Ethylene oxide polymerization catalyzed by aluminum complexes of sulfur-bridged polyphenols

Article abstract of DOI:10.1021/ma049209d

The products derived from the reaction of sterically hindered sulfur-bridged bisphenols with aluminum trialkyls enable the efficient polymerization of ethylene oxide. The activity of the catalyst is largely determined by the structure of the bisphenol lig

Full text of DOI:10.1021/ma049209d

322
Macromolecules 2005, 38, 322-333
Ethylene Oxide Polymerization Catalyzed by Aluminum Complexes of
Sulfur-Bridged Polyphenols
Eric P. Wasserman,* Ioana Annis, Lamy J. Chopin, III, and Philip C. Price
The Dow Chemical Company, 171 River Road, Piscataway, New Jersey 08854
Jeffrey L. Petersen
Department of Chemistry, West Virginia University, Morgantown, West Virginia 26506-6045
Khalil A. Abboud
Department of Chemistry, University of Florida, 127 Chemistry Research Building,
Gainesville, Florida 32611-7200
Received April 23, 2004; Revised Manuscript Received October 22, 2004
ABSTRACT: The products derived from the reaction of sterically hindered sulfur-bridged bisphenols with
aluminum trialkyls enable the efficient polymerization of ethylene oxide. The activity of the catalyst is
largely determined by the structure of the bisphenol ligand and the size of the aluminum alkyl groups.
Bonds of sulfur to aluminum are a common feature of the solid-state structures of compounds examined
to this point. In solution, precatalysts of the formula (3-t-Bu-5-Me-2-OAlEt2-C6H2)2S are fluxional, and
two processes appear to contribute to the equilibration of all ethyl substituents. The addition of a hindered
monomer, 1,2-epoxyhexane, causes the initial formation of solvation complexes with the aluminum
precatalysts and effects the disproportionation of the initial dialuminum complex of the bisphenol. One
of the polymer end groups appears to be easily replaced by a halide atom during acid workup.
Introduction
contributes the alkoxide which attacks this ring. This
reaction path, which may include the concomitant
exchange of a charge-balancing ligand between the two
aluminum centers, was postulated by Vandenberg as
early as 1960 to be the route taken by aluminum-based
epoxide-polymerization catalysts.3
High-molecular-weight poly(ethylene oxide) (MW >
1× 105 Da) is a water-soluble polymer which finds
application in such areas as flocculation, rheological
modification of aqueous solutions, drug release, and
polymeric electrolytes.1 A large proportion of the sub-
stances reported to catalyze the polymerization of EO
to high MW are inorganic solids, whose mechanisms for
polymerization can best be characterized as heteroge-
neous.2 Given the large discrepancy observed in such
polymerizations between the number of metal atoms
contained in the catalyst charged to the reactor and the
number-average MW of the polymer produced, one may
conclude that only a small fraction of the metal centers
present in the system are involved in the initiation and
propagation of polymerization at any one time. These
factors make the elucidation of the structure of the
catalyst active site extremely difficult. To better under-
stand the chemical steps involved in EO polymerization
and therefore to improve the catalysis of this process
through rational design, researchers have turned to the
synthesis of well-defined catalyst precursors.
Although many classes of compounds catalyze the
ring-opening polymerization of oxiranes, aluminum
aryloxide complexes have received recent attention as
catalysts4 and cocatalysts5 for this reaction, as well as
for the polymerization of styrene and methyl acrylate6
and lactones.7 There are two clear reasons for this
interest. First, the catalysts form homogeneous solu-
tions, allowing detailed in-situ analysis of their struc-
tures. Second, the catalytic behavior reflects the struc-
ture of the precursor’s ligand environment, enabling
correlations to be made between ligand structure and
polymer microstructure. It appears that bulky phenolate
ligands confer a degree of resistance to alkyl- or alkox-
ide-bridged aluminum cluster formation and influence
the tacticity and regiospecificity of epoxide polymeriza-
tion.8
Trivalent aluminum complexes have a combination
of properties that makes them predisposed to catalyze
polymerization of energetic monomers such as ethylene
oxide (EO). Bearing basic groups such as alkyl or
alkoxide fragments, these species are quite reactive
toward electrophilic carbon atoms, while the open
coordination site forms strong associations with Lewis
basic atoms. Aluminum compounds are also known to
undergo ligand-exchange reactions. Therefore, it has
been possible to construct mechanisms for oxirane ring
opening which involve the activation of the epoxide ring
by one aluminum atom while another aluminum atom
We wish to extend the general body of knowledge
about this class of catalysts by including our recent
studies of a specific family of aluminum phenoxide
catalysts for EO polymerization. Our work with alumi-
num phenoxide catalysts has shown9 that some of these
systems, namely those bearing sulfur bridges between
the phenolate groups, are highly active toward the
production of high-MW poly(ethylene oxide) and copoly-
mers of EO with other oxiranes. Ligand structure has
a profound influence on catalyst behavior, leading us
to investigate the role of the ligand in the steps leading
to polymerization. The work presented herein deals with
experiments designed to shed light on three important
aspects of catalysis: (a) the structure of catalyst precur-
sors in the solid state and in solution; (b) the changes
* Author to whom correspondence should be addressed. E-
mail: wasserep@dow.com.
10.1021/ma049209d CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/30/2004

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 323
Table 1. Productivity of Catalysts in Ethylene Oxide
Homopolymerizations Run at 25 °C in Hexane (See
Experimental Section for Details of Run Procedure)
7 (see Scheme 1) enabled polymerization to proceed with
productivity ranging from 2.2 (4c) to 15 (5a) g/mmol(Al)
with TiBA. Among these ligands is a thiacalixarene (7),
which indicates that oligomeric analogues of sulfide-
bridged bisphenols may also display high activity when
combined with aluminum alkyls. The ligands associated
with high productivity share a structural motif: an
o-sulfide bridge between two phenol rings, with steri-
cally demanding t-butyl groups flanking the hydroxyl
groups at the remaining ortho positions. This com-
monality suggests that a divalent sulfur atom may have
an important role in determining the structure and
reactivity of the catalyst precursor and the active site.
