Synthesis, characterization, and catalytic activity of sodium ketminiate complexes toward the ring-opening polymerization of l-lactide

Article abstract of DOI:10.1039/c6ra00373g

Studies of the ring-opening polymerization of l-lactide (LA) using Na complexes with Schiff base ligands as catalysts have revealed high catalytic activity but poor controllability of the polymer molecular weight. In this study, Na complexes bearing ketiminate ligands instead of Schiff base ligands were synthesized and their application in LA polymerization was tested. The polymerization results revealed that the catalytic activity of Na complexes bearing ketiminate ligands was higher than that of Na complexes bearing Schiff base ligands, but the poor controllability of polymer molecular weight was still a drawback. However, the poor controllability could be improved by means of using a high concentration of initiators in the polymerization system at 0 °C for 1 min. L^Py-Na revealed the excellent controllability of polymer molecular weight depending on the ratio of [LA]/[initiator] (the molar averages of the number from 4500 to 35 000) with narrow polydispersity indexes, ranging from 1.29 to 1.35.

Full text of DOI:10.1039/c6ra00373g

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Synthesis, characterization, and catalytic activity of
sodium ketminiate complexes toward the ring-
opening polymerization of L-lactide†
Cite this: RSC Adv., 2016, 6, 33014
Wan-Jung Chuang,a Yen-Tzu Huang,a Yu-Hsieh Chen,a Yu-Shan Lin,a Wei-Yi Lu,a
a
ab
a
a
*
*
*
Yi-Chun Lai, Michael Y. Chiang,
Sodio C. N. Hsu and Hsuan-Ying Chen
Studies of the ring-opening polymerization of L-lactide (LA) using Na complexes with Schiff base ligands as
catalysts have revealed high catalytic activity but poor controllability of the polymer molecular weight. In
this study, Na complexes bearing ketiminate ligands instead of Schiff base ligands were synthesized and
their application in LA polymerization was tested. The polymerization results revealed that the catalytic
activity of Na complexes bearing ketiminate ligands was higher than that of Na complexes bearing Schiff
base ligands, but the poor controllability of polymer molecular weight was still a drawback. However, the
poor controllability could be improved by means of using a high concentration of initiators in the
polymerization system at 0 ꢀC for 1 min. LPy–Na revealed the excellent controllability of polymer
molecular weight depending on the ratio of [LA]/[initiator] (the molar averages of the number from 4500
to 35 000) with narrow polydispersity indexes, ranging from 1.29 to 1.35.
Received 6th January 2016
Accepted 24th March 2016
DOI: 10.1039/c6ra00373g
www.rsc.org/advances
Recently, we reported the ROP of L-LA by using Na complexes
(Fig. 1) bearing Schiff base ligands as catalysts, and the results
Introduction
revealed that these Na complexes were highly catalytically
active. Compared with Schiff base ligands, ketimine ligands
have a similar backbone, but exhibit a weak resonance effect.
According to the literature (Fig. 2), Zn complexes bearing keti-
minate ligands5a,b demonstrated higher catalytic activity for LA
polymerization than Zn complexes bearing Schiff base ligands
did.5c This led us to consider whether the catalytic activity of Na
complexes in LA polymerization can be improved if the keti-
mine ligands replace Schiff base ligands. In this study, the
preparation of a series of ketimine ligands (Scheme 1) with aryl
and alkyl amines and associated Na complexes is described to
discuss the relationship between the coordination of various
amines and the catalytic activity for L-lactide polymerization.
Environmental pollution caused by abandoned waste composed
of petrochemical materials has led people to consider using
renewable energy resources and environmentally friendly
materials. Polylactide (PLA)1 is a common replacement for
petrochemical plastics because of its short degradation time
and its renewable precursor lactide (LA). PLA is also used in
protein encapsulation and delivery, hydrogels, medical appli-
cations, drug delivery systems, and microsphere development
because of its biodegradability, biocompatibility, and perme-
ability.2 Many metal catalysts3a–p and organic catalysts3r–z have
been used in the ring-opening polymerization (ROP) of LA,
which is the main method of synthesizing PLA. However, metal
residues in polymers must be managed when PLA is used as
a biomaterial. Therefore, Na complexes4 (Fig. 1) have been
extensively researched with regard to LA polymerization. In
addition, the precursors of Na complexes are inexpensive, and
the synthetic process is simple.
