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TABLE 1 Condensation PLA and the Isomeric Mixture of 1b and 2b
LA in the
1b þ 2b in the
Sn(Oct)2 in the
Feed (% wt)
Molar Percentage of
1b þ 2b in the Polymerb
PDIa
a
a
Sample
Feed (mol)
Feed (mol)
T (ꢁC)
Mn
Mw
II
III
a
0.0205
0.0200
7.4 ꢀ 10ꢂ4
5.5 ꢀ 10ꢂ4
0.4
0.8
170
145
1,279
537
2,292
780
1.79
1.40
3.5%
1.8%
Determined by SEC using narrow polystyrene standards and CHCl3 as eluent.
Determined by 1H NMR in CDCl3 by comparison of the integral of the signals relative to the aromatic hydrogen atoms on the trytil sulfur-protecting
b
group with the integral of the CH of the PLA main chain.
(400 MHz, CDCl3, d, ppm): 21.0 (CH3), 60.5 (CH2S), 68.9
(CHOH), 122.1, 130.2, 131.9, 137.9 (ArAC), 175.9 (COOH).
Copolymerization of 2-Hydroxy-3-(tritylsulfanyl)-propionic
acid (1b), 3-Hydroxy-2-(tritylsulfanyl)-propionic acid (2b),
and L-Lactic Acid. Samples (II–III)
Synthesis of 2-Hydroxy-3-(tritylsulfanyl)-propionic acid
(1b) and 3-Hydroxy-2-(tritylsulfanyl)-propionic acid (2b)
The reaction was performed as earlier, but tritylthiol was used
instead of 4-methylbenzenethiol. Ester hydrolysis was carried
out in the presence of LiOH (2 equv.) in a 3:1:1 THF:methanol:
water solution for 12 h with stirring. Then, the mixture was
acidified with HCl, extracted with ethyl acetate, and washed
with brine. The organic phase was dried over MgSO4, and the
solvent was removed under reduced pressure to afford the
product as an isomeric mixture of 1b and 2b in a 75:25 molar
The polymerizations were performed as earlier, but the iso-
meric mixture of 1b and 2b was used without separation.
Polymerization conditions, SEC analysis data, and the compo-
sitions of the copolymers are summarized in Table 1. For
copolymer 3, the maximum temperature was 170 ꢁC,
whereas copolymer 6 was synthesized from 100 to 145 ꢁC.
The copolymers were dissolved in THF, filtered on a small
column of silica gel, precipitated in an excess of n-hexane,
and dried in vacuum. 1H NMR (400 MHz, CDCl3, d, ppm):
1.53 (m, CH3), 4.34 (m, CHCOOH), 5.12 (m, CH), 7.07 (d,
ArAH), 7.15 (t, ArAH), 7.23 (t, ArAH). 13C NMR (400 MHz,
CDCl3, d, ppm): 15.5, 16.5 (CH3), 29.3, 29.5 (CH2), 56.6 (CH),
66.5, 68.9, 72.3 (CH), 126.1, 128.1, 129.2, 143.7 (ArAC),
167.7, 169.5, 174.2, 174.9 (COOA).
1
ratio (Yield ¼ 85%). H NMR (400 MHz, CDCl3, d, ppm): 2.64
(1H, dd, CHaHbS, 1b), 2.70 (1H, dd, CHaHbS, 1b), 3.13 (2H, m,
CH2OH, 2b), 3.44 (1H, dd, CHS, 2b), 3.89 (1H, dd, CHOH, 1b),
7.19–7.49 (2H, m, ArAH, 1b and 2b).13C NMR (400 MHz,
CDCl3, d, ppm): 36.22 (CH2S, 1b), 48.92 (CHS, 2b), 62.75
(CH2OH, 2b), 67.07 (CPh3, 1b), 68.67 (CPh3, 2b), 69.06 (CHOH,
1b), 127.03, 127.27 (ArAC, p), 128.19, 128.25, 129.65 (ArAC,
o, m), 144.03, 144.41 (ArAC, o, m), 176.24 (COOH, 2b), 176.76
(COOH, 1b).
