Macromolecules
Article
this procedure proved problematic because it utilized barium
stirred under reflux for 16 h. The resulting mixture was then acidified
with NaHSO to quench the reaction. The product was extracted out
carbonate (BaCO ), a toxic reagent, as an “acid scavenger”. To
4
3
27
with several washes of CHCl . This organic layer was then washed
avoid this, Chret
́
ien et al. described an alternative acid
3
with DI water, dried with MgSO , and then excess solvent was
4
scavenger in calcium carbonate (CaCO ) that still works as
3
removed using a rotary evaporator to produce a brown solid. This
solid was then redissolved in CHCl3 and precipitated into cold
efficiently while avoiding issues of toxicity. The procedure
described in this Article uses a synthetic methodology for ring-
opening benzylidene acetals similar to that reported by
hexanes (1:10) to produce a white powder (4.91 g, 84.7%, M 2200).
n
+
MALDI-ToF MS (Figure 3): calcd m/z + Na [2085.92 m/z], obs.
m/z + Na [2085.62 m/z]. H NMR (Figure 4) (CDCl , 300 MHz):
Chret
́
ien et al. (Scheme 1). This synthetic approach was
+
1
3
used to synthesize BBM, which was subsequently used to
produce a linear benzoyl-protected bis-MPA homopolyester
δ 1.24 (m, CH3 backbone), 1.33 (s, CH3 end group), 3.62 (m, CH −Br),
2
4.35 (m, CH backbone), 7.37, (m, CHmeta Ar−H, para Ar−H), 7.85 (m,
2
1
3
(
PBBM), both of these for the first time. PBBM is later
CHortho Ar−H). C NMR (Figure 4) (75 MHz, CDCl
): δ 17.7 (CH ),
3 3
compared to its dendritic analogs through a preliminary size
comparison study.
46.7 (Cquatenary), 65.70 (CH ), 128.39 (CHmeta Ar−C), 129.36
2
(
(
(
CHortho Ar−C), 129.54 (Cquaternary Ar−C), 133.15 (CHpara Ar−C), 165.55
C(O)Bz), 171.75 (C(O)backbone). GPC (Figure 3) (THF, RI): Mn
−
1
Đ) = 1800 g mol (1.02). Anal. Calcd for 10-mer C120H121BrO : C,
EXPERIMENTAL SECTION
■
63.1%; H, 5.3%. Found: C, 63.5%; H, 5.4%. IR stretches (Figure S5):
−
1
−1
Benzylidene-Protected Bis-MPA (5-Methyl-2-phenyl-1,3-di-
1670−1820 cm COBz and CO, 2800−3100 cm Ar−H,
2
8
−1
oxane-5-carboxylic Acid). A round-bottom flask was charged
3100−3700 cm O−H.
with a stir bar and acetone (1925 mL). While being stirred, bis-MPA
Characterization. Nuclear magnetic resonance (NMR) spectros-
(
345.55 g, 258 mmol) was added slowly to prevent the stir bar from
MHz) experiments were performed at 298 K at a concentration of 3
1
seizing because the solution is a suspension. Benzaldehyde dimethyl
acetal (588.12 g, 386 mmol, 580 mL) then was added, followed by
para-toluene sulfonic acid (p-TsOH, 4.19 g, 25 mmol). The reaction
mg/mL in chloroform-d (CDCl ) or methanol-d (MeOD),
3
4
mixture was stirred for 16 h under inert atmosphere (N ) as a
purchased from Cambridge Isotope Laboratories (Andover, MA).
2
1
3
13
suspension of white solid. The solution was then filtered to isolate the
white solid, and the white solid was washed several times with cold
acetone. The white solid was then dried under a high vacuum to
C and C DEPT 135 (75 MHz) experiments were performed at
2
98 K at a concentration of 10 mg/mL in chloroform-d (CDCl ) or
3
dimethyl sulfoxide-d (DMSO). HSQC-NMR was performed at 298
6
1
remove residual acetone (266.168 g, 46.4%). H NMR (Figure S1)
K at a concentration of 20 mg/mL in dimethyl sulfoxide-d (DMSO).
6
(
CDCl , 300 MHz): δ 1.11 (s, 3H, CH ), 3.70 (d, J = 11.7 Hz, 2H,
3
3
Enough scans were collected to generate sufficient signal-to-noise with
a relaxation delay of 3−6 s depending on the sample.
CH ), 4.63 (d, J = 11.7 Hz, 2H, CH ), 5.49 (s, 1H, CHacetal), 7.41 (m,
2
2
13
5
H, ArH). C NMR (Figure S2) (CD S(O)CD , 75 MHz): δ 17.6
3 3
A Bruker Autoflex III MALDI-ToF mass spectrometer (Bruker
positive reflectron ion detection mode. Typical sample preparation for
MALDI-ToF MS data was performed using two types of sample
preparation. Stock solutions of matrix (20 mg/mL), polymer−analyte
(
(
(
CH ), 41.5 (C
), 72.6 (CH ), 100.3 (CHacetal), 126.1
quaternary 2
3
CHortho Ar−H), 128.0 (CHmeta Ar−H), 128.7 (CHpara Ar−H), 138.4
Cquaternary Ar−H), 173.9 (C(O)).
