Magnesium complexes incorporated by sulfonate phenoxide ligands as efficient catalysts for ring-opening polymerization of ε-caprolactone and trimethylene carbonate

Article abstract of DOI:10.1002/pola.24133

Two novel sulfonate phenol ligands-3, 3′-di-tert-butyl2′- hydroxy-5, 5′,6, 6′-tetramethyl-biphenyl-2-yl 4-X-benzenesulfonate (X=CF₃, L^CF3 - H, and X=OCH₃, L ^OMe -H)-were prepared through the sulfonylation of 3, 3′-di-tert-butyl-5, 5′, 6, 6′-tetramethylbiphenyl-2, 2′-diol with the corresponding 4-substituted benzenesulfonyl chloride (1 equiv.) in the presence of excess triethylamine. Magnesium (Mg) complexes supported by sulfonate phenoxide ligands were synthesized and characterized structurally. The reaction of MgⁿBu₂ with L-H (2 equiv.) produces the four-coordinated monomeric complexes (L^CF3)₂Mg (1) and (L^OMe)₂Mg (2). Complexes 1 and 2 are efficient catalysts for the ring-opening polymerization of ε-caprolactone (ε-CL) and trimethylene carbonate (TMC) in the presence of 9-anthracenemethanol; complex 1 catalyzes the polymerization of ε-CL and TMC in a controlled manner, yielding polymers with the expected molecular weights and narrow polydispersity indices (PDIs). In ε-CL polymerization, the activity of complex 1 is greater than that of complex 2, likely because of the greater Lewis acidity of Mg²⁺ metal caused by the electron-withdrawing substitute trifluoromethyl (-CF₃) at the 4-position of the benzenesulfonate group.

Full text of DOI:10.1002/pola.24133

Magnesium Complexes Incorporated by Sulfonate Phenoxide Ligands
as Efficient Catalysts for Ring-Opening Polymerization of e-Caprolactone
and Trimethylene Carbonate
PO-SHENG CHEN, YI-CHANG LIU, CHIA-HER LIN, BAO-TSAN KO
Department of Chemistry, Chung Yuan Christian University, Chung-Li 320, Taiwan, Republic of China
Received 12 January 2010; accepted 16 May 2010
DOI: 10.1002/pola.24133
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: Two novel sulfonate phenol ligands—3,30-di-tert-butyl-
20-hydroxy-5,50,6,60-tetramethyl-biphenyl-2-yl
4-X-benzenesulfo-
OMe-H)—were prepared
merization of e-CL and TMC in a controlled manner, yielding poly-
mers with the expected molecular weights and narrow
polydispersity indices (PDIs). In e-CL polymerization, the activity of
complex 1 is greater than that of complex 2, likely because of the
greater Lewis acidity of Mg2þ metal caused by the electron-with-
nate (X¼CF3,
L
CF3-H, and X¼OCH3,
L
through the sulfonylation of 3,30-di-tert-butyl-5,50,6,60-tetramethyl-
biphenyl-2,20-diol with the corresponding 4-substituted benzene-
sulfonyl chloride (1 equiv.) in the presence of excess triethylamine.
Magnesium (Mg) complexes supported by sulfonate phenoxide
ligands were synthesized and characterized structurally. The reac-
tion of MgnBu2 with L-H (2 equiv.) produces the four-coordinated
monomeric complexes (LCF3)2Mg (1) and (LOMe)2Mg (2). Complexes
1 and 2 are efficient catalysts for the ring-opening polymerization
of e-caprolactone (e-CL) and trimethylene carbonate (TMC) in the
presence of 9-anthracenemethanol; complex 1 catalyzes the poly-
drawing substitute trifluoromethyl (ACF3) at the 4-position of the
C
V
benzenesulfonate group. 2010 Wiley Periodicals, Inc. J Polym Sci
Part A: Polym Chem 48: 3564–3572, 2010
KEYWORDS: e-caprolactone; catalysts; magnesium; polycarbon-
ates; polyesters; ring-opening polymerization; sulfonate phenox-
ide; trimethylene carbonate
INTRODUCTION Because of their biodegradable, biocompatible,
and permeable properties, aliphatic polyesters and polycarbon-
ates such as poly(e-caprolactone) (PCL), polylactide (PLA), and
poly(trimethylene carbonate) (PTMC), as well as their copoly-
mers, have attracted considerable attention and have been
widely used in the biomedical, pharmaceutical and environmen-
tal fields.1 A common chemical synthetic route to PCL, PLA, and
PTMC is the ring-opening polymerization (ROP) of cyclic esters
and carbonates using metal-alkoxide initiators or catalysts
derived from various main-group metal complexes,2 such as
lithium,3 calcium,4 zinc,5 tin(II),6 and aluminium7 as well as
magnesium complexes.8 These metal complexes are efficient ini-
tiators and catalysts for the preparation of polyesters with con-
trolled molecular weight and its narrow distribution. Among
these metals, magnesium is nontoxic and essential for human
life9; therefore, magnesium complexes are worthy candidates as
catalysts and initiators of ROP for biomedical purposes.
