1%), and benzyl phenyl
ketone (62 mg, 6.9%) and other incompletely characterized
products, including aromatic compounds and paramagnetic
compounds.
Reaction of PS-PPES with Co2(CO)8.13 In a representa-
tive procedure, a solution of PS173-PPES67 (0.298 g, 9.27 µmol,
Mn (NMR) ) 32.2 kg/mol; Mw/Mn ) 1.17) in dry toluene (12
mL) was treated with Co2(CO)8 (0.212 g, 0.621 mmol) in
toluene (5.0 mL) in a N2-filled glovebox. The dark brown
reaction mixture was heated at reflux under N2 for 1 h followed
by removal of the volatiles under vacuum. The dark brown
solid residue was dissolved in CH2Cl2 (∼2 mL) and precipitated
in dry hexanes (200 mL). The supernatant was decanted, and
the polymer was washed with hexanes and dried under
vacuum to give PS173PPES67[Co2(CO)6]61 (composition esti-
mated by elemental analysis by fitting found % Co) as a dark
PPES. In a representative procedure, PES (0.497 g, 2.44
mmol), PhEt-TEMPO (0.008 g, 0.0316 mmol), and acetic
anhydride (0.005 g, 0.053 mmol, 1% w/w) were degassed with
three freeze-pump-thaw cycles, sealed under nitrogen, and
heated at 95 °C for 7 h. The resulting polymer was dissolved
in dichloromethane and precipitated into hexanes to yield
PPES as a white powder (0.145 g, 34%). SEC (THF, vs PS
1
standards): Mn ) 13.3 kg/mol, Mw/Mn ) 1.34. H NMR (500
MHz, CDCl3): δ 6.2-7.7 (br m, 9H per repeat unit, ArH),
1.0-2.2 (br m, overlapping polymer backbone protons, 3H per
repeat unit, and TEMPO -CH2-, 6H), 0.9 (br s, 3H, TEMPO
CH3), 0.4 (br s, 3H, TEMPO CH3), 0.25 (br s, 6H, TEMPO CH3).
1
brown powder (0.379 g, 85%). H NMR (500 MHz, CDCl3): δ
13C NMR (125 MHz, CDCl3):
δ 40-44 (CH2CH), 89.2
1.43 (br); 1.87 (br); 2.05 (br); 6.47 (br), 7.06 (br); 7.1 (br), 7.27
(br); 7.47 (br). 13C NMR (125 MHz, CDCl3): δ 40-41 (CH2CH);
92.1 (Ph-CtC, Ph-C≡C); 125.6, 125.9, 127.4-128.4,
129.0, 129.3, and 145.6 (Ar); 199.4 (Co-CtO). Anal. Calcd
for complete reaction with Co2(CO)8, (C7H5O2)PS173PPES67-
(Co2(CO)6)67(C9H18NO): C, 67.47; H, 4.37; N, 0.03; Co, 15.45.
Anal. Calcd for (C7H5O2)PS173PPES67(Co2(CO)6)61(C9H18NO): C,
68.96; H, 4.52; N, 0.03; Co, 14.55. Found: C, 68.61; H, 4.68;
N, <0.10; Co, 14.50. IR (NaCl): νCH 3047, νCH 3015, νCH2 2916,
(Ph-CtC), 89.8 (Ph-CtC), 121.0 (Ar, C4), 123.7 (Ar′, C1),
127.7 (Ar, C2), 128.4(Ar′, C4), 128.8 (Ar′, C3), 129.2 (Ar′, C2),
131.6 (Ar, C3), 132.2 (Ar, C2), 145.1 (Ar, C1). IR (KBr
powder): νCH 3053, νCH 2925, νCH 2849, νC≡C 2216 w, σCH(overtone)
1948, σCH(overtone) 1908,2σCH(overtone2) 1800, σCH(overtone) 1720, σCH(o
-
vertone) 1670, νCdC 1596, νCdC 1507, νCdC 1441, νCdC 1411, σCH
1177, σCH 1105, σCH 1066, σCH 1018, σCH 911, σCH 833, σCH 755,
σCH 689, σCdC 566, and σCdC 525 cm-1
.