The dependence of activity upon the oxidation state of
sulfur is not easy to predict on the basis of known
chemistry. Ohba and co-workers, studying the Lewis-
acid-catalyzed rearrangement of aromatic epoxides to
ketones by aluminum complexes, found that sulfoxide-,
sulfone-,11 and trisulfido-bridged12 biphenol ligands all
support high activity for this reaction.
productivity
alkyl-
g(PEO)/
aluminum ligand ligand:Al
mmol(Al)
Mw/1000 Mw/Mn
AlEt3
[none]
1
0.7
1.1
0.4
0.3
0.8
3.4
6.0
5.2
2.2
15
1:1
1:2
1:2
1:2
1:2
1:2
1:2
1:2
1:1
1.2:1
1:1
1:1
1:2
1:1
1:4
1:2
1:1
2a
2b
3
213.0
4.6
97.3
49.0
23.1
23.8
32.4
103.7
62.8
66.8
95.3
6.0
5.6
1.3
1.1
1.1
1.2
1.1
1.2
1.2
4a
Al(i-Bu)3 4a
4b
4c
5a
5b
5b
5c
5d
6
13
11
9.8
4.4
4.3
7.3
1.0
3.1
7
78.3
29.0
1.3
1.2
8
9
Focusing on structural details within groups 4 and
5, we see that alkylation of one of the hydroxyl groups
dramatically increases productivity. Within ligand fam-
ily 5, the smallest capping group (R1 ) Me, 5a) imparts
the highest productivity. It is worth remarking that,
whereas the conversion of one of the OH groups to an
alkyl or silyl ether increases activity, elimination of one
of the oxygenated groups lowers activity: note that the
productivity of TiBA/9 is only half that of TiBA/4a. Also
interesting is the preservation of moderate activity in
the TiBA complex of ligand 6 (which has no OH groups)
compared with that for TiBA alone.10 The surprising
persistence of catalytic activity upon mono- and dialky-
lation of a supporting bisphenolate ligand was also
observed in the area of Meerwein-Ponndorf-Verley
transfer hydrogenation by Nguyen and co-workers.13 No
significant change in productivity is observed upon
in structure effected by the introduction of monomer;
and (c) the initiation of polymerization. The sulfur atom
of the ligand appears to play an important role in each
of these three phases of catalyst formation.
Results and Discussion
Ethylene oxide polymerizations. In our initial
screen for catalytic activity, a number of combinations
of trialkylaluminum compounds with phenols were
evaluated in their ability to produce poly(EO) at room
temperature in hexane (Table 1). Under our conditions,
triethylaluminum (TEAl) performed poorly.10 By con-
trast, mixtures of certain phenols with trialkylalumi-
num compounds, especially with triisobutylaluminum
(TiBA), gave fairly high productivity. In particular,
those ligands belonging to structure families 4, 5, and
Table 2. X-raya Crystallographic Parameters for Compounds 10, 11, and 12
10 11
30H48Al2O2S
compound
12
empirical formula
formula weight
temperature (K)
crystal system
space group
a (Å)
C
C25H37AlO2S
428.59
C28H43AlO3S
486.66
526.70
223(2)
monoclinic
P21/c
173(2)
monoclinic
P21/n
223(2)
orthorhombic
Pbca
17.632(3)
16.211(2)
20.041(3)
90
16.925(2)
9.924(2)
19.268(3)
90
92.85(1)
90
9.9515(10)
9.0271(9)
27.670(3)
90
94.909(2)
90
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
90
90
volume (Å3)
Z
3232.3(9)
4
2476.5(4)
4
5728.3(14)
8
density (calcd, g/cm3)
absorption coeff (cm-1
F(000)
1.082
1.149
1.129
)
1.77
1144
1.84
928
1.69
2112
crystal size (mm)
Θ range (deg)
index ranges
0.22 × 0.36 × 0.38
2.12-22.50
0 e h e 18
-1 e k e 10
-20 e l e 20
4335
0.28 × 0.11 × 0.06
3.72-25.01
-6 e h e 11
-10 e k e 10
-32 e l e 32
10655
0.25 × 0.30 × 0.42
1.99-27.49
-22 e h e 22
-20 e k e 20
-25 e l e 23
38768
reflections collected
independent reflections
R(int)
4172
4211
6550
0.0595
0.976
0.0545
1.032
0.0678
1.036
GOF on F2
final R indices [I>2σ(I)]
b
R1
0.0749
0.1074
0.0537
0.1182
0.0566
0.1414
c
wR2
a Obtained with monochromatic Mo KR radiation (λ ) 0.71073 Å). Refinement method: full-matrix least-squares on F2. b R1 ) ∑(||Fo|
- |Fc||)/∑|Fo|. c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo2)2]].1/2
2
2