Chart 1) have been modified on introducing various functional
groups, and their metal complexes have shown to have promis-
ing catalytic activities for ROP.7(f,j,l),12 Magnesium complexes
supported by monovalent phenols derived from 2,20-ethylidene-
bis(4,6-di-tert-butylphenol) (EDBP-H2), including EDBP-RTs-H
(Type II, Chart 1)13 and EDBP-(Me)-H (Type III, Chart 1),14
have been synthesized and structurally characterized; these
complexes bearing bidentate monovalent phenoxide ligands
have proved to be effective initiators for ROP of lactides and
demonstrated that their catalytic activities were greatly
increased relative to the bisphenol system. Encouraged by these
results from the modified EDBP system, we are interested in
developing the sulfonate phenol ligand derived from another
bisphenol—3,30-di-tert-butyl-5,50,6,60-tetramethyl-biphenyl-2,20-
diol—to investigate the catalytic behavior of these complexes
bearing such a ligand. As a result, a novel 4-substituted benze-
nesulfonate phenol ligand (L-H, Chart 1) has been designed and
synthesized. Herein, we describe the synthesis, characterization,
and ROP catalytic studies of magnesium derivatives supported
by novel sulfonate phenoxide ligands of this kind.
So-called single-active-site metal complexes supported by
various ligands such as b-diketiminate,5(c,d,g) Schiff base,10
anilido-aldiminate,11 and many others have been developed
to achieve great activity with effective molecular weight in a
controlled manner. In particular, the bisphenolate system
receives increasing attention because of easy modification
and functionalization. Many bisphenolato ligands (Type I,
EXPERIMENTAL
General
All manipulations were carried out under a dry nitrogen
atmosphere. Solvents and reagents were dried by refluxing for
Additional Supporting Information can be viewed in the online issue of this article. Correspondence to: B.-T. Ko (E-mail: btko@cycu.edu.tw)
C
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Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 48, 3564–3572 (2010) 2010 Wiley Periodicals, Inc.
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ARTICLE
(0.87 g, 3.50 mmol), and 4-(dimethylamino)pyridine (DMAP,
0.069 g, 0.57 mmol, catalyst) were dissolved in 50 mL of
freshly distilled CH2Cl2 and the resulting solution cooled to
0
ꢀC. Neat triethylamine (NEt3, 0.6 mL, 3.85 mmol) was
added dropwise to the solution, which was then stirred at
ambient temperature for 48 h. The solution was filtered, and
the filtrate was washed with 50 mL of water three times.
The dichloromethane layer was collected and dried over an-
hydrous MgSO4 and filtered through Celite again to remove
MgSO4. The resulting filtrate was then dried under vacuum,
and the residue was recrystallized from an acetonitrile
solution.
LCF3-H: Yield: 1.59 g (81%).1H NMR (298 K, CDCl3, 300 MHz,
ppm): d 6.63–7.51 (6H, m, ArH), 4.94 (1H, s, OH), 2.33 (3H,
s, CH3), 1.75 (3H, s, CH3), 1.72 (3H, s, CH3), 1.52 (3H, s,
CH3), 1.61 (9H, s, C(CH3)3), 1.44 (9H, s, C(CH3)3). 13C NMR
(298 K, CDCl3, 75 MHz, ppm): d 150.63, 147.00, 141.30,
141.11, 136.83, 136.27, 133.72, 133.33, 133.29, 132.71,
130.62, 129.94, 128.24, 127.27, 125.60, 125.46, 125.10(CF3),
35.07, 34.35, 31.17, 29.58, 20.75, 19.67, 16.04, 15.90. Anal.
calcd for C31H37F3O4S: C, 66.17; H, 6.63. Found: C, 66.55; H,
6.68%.
