Table 1 Performed ADMET polymerizations of monomer 2
a
b
Entry
Monomer/mmol
4/mmol
Zhan-1B/mmol
p-BQ/mmol
M
n (1 h)/g mol-1
M
n (1 h)/g mol-1
PDI
DIc
1
2
3
4
5
6
7
1.07
1.05
1.05
1.06
1.06
1.07
1.08
0.00
0.00
0.01
0.02
0.04
0.07
0.16
0.01
0.01
0.01
0.01
0.01
0.01
0.01
0.00
0.02
0.02
0.02
0.02
0.02
0.02
15950
18500
17900
17300
15100
8050
—
32750
n.a.
n.a.
n.a.
19050
6389
1.67
1.61
1.58
1.57
1.65
1.92
2.02
64
12
7
12
4
7
—
5450
a GPC calculation results after a 1 h reaction time. b 1H-NMR calculation results. c GCMS calculation results of hydrolyzed polymers (see Experimental
section).
dropping funnel. Undec-10-enoyl chloride (6.52 g, 32.16 mmol)
in 50 mL of CH2Cl2 was added to the reaction mixture drop-wise
while stirring and refluxing for 2 h. Then, the reaction mixture
was cooled down, the solvent removed in vacuo and the residue
collected with hexane, and quickly filtered from a small plug
of Na2SO4 to remove the by-product, the triethylammonium
chloride salt. The filtrate was concentrated in vacuo and the
unreacted acid chloride, if any, was removed by reduced pressure
at 120 ◦C. The remaining product was a light-brown liquid
with a quantitative yield. dH (300 MHz, CDCl3, Me4Si): 5.82
(tdd, J = 16.91, 10.16, 6.66 Hz, 2H, vinylic), 5.06–4.89 (m, 4H,
vinylic), 2.45 (t, J = 7.43 Hz, 4H, –CH2(C O)O–), 2.05 (q,
J = 6.86 Hz, 4H, allylic), 1.73–1.60 (m, 4H, aliphatic), 1.36 (m,
20H, aliphatic). dC (300 MHz, CDCl3, Me4Si): 170.0 (C O),
139.5 (H2C CH–), 114.5 (H2C CH–), 35.7 (C O–CH2–),
34.1 (H2C HC–CH2–), 29.4 (–CH2– aliphatic), 24.6 (–CH2–
aliphatic). MS (ESI-positive, CH2Cl2): m/z = 373.29 ([M + Na]+,
calc. 373.27).
General procedure for thiol-ene polymerization. Into a dry re-
action vessel were introduced the diene monomer(s) (0.5 equiv.,
in case of copolymer 0.25 : 0.25 equiv.), di(2-mercaptoethyl)
ether (3, 0.5 equiv.) and AIBN (0.025 equiv.), and stirred
magnetically (500 rpm) for 5 min at RT, and then at 80 ◦C
for 2 h with continuous nitrogen purging. The reaction mixture
was dissolved in THF and precipitated into the corresponding
solvent.
Polyanhydride via thiol-ene (P3). The polymer was precipi-
tated into hexane (70.4%). dH (300 MHz, CDCl3, Me4Si): 3.64
(m, –CH2–O–CH2–), 3.10 (t, J = 6.5 Hz, –CH2–SC O–), 2.72
(t, J = 7 Hz, –S–CH2–), 2.56 (t, –CH2–S–), 2.46 (t, J = 7.4 Hz, –
CH2–C O–OC O–CH2–), 2.36 (t, 3H, –CH2–COOH), 2.11–
1.99 (m, 1H), 1.75–1.47 (m, aliphatic), 1.46–1.21 (m, aliphatic).
Polyester via thiol-ene (P4). The polymer was precipitated
into methanol (85.0%). dH (300 MHz, CDCl3, Me4Si): 4.12 (t,
J = 6.7 Hz, ester), 3.63 (t, J = 7 Hz, –CH2–O–CH2–), 2.74 (t,
J = 7 Hz, –S–CH2–), 2.54 (t, –CH2–S–), 1.78–1.52 (m, aliphatic),
1.45–1.17 (m, aliphatic).