324 Wasserman et al.
Macromolecules, Vol. 38, No. 2, 2005
Scheme 1
Table 3. Selected Bond Distances (Å) and Angles (deg)
for Compound 10
Table 4. Selected Bond Distances (Å) and Angles (deg)
for Compound 11
Bond Distances
Bond Distances
S-Al(1)
2.453(3)
1.770(8)
1.799(6)
1.954(8)
1.946(5)
1.948(9)
1.855(4)
Al(1)-C(25)
Al(2)-O(2)
Al(2)-C(29)
O(1)-C(1)
1.936(7)
S-C(1)
S-C(7)
S-Al
1.780(3)
1.798(2)
2.4926(11)
1.768(2)
1.940(3)
1.948(3)
O(1)-C(2)
O(2)-C(8)
O(2)-C(20)
C(1)-C(6)
C(1)-C(2)
1.339(3)
1.393(3)
1.446(3)
1.392(4)
1.399(4)
S-C(13)
1.765(5)
1.975(10)
1.404(7)
1.354(8)
1.378(8)
1.383(9)
S-C(2)
Al(1)-C(23)
Al(2)-O(1)
Al(2)-C(27)
Al(1)-O(1)
Al-O(1)
Al-C(13)
Al-C(14)
O(2)-C(12)
C(1)-C(2)
C(12)-C(13)
Bond Angles
Bond Angles
C(1)-S-C(7)
C(1)-S-Al
C(7)-S-Al
105.50(12)
91.35(9)
C(13)-Al-S
C(14)-Al-S
C(2)-O(1)-Al
123.08(10)
96.56(11)
125.45(18)
C(13)-S-C(2)
C(2)-S-Al(1)
107.6(3)
87.8(3)
C(12)-C(13)-S
C(13)-S-Al(1)
O(1)-Al(1)-C(25)
121.1(7)
114.5(3)
118.6(3)
105.49(9)
O(1)-Al(1)-C(23) 109.2(3)
O(1)-Al-C(13) 109.16(12)
O(1)-Al-C(14) 115.93(13)
C(13)-Al-C(14) 121.91(14)
C(8)-O(2)-C(20) 113.9(2)
O(1)-Al(1)-S
C(23)-Al(1)-S
84.6(2)
98.0(3)
C(25)-Al(1)-C(23) 118.6(3)
C(2)-C(1)-S
O(1)-C(2)-C(1) 120.5(2)
116.7(2)
C(25)-Al(1)-S
121.6(2)
96.3(2)
111.1(5)
O(2)-Al(2)-C(27) 115.6(6)
O(2)-Al(2)-C(29) 105.7(5)
O(1)-Al(2)-C(29) 103.8(4)
O(1)-Al(2)-O(2)
O(1)-Al(2)-C(27)
O(1)-Al-S
84.39(7)
C(27)-Al(2)-C(29) 121.0(6)
C(1)-O(1)-Al(1)
111.1(4)
C(1)-O(1)-Al(2)
C(12)-O(2)-Al(2)
C(1)-C(2)-S
113.4(4)
134.8(5)
118.6(6)
X-Ray Structural Analysis. To better understand
the relationship between ligand constituents and cata-
lyst behavior, combinations of aluminum alkyl com-
pounds with representatives of the two most productive
ligand families were subjected to crystallographic analy-
sis. The reaction of two equiv of TEAl with the bisphenol
4a produces 10, whose crystal structure is shown in
Figure 1. Both aluminum atoms are each covalently
bound to two alkyl groups and one phenoxide. Clearly,
a reaction of the type
Al(1)-O(1)-Al(2) 112.5(2)
C(2)-C(1)-O(1) 117.5(6)
replacing the methyl groups para to the oxygen atoms
in 4a with t-butyl groups (compare productivities of 4a/
TiBA with 4b/TiBA).
In addition to high productivity, catalyst combinations
of TiBA and polyphenolic ligands show fairly narrow
molecular-weight distributions (1.1 e Mw/Mn e 1.25).
This implies that catalyst initiation is relatively fast
relative to propagation and also that chain termination
and transfer pathways are much slower than propaga-
tion, but it cannot tell us about the homogeneity of
catalyst structure. From a comparison between number-
average MW (Mn) and catalyst productivity, one can
estimate the number of polymer chains produced per
metal atom. Given that this numbersca. 0.2-0.4 for
mixtures of TiBA and ligand groups 4 and 5sis sub-
stantially less than one, it is possible that initiation of
polymerization may involve multiple metal centers.
ArOH + AlR3 f ArOAlR2 + R-H
has occurred at both sides of 4a. The coordination
environments of the two tetrahedral Al centers are
different. Although both Al atoms have two ethyl
substituents, Al(1) is bound to one phenoxide oxygen,
O(1), and the bridging sulfur, S, whereas Al(2) is bonded
to both phenoxide oxygens, O(1) and O(2). Similar
oxygen sharing is observed in the structures of 2,2′-
methylenebis(6-t-butyl-4-methylphenoxy)aluminum me-

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 325
Figure 2. X-ray crystal structure of 11.
Figure 1. X-ray crystal structure of 10. The thermal ellipsoids
were scaled to enclose 30% probability. Carbons C(27), C(28)
and C(29), C(30) suffer from a two-site (80:20) disorder; only
the major conformer is depicted.
Table 5. Selected Bond Distances (Å) and Angles (deg)
for Compound 12
Bond Distances
S(1)-C(17)
S(1)-C(6)
S(1)-Al(1)
Al(1)-O(2)
Al(1)-O(1)
Al(1)-C(23)
Al(1)-O(3)
1.775(2)
O(1)-C(1)
1.348(3)
1.345(3)
1.403(3)
1.396(3)
1.472(6)
1.461(3)
1.466(6)
1.776(2)
O(2)-C(12)
C(1)-C(6)
2.6603(10)
1.7584(17)
1.7594(18)
1.961(3)
C(12)-C(17)
C(23)-C(24)
O(3)-C(25)
O(3)-C(27)
1.969(2)
Bond Angles
C(17)-S(1)-C(6) 104.03(11)
O(1)-Al(1)-S(1)
C(23)-Al(1)-S(1)
O(3)-Al(1)-S(1)
C(1)-O(1)-Al(1)
81.04(6)
92.65(12)
168.45(7)
130.12(15)
C(17)-S(1)-Al(1)
C(6)-S(1)-Al(1)
O(2)-Al(1)-O(1)
88.58(8)
89.95(8)
115.03(9)
Figure 3. The proton NMR spectrum of 10 as a function of
temperature.
O(2)-Al(1)-C(23) 123.25(14)
O(1)-Al(1)-C(23) 119.31(14)
C(12)-O(2)-Al(1) 127.68(15)
O(1)-C(1)-C(6)
C(1)-C(6)-S(1)
120.4(2)
118.22(18)
situation does not exist for the even more active
catalysts related to monomeric 11. During EO polym-
erization, do both aluminum atoms on structures akin
to 10 participate in the creation of a single PEO chain?
