Article
Macromolecules, Vol. 43, No. 7, 2010 3269
AB2 monomers with the lowest DB of this comonomer system
being limited to 29%. In this article we present the more complex
ABB*/AB2 approach in order to obtain polymers with lower DB
values. Finally, the dilute solution properties of both polymer
systems will be compared.
and the combined extracts were washed with distilled water (2 ꢀ
150 mL), dried over sodium sulfate, and evaporated to dryness.
The crude product was purified by flash chromatography eluting
with 1:7 ethyl acetate-n-hexane gradually increasing to 3:7 to give
monosubstituted acid as a white solid (yield 40%).
The atomic numbering is in accordance with Scheme 4 with
R = TBDMS and n = 1.
1H NMR (DMSO-d6): δ (ppm) = 0.17 (s, 6H, H10), 0.93 (s,
9H, H12), 1.48 (s, 3H, H5), 1.91 (t, 2H, H2), 2.23 (t, 2H, H3), 6.65
Experimental Part
Materials. All reagents and solvents were purchased from
Aldrich (Germany), Acros (Germany), or Fluka (Germany)
and used without further purification. 4-(N,N-Dimethylami-
no)pyridinium 4-tosylate (DPTS) was synthesized and purified
according to the work of Moore.23 The synthesis of hyper-
branched poly[4-bis(4,40-hydroxyphenyl)pentanoic acid] (OH-50)
is done according to Schallausky et al.17 All glassware was dried
for several hours at 80 °C.
0
0
(d, 2H, H8 ), 6.72 (d, 2H, H8), 6.93 (d, 2H, H7 ), 7.01 (d, 2H, H7),
9.16 (s, OH), 11.96 (s, COOH). 13C NMR): δ (ppm) = -4.46
(C10), 17.91 (C11), 25.59 (C12), 27.22 (C5), 29.99 (C2), 36.42 (C3),
0
43.99 (C4), 114.81 (C8), 119.09 (C8 ), 127.82 (C7), 127.98 (C7 ),
0
0
0
138.97 (C6), 142.09 (C6 ), 152.79 (C9 ), 155.16 (C9), 174.65 (C1).
Polymerization of ABB* Monomer Resulting in SY-0. ABB*
(7.00 g, 17.5 mmol) and DPTS (3.59 g, 12.3 mmol) were
dissolved in dichloromethane (60 mL) under an argon atmo-
sphere at room temperature. After 30 min, dicyclohexylcarbo-
diimide (DCC) (7.22 g, 35.00 mmol) was added, and the stirring
at room temperature under argon was continued from 1 to 24 h.
The formed DCC-urea was filtered out and carefully washed
with CH2Cl2. Then the solvent was reduced, and the polymer
was purified by double precipitation into methanol (70%).
The atomic numbering is in accordance with Scheme 4 with
R = TBDMS for a linear polymer.
Characterization. 1H NMR and 13C NMR measurements
were carried out on a Bruker DRX 500 NMR spectrometer at
500.13 and 125.75 MHz, respectively. DMSO-d6 and CDCl3
were used as solvents. For internal calibration the solvent peaks
were used: DMSO-d6: δ(13C) = 39.60 ppm, δ(1H) = 2.50 ppm;
CDCl3: δ(13C) = 77.00 ppm, δ(1H) = 7.26 ppm. Quantitative
13C NMR spectra were recorded using inverse gated decoupling
and a delay time of 8 s. The absolute error of quantitative 13
C
NMR is estimated to (2%.
1H NMR (CDCl3): δ (ppm) = 0.19 (s, H10), 0.98 (s, H12), 1.63
Determination of the molar masses was performed by size
exclusion chromatography (SEC) equipped with HPLC pump
(Knauer, Germany) and coupled to a viscosity, differential
refractive index (RI) dual detector (ETA-2020, WGE Dr. Bures,
Germany) and a multiangle laser light scattering detector
(MALLS) DawnEOS (Wyatt Technologies, λ = 632 nm). A
PLgel 5 μm Mixed C chromatography column (300 mm ꢀ
7.5 mm, Polymer Laboratories, Ltd., UK) was used with THF
(Acros, Germany) as a solvent. Flow rate was 1 mL/min. All
evaluations were made with the software ASTRA 4.9 (Wyatt
Technology Corp.). For interpretation of SEC-MALLS mea-
surements dn/dc values were externally determined at 25 °C
using RI detector Dn 2010 (WGE Dr. Bures, Germany, λ =
620 nm). For this purpose different concentrations of the sample
in THF in the range of 0.4, 0.8, 1.6, 2.0, 2.4, and 3.2 mg/mL were
prepared. Refractive index increments dn/dc = 0.195 mL/g for
OH-terminated samples and dn/dc = 0.155 mL/g for SY-termi-
nated samples were determined.
MALDI-TOF-MS spectra were recorded on a Shimadzu
Biotech Axima TOF2 MALDI instrument. 1,8,9-Trihydroxyan-
thracene was used as a matrix. Lithium chloride was used as a
salt for ionization. The irradiation source was a pulsed nitrogen
laser with a wavelength of 373 nm. The length of one laser pulse
was 3 ns. The measurements were carried out using the following
conditions: polarity-positive, flight-path-linear, mass high
(20 kV acceleration voltage), 100-150 pulses per spectrum.