LOMe-H: Yield: 1.47g (80%). 1H NMR (298 K, CDCl3, 300
MHz, ppm): d 6.67–7.35 (6H, m, ArH), 5.02 (1H, s, OH), 3.86
(1H, s, OCH3), 2.31 (3H, s, CH3), 2.01 (3H, s CH3), 1.84 (3H,
s, CH3), 1.52 (3H, s, CH3), 1.58 (9H, s, C(CH3)3), 1.45 (9H, s,
C(CH3)3). 13C NMR (298 K, CDCl3, 75 MHz, ppm): d 162.39,
150.81, 146.73, 141.08, 136.63, 135.70, 133.41, 132.84,
131.26, 129.92, 129.87, 127,96, 127.67, 127.34, 126.46,
113.27, 55.54, 35.19, 34.40, 31.35, 29.71, 20.78, 19.89,
16.15, 15.93. Anal. calcd for C31H40O5S: C, 70.96; H, 7.68.
Found: C, 70.69; H, 7.98%.
CHART 1
at least 24 h over sodium/benzophenone (hexane, toluene,
and tetrahydrofuran [THF]), or over calcium hydride (CH2Cl2).
Deuterated solvents, triethylamine, and e-caprolactone (e-CL)
were dried over 4 Å molecular sieves. Trimethylene carbonate
(TMC) was purchased from Boehringer Ingelheim (http://
www.boehringer-ingelheim.com) and was recrystallized from a
toluene solution before use. 3,30-di-tert-butyl-5,50,6,60-tetra-
methylbiphenyl-2,20-diol (Strem), 4-(trifluoromethyl)benzene-
sulfonyl chloride (Acros), 4-methoxybenzene-1-sulfonyl chlo-
ride (Acros), 9-anthracenemethanol (9-AnOH) (Acros), 1-
pyrenebutanol (Acros), and 4-dimethylaminopyridine (Alfa)
were purchased and used without further purification. MgnBu2
(1.0 M in heptane) was purchased from Aldrich (http://
Synthesis of Magnesium Complexes
[(LCF3)2Mg] (1): nBu2Mg (1.0 mL, 1.0 M in heptane, 1.0
mmol) was added slowly to an ice cold solution (0 ꢀC) of
LCF3-H (1.12 g, 2.0 mmol) in 30.0 mL of toluene under a dry
nitrogen atmosphere. The mixture was then stirred for 24 h
while the temperature was slowly increased to ambient tem-
perature. Volatile materials were removed under vacuum
and the residue was recrystallized from a hexane solution to
give white solids. Yield: 0.84 g (73%). The resulting solids
were crystallized from the saturated hexane solution to yield
colorless crystals.
www.sigmaaldrich.com) and used as received. H NMR and 13C
1
NMR spectra were recorded on a Bruker Avance (300 MHz)
spectrometer with chemical shifts given in parts per million
(ppm) from the peak of internal tetramethylsilane. Microanaly-
ses were performed using a Heraeus CHNAOARAPID instru-
ment. Gel permeation chromatography (GPC) measurements
were performed on a JASCO PU-2080 plus system equipped
with a RI-2031 detector using THF (HPLC grade) as an eluent.
The chromatographic column was Phenomenex Phenogel 5 l
103 Å, and the calibration curve used to calculate Mn(GPC)
was produced from polystyrene standards. The GPC results
were calculated using the Scientific Information Service Corpo-
ration (SISC) chromatography data solution 3.1 edition.
1H NMR (298 K, CDCl3, 300 MHz, ppm): d 6.45–7.56 (6H, m,
ArH), 2.29 (3H, s, CH3), 1.74 (3H, s, CH3), 1.66 (3H, s, CH3),
1.34 (3H, s, CH3), 1.47 (9H, s, C(CH3)3), 1.31 (9H, s,
C(CH3)3). 13C NMR (298 K, CDCl3, 75 MHz, ppm): d 160.81,
147.21, 139.16, 139.05, 138.19, 136.62, 135.01, 134.94,
133.92, 131.44, 128.41, 127.98, 126.93, 125.51, 125.47,
124.77, 120.30, 34.73, 34.33, 31.21, 29.37, 21.08, 19.52,
16.12, 15.96. Anal. calcd for C62H72F6MgO8S2: C, 64.89%; H,
6.32%. Found: C, 64.79%; H, 6.70%.
General Procedures for Synthesis of the Sulfonate
Phenol Ligands
3,30-di-tert-butyl-5,50,6,60-tetramethylbiphenyl-2,20-diol (1.24
g, 3.50 mmol), 4-(trifluoromethyl)-benzenesulfonyl chloride
[(LOMe)2Mg] (2): To an ice cold solution (0 ꢀC) of LOMe-H
(1.05 g, 2.0 mmol) in 30.0 mL of toluene was slowly added a
nBu2Mg (1.0 mL, 1.0 M in heptane, 1.0 mmol) under a dry
SULFONATE PHENOXIDE MAGNESIUM COMPLEXES AS CATALYSTS, CHEN ET AL.