Second, the methoxy group in 11 does not participate
in either inter- or intramolecular bonding to aluminum.
The literature contains examples of methyl ethers
binding to aluminum, as in the complex LAlMe (LH2 )
25,27-dimethoxy-26,28-dihydroxy-p-t-butylcalix[4]-
arene), wherein both aryl methyl ether groups coordi-
nate to the aluminum atom.17 However, in another case,
a phenoxyaluminum complex active for the polymeri-
zation of ꢀ-caprolactone, bearing a 4-methoxyphenyl
group attached to the biphenol bridge, shows no bonding
interaction between ether function and aluminum.18 If
the methoxy group of 5a does not bind to the active
center of the catalyst, why then is the productivity of
5a/TiBA so much higher than that of 9/TiBA, a complex
lacking this methoxy group?
Proton NMR Analysis of Catalyst Solutions. The
variable-temperature 1H NMR spectra of 10 in toluene-
d8, shown in Figure 3, reveal the existence of rapid
interconversion of structures. As the temperature is
lowered from 50 to -80° C, the ethylaluminum portion
of the spectrum appears to pass through three regimes.
From about 50 down to 10° C, the metal alkyl reso-
nances take the form of two very broad resonances at
0.4 and 1.2 ppm, respectively. From 10 to -50° C, these
signals decoalesce and form a well-defined pattern with
1H-1H coupling. Below -50° C, some of the peaks
O(2)-Al(1)-O(3)
O(1)-Al(1)-O(3)
C(23)-Al(1)-O(3)
O(2)-Al(1)-S(1)
93.00(8)
93.34(8)
98.90(14)
80.43(6)
O(2)-C(12)-C(17) 120.5(2)
C(12)-C(17)-S(1) 117.71(18)
C(25)-O(3)-C(27) 114.9(3)
thide.14 No other Al-Al bridging interactions, whether
intra- or intermolecular, are observed. Some disorder
is present which affects the methyl carbons of the ethyl
groups, but this has no meaningful impact on the
structure.
Compound 11, prepared from the reaction of equimo-
lar quantities of trimethylaluminum15 and ligand 5a,
presents a simpler geometry (Figure 2). In this case, the
aluminum atom’s tetrahedral ligand environment con-
sists of one phenoxide oxygen, two methyl groups, and
the bridging sulfur atom. Again, no intermolecular
bridging interactions are noted. The monomeric nature
of 11 shows this sulfur bridge to be a ligand of sufficient
binding energy to compete effectively with solvation by
an aluminum-bound methyl group from another mol-
ecule of 11. A similar effect was observed by Dagorne
et al.4g in complexes of aluminum with monophenolate
ligands to which are appended o-dialkylaminomethyl
groups, these compounds being monomeric in the solid
state.
The fact that the structure of 11 is as simple as it is
raises two interesting questions. First, although one
might be tempted to attribute the high activity of
complexes of the type 10 to the fact that two aluminum
centers lie in close proximity to each other,16 this

326 Wasserman et al.
Macromolecules, Vol. 38, No. 2, 2005
Scheme 2
broaden or disappear, although the triplets at both 1.8
and 0.65 ppm remain fairly well-resolved. At -40° C,
where the peaks are best resolved, two-dimensional
analysis (COSY) reveals that there are three coupled
sets of resonances associated with the methyl and
methylene groups of the two diethylaluminum moieties
which exist in a 1:2:1 ratio (Figure 4).One explanation
two Al-Et groups exchange rapidly at -40° C, it is
reasonable to postulate that either A or B (but not both)
is fast relative to the NMR time scale at that temper-
ature, whereas process C begins to affect the spectrum
only around 10 °C. The existence of other exchange
mechanisms, such as inter- or intramolecular Al-C
bond metathesis, cannot be ruled out, but no other
scheme seems able to offer as simple an explanation for
the observations.
In addressing the question of structural change upon
addition of monomer to the catalyst solution, we were
obliged to work with more sterically demanding mono-
mers, as the addition of even propylene oxide caused
changes in the spectrum which were too rapid to be
followed by NMR. 1,2-Epoxyhexane (EH) was chosen
because, in this case, an initial monomer-catalyst
complex could be studied at room temperature, and the
disappearance of monomer was not complete for several
1
hours. The H NMR spectra of mixtures of EH and 10
measured prior to the onset of oligomerization are
remarkably dependent upon the EH:Al ratio (Figure 5).
Figure 4. The aluminum alkyl region of the proton NMR
spectrum of 10, observed at -40 °C, showing the three sets of
methyl and methylene resonances associated with ethylalu-
minum groups as revealed by two-dimensional NMR spectros-
copy (COSY). The protons in these sets are in a 1:2:1 intensity
ratio (A:B:C).
for this behavior is that there are two processes which
interconvert the environments of the aluminum alkyl
groups with activation barriers of different magnitude.
Using the crystal structure of 10 as the basis for the
discussion of exchange pathways, three possible routes
for the equilibration of all ethyl signals can be proposed
(Scheme 2). In the first process (A), rupture of the Al-S
donor interaction permits the rotation of the diethyla-
lumino group about the Al-O bond axis. A similar
process, B, interconverts the other two ethylaluminum
groups through the cleavage of the Al-O donor interac-
tion. Both paths work with both enantiomers of the
initial complex. However, neither A, B, nor the combi-
nation of both suffices to equilibrate all the ethyl groups.
A third process, C, in which the two donor atom-
aluminum interactions are exchanged, is required. Since
Figure 5. Proton NMR spectra of 10 with varying levels of
EH: (a) EH/Al ) 0.27; (b) EH/Al ) 0.5; (c) EH/Al ) 1.1; (d)
EH/Al ) 1.6; and (e) EH/Al ) 5. Dotted lines indicate the shifts
in peak positions for the three protons on carbons 1 and 2 of
EH.
