Electronic Supplementary Information
1. Polymerization with using n-butylamine as an initiator
A solution of N-(4-nitrophenoxycarbonyl)-γ-benzyl-L-glutamate 1 (0.20 g, 0.5 mmol)
and n-butylamine (4.0 μL; 3.0 mg, 0.02 mmol) in N,N-dimethylacetamide (DMAc)
(0.25 mL) was stirred at 60 ºC for 48 h under nitrogen. The reaction mixture was
poured into ether (200 mL), and the resulting precipitate was collected by filtration with
suction and dried under vacuum to obtain poly(BLG) a whitish brown solid in 78 %
yield: 1H NMR (CDCl3): δ= 0.89 (br, 3H, -CH2-CH3), 1.33 (br, -CH2-CH3), 1.49 (br, 2H,
-CH2-CH2-CH3), 1.57-2.86 (br, 4H, -CH2-CH2-C(=O)-O- and -CH2-CH2-C(=O)-O-),
3.21, (br, 2H, -NH-CH2-CH2-), 3.96 (br, 1H, >CH-CH2-CH2-), 5.05, (s, 2H,
-O-CH2-C6H5), 7.27 (br, 5H, -O-CH2-C6H5).
Scheme S-1
2.
1
H
NMR
spectrum
of
poly(γ-benzyl-L-glutamate)
obtained
by using
p-(tert-butyl)phenylmethylamine
Figure S-1.
1
H NMR spectrum of poly(γ-benzyl-L-glutamate) obtained by using
p-(tert-butyl)phenylmethylamine.
3. MALDI TOF-Mass analysis
Matrix-assisted laser desorption / ionization time-of-flight mass spectrometry
(MALDI-TOF MS) was carried out on a PerSeptive Biosystems Voyager DE Pro Bio
Spectrometry workstation. 2-(4’-Hydroxyphenylazo)benzoic acid was used as matrix.
Poly(BLG) samples (1.5 mg) and 2-(4’-hydroxyphenylazo)benzoic acid (10 mg) were
dissolved 1 mL of tetrahydrofuran, and stirred for 10 minutes. 2 μL of this solution
was dropped to a sample plate and was dried under air. For ionization of the sample,
337 nm nitrogen laser was irradiated. The resulting ionized polymers were detected in
a positive mode with 20 kV for ion acceleration.
Poly(BLG) obtained by using 4-(tert-Butyl)phenylmethylamine (2) or n-butylamine
were analyzed by MALDI-TOF mass spectrometry.
Figure S-1a (in this
Supplementary Information) is the spectrum of the polymer obtained by using 2 as an
initiator.
In the spectrum, two series of signals are observed:
The series-A involves
signals with m/z=1151, 1370, 1589, and 1808, and the series-B involves 1167, 1386,
1605, and 1824.
In both of the series, the signals are regularly located with an interval
of 219 Da, which corresponds to the formula weight of the repeating unit. Similarly, in
the spectrum of the polymer obtained by using butyl amine as an initiator (Figure S-1b),
two series of mass signals were observed (series A’: m/z=1062, 1281, 1500, 1719; series
B’: 1078, 1297, 1517, 1736) and in both cases, the interval was 219 Da.
The simple
spectra with the regular intervals supported the polymerizations proceeded without any
significant damage on the side chains.
Between the series-A and the series-A’, there was a gap of 90 Da.
Similarly,
between the series-B and the series-B’, there was also a gap of 90 Da. This gap agrees
with the difference in molecular weight between the initiators, 2 and butylamine.
Consequently, all of the signals would be attributable to the polymers having the
amine-derived residue at the initiating end.
The final issue is the structure of X in the other terminal.
Between the series-A and
the series-B (for the polymers obtained by the 2-initiated polymerization), there is a gap
of 16 Da.
In both cases, the polymers would have the 2-derived structure at the
initiating end, and thus there would be two kinds of terminating end structures, X1 and
X2, of which formula weights were calculated to be 112 and 130, respectively. An
analogous discussion on the series-A’ and the series-B’ leads to the conclusion that the
polymers obtained by the butylamine-initiated polymerization would also have the same
X1 and X2 as terminal structures. The most reasonable candidate for X1 would be a
five-member cyclic amide-type one, which can be formed by intramolecular
nucleophilic attach of the terminal amino group to the benzyl ester in the previous
unit.[1]
For X2, a candidate could be acyclic amino acid-type one, which may be
formed by hydrolysis of the five-membered cyclic amide.
Figure S-2.
Table S-1.
MALDI-TOF Mass Spectra of the Polymers
Candidate Structures of Terminating End of the Polymers and the
Corresponding Calculated Formula Weights.
4.
1
H-NMR analysis of the reaction mixture
The reaction of 1 in the presence of n-butylamine ([1]/[n-butylamine] = 50) in DMAc
at 60 ºC was monitored with 1H NMR.
After 3h, a small amount of reaction mixture
was taken out and was diluted with CDCl3.
The 1H NMR spectrum of this sample was
shown in Figure S-3. At 4.4 ppm, a signal assignable to the methine proton of
unconsumed 1 was observed. The signal at 3.8-4.2 ppm was assigned to the methine
proton of poly(BLG).
Besides these signals, there was a signal at 4.7 ppm, which was
assigned to the methine proton of BLG-NCA.
1
This assignment was confirmed by the
H NMR analysis of the authentic BLG-NCA, which was prepared by the treatment of
BLG with triphosgen and purified by recrystallization.
The abovementioned results
obtained by 1H NMR analyses of the polymerization confirmed that the ring-opening
polymerization of BLG-NCA would be one of the major pathways to give poly(BLG).
Figure S-3. 1H NMR analysis of the reaction of 1 in DMAc with using n-butylamine
([1]/[n-butylamine] = 50) at 3 h.
Solvent for the measurement= CDCl3.
5. Possible pathways involved in the present polymerization system
Scheme S-2
6.
1
H NMR spectrum of poly(γ-benzyl-L-glutamate-co-ethylene glycol)
Figure S-4. 1H NMR spectrum of poly(γ-benzyl-L-glutamate-co-ethylene glycol).