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nitrogen atmosphere. The mixture was then stirred for 24 h
while the temperature was slowly increased to ambient tem-
perature. Volatile materials were removed under vacuum
and the residue was recrystallized from a hexane solution to
give white solids. Yield: 0.75 g (70%). The resulting solids
were crystallized from the saturated hexane solution to yield
colorless crystals.
zation for 15 min, TMC (0.51 g, 5.0 mmol) in CH2Cl2 (5.0
mL) was added. After another 30 min, the reaction was
quenched using the procedures described previously. Yield:
1.35 g (82%).
X-Ray Crystallographic Studies
Suitable crystals of complexes 1 and 2 were sealed in thin-
walled glass capillaries under nitrogen atmosphere and were
mounted on Brucker SMART APEX2 or Oxford Gemini R
Ultra diffractometer. Intensity data were collected in 1350
frames with increasing w (width of 0.3ꢀ per frame). The
absorption correction was based on the symmetry-equivalent
reflections using SADABS program. The space group determi-
nation was based on a check of the Laue symmetry and
systematic absence and was confirmed using the structure
solution. The structures were solved with direct methods
using a SHELXTL package. All non-H atoms were located
from successive Fourier maps, and hydrogen atoms were
refined using a riding model. Anisotropic thermal parameters
were used for all non-H atoms, and fixed isotropic parame-
ters were used for H-atoms.
1H NMR (298 K, CDCl3, 300 MHz, ppm): d 6.61–7.21 (6H, m,
ArH), 3.87 (3H, s, OCH3), 2.29 (3H, s, CH3), 1.77 (3H, s, CH3),
1.75 (3H, s, CH3), 1.45 (9H, s, C(CH3)3), 1.34 (12H, s, CH3
þ
C(CH3)3). 13C NMR (298 K, CDCl3, 75 MHz, ppm): d 162.94,
161.22, 146.58, 139.25, 137.96, 136.04, 135.45, 134.99,
131.54, 128.40, 127.64, 127.46, 127.41, 119.90, 113.82,
113.66, 55.59, 34.88, 34.39, 31.40, 29.57, 21.10, 19.73,
16.20, 16.00. Anal. calcd for C62H78MgO10S2: C, 69.48% ; H,
7.34%. Found: C, 69.71%; H, 7.29%.
Polymerization of e-CL Catalyzed by the Sulfonate
Phenoxide Magnesium Complex
A typical polymerization procedure was exemplified by the
synthesis of PCL-50 (the number 50 indicates the designed
[CL]0/[9-AnOH]0). To
a
rapidly stirring solution of
RESULTS AND DISCUSSION
[(LCF3)2Mg] (1) (0.057 g, 0.05 mmol) and 9-anthraceneme-
thanol (9-AnOH, 0.021 g, 0.1 mmol) in toluene (15 mL) was
added e-caprolactone (0.55 mL, 5.0 mmol). The reaction mix-
ture was stirred at 25 ꢀC for 5 min. The conversion yield
(99%) of PCL-50 was analyzed by 1H NMR spectroscopic
studies. After the reaction was quenched by the addition of
excess water (1.0 mL), the polymer was precipitated into
hexane (100 mL). The white precipitate was purified by
redissolving the polymer in THF (5.0 mL) and then precipi-
tated into MeOH (60 mL). Finally, the white polymer was
dried under vacuum giving white solids. Yield: 0.45 g (79%).