As EH:Al is raised from 0.27:1 to 5:1, the three reso-
nances associated with the three oxirane C-H bonds
of EH first move downfield, then upfield. Although they

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 327
Figure 6. Comparison of proton NMR spectra for (a) EH +
10 (EH/Al ) 2.2); (b) EH + triethylaluminum; and (c) EH
alone.
remain broad at EH/Al ) 5, these three signals are fairly
close to their positions in spectra of EH alone. At lower
ratios, the average magnetic environments of the three
oxirane protons are significantly altered, this effect
being most pronounced at EH/Al ≈ 1. The aluminum
alkyl portion of the spectrum is also quite dependent
upon the relative amount of EH. To varying degrees,
the broad signals that characterized solutions of 10
alone at ambient temperature (Figure 3) have collapsed
into well-resolved methyl and methylene patterns. It
appears that reversible coordination of oxirane to
aluminum accounts for both the broadened EH patterns
and the suppression of the exchange processes which
interconvert the aluminum alkyl groups in complex 10.
The ethylaluminum peaks in the proton NMR spec-
trum of 10 + 2.2 equiv of EH (Figure 5c) show two
methylene quartets at 0.45 and 0.10 ppm in a 1:2.7
intensity ratio. This reflects the existence of two distinct
aluminum centers, one with three ethyl groups and one
with a single alkyl group. By comparing this spectrum
with that for the complex formed between triethylalu-
minum and one equivalent of EH (Figure 6c), one can
reasonably attribute the methylene signals centered at
0.1 ppm and the associated methyl triplet at 1.36 ppm
to Et3Al‚EH. The remaining ethylaluminum peaks can
then be assigned to the EH-solvate of the dispropor-
tionation product 2,2′-thiobis(6-t-butyl-4-methylphenoxy)-
(ethyl)aluminum. Further support for this hypothesis
can be found in the spectrum of the diethyl ether solvate
of the disproportionation adduct 12 which shows a
quartet at 0.4 ppm. The crystal structure of 12 (Figure
7) features a pentacoordinate aluminum atom having
donor-acceptor interactions with both the sulfur bridge
and the diethyl ether molecule. Okuda has also found
that 4a can act as a tridentate OSO ligand, adopting a
facial geometry when bound to Ti(IV).19
Figure 7. X-ray crystal structure of 12. Atoms C(27) and
C(28) suffer from a 70:30 two-site disorder; only the major
conformer is depicted.
Figure 8. Expansion of complex multiplet centered at -0.76
ppm observed in the proton NMR spectrum of 10 in the
presence of 1.0 equiv EH (upper) along with simulation (lower),
generated using parameters described in the text and a line
width of 0.75 Hz. Asterisks denote peaks excluded from
simulation.
Scheme 3
This pattern is adequately simulated20 by a model
that has the absolute value of the 1H-1H coupling
constant between the geminal methylene protons equal
to 14.8 Hz, all the coupling constants between methyl
and methylene protons equal to 8.2 Hz, and the two
chemical shifts for the methylene protons equal to
-0.738 and -0.778 ppm.
The initial reactions which occur when EH is added
to 10 can now be described (see Scheme 4). At substo-
ichiometric levels, the EH causes the disproportionation
of 10 into an epoxide solvate of the trialkylaluminum
and an alkylaluminum bis(phenoxide), the latter pos-
sibly existing as a dimer. As the level of EH rises to
molar equivalence to Al, the bisphenoxyaluminum
At EH:Al ratios less than 1:1 (Figure 5a and b) the
combination of 10 with EH yields a more complicated
spectrum with one very distinct feature: a complex
multiplet centered at -0.76 ppm. The appearance of this
multiplet, expanded in Figure 8, in the region associated
with the methylene group attached to aluminum, indi-
cates a diastereotopic environment for the methylene
protons. On the basis of spectroscopy of a similar
compound reported by Taden et al.,7c one can represent
this complex as in Scheme 3, in which dimerization of
the monoethyl complex through one oxygen of each
diphenoxyaluminum molecule leads to a loss of sym-
metry.

328 Wasserman et al.
Macromolecules, Vol. 38, No. 2, 2005
Scheme 4
compound(s) are solvated by epoxide to form a well-
defined structure similar to that of 12. Interestingly,
although AlEt3‚EH is preferentially formed over the EH
solvate of the bisphenoxyaluminum species, the oxirane
protons of EH are more perturbed by coordination to
the latter than to the trialkylaluminum, as judged by
the relative deviations from the spectrum of free EH
(Figure 6). This may indicate that the oxirane ring is
more predisposed to opening in when bound to the
monoaluminum bisphenoxide. At high levels of EH,
epoxide coordinated to both aluminum compounds
exchanges with free epoxide.
If we turn to the coordination chemistry of the
aluminum complex of the monoalkylated bisphenol, we
see more subtle changes than are observed with 10. In
this case, we are dealing with complex 13, the reaction
product of ligand 5a with one equivalent of triethyla-
luminum. The proton spectra of 13 and 13 + 1 equiv of
EH (Figure 9) are fairly similar, in that no new
substituent moves 0.2 ppm downfield from its original
position at 3.7 ppm when EH is added, returning to
approximately the same position found in the spectrum
of the unreacted ligand (4.0 ppm). Although not con-
clusive, this evidence suggests that, in solution, the
methyl aryl ether group of ligand 5a interacts in some
fashion with the aluminum atom and that this interac-
tion (whether intra- or intermolecular) is disrupted by
the addition of a donor molecule. The participation of
the methoxy group in the coordination environment of
13, though not apparent in the crystal structure of
related complex 11, may help explain the unusually
high epoxide polymerization activity of adducts of
ligands in its family (5) with trialkylaluminum com-
pounds. Perhaps this weak donor interaction between
the methoxy group and an aluminum center acts as a
placeholder for incoming monomer, preventing the
formation of stronger bridging interactions between
aluminum centers which would slow polymerization.