Results and discussion
Synthesis and characterization of Na complexes
All ligands were prepared by reuxing a mixture of 2,4-penta-
nedione and alkylamine (or aniline) with p-toluenesulfonic acid
in EtOH.7 The ligands reacted with a stoichiometric quantity of
NaN(SiMe3)2 in THF to correspondingly produce a moderate
aDepartment of Medicinal and Applied Chemistry, Kaohsiung Medical University,
Kaohsiung 80708, Taiwan, Republic of China. E-mail: hchen@kmu.edu.tw;
sodiohsu@kmu.edu.tw; Fax: +886-7-3125339; Tel: +886-7-3121101-2585; +886-7- yield of Na compounds (Scheme 1). The formula and structure
of Na complexes were conrmed through elemental analysis, 1H
3121101-6984
bDepartment of Chemistry, National Sun Yat-sen University, Kaohsiung, Taiwan,
and 13C NMR spectroscopy, and X-ray crystallographic analysis
80424, Republic of China. E-mail: michael@mail.nsysu.edu.tw; Tel: +886-7-
for LPy–Na. The X-ray structure of LPy–Na (Fig. 3) demonstrates
5252000-3949
that the Na complex is a tetramer and features a ve-coordinate
† Electronic supplementary information (ESI) available: Polymer characterization
Na atom in distorted trigonal bipyramidal geometry with the tau
(s) parameter6 of 0.25. According to the literature,4i Na
data, and details of the kinetic study. CCDC 1422660. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c6ra00373g
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Fig. 1 Na complexes in ROP.
complexes bearing ketiminate ligands revealed a tetramer of 1.39–2.86), which is due to the transesterication accompanied
cubic form that was similar to that of Na complexes bearing by high catalytic activity. To improve the controllability of Na
Schiff base ligands.
complexes, the experiments with more initiators at 0 ꢀC was
performed (entries 11–20, Table 1). The results revealed that
LBn–Na, LBu–Na, LC2O–Na, LC3O–Na, and LPy–Na displayed high
catalytic activity, and their controllability of polymer molecular
weight improved with the acceptable PDIs (1.29–1.48). However,
LC2N–Na, LPhC2–Na, and LPhC3–Na exhibited no catalytic activity
in this condition. This revealed that aryl groups on N-substit-
uent with bulky substituent and 2-(dimethylamino)ethyl groups
on N-substituent of the ketiminate ligands were unfavorable for
the catalytic activity of Na complexes for LA polymerization at
0 ꢀC, and the reason may be that these N-substituents increased
the repulsion around Al atom and further decreased the L-LA
Polymerization of L-lactide
The polymerizations of L-LA by using Na complexes with BnOH
as an initiator in CH2Cl2 were investigated under a nitrogen
atmosphere at 25 ꢀC (entries 1–10, Table 1). The catalytic activity
of Na complexes with ketiminate ligands was higher (1 min,
conversion > 94%) than that of Na complexes bearing Schiff
base ligands. However, the controllability of polymer molecular
weight was also poor (the values of MnCal., MnNMR, and MnGPC
were not similar) with the broad polydispersity indexs (PDIs:
Fig. 2 Comparison of catalytic activity of Zn complexes with ketimine and Schiff base ligands in ROP.
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Scheme 1 Synthesis of ketimine ligands and associated Na complexes.
polymerization comparison between LBu–Na and L3Na4f (Fig. 1)
was studied (Table 1, entries 26 and 27). The results revealed
that the conversion was up to 80% in 1 min by using LBu–Na as
a catalyst in the severe condition (0 ꢀC, CH2Cl2 (30 mL), [LA] ¼
0.67 M, [LA] : [BnOH] : [Cat] ¼ 200 : 4 : 0.2); however, L3Na was
inactive in this condition. It proves that Na complexes bearing
ketiminate ligands have greater catalytic activity than that of Na
complexes bearing Schiff base ligands.
LA polymerization was satisfactorily controlled using LBu–Na
as a catalyst, as demonstrated in the linear relationship between
MnGPC and [LA]0 ꢁ conv./[BnOH]0 (entries 21–25, Table 1,
Fig. 4), and polymers with low PDIs, ranging from 1.10–1.26
were obtained.