Reaction of Sample (II) with I2
Sample (II) (200 mg) was dissolved in THF (20 mL), and
then 0.5 mL of solution of I2 in THF (0.01 M) was added.
The solution was kept under stirring at room temperature
for 1 h. The solution was concentrated to about 5 mL and
then added, under stirring, to a beaker containing 150 mL of
n-hexane. The precipitated polymer was recovered, washed
with n-hexane, and dried in vacuum. 1H NMR (400 MHz,
CDCl3, d, ppm): 1.53 (m, CH3), 4.34 (m, CHCOOH), 5.12 (m,
CH). 13C NMR (400 MHz, CDCl3, d, ppm): 15.5, 16.5 (CH3),
25.7 (CH2), 54.8 (CH), 66.7, 68.9, 72.3 (CH), 169.5, 174.2,
174.9 (COOA). GPC: Mn 1676, Mw 2644, and PD 1.6.
Condensation PLA
The condensation polymerization was performed in bulk and
under vacuum. LA (2.00 g) and Sn(Oct)2 (12 mg) were
weighed into a round-bottomed flask under a nitrogen atmos-
phere. The flask was immersed in an oil bath at 100 ꢁC. The
ꢁ
temperature was, thereafter, gradually raised to 170 C during
1
ꢁ
4 h and then kept at 170 C for 2 h. H NMR (400 MHz, CDCl3,
d, ppm): 1.56 (m, CH3), 5.18 (m, CH) 13C NMR (400 MHz,
CDCl3, d, ppm): 16.4 (CH3), 66.8 (CH), 169.4, (COOA).
Reaction of Sample (III) with I2
The reaction was performed as earlier by dissolving sample
(III) (200 mg) in THF (20 mL), and then adding 0.25 mL of
a 0.01 M solution of I2 in THF. GPC: Mn 839, Mw 1028, and
PD 1.2.
Copolymerization of 2-Hydroxy-3-(4-methyl-phenylsulfanyl)-
propionic acid (1a) and L-Lactic Acid. Sample (I)
All the copolymerization reactions were performed in bulk
and under vacuum. In a typical copolymerization, 2-hydroxy-
3-(4-methyl-phenylsulfanyl)-propionic acid (0.270 g), LA
(1.900 g), and Sn(Oct)2 (12 mg) were weighed into a round-
bottomed flask under a nitrogen atmosphere. The flask was
immersed in an oil bath at 100 ꢁC. Thereafter, the tempera-
ture was gradually raised to 170 ꢁC during 4 h, and then,
kept at 170 ꢁC for 2 h. 1H NMR (400 MHz, CDCl3, d, ppm):
1.56 (m, CH3), 2.34 (m, ArACH3), 3.10–3.50 (m, CH2S), 5.18
(m, CH), 7.06–7.40 (4H, m, ArAH). 13C NMR (400 MHz,
CDCl3, d, ppm): 16.5 (CH3), 20.4 (ArACH3), 36.2 (CH2), 66.6,
68.9 (CH), 125.2, 128.1, 129.0, 137.9 (ArAC), 169.2, 169.6,
174.9, 175.9 (COOA).GPC: number-average molecular weight
(Mn) 1071, Mw 1819, and polydispersity index (PDI) 1.7.
Reaction of Sample (I) with I2
The reaction was performed as earlier by dissolving sample
(I) (200 mg) in THF (20 mL) and then adding 1.0 mL of a
0.01 M solution of I2 in THF. 1H NMR (400 MHz, CDCl3, d,
ppm): 1.56 (m, CH3), 2.34 (m, ArACH3), 3.10–3.50 (m,
CH2S), 5.18 (m, CH), 7.06–7.40 (4H, m, ArAH). GPC data: Mn
880, Mw 1734, and PD 1.9.
Characterization
Nuclear Magnetic Resonance Spectroscopy
1
The H NMR and 13C NMR analyses were performed using a
Bruker Avance DPX-400 NMR spectrometer operating at 400
and 100 MHz, respectively. The samples were prepared by
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JOURNAL OF POLYMER SCIENCE PART A: POLYMER CHEMISTRY 2012, 50, 792–800