Syntheses and Crystal Structure Determination
The synthetic routes of sulfonate phenol ligands (LCF3-H and
LOMe-H) and their Mg complexes (1 and 2) are outlined in
Scheme 1. These 4-substituted benzenesulfonate phenol
derivatives (3,30-di-tert-butyl-20-hydroxy-5,50,6,60-tetramethyl-
biphenyl-2-yl 4-X-benzenesulfonate) were prepared in high
yield (~80%) on the reaction of 3,30-di-tert-butyl-5,50,6,60-tet-
ramethylbiphenyl-2,20-diol with the corresponding 4-substi-
tuted benzenesulfonyl chloride (4-XAC6H4SO2Cl, X¼¼CF3 or
OCH3, 1 molar equiv.) in the presence of excess triethyl-
amine, using 4-dimethylaminopyridine (DMAP) as catalyst
and dichloromethane as solvent at ambient temperature.15
These ligands (LCF3-H and LOMe-H) were isolated as white
solids and easily purified on recrystallization from acetoni-
trile or hexane solution. These two ligands were character-
ized by 1H and 13C NMR spectra and microanalyses. The 1H
NMR spectrum of the ligands exhibited resonances approxi-
mately d 5.0 ppm for the only hydroxyl proton of the phenol
group, and signals of methyl or tert-butyl group on biphenyl
backbone in two sets, indicating the formation of the desired
monobenzenesulfonylate phenol ligand. For instance, four
resonance peaks corresponding to methyl protons (d ¼ 1.52,
1.72, 1.75, 2.33 ppm, 3H each) and two peaks arising from
tert-butyl groups (d ¼ 1.44, 1.61 ppm, 9H each) were
observed for LCF3-H. Compounds 1 and 2 were further syn-
thesized via alkane elimination in toluene. Treatment of the
ligand (LCF3-H or LOMe-H, two equiv.) with MgnBu2 affords
the tetra-coordinated monomeric complex [L2Mg] (1:
(LCF3)2Mg; 2: (LOMe)2Mg) in 73% and 70% yields, respec-
tively. Attempts to obtain the butylmagnesium complexes
modified by the sulfonate phenolate ligand were unsuccess-
ful. Complexes 1 and 2 were obtained as white crystalline
solids after recrystallization from hexane solution and have
been fully characterized by spectroscopic studies and X-ray
structural determinations.
Polymerization of TMC Catalyzed by the Sulfonate
Phenoxide Magnesium Complex
A typical polymerization procedure was exemplified by the
synthesis of PTMC-100 (the number 100 indicates the
designed [TMC]0/[9-AnOH]0). To a rapidly stirring solution
of [(LCF3)2Mg] (1) (0.057 g, 0.05 mmol) and 9-anthracene-
methanol (9-AnOH, 0.021 g, 0.1 mmol) in CH2Cl2 (10 mL)
was added TMC (1.02 g, 10 mmol) in CH2Cl2 (10 mL). The
ꢀ
reaction mixture was stirred at 0 C for 60 min. The conver-
sion yield (98%) of PTMC-100 was analyzed by 1H NMR
spectroscopic determinations. After the reaction was
quenched by the addition of excess water (1.0 mL), the poly-
mer was precipitated into hexane (100 mL). The white pre-
cipitate was purified by redissolving the polymer in THF (5.0
mL) and then precipitated into MeOH (60 mL). Yield: 0.92 g
(90%).
Synthesis of PCL-b-PTMC Diblock Copolymer Catalyzed
by the Sulfonate Phenoxide Magnesium Complex
A typical polymerization procedure was exemplified by the
synthesis of PCL(100)-b-PTMC(50) (the number 100 or 50
indicates the designed [CL]0/[9-AnOH]0 or [TMC]0/[9-
AnOH]0). The living prepolymer PCL-100 was synthesized by
a similar approach as described above, but e-CL (1.10 mL,
10.0 mmol) in CH2Cl2 (15.0 ml) was used. After prepolymeri-
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ARTICLE
SCHEME 1 Synthetic routes for (a)
ligands
CF3-H OMe-H and (b)
complexes (1)–(2).
L
& L
Single crystals of complexes 1 and 2 suitable for X-ray struc-
tural determinations were obtained on cooling a saturated
hexane solution. Oak Ridge Thermal Ellipsoid Plot drawings
displaying selected bond lengths and angles of the molecular
structure of 1 and 2 appear in Figures 1 and 2, respectively.
The molecular structures of compound 1 and 2 are isostruc-
tural, except either a trifluoromethyl (ACF3) or a methoxy
(AOCH3) substituent at the 4-position of the benzenesulfo-
nate group. Both exhibit the homoleptic and monomeric fea-
ture with a four-coordinated magnesium center supported
by oxygen atoms of sulfonate phenoxide ligands, forming
two nine-membered chelating rings. The bond angles around
Mg in 1 in a range 97.12(10)–135.61(11)ꢀ and around Mg in
2 in the range 97.08(6)–136.88(6)ꢀ all show a distorted tet-
rahedral geometry. The average bond lengths of Mg–O(phe-
noxy oxygen) are 1.876(2) Å for 1 and 1.883(1) Å for 2,
respectively, which are within a normal range for the four-
coordinated magnesium phenoxide complexes.13,14 The oxy-
gen atoms of the sulfonate groups coordinate the magnesium
ion with an average MgAO(sulfonate oxygen) bond distance
of 2.028(2) Å for 1 and 2.003(1) Å for 2, greater than the
covalent Mg–O(phenoxy oxygen) bond. The slightly shorter
FIGURE 1 Oak Ridge Thermal
Ellipsoid Plot drawing of complex
1
with probability ellipsoids
drawn at the 20% level. Hydrogen
atoms are omitted for clarity.