The 1H NMR spectrum of PLA prepared using LPy–Na (entry
19, Table 1) showed that one benzyl group and hydroxy chain
ends with an integral ratio of 5 : 2 for Ha and He, suggesting that
initiation occurred through the insertion of the BnOH into L-LA
(Fig. 5).
A survey of recent studies on LA polymerization by using Na
complexes as catalysts is provides in Fig. 6. LBu–Na revealed the
highest catalytic activity of L-LA polymerization with the poor
controllability of polymer molecular weight and the broad PDI
at room temperature; however, the controllability could be
improved in the condition with more initiators at 0 ꢀC. Only
Na complexes4k bearing 6,60-(oxobis(methylene))bis(2,4-bis(2-
Fig. 3 Molecular structure of complex LPy–Na as 20% ellipsoids (all of
the hydrogen atoms were omitted for clarity). CCDC number:
1422660. Selected bond lengths (A˚) and bond angles (deg): Na(1)–O(1)
2.255(2), Na(1)–O(4) 2.340(2), Na(1)–O(2) 2.358(2), Na(1)–N(1) 2.367(3),
Na(1)–N(2) 2.404(3), O(1)–Na(1)–O(4) 91.70(8), O(1)–Na(1)–O(2)
90.18(8), O(4)–Na(1)–O(2) 90.18(8), O(1)–Na(1)–N(1) 81.74(8), O(4)–
Na(1)–N(1) 133.38(9), O(2)–Na(1)–N(1) 135.61(9), O(1)–Na(1)–N(2)
152.09(9), O(4)–Na(1)–N(2) 99.28(9), O(2)–Na(1)–N(2) 115.18(9), and
N(1)–Na(1)–N(2) 72.03(9).
coordination with Al atom. This polymerization character is phenylpropan-2-yl)phenolate) ligand was active for L-LA poly-
similar with Al complexes3p bearing ketiminate ligands. To merization at 0 ꢀC in CH2Cl2 (5 min, conversion > 99%),
compare with Na complexes bearing Schiff base ligands, the
compared with other Na complexes at room temperature. In
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Table 1 Polymerizations of L-lactide by using Na complexes with BnOH as an initiator
b
a
c
Entry
Catalyst
Time (min)
Conv.a (%)
MnCal
MnNMR
MnGPC
PDIc
1d
LBn–Na
LBu–Na
LC2N–Na
LC2O–Na
LC3O–Na
LPy–Na
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
5
5
5
5
5
1
1
99
99
99
99
94
97
99
99
99
99
99
99
0
14 500
14 500
14 500
14 500
14 500
14 100
14 500
14 500
14 500
14 500
5900
5900
—
5900
5900
5900
2400
—
—
18 200
28 200
6300
17 300
14 600
11 200
12 000
6600
22 600
17 300
6400
5200
—
10 600
11 100
13 100
20 100
30 300
11 700
13 300
17 500
20 100
16 000
11 000
7600
—
4600
6900
4000
1900
—
—
65 300
9000
2.57
2.86
2.31
1.95
2.04
2.32
1.93
2.24
1.98
2.19
1.65
1.46
—
2d
3d
4d
5d
6d
7d
LTHF–Na
LPhC2–Na
LPhC3–Na
LPhiPr–Na
LBn–Na
LBu–Na
LC2N–Na
LC2O–Na
LC3O–Na
LPy–Na
8d
9d
10d
11e
12e
13e
14e
15e
16e
17e
18e
19e
20e
21f
22g
23h
24i
25j
26k
27k
99
99
99
40
0
6200
8000
5000
2400
—
1.36
1.29
1.08
1.04
—
LTHF–Na
LPhC2–Na
LPhC3–Na
LPhiPr–Na
LBu–Na
LBu–Na
LBu–Na
LBu–Na
LBu–Na
LBu–Na
L3Na
0
—
—
99
99
99
99
99
99
80
0
5900
3700
9800
7100
13 200
22 200
32 000
46 100
9600
—
1.13
1.19
1.25
1.26
1.18
1.10
1.17
—
14 500
28 900
43 300
57 700
5900
24 500
35 400
43 400
54 200
9200
—
—
a
Obtained from 1H NMR analysis. b Calculated from the molecular weight of LA ꢁ [LA]0/[BnOH]0 ꢁ conversion yield + Mw(BnOH). c Obtained from
GPC analysis and calibrated using the polystyrene standard. Values in parentheses are the values obtained from GPC ꢁ 0.58. d Reaction condition:
room temperature, CH2Cl2 (10 mL), [LA] ¼ 1.00 M, [LA] : [BnOH] : [Cat] ¼ 100 : 1 : 0.125. e Reaction condition: 0 ꢀC, CH2Cl2 (20 mL), [LA] ¼ 1.00 M,
f
g
[LA] : [BnOH] : [Cat] ¼ 200 : 5 : 0.375. Reaction condition: 0 ꢀC, CH2Cl2 (15 mL), [LA] ¼ 0.16 M, [LA] : [BnOH] : [Cat] ¼ 25 : 1 : 1. Reaction
h
condition: 0 ꢀC, CH2Cl2 (15 mL), [LA] ¼ 0.66 M, [LA] : [BnOH] : [Cat] ¼ 100 : 1 : 1. Reaction condition: 0 ꢀC, CH2Cl2 (15 mL), [LA] ¼ 1.32 M,
i
j
[LA] :[ BnOH] : [Cat] ¼ 200 : 1 : 1. Reaction condition: 0 ꢀC, CH2Cl2 (15 mL), [LA] ¼ 1.98 M, [LA] : [BnOH] : [Cat] ¼ 300 : 1 : 1. Reaction
k
condition: 0 ꢀC, CH2Cl2 (15 mL), [LA] ¼ 2.64 M, [LA] : [BnOH] : [Cat] ¼ 400 : 1 : 1. Reaction condition: 0 ꢀC, CH2Cl2 (30 mL), [LA] ¼ 0.67 M,
[LA] : [BnOH] : [Cat] ¼ 200 : 4 : 0.2.
this study, the catalytic activity of Na complexes bearing keti- 0 ꢀC. However, the Na complexes bearing the ketiminate ligands
minate ligands for LA polymerization (1 min, conversion > 99%) with 2-(dimethylamino)ethyl and aryl groups on the N-substit-
was higher than that of Na complexes4k bearing 6,60- uent of were inactive at 0 ꢀC. Compared with other Na
(oxobis(methylene))bis(2,4-bis(2-phenylpropan-2-yl)phenolate) complexes mentioned in the literature,4 Na complexes bearing
ligand.
ketiminate ligands as catalysts had the highest catalytic activity
for the L-LA polymerization at 0 C.
ꢀ
Conclusions
Experimental section
General
A series of ketimine ligands and associated Na complexes were
synthesized. These complexes had a cubic tetramer which was
similar to that of Na complexes bearing Schiff base ligands. All Standard Schlenk techniques and a N2-lled glovebox were used
Na complexes demonstrated high catalytic activity for L-LA throughout the isolation and handling of all the compounds.
polymerization but the poor controllability of polymer molec- Solvents, 3-caprolactone, and deuterated solvents were puried
ular weight with the broad PDIs at room temperature. The prior to use. 2,4-Pentanedione, p-toluenesulfonic acid, 2,4,6-
controllability of polymer molecular weight was improved using trimethylaniline, 3,5-dimethylaniline, 2,6-diisopropylaniline,
a high concentration of BnOH in the polymerization system at pyridin-2-ylmethanamine, (tetrahydrofuran-2-yl)methanamine,
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Synthesis of LBn–Na
A mixture of LBn–H (3.79 g, 20 mmol) and sodium hydride (0.6 g,
20 mmol) in THF (30 mL), was stirred for 24 h. Volatile materials
were removed under vacuum to give yellow powder, and then
the residue was washed with hexane (50 mL) and a light yellow
powder was obtained aer ltration. Yield: 2.75 g (65%). 1H
NMR (C6D6, 200 MHz): d 7.19–7.05 (4H, m, ArH), 4.71 (1H, s, b-
H), 4.28 (2H, s, NCH2Ph), 1.79 (3H, s, CH3CN), 1.64 (3H, s,
CH3C]O). 13C NMR (C6D6, 50 MHz): d 178.19 (C]O), 170.15
(C]C–N), 142.41, 128.89, 127.51, 126.50 (Ar), 97.02 (b-C) 54.31
(NCH2Ph), 29.26 (CH3CO), 20.70 (NCCH3)2. Anal. calcd (found)
for C11H15N2ONaꢀ: C, 68.23 (68.19); H, 6.68 (7.02); N, 6.63
(6.76)%. Mp: 125 C.