TGA measurements were carried out with a TGA-Q5000 of
TA Instruments in the temperature range 30-750 °C at a
heating rate of 10 K/min under a nitrogen atmosphere. DSC
measurements were carried out with Q1000 of TA Instruments
in the temperature interval from -60 to 200 °C under a nitrogen
atmosphere. The modulated DSC measurements were carried
out in the same temperature range at 2 K/min with a modulated
amplitude of 0.31 K and modulation period of 40 s. For the
calculation of glass transition temperatures the reversing signal
was used.
0
(s, H5), 2.33 (t, H2), 2.51 (t, H3), 6.75 (d, H8 ), 6.95 (d, H8), 7.05
0
(d, H7 ), 7.19 (d, H7). 13C NMR (CDCl3): δ (ppm) = -4.42
(C10), 18.13 (C11), 25.64 (C12), 27.81 (C5), 30.46 (C2), 36.43 (C3),
0
44.95 (C4), 119.54 (C8 ), 120.92 (C8), 128.12 (C7), 128.25 (C7 ),
0
0
0
140.50 (C6 ), 146.44 (C6), 148.67 (C9), 153.74 (C9 ), 172.30 (C1).
Deprotection of SY-0 Resulting in OH-0. SY-0 (4.79 g,
12.5 mmol) was dissolved in DMF (35 mL) under an argon
atmosphere, and then trifluoroacetic acid (TFA) (2.8 mL) was
added drop by drop to avoid polymer precipitation; afterward,
the mixture was stirred for 54 h. The deprotection conversion
1
was controlled by H NMR. After the reaction was complete,
the solvent was reduced and the polymer was precipitated into
diethyl ether, followed by reprecipitation into water. The final
product was obtained as white flakes (50%).
The atomic numbering is in accordance with Scheme 4 with
R = H for a linear polymer.
1H NMR (DMSO-d6): δ (ppm) = 1.51 (s, H5), 2.29 (t, H2),
0
0
2.41 (t, H3), 6.69 (d, H8 ), 6.99 (H7 and H8), 7.18 (d, H7), 9.23
(OH). 13C NMR (DMSO-d6): δ (ppm) = 27.18 (C5), 29.97 (C2),
0
35.92 (C3), 44.43 (C4), 114.97 (C8 ), 121.21 (C8), 127.83 and
0
127.98 (C7 and C7 ), 138.11 (C6 ), 146.71 (C6), 148.32 (C9),
0
0
155.37 (C9 ), 171.84 (C1).
Synthesis of OH-50. OH-terminated hb polyester OH-50 was
synthesized by a procedure described in detail by Schallausky
et al.17 and will not be repeated here.
Modification of OH-50 Resulting in SY-50. OH-50 (5 g,
18.63 mmol) and imidazole (3.17 g, 46.58 mmol) were dissolved
in DMF (25 mL) under an argon atmosphere at room tem-
perature. After 30 min tert-butyldimethylsilyl chloride (5.69 g,
37.26 mmol) was added, and the stirring at room temperature
under argon was continued for 48 h. Then, the solvent was reduced
in vacuum, and the polymer was purified by double precipitation
into methanol and dried under vacuum at 70 °C (55%).
The atomic numbering is in accordance with Scheme 4 with
R = TBDMS for a hyperbranched polymer, and the abbrevia-
tions T, L, and D denote the terminal, linear, and dendritic units.
1H NMR (CDCl3): δ (ppm) = 0.19 (H10), 0.97 (H12), 1.60
Synthesis. Preparation of ABB* Monomer. To a solution of
4,4-bis(40-hydroxyphenyl)pentanoic acid as an AB2 monomer
(25.0 g, 83.0 mmol) in dry THF (100 mL) tert-butyldimethylsilyl
chloride (25.0 g, 166.0 mmol) and imidazole (13.6 g, 199.2 mmol)
were added. The mixture was heated at reflux for 12 h, cooled
down, and evaporated to dryness. Glacial acetic acid (40 mL) was
added followed by water (60 mL), and the reaction was stirred at
room temperature for 2 h and then poured into water (300 mL).
The organic phase was extracted with ethyl acetate (3 ꢀ 75 mL),
0
(H5T), 1.63 (H5 L), 1.65 (H5D), 2.33 (H2), 2.50 (H3), 6.74 (H8 ),
0
6.96 (H8), 7.05 (H7 ), 7.19 (H7). 13C NMR (CDCl3): δ (ppm) =
-4.42 (C10), 18.12 (C11), 25.64 (C12), 27.81 (C5 L, C5D), 27.89
(C5T), 30.55 (C2D), 30.44 (C2 L), 30.53 (C2T), 36.31 (C3D), 36.42
(C3 L), 36.56 (C3T), 44.64 (C4T), 44.95 (C4 L), 45.26 (C4D), 119.38
0
(C8 T), 119.54 (C8 L), 120.92 (C8 L), 121.10 (C8D), 128.17, 128.17,
0
and 128.24 (C7 and C7 ), 140.52 (C6 L), 141.35 (C6 T), 145.52
0
0
0