Polymer End-Group Analysis. To fully understand
how catalyst structure affects polymerization behavior,
one must know the mechanism of initiation. Unfortu-
nately, EH, though it is useful for the study of coordina-
tion to aluminum compounds, initiates very slowly
compared with propagation, leading to very high-MW
poly(EH) (Mw > 1 × 105) even at very low EH:Al. Thus,
no useful information regarding the initial ring-opening
step can be gleaned from the system. End-group analy-
sis of samples of low-MW poly(ethylene oxide) produced
by adducts of ligands 4a and 5a with TiBA, however,
may help us identify the initiating group. For the 4a/
2TiBA catalyst, the end-group analysis has not been
fruitful: samples quenched with HCl show a number
of possible end groups by 13C NMR analysis, along with
free ligand; the MALDI-TOF results of the polymer are
also unsatisfactory, with several trains of peaks sepa-
rated by the mass of EO.
Figure 9. Proton NMR spectra of (a) 13; (b) 13 with 1 equiv
of EH.
In contrast, the corresponding analysis of the polymer
produced by 5a/TiBA is more straightforward. In the
13C NMR spectrum (Figure 10) of the sample quenched
by HCl, both free ligand 5a and chloride-terminated
polymer are observed. The analogous NMR spectrum
for the HBr-quenched material is nearly identical,
except the peak associated with the carbon of the CH2-
Cl group at 42.6 ppm is missing and a new peak appears
ethylaluminum resonances appear and the original
peaks are only slightly shifted upon EH addition. That
EH is coordinated to aluminum is clear by the position
of the oxirane proton resonances, which are shifted by
up to 0.5 ppm downfield from their positions in the
spectrum of free EH (Figure 6c).21 Perhaps most sur-
prising is that the singlet for the protons of the methoxy

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 329
Figure 11. MALDI-TOF spectrum of poly(ethylene oxide)
produced by the catalyst 5a/TiBA, quenched with HCl/MeOH.
Mass series a: ligand-terminated poly(ethylene oxide); mass
series b: chloride-terminated poly(ethylene oxide).
Figure 10. 13C NMR spectrum of poly(ethylene oxide) pro-
duced by the catalyst 5a/TiBA quenched by HCl/MeOH, with
assignments; peaks for neutralized ligand 5a are marked L.
at 33.3 ppm attributable to the CH2Br group. Integra-
tion of the haloethyl chain end peaks finds them to be
roughly equal in intensity to the corresponding CH2-
OH ends. A reasonable conclusion from the data is that
the hydroxyl-bearing chain ends result from the reaction
of acid with the growing chain end of structure -CH2O-
[Al], while the haloethyl end group results from the
displacement of the original initiating group from the
polymer.
By GPC, the two polymer samples have low molecular
weights and narrow molecular-weight distributions: Mn
) 11 000 (HCl-quenched); Mn ) 13 000 (HBr-quenched);
Mw/Mn ) 1.07 in both cases. This indicates that the
reaction of HCl or HBr with the polymer does not
involve the cleavage of C-O bonds randomly along the
polymer chain, as this would cause the value of Mw/Mn
to approach the value of 2.0 as the proportion of chain
termini derived from chain scission increases.22 Molec-
ular-weight analysis also finds the number of polymer
molecules in these two samples to be approximately half
the number of molecules of 5a/TiBA complex introduced
to the reactor. Again, the narrowness of the polymer
molecular-weight distributions argues against the idea
that those aluminum atoms in excess of the number of
polymer molecules failed to initiate polymerization due
to a prolonged induction period. It is more likely that
the structure responsible for polymer propagation in-
volves one growing polymer chain, two phenoxide
ligands, and two aluminum atoms.
Figure 12. A portion of the MALDI-TOF spectrum of HCl-
quenched poly(ethylene oxide) prepared from 5a/TiBA, show-
ing experimental signal and, below it, the calculated isotopic
distribution for the ligand-terminated polymer with formula
C97H180O39SNa.
MALDI-TOF spectrometry (Figure 11) confirms the
existence of halide-terminated poly(ethylene oxide),
which not only contributes sequences of mass peaks
(separated by 44 daltons) as predicted for such struc-
tures but also yields characteristic isotopic distributions
at the parent ion for each oligomer, corresponding to
the calculated isotopic distributions (Figure 12). How-
ever, in addition to these sequences, a major series of
mass peaks is observed which is identical for both HCl-
and HBr-quenched polymer samples; this mass se-
quence and its isotopic distributions correspond exactly
to those predicted for a poly(ethylene oxide) structure
with one end group composed of ligand 5a (Figure 13).
This structure appears to be somewhat unstable; a
second sample of HCl-quenched polymer prepared in the
same way yielded only the chloroethyl-terminated poly-
mer mass sequence in the MALDI-TOF spectrum and
Figure 13. A portion of the MALDI-TOF spectrum of HCl-
quenched poly(ethylene oxide) prepared from 5a/TiBA, show-
ing experimental signal and, below it, the calculated isotopic
distribution for the chloride-terminated polymer with formula
C116H233O58ClNa.
an NMR spectrum similar to that shown in Figure 10.
This instability could explain why ligand-terminated
polymer is not observed as a major component in the
13C NMR spectra.
Given our current state of knowledge, we cannot
determine the actual structure of the ligand-terminated
chain end. However, if it is easily converted by the

330 Wasserman et al.
Macromolecules, Vol. 38, No. 2, 2005
the active site structure in this chemistry. The adduct
of a singly capped bis(phenol) does not disproportionate
upon making an epoxide donor complex. Coordination
of 1,2-epoxyhexane to aluminum species induces sub-
stantial shifts in the oxirane proton NMR positions,
shifts which are most pronounced for the solvate of an
ethylaluminum thiobis(phenoxide) compound. Competi-
tion for oxirane initially favors triethylaluminum, formed
along with this ethylaluminum thiobis(phenoxide)
through disproportionation, despite the greater pertur-
bation of the oxirane coordinated to the latter. The first
ring-opening reaction for catalysts containing the singly
capped bisphenol ligand seems to involve the attack of
a group easily cleaved from the polymer by hydrochloric
acid. Propylene oxide polymerization proceeds with low
regioselectivity. The sulfur atom of the ligands appears
to prevent the clustering of aluminum-containing spe-
cies by providing an intramolecular Lewis base and may
also be involved in the first ring-opening event.