Synthesis of LBu–Na
Fig. 4 Linear plot of MnGPC vs. [LA]0/[BnOH], with polydispersity
indexes indicated by closed circles (Table 1, entries 21–25).
Using a method similar to that for LBn–Na except LBu–H was
used in place of LBn–H. The white powder was obtained. Yield:
2.37 g (67%). 1H NMR (C6D6, 200 MHz): d 4.70 (1H, s, b-H), 2.11
benzylamine, N,N-dimethylethane-1,2-diamine, 2-methoxyethan-1-
amine, 3-methoxypropan-1-amine, tert-butylamine, and deuter-
ated chloroform were purchased from Acros. Benzyl alcohol was
purchased from Alfa. 1H and 13C NMR spectra were recorded on
a Varian Gemini2000-200 (200 MHz for 1H and 50 MHz for 13C)
spectrometer with chemical shis given in ppm from the
internal TMS or center line of CDCl3 and C6D6. Microanalyses
were performed using a Heraeus CHN-O-RAPID instrument.
GPC measurements were performed on a Jasco PU-2080 PLUS
HPLC pump system equipped with a differential Jasco RI-2031
PLUS refractive index detector using THF (HPLC grade) as an
eluent (ow rate 1.0 mL minꢂ1, at 40 ꢀC). The chromatographic
column was JORDI Gel DVB 103 A, and the calibration curve was
made by primary polystyrene standards to calculate Mn(GPC).
LBn–H,7 LC2N–H,7 LPy–H,7 LPhC2–H,7 LTHF–H,7 LPhC3–H,7 LBu–H,8a
LPhiPr–H,7 LC2O–H,8b and LC3O–H,8a,b were prepared following
literature procedures.
(3H, s, CH3CN), 1.88 (3H, s, CH3C]O), 1.34 (9H, s, C(CH3)3. 13
C
NMR (C6D6, 50 MHz): d 194.07 (C]O), 168.17 (C]C–N), 96.16
(b-C), 54.03 (NC(CH3)3), 32.01 (CH3CO), 25.70 (NCCH3)2), 20.14
(NC(CH3)3). Anal. calcd (found) for C9H16NONa: C, 61.00
ꢀ
(61.19); H, 9.10 (8.79); N, 7.90 (7.76)%. Mp: 106 C.
Synthesis of LC2N–Na
Using a method similar to that for LBn–Na except LC2N–H was
used in place of LBn–H. The brown powder was obtained. Yield:
3.30 g (86%). 1H NMR (C6D6, 200 MHz): d 4.82 (1H, s, b-H), 3.10
(2H, br, NCH2CH2), 2.35 (2H, br, NCH2CH2), 2.01 (6H, s,
N(CH3)2), 1.95 (3H, s, CH3CN), 1.73 (3H, s, CH3C]O). 13C NMR
(C6D6, 50 MHz): d 193.95 (C]O), 161.61 (C]C–N), 95.37 (b-C)
61.17 (NCH2), 59.07 (NCH2CH2), 45.32 (N(CH3)2), 28.98 (CH3CO),
18.59 (NC(CH3)2). Anal. calcd (found) for C9H17N2ONa: C, 56.23
(55.99); H, 8.91 (9.02); N, 14.57 (14.76)%. Mp: 129 ꢀC.
Fig. 5 1H NMR spectrum of PLLA (polymerization by LPy–Na, entry 19, Table 1).
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Fig. 6 Survey of recent studies on LA polymerization, in which Na complexes were used as catalysts.
Synthesis of LPy–Na
128.48, 127.99, 127.50 (Py), 96.89 (b-C) 56.14 (NCH2Py), 29.28
(CH3CO), 20.88 (NC(CH3)2). Anal. calcd (found) for C11H13N2ONa:
C, 62.25 (61.99); H, 6.17 (6.09); N, 13.20 (13.56)%. Mp: 148 ꢀC.