˚
Selected bond lengths/A and
angles/deg: MgAO(1) 1.867(2),
MgAO(5)
1.884(2),
MgAO(7)
2.013(2), MgAO(3) 2.042(2), O(1)A
MgAO(5) 135.61(11), O(1)A MgA
O(7) 113.62(10), O(5)AMgA O(7)
101.97(9), O(1)AMgAO(3) 97.12
(10), O(5)AMgAO(3) 100.05 (10),
O(7)AMgAO(3) 102.80(10).
SULFONATE PHENOXIDE MAGNESIUM COMPLEXES AS CATALYSTS, CHEN ET AL.
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FIGURE 3 Polymerization of e-CL catalyzed by 1 in toluene at
25 oC. The relationship between Mn(n)/(PDI(h) of polymer and
the initial molar ratio [CL]0/[9-AnOH]0 is shown.
FIGURE 2 Oak Ridge Thermal Ellipsoid Plot drawing of complex 2
MgAO(sulfonate oxygen) bond in 2 is consistent with the
effective electron-donating group, AOCH3 on the sulfonate
group, that increases the electron density to form a stronger
dative bond. These MgAO(sulfonate oxygen) bond distances
of bis(sulfonate phenoxide) Mg complexes in this work are
somewhat smaller than those (ꢁ2.090(2) Å) found in alkyl
Mg complexes, but are similar to those (ꢁ2.010(2) Å) of Mg
alkoxide complexes with EDBP-RT ligands.13
with probability ellipsoids drawn at the 50% level. Hydrogen atoms
˚
are omitted for clarity. Selected bond lengths/A and angles/deg:
MgAO(1) 1.8929(14), MgAO(3) 1.9987(14), MgAO(6) 1.8739(14),
MgAO(8) 2.0077(14), O(6)AMgAO(1) 136.88(6), O(1)AMgAO(8)
98.84(6), O(1)AMgAO(3) 106.36(6), O(6)AMgAO(3) 109.93(6),
O(6)AMgAO(8) 97.08(6), O(3)AMgAO(8) 99.97(6).
TABLE 1 Ring-Opening Polymerization of e-Caprolactone (e-CL) Catalyzed by Complexes 1 and 2 in the Presence of ROHa
Entry
Catalyst
[CL]0/[Mg]0/[ROH]0
Conversion yield (%)b
t (min)
Mn (calcd.)c
Mn (obsd.)d
Mn (NMR)b
PDId
e
f
1
1
1
1
1
1
1
2
2
2
2
2
1
25/1/0
25/1/1
50/1/2
100/1/2
200/1/2
400/1/2
25/1/0
50/1/2
100/1/2
200/1/2
400/1/2
50/1/2
99
99
98
99
99
99
99
99
99
99
92
96
5
5
2,800.
37,000(20,700)
7,000(3,900)
–
1.77
1.06
1.17
1.08
1.06
1.14
2.05
1.14
1.06
1.14
1.18
1.07
2
3,000
3,000
5,500
3,200
3
5
5,700(3,200)
f
4
5
5,900
10,300(5,800)
21,200(11,900)
42,700(23,900)
17,800(10,000)
5,300(3,000)
6,400.
5
5
11,500
22,800
15,000
6
5
33,700
e
f
7
15
15
15
15
15
5
2,800.
–
8
3,000
5,900
3100
6,700
9
11,000(6,200)
20,600(11,500)
32,400(18,100)
6,900(3,900)
10
11
12g
a
11,500
21,200
3,000
13300
27,100
3,300
e
0.05 mmol complexes, 25 ꢀC, 15 mL of toluene, 9-AnOH was used as
the alcohol.
Calculated from the molecular weight of e-caprolactone ꢂ 25 ꢂ con-
version yield.
b
f
Obtained from 1H NMR determination.
Not available.
c
g
Calculated from the molecular weight of e-caprolactone ꢂ times [CL]0/
1-pyrenebutanol was used as the alcohol.
[ROH]0 ꢂ conversion yield plus the molecular weight of ROH.
d
Obtained from GPC analysis and calibrated by polystyrene standard.