Figure 14. Spectra obtained from 2-D NMR experiment
(DEPT) on poly(propylene oxide) made with catalyst 4a/TiBA
(1:2), showing the assignments based on ref 4e.
action of HX (X ) Cl, Br) into a haloethyl chain end, it
may be that the initiating group is the sulfur atom,
rather than the oxygen atom of the phenoxy moiety. The
reaction of thioethers with ethylene oxide has been
postulated to lead to addition products with sulfonium
structures.23
Experimental Section
Materials. Unless otherwise specified, all chemical reac-
tions were performed under nitrogen. Toluene, diethyl ether,
and tetrahydrofuran were passed through a deoxo/sieves train
before use, while hexanes were passed through molecular
sieves. Triethylaluminum (1.56 mol/L solution in heptane) and
triisobutylaluminum (0.865 mol/L solution in hexanes) were
obtained from Akzo Nobel. Trimethylaluminum was obtained
from Aldrich as a 2 mol/L solution in hexane. m-Xylene-2-
sulfenyl chloride was prepared in a manner analogous to that
for 2-mesitylenesulfenyl chloride reported by Hicks et al.24 2,6-
Di-t-butylphenol (1), sulfur dichloride (80%), sodium hydride
(95%), ethyl p-toluenesulfonate (98%) and methyl p-toluene-
sulfonate (98%) were used as received from Aldrich. Sodium
t-butoxide (98%) was used as received from Alfa Aesar. 2,4-
Di-t-butylphenol (97%) was used as received from Acros
Organics. 2,2′-Methylenebis(6-t-butyl-4-methylphenol) (2a) was
obtained from R. T. Vanderbilt Company, Inc. 2,2′-Eth-
ylidenebis(4,6-di-t-butylphenol) (2b) and 2,2′-thiobis(6-t-butyl-
4-methylphenol) (4a) were obtained from Ciba Specialty
Chemicals. 4,4′-Thiobis(2-t-butyl-5-methylphenol) (3) was ob-
tained from Monsanto. Syntheses of 2,2′-thiobis(4,6-dimeth-
ylphenol)25 (4c) and 2-t-butyl-6-[(3-t-butyl-2-methoxy-5-meth-
ylphenyl)thio]-4-methylphenol26 (5a) were similar to reported
preparations.
2,2′-Thiobis(4,6-di-t-butylphenol) (4b).27 To a solution of
33.18 g of 2,4-di-t-butylphenol (161 mmol) in 175 mL of
hexanes was added dropwise a solution of 4.8 mL of sulfur
dichloride (76 mmol, 0.47 equiv) in 55 mL of hexanes at room
temperature over a period of 45 min, with some gas evolution.
The yellow solution was brought to reflux, which was main-
tained overnight. The organic fraction was dried with anhy-
drous sodium sulfate, filtered, and reduced by rotary evapo-
ration to a yellow oil. Crystals were obtained by dissolution
in 100 mL of acetonitrile and chilling to 0 °C. After filtration
and drying in vacuo overnight at room temperature, we
obtained 19.999 g of slightly yellow crystals which contained,
by NMR, 0.5 equiv of acetonitrile. Correcting for this, the yield
is 57% based on SCl2. (The sample used in the preparation of
polymerization catalysts was purified by column chromatog-
raphy (7:1 hexanes/toluene), which resulted in poorer yield but
no MeCN impurity; the samples are otherwise spectroscopi-
cally indistinguishable.) 1H NMR (CDCl3), δ (ppm): 7.29 (d, J
) 2.4 Hz), 2H, Ar-H; 7.18 (d, J ) 2.4 Hz), 2H, Ar-H; 6.50 (s),
2H, OH; 2.03 (s), 1.6 H, (MeCN); 1.43 (s), 18H, t-Bu; 1.24 (s)
18H, t-Bu. 13C{1H} NMR (CDCl3), δ (ppm): 151.8, 143.0, 136.0,
127.8, 125.2, 118.9, 35.2, 34.3, 31.4, 29.5.
Poly(Propylene Oxide) Analysis. Poly(propylene
oxide) (PPO) produced by catalyst 4a/TiBA (molar ratio
1:2) was examined by DEPT NMR analysis to probe the
regiochemistry of insertion. Using the assignments of
Antelmann et al.,4e the methylene and methine portions
of the 13C spectrum, shown in Figure 14, can be broken
down into those carbons associated with the hydroxyl
end groups and those associated with the bulk poly-
ether. The fact that both methylene and methine
carbons are bound to hydroxyl groups is strong evidence
that the initial insertion is not regioselective. Similarly,
the level of head-to-head and tail-to-tail insertion is
roughly that of head-to-tail insertion, indicating a
polymerization operating essentially without regio-
chemical control. We did not attempt to reproduce the
elegant analysis of Antelmann et al.4e to determine the
stereospecificity of the various ring-opening events and
so cannot distinguish our polymerization mechanism
from the one employed by simple Lewis acid catalysts
such as BF3. However, the PPO described in our work
bears a strong resemblance to that made by [(C30H44O2)-
AlCl]2, the catalyst used in theirs.