Using a method similar to that for LBn–Na except LPy–H was used
in place of LBn–H. The deep brown powder was obtained. Yield:
2.21 g (52%). 1H NMR (C6D6, 200 MHz): d 8.58 (1H, d, J ¼ 6.00 Hz,
Py-H), 7.03–6.68 (3H, m, Py-H), 4.81 (1H, s, b-H), 4.41 (2H, s,
NCH2Py), 1.94 (3H, s, CH3CN), 1.68 (3H, s, CH3C]O). 13C NMR
(C6D6, 50 MHz): d 190.62 (C]O), 162.09 (C]C–N), 150.00, 136.21,
Synthesis of LC2O–Na
Using a method similar to that for LBn–Na except LC2O–H was
used in place of LBn–H. The yellow powder was obtained. Yield:
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2.58 g (72%). 1H NMR (C6D6, 200 MHz): d 4.85 (1H, s, b-H), 3.23–
3.10 (7H, br, NCH2CH2OCH3), 2.09 (3H, s, CH3CN), 1.66 (3H, s,
CH3C]O). 13C NMR (C6D6, 50 MHz): d 177.65 (C]O), 168.10
(C]C–N), 96.56 (b-C), 74.00 (CH2OCH3), 58.51 (CH2OCH3),
50.21 (NCH2), 29.46 (CH3C]O), 20.73 (NC(CH3)2). Anal. calcd
(found) for C8H14NO2Na: C, 53.62 (53.92); H, 7.88 (8.05); N, 7.82
Synthesis of LPhiPr–Na
Using a method similar to that for LBn–Na except LPhiPr–H was
used in place of LBn–H. The brown powder was obtained. Yield:
2.11 g (75%). 1H NMR (C6D6, 200 MHz): d 7.31–7.12 (3H, m,
Ar-H), 5.20 (1H, s, b-H), 3.03 (2H, Sep, J ¼ 8 Hz, CH(CH3)2), 2.12
(3H, s, CH3CN), 1.63 (3H, s, CH3C]O), 1.22, 1.15 (12H, d, J ¼ 8
Hz, CH(CH3)2). 13C NMR (C6D6, 50 MHz): d 195.81 (C]O),
170.00 (C]C–N), 162.81, 146.26, 128.21, 123.44 (Ar), 95.46 (b-C),
29.52 (CH3CO), 28.39 (CH(CH3)2), 24.50, 22.56 (CH(CH3)2),
19.00 (CH3CN). Anal. calcd (found) for C17H24NONa: C, 71.92
ꢀ
(7.51)%. Mp: 116 C.
Synthesis of LC3O–Na
Using a method similar to that for LBn–Na except LC3O–H was
used in place of LBn–H. The yellow powder was obtained. Yield:
2.66 g (69%). 1H NMR (C6D6, 200 MHz): d 4.76 (1H, s, b-H), 3.28
(4H, br, NCH2CH2CH2OCH3), 3.06 (3H, s, OCH3), 2.11 (3H, s,
CH3CN), 1.91 (2H, br, NCH2CH2CH2OCH3), 1.75 (3H, s, CH3C]O).
13C NMR (C6D6, 50 MHz): d 178.19 (C]O), 169.09 (C]C–N),
96.19 (b-C), 74.13 (CH2OCH3), 58.46 (CH2OCH3), 50.45 (NCH2),
32.12 (NCH2CH2CH2O), 29.13 (CH3C]O), 20.73 (NC(CH3)2).
Anal. calcd (found) for C9H16NO2Na: C, 55.95 (55.92); H, 8.35
ꢀ
(72.57); H, 9.05 (8.60); N, 4.98 (4.72)%. Mp: 196 C.
X-ray crystallographic studies
The suitable crystals of complexes LPy–Li were sealed in a thin-
walled glass capillary under a dry nitrogen atmosphere and
mounted on a Bruker AXS SMART 1000 diffractometer. Intensity
data were collected in 1350 frames with increasing (width of
0.3ꢀ per frame). The absorption correction was based on the
symmetry-equivalent reections using the SADABS program.
The space group determination was based on a check of the
Laue symmetry and systematic absences and conrmed by
using the structure solution. The structure was solved by direct
method using an SHELXTL package. All non-H atoms were
located from successive Fourier maps, and hydrogen atoms
were rened using a riding model. Anisotropic thermal
parameters were used for all non-H atoms, and xed isotropic
parameters were used for H atoms.
ꢀ
(8.21); N, 7.25 (7.69)%. Mp: 123 C.