Polymerization of PES from PS-TEMPO.13 In a typical
polymerization, an air free tube was loaded with PS-TEMPO
(1.20 g, 62.4 µmol, Mn ≈ 19.2 kg/mol, Mw/Mn ≈ 1.08), 4-(phen-
ylethynyl)styrene (2.29 g, 11.2 mmol), and toluene (11.6 mL).
The reaction mixture was degassed by three freeze-pump-
thaw cycles, sealed under N2, and heated at 125 °C for 16.5 h
νCH 2839, νCO 2083, νCH 2048, νCH 2015, σCH(overtone) 1871, νC≡C/Co
2
1600, νCdC 1493, νCdC 1449, σCH 751, and σCH 695 cm-1
.
Results and Discussion
4-(Phenylethynyl)styrene (PES, 1) was prepared in
high yield by Sonogashira coupling of 4-bromostyrene
with phenylacetylene.14 Nitroxide-mediated preparation
of homopolymers of PES was carried out with three
initiating systems: benzoyl peroxide/TEMPO, PhEt-
TEMPO, and PhEt-TIPNO (Scheme 1). Typical high
temperatures (125 °C) used for the TEMPO-mediated
polymerization of styrene led to rapid polymerization
of PES (50% conversion in 1 h) to afford poly(4-
phenylethynylstyrene) (PPES) with multimodal molec-
ular weight distributions and, at longer reaction times,
cross-linked material. Polymerizations run at 95 °C
afforded PPES with narrow, unimodal molecular weight
distributions and controllable molecular weights (Table
1). Both 13C NMR (δ 89.2, 89.8) and IR spectroscopy
(CtC stretch at 2216 cm-1) support the presence of
alkyne groups in the resulting PPES.
1
(30% conversion by H NMR) to afford a pale yellow, slightly
opaque viscous liquid. CH2Cl2 (1 mL) was added, and the
resulting solution was precipitated into hexanes (800 mL),
filtered, washed with hexanes, and dried under vacuum to give
1
PS181-PPES56 (1.46 g, 77% based upon conversion). H NMR
(500 MHz, CDCl3): δ 1.45 (br, CH2); 1.85 (br, CH); 2.12 (br,
CH); 6.53 (br, ArH); 7.08 (br, ArH); 7.25 (br, ArH); 7.48 (br,
ArH). 13C NMR (125 MHz, CDCl3): δ 40-44 (br, CH2CH); 89.1
(Ph-CtC-); 89.8 (Ph-CtC-); 120.9, 123.6, 125.7, 125.8,
127.5-128.5, 131.8, and 145.3. Mn(1H NMR): 30.3 kg/mol; 37
wt % PPES. SEC: Mw/Mn ) 1.16. IR (NaCl): νCH 3080, νCH
3062, νCH 3025, νCH 2926, νCH 2855, νC≡C 2225w, νCdC
2
2
1601, νCdC 1513, νCdC 1492, νCdC 1454, σCH 1030, σCH 832,
σCH 755, and σCH 700 cm-1. Anal. Calcd for (C7H5O2)-
PS181PPES56(C9H18NO): C, 92.71; H, 7.08; N, 0.05. Found: C,
92.77; H, 7.21; N, 0.17.
Model Reaction of PhEtTEMPO with Diphenylacety-
lene. In a Schlenk tube, diphenylacetylene (DPA) (0.818 g,
4.59 mmol) and PhEt-TEMPO (1.20 g, 4.58 mmol) were
dissolved in m-xylene (4.0 mL). The resulting solution was
degassed, sealed under nitrogen, and heated at 125 °C for 24
h to give a red solution. The mixture was separated by column
Decreasing the ratio of TEMPO to BPO from 1.5 to 1
led to an increase in polymerization rate with an
apparent decrease in control as evidenced by increasing
polydispersity index (Table 1: entries 1-3). The inclu-