Polymerization reactions
Poly(anhydride-co-ester) via thiol-ene (P6). The polymer
was precipitated into methanol (70.4%). dH (300 MHz, CDCl3,
Me4Si): 4.16 (t, J = 6.3 Hz, ester), 3.64 (t, J = 7 Hz, –CH2–O–
CH2–), 2.71 (t, J = 7 Hz, –S–CH2–), 2.56 (t, –CH2–S–), 2.46
(t, J = 7.4 Hz, –(C O)OC O–), 2.31 (t, J = 7.5 Hz, OC O–
CH2–), 2.08–1.91 (m, allylic), 1.78–1.50 (m, aliphatic), 1.33 (m,
aliphatic).
General procedure for ADMET polymerizations. Into a
flash-dried three-necked flask were introduced the diene
monomer(s) (in the case of copolymers 1 : 1 equiv.), methyl 10-
undecenoate (when used, see Table 1), p-benzoquinone (when
used, BQ, 0.02 equiv.) and Zahn-1B (0.01 equiv.) and stirred
mechanically (500 rpm) at 80 ◦C for 1 h under a 100 ( 20) mbar
continuous vacuum. The reaction was quenched with ethyl vinyl
ether (EVE, 50 equiv., considering the catalyst amount) in THF
and precipitated into the corresponding solvent.
Results and discussion
We started our investigations by synthesizing anhydride-
functional monomer 1 from 10-undecenoic acid and the cor-
responding acid chloride. A number of methods in the literature
deal with the synthesis of anhydrides. Typically, anhydride
synthesis is carried out using carboxylic acids and a dehydrating
agent such as dicyclohexylcarbodiimide,19 carbodimidazole,
phosgene, diphosgene or methoxyacetylene.20 However, these
methods produce a mixture of symmetric and mixed anhy-
drides, which require challenging purification methods in order
to gather pure symmetric anhydrides. The condensation of
carboxylic acids with acetic anhydride in the presence of het-
erogeneous coordination catalysts21 also requires high reaction
temperatures, a vacuum and long reaction times. On the other
hand, the condensation of a carboxylic acid and an acid chloride
in the presence of an acid scavenger (e.g. triethylamine or pyri-
dine) results in an almost complete conversion into symmetric
anhydrides by much milder conditions, although a negligible
Polyanhydride via ADMET (P1). The polymer was pre-
cipitated into hexane (74.8%). dH (500 MHz, CDCl3,
Me4Si): 5.54–5.29 (m, vinylic), 3.68 (s, ester), 2.46 (t, J =
7.5 Hz, (C O)OC O–CH2–), 2.10–1.89 (m, allylic), 1.68 (m,
aliphatic), 1.48–1.15 (m, aliphatic).
Polyester via ADMET (P2). The polymer was precipitated
into methanol (82.4%). dH (500 MHz, CDCl3, Me4Si): 5.51–
5.25 (m, vinylic), 4.16 (t, J = 6.3 Hz, ester), 3.68 (s, methyl ester),
2.30 (t, J = 7.6 Hz, OC O–CH2–), 1.97 (m, allylic), 1.61 (m,
aliphatic), 1.44–1.06 (m, aliphatic).
Poly(anhydride-co-ester) via ADMET (P5). The polymer
was precipitated into methanol (73.6%). dH (300 MHz, CDCl3,
Me4Si): 5.58–5.23 (m, vinylic), 4.15 (t, J = 6.3 Hz, ester), 2.46
(t, J = 7.4 Hz, –CH2–(C O)OC O–), 2.31 (t, J = 7.5 Hz,
OC O–CH2–), 2.12–1.89 (m, allylic), 1.77–1.47 (m, aliphatic),
1.48–1.13 (m, aliphatic).
316 | Green Chem., 2011, 13, 314–320
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The Royal Society of Chemistry 2011
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