Synthesis of LTHF–Na
Using a method similar to that for LBn–Na except LTHF–H was
used in place of LBn–H. The yellow powder was obtained. Yield:
1.84 g (45%). 1H NMR (C6D6, 200 MHz): d 4.89 (1H, s, b-H), 3.85–
3.71 (3H, br, NCH2CHOCH2), 3.19–2.94 (2H, m, NCH2), 2.12 (3H,
s, CH3CN), 1.74 (3H, s, CH3C]O), 1.51–1.15 (4H, br, CH2CH2).
13C NMR (C6D6, 50 MHz): d 176.78 (C]O), 166.96 (C]C–N),
96.47 (b-C), 80.58, 67.89 (CH2OCH2), 56.49 (NCH2), 29.35
(CH3C]O), 25.97, 25.92 (CH2CH2), 20.89 (NC(CH3)2). Anal.
calcd (found) for C10H16NO2Na: C, 58.52 (59.01); H, 7.86 (7.99);
General procedures for the polymerization of L-lactides
ꢀ
N, 6.82 (6.25)%. Mp: 132 C.
A typical polymerization procedure was exemplied by the
synthesis of entry 1 (Table 1) using complex LBn–Na as a catalyst.
The polymerization conversion was analyzed by H NMR spec-
1
Synthesis of LPhC2–Na
troscopic studies. CH2Cl2 (10.0 mL) was added to a mixture of
complex LBn–Na (0.01 g, 0.0125 mmol), BnOH (0.01 g, 0.1
mmol), and L-lactide (1.44 g, 10 mmol) at 25 ꢀC. Aer the
solution was stirred for 6.5 min, the reaction was then
quenched by adding to a drop of ethanol, and the polymer was
precipitated pouring into n-hexane (30.0 mL) to give white
solids. The white solid was dissolved in CH2Cl2 (5.0 mL) and
then n-hexane (70.0 mL) was added to give white crystalline
solid. Yield: 1.24 g (86%).
Using a method similar to that for LBn–Na except LPhC2–H was
used in place of LBn–H. The white powder was obtained. Yield:
2.52 g (56%). 1H NMR (C6D6, 200 MHz): d 6.51 (1H, s, Ar-H), 6.16
(2H, s, Ar-H) 4.91 (1H, s, b-H), 2.14 (9H, br, CH3CN, Ph(CH3)2),
1.68 (3H, s, CH3C]O). 13C NMR (C6D6, 50 MHz): d 191.76
(C]O), 180.69 (C]C–N), 154.07, 137.86, 120.16, 117.67 (Ar),
96.77 (b-C), 25.67 (CH3C]O), 22.54 (NCCH3), 21.51 (Ph(CH3)2).
Anal. calcd (found) for C13H16NꢀONa: C, 69.31 (69.03); H, 7.16
(6.95); N, 6.22 (6.53)%. Mp: 168 C.
Acknowledgements
Synthesis of LPhC3–Na
Using a method similar to that for LBn–Na except LPhC3–H was This study is supported by Kaohsiung Medical University “Aim
used in place of LBn–H. The white powder was obtained. Yield: for the top 500 universities grant" under Grant No. KMU-
2.68 g (56%). 1H NMR (C6D6, 200 MHz): d 6.79 (2H, s, Ar-H), 4.86 DT103007, NSYSU-KMU JOINT RESEARCH PROJECT (NSYSU
(1H, s, b-H), 2.19 (3H, s, CH3CN), 2.02 (9H, br, Ph(CH3)3), 1.50 KMU 103-I004), NSYSU-KMU JOINT RESEARCH PROJECT,
(3H, s, CH3C]O). 13C NMR (C6D6, 50 MHz): d 194.07 (C]O), (#NSYSUKMU 104-P006), and the Ministry of Science and
176.23 (C]C–N), 168.17, 127.92, 127.52, 127.44 (Ar), 98.16 (b-C), Technology (Grant MOST 104-2113-M-037-010). We thank
32.52 (Ph(CH3)2), 31.05 (Ph(CH3)) 25.70 (CH3C]O), 20.14 Center for Research Resources and Development at Kaohsiung
(NCCH3). Anal. calcd (found) for C14H18NONa: C, 70.27 (69.87); Medical University for the instrumentation and equipment
ꢀ
H, 7.58 (7.59); N, 5.85 (5.55)%. Mp: 175 C.
support.
33020 | RSC Adv., 2016, 6, 33014–33021
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