3
-(Benzoyloxy)-2-(bromomethyl)-2-methylpropanoic Acid
(
BBM). To a round-bottom flask were added benzylidene-protected
bis-MPA (10.0 g, 45 mmol), N-bromosuccinimide (NBS, 8.81 g, 49
(
(
5
1 mg/mL), and a cation source (1 mg/mL) in tetrahydrofuran
THF) (VWR) were made. The stock solutions were combined in a
/1/1 μL ratio (v/v/v) (matrix/analyte/cation) and plated via the
mmol), and CaCO (5.45 g, 54 mmol). The flask was charged with a
stir bar and placed under a reflux condenser. Carbon tetrachloride
3
(
CCl , 50 mL) was added to the flask, and the reaction was stirred at
4
dried droplet method. Sodium trifluoroacetate was used as the cation
source, and trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-
propenylidene]malononitrile (DCTB) (TCI) was used as the matrix
in the first sample preparation method. The second method involved
applying graphite from a #2 Ticonderoga pencil to the plate as the
matrix, and then addition of 1 μL of polymer−analyte stock solution
and 1 μL of cation stock solution via the dried droplet method.
MALDI-ToF MS spectra were calibrated against SpheriCal dendritic
calibrants (Polymer Factory, Sweden).
8
5 °C for 3 h. The reaction mixture started as a white slurry and then
turned to a red-orange slurry approximately 15 min after heating.
After reacting, the red-orange slurry was then allowed to cool to room
temperature and filtered to remove CaCO . The resulting red-orange
translucent solution was then washed with sodium sulfite (Na SO ),
sodium hydrogen sulfate (NaHSO ), and deionized H O. The red-
orange solution turned orange after all of the washes and was then
3
2
3
4
2
dried with magnesium sulfate (MgSO ), filtered, and the solvent was
4
removed via rotary evaporator. After concentration, the orange
solution turned to a red viscous oil. The resulting red oil was dried
m/z + Na [322.94 m/z]. H NMR (Figure 1) (CDCl , 300 MHz): δ
1
1
(
Gel permeation chromatography (GPC) was performed on a
Waters model 1515 isocratic pump and a Waters model 2414
differential refractometer detector (Waters Corp., Milford, MA) with
three PSS SDV analytical 500 Å (8 × 300 mm) columns in series
+
+
1
3
.48 (s, 3H, CH ), 3.69 (d, J = 10.4 Hz, 1H, CH −Br), 3.74 (d, J =
3
2
rate of 1 mL/min at 30 °C. Samples for the size comparison study
were collected by fractionation using a Waters model 1515 isocratic
pump and a Waters model 2414 differential refractometer detector
0.4 Hz, 1H, CH −Br), 4.52 (d, J = 11.2 Hz, 1H, CH −OBz), 4.57
2
2
d, J = 11.2 Hz, 1H, CH −OBz), 7.43 (t, J = 7.4 Hz, 2H, CH
),
2
meta Ar−H
7
.57 (t, J = 7.4, 1.6 Hz, 1H, CH
para Ar−H
1
3
13
CCHortho Ar−H). C and C DEPT 135 NMR (Figure S3)
(
2
Waters Corp., Milford, MA) with one PSS SDV Prep 1000 Å (40 ×
(
(
(
(
4
1
CD S(O)CD , 75 MHz): δ 19.85 (CH ), 38.03 (CH −Br), 47.24
3
3
3
2
50 mm) (Polymer Laboratories Inc., Amherst, MA). This was done
C
), 67.37 (CH −O−C(O)), 129.32 (CH
), 129.67
quaternary
2
ortho Ar−H
in THF at a flow rate of 8 mL/min at 30 °C.
Attenuated total reflection Fourier-transform infrared (ATR-FTIR)
Cquaternary Ar−H), 129.72 (CHmeta Ar−H), 134.05 (CHpara Ar−H), 165.69
C(O)Bz), 173.89 (C(O)backbone). Anal. Calcd for C H BrO : C,
12
7.9%; H, 4.4%. Found: C, 48.9%; H, 4.5%. IR stretches (Figure S5):
−
1
−1
(
4
000 and 400 cm at a resolution of 4 cm , and 32 scans were
650−1800 cm COBz and COOH, 2350−2800 cm C
−
1
−1
−1
−1
OOH, 2800−3100 cm Ar−H, 3100−3700 cm O−H.
Poly(3-(benzoyloxy)-2-(bromomethyl)-2-methylpropanoic
acid) (PBBM). A round-bottom flask was charged with a stir bar,
BBM (8.00 g, 27 mmol), and K CO (14.7 g, 106 mmol). Ethyl
averaged for each spectrum.
Thermogravimetric analysis (TGA) (Figure 6) was performed on a
Q500 thermogravimetric analyzer (TA Instruments Inc.) at a 10 mg
scale under a flowing nitrogen atmosphere at a heating rate of 10 °C/
2
3
acetate (266 mL) was then added, and the reaction mixture was
C
Macromolecules XXXX, XXX, XXX−XXX