Values in parentheses are the values obtained from GPC ꢂ 0.56.17
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FIGURE 4 1H NMR spectra of PCL-25 (Table 1, entry 3) in CDCl3.
Ring-Opening Polymerization of e-Caprolactone
general, polymerizations were performed in toluene (15 mL)
with a prescribed equivalent ratio on the catalyst (0.05
mmol), monomers, and 9-anthracenemethanol (9-AnOH) for
the prescribed duration. After the reaction was quenched
with the addition of water, the polymer was precipitated into
hexane. The results of the polymerization of e-CL catalyzed
by 1 or 2 under varied conditions are listed in Table 1. The
Based on some successful lactone polymerizations catalyzed
by calcium bis(NNO tridentate Schiff-base),16(a) magnesium
bis(amido-oxazolinate)16(b) or magnesium/zinc bis(phenolate)
derivatives,12(f,i,k) the bis(sulfonate phenoxide) Mg complexes
1 and 2 were expected to behave as catalysts toward the
ROP of e-caprolactone (e-CL) in the presence of alcohol. In
TABLE 2 Ring-Opening Polymerization of Trimethylene Carbonate (TMC) Catalyzed by Complexes 1 and 2 in the
Presence of 9-AnOH, and Copolymerization of PCL-b-PTMC Catalyzed by Complex 1
Entry Catalyst [M]0/[Mg]0 /[9-AnOH]0 Conversion yield (%)a Temperature (ꢀC) t (min) Mn (calcd.)b Mn (obsd.)c Mn (NMR)a PDIc
1d
2e
3f
4f
5f
6f
7f
8f
1
1
1
1
1
1
1
2
1
1
200/1/2
97
25
25
25
0
10
30
10100
8,500
9,100
10,200
7,200
4,700
2,400
10,300
21,900
11,500
19,800
24,700
14,700
9,200
7,500
9,500
1.46
1.74
1.44
1.30
1.30
1.30
1.27
1.66
1.18
1.19
200/1/2
81
200/1/2
87
20
14,800
13,900
9,300
200/1/2
98
60
150/1/2
91
0
60
100/1/2
89
0
80
5,100
50/1/2
87
0
120
60
5,800
3,800
200/1/2
99
0
20,400
22,900
34,100
14,700
10,300
16,100
9g
10g
a
100/1/2; 100/1/2
200/1/2; 100/1/2
>99; 90
>99; 95
25
25
15; 30 10,500.
h
h
15; 30 16,500.
Obtained from 1H NMR determination.
20 mL of CH2Cl2 was used as the solvent.
f
b
g
Calculated from the molecular weight of TMC ꢂ [TMC]0/[9-AnOH]0
ꢂ
Prepolymerization of CL in CH2Cl2 (15 mL) for 15 min followed by the
conversion yield plus the molecular weight of 9-AnOH.
addition of TMC in CH2Cl2 (5 mL) for another 30 min.
c
h
Obtained from GPC analysis and calibrated by polystyrene standard.
0.05 mmol complexes, 10 mL of CH2Cl2.
Calculated from the molecular weight of CL ꢂ [CL]0/[9-AnOH]0 plus
d
the molecular weight of TMC ꢂ [TMC]0/[9-AnOH]0 ꢂ conversion yield
e
10 mL THF was used as the solvent.
plus the molecular weight of 9-AnOH.
SULFONATE PHENOXIDE MAGNESIUM COMPLEXES AS CATALYSTS, CHEN ET AL.
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JOURNAL OF POLYMER SCIENCE: PART A: POLYMER CHEMISTRY DOI 10.1002/POLA
1.17. The 1H NMR spectrum of PCL-25 (‘‘25’’ indicates the
designed [CL]0/[9-AnOH]0 ratio; Fig. 4) indicates that the
polymer chain is capped with one 9-anthracenemethyl ester
and one hydroxyl chain end. This result indicates that the
Mg(sulfonate phenoxide)2/9-AnOH system might undergo an
‘‘activated-monomer’’ path, whereas monomer or 9-AnOH are
activated by 1 and 9-AnOH behaves as a nucleophile.12(l,k),16(b)
Relative to complex 1, e-CL polymerization catalyzed by com-
plex 2 shows similar activities and a ‘‘controlled’’ manner (Ta-
ble 1, entries 8–11), but with duration of polymerization up
to 15 min to attain conversion >92%. According to the litera-
ture,12(f,i,k),14 magnesium catalyst 1 reveals the greatest cata-
lytic activity and ‘‘controlled’’ character toward ROP of e-CL
among magnesium or zinc complexes bearing bisphenoxide
derivative ligands. The catalytic activities are little affected
when the 1-pyrenebutanol is altered as initiator. As expected,
the synthesized PCL with the 1-pyrenebutyl ester end group
displayed the desired molecular weight and low PDI (Table 1,
entry 12).
FIGURE 5 Polymerization of TMC catalyzed by 1 in CH2Cl2 at 0 ꢀC.
The relationship between Mn(n)/(PDI(h) of polymer and the initial
molar ratio [TMC]0/[9-AnOH]0 ꢂ the conversion yield is shown.
results indicate that both complexes 1 and 2 show a great
catalytic activity for the ROP of e-CL in the presence of 9-
AnOH, whereas polymerizations with uncontrollable behav-
iors are observed in the absence of 9-AnOH (Table 1, entries
1 and 7). Complex 1 was chosen to investigate the effects of
polymerization conditions in detail because it showed
greater catalytic activity than complex 2. The effect of the ra-
tio of 9-AnOH to the catalyst was examined; a great catalytic
activity and the ‘‘controlled’’ character were obtainable with
a Mg: 9-AnOH molar ratio of 1:2 (Table 1, entries 2 vs. 3).
Polymerizations of e-CL under these optimal conditions were
then systematically investigated (Table 1, entries 3–6). The
conꢀversion yield attained >98% in toluene within 5 min at
25 C with the ratio [M]0/[9-AnOH]0 in a range 25–200. The
‘‘living’’ character of the polymerization is demonstrated by a
linear relationship between the number-averaged molecular
weight (Mn) and the ratio ([CL]0/[9-AnOH]0) of monomer to
initiator as shown in Figure 3, and the produced PCL with
narrow polydispersity indices (PDIs), ranging from 1.06 to
Ring-Opening Polymerization of TMC
Encouraged by the excellent catalytic activities of ROP of e-
CL catalyzed with bis(sulfonate phenoxide) Mg catalysts, we
explored the catalytic activity in the ROP of TMC. In this con-
text, the ROP of TMC using 1 or 2 as catalyst in the presence
of 9-AnOH under dry N2 was systematically examined as
shown in Table 2; Mg complex 1 is an effective catalyst for
the polymerization of TMC. The conversion yield >95% of
polymerization was achieved within 10 min at 25 ꢀC in
CH2Cl2 (Table 2, entry 1). To obtain the optimal catalytic
condition, we investigated the effects of solvent, concentra-
tion, and temperature on the TMC polymerization. After sev-
eral trials of polymerization with THF as solvent, decreased
concentration and decreased temperature using 1 as the cat-
alyst, optimum conditions were found to be CH2Cl2 (20 mL,
0
ꢀC) in the presence of 9-AnOH (Table 2, entries 2–4).
According to these results for the optimal conditions (Table
2, entries 4–7), the PDIs of poly(TMC)s produced are narrow
FIGURE
6
1H NMR spectra of
PTMC-25 (Table 2, entry 7) in
CDCl3.
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INTERSCIENCE.WILEY.COM/JOURNAL/JPOLA

ARTICLE
nesulfonate group seems to increase the Lewis acidity of
Mg2þ metal, so that the harder Mg2þ center of complex 1
provides a superior combination of monomer activation and
alkoxide nucleophilicity, producing an improved catalytic
performance for polymerization. These catalysts demonstrate
a new family of ROP catalytic system and show the highest
catalytic activity (25 ꢀC, 5 min) and ‘‘controlled’’ character
(PDI<1.2) toward ROP of e-CL among magnesium complexes
bearing the bisphenoxide derivatives. The controlled charac-
ter of complex 1 also enabled preparation of PCL-b-PTMC
copolymers.
Financial support from the National Science Council, Taiwan
(NSC97-2113-M-033-005-MY2) and from the project of the
specific research fields in the Chung Yuan Christian University,
Taiwan (No. CYCU–98–CR–CH) are greatly appreciated. We also
thank Chu-Chieh Lin and Ya-Sen Sun for their valuable
discussions.
FIGURE 7 GPC profiles of copolymerization of PCL-b-PTMC cat-
alyzed by complex 1: (line A) after prepolymerization of CL
(100 equiv to 9-AnOH, 15 min, Mn ¼ 19700 (PDI ¼ 1.06)); (line
B) after block copolymerization of PCL-b-PTMC ([CL]0/[9-
AnOH]0/[TMC]0 ¼ 100/1/50, Mn ¼ 34100 (PDI ¼ 1.19)).
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