Conclusions
The reaction of sulfur-bridged bis(phenol) compounds
with trialkylaluminum species yields highly active
catalysts for EO polymerization. The sulfur atom binds
to aluminum in the solid-state structures of these
catalyst precursors. Greater steric bulk at the ortho
positions of the phenols and in the aluminum alkyl
groups increases catalyst productivity. Alkylation of one
of the phenol oxygens causes a large increase in catalytic
activity. In solution, donor-aluminum interactions in
the compound (3-t-Bu-5-Me-2-OAlEt2-C6H2)2S are flux-
ional, and interconvert via at least two distinct path-
ways. Upon addition of monomer, these species react
differently depending on ligand structure. Addition of
an epoxide to one dialuminum bis(phenoxide) complex
causes its disproportionation to the epoxide solvates of
both trialkylaluminum species and monoaluminum bis-
(phenoxide). Thus, it is unlikely that a bisphenol adduct
comprising two phenoxyaluminum moieties represents
2-t-Butyl-6-[(3-t-butyl-2-ethoxy-5-methylphenyl)thio]-
4-methylphenol (5b). To a solution of 10.036 g 4a (28.0
mmol) in 100 mL of THF was added 0.685 g of sodium hydride
(28.5 mmol, 1.02 equiv), and the mixture was refluxed for 2 h.
While the reaction mixture was still refluxing, a solution of

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 331
5.595 g of ethyl p-toluenesulfonate (27.9 mmol, 1 equiv) was
added over a period of 3 h. (During this period, an additional
50 mL of THF were injected into the flask to make up for
solvent apparently lost to a leaky joint.) The thick blue-green
slurry with white precipitate was refluxed overnight. Next,
the slurry was quenched with 200 mL of water and mixed with
200 mL of diethyl ether to extract the reaction product. The
aqueous phase was washed with a further 50 mL of diethyl
ether. The combined organic fractions were dried over anhy-
drous sodium sulfate, filtered, and reduced to a viscous yellow
fluid by rotary evaporation. The material was purified first
by column chromatography in hexanes/toluene at a volume
ratio of 40:1, with one less-pure fraction recrystallized from
ethanol. Three crops were recovered, with a total weight of
+ 18) (calcd 456.31). Calcd for C29H44O2S (%): C, 76.26; H,
9.71; O, 7.01; found: C, 76.15; H, 10.06; O, 7.19.
Bis(3-t-butyl-2-methoxy-5-methylphenyl)sulfide (6).26
To a refluxing mixture of 1.569 g of sodium hydride (65.4
mmol) and 40 mL of THF was added a solution of 9.992 g of
4a (27.9 mmol) in 15 mL of THF dropwise over a period of 5
h. The reaction mixture was refluxed for 3 days. To the slurry
was then added a solution of 12.990 g of methyl p-toluene-
sulfonate (69.75 mmol) in 25 mL of THF over a period of 2.5
h. This reaction was continued under reflux for 17 h then
allowed to cool. The slurry was poured into a mixture of ice
and sodium chloride and then brought to a pH of 3 with the
addition of hydrochloric acid. The mixture was poured into a
separatory funnel, and extracted with one 100 mL portion and
two 65 mL portions of hexanes. The combined organic fractions
were dried over anhydrous sodium sulfate, filtered, and
reduced to an off-white solid by rotary evaporation. The pure
compound was recovered by recrystallization from ethanol.
1
5.36 g (50%). M.p. 116.7 °C. H NMR (CDCl3), δ (ppm): 7.22
(d, J ) 2.0 Hz), 1H, Ar-H; 7.17 (s), 1H, OH; 7.11 (d, J ) 2.0
Hz), 1H, Ar-H; 6.93 (d, J ) 2.0 Hz), 1H, Ar-H; 6.50 (d, J )
2.0), 1H, Ar-H; 4.15 (q, J ) 7.0 Hz), 2H, CH2CH3; 2.24 (s),
3H, Ar-CH3; 2.12 (s), Ar-CH3; 1.52 (t, J ) 7.0 Hz), CH2CH3;
1.36 (s), t-Bu. 13C{1H} NMR (CDCl3), δ (ppm): 154.3, 153.7,
143.4, 136.3, 134.5, 133.9, 130.4, 129.2, 128.2, 127.2, 117.3,
70.3, 35.4, 35.2, 31.3, 29.5, 21.4, 20.9, 15.4. IR (cm-1): 3386
(br), 2958, 1437, 1238, 1220, 1030. MS (m/z): 387 (M + 1),
404 (M + 18) (calcd 386.23). Calcd for C24H34O2S (%): C, 74.56;
H, 8.86; O, 8.28; found: C, 74.19; H, 9.22; O, 8.31.
2-t-Butyl-6-([3-t-butyl-5-methyl-2-(trimethylsilyloxy)-
phenyl]thio)-4-methylphenol (5c). A round-bottom flask
was charged with a stirbar, 10.035 g of 4a (28.0 mmol), 5 mL
of triethylamine (36 mmol, 1.3 equiv), and 100 mL of hexanes.
The flask was immersed in an ice-water bath. To this solution
was added dropwise a solution of 4.6 mL of chlorotrimethyl-
silane (36 mmol, 1.3 equiv) in 50 mL of hexanes, with the
formation of a white precipitate. The slurry was allowed to
reach ambient temperature and stirred for 3 days. The slurry
was then filtered twice through a medium glass frit then
washed with 125 mL of water. The aqueous solution was then
washed with 75 mL of hexanes, and the combined organic
fractions were dried over anhydrous magnesium sulfate. After
filtering, the organic phase was reduced by rotary evaporation
to 10.39 g of white powder (86%). M.p. 103.29 °C. 1H NMR
(CDCl3), δ (ppm): 7.14 (m), 2H, Ar-H; 6.90 (s) 1H, Ar-H; 6.73
(s), 1H, OH; 6.31 (m), 1H, Ar-H; 2.25 (s), 3H, Ar-CH3; 2.08,
3H, Ar-CH3; 1.37, 1.38 (two s), 18H, t-Bu; 0.47, 9H, Si-CH3.
13C{1H} NMR (CDCl3), δ (ppm): 151.1, 146.5, 137.9, 133.6,
131.4, 128.3, 127.5, 126.7, 124.0, 123.8, 123.5, 114.4, 32.4, 32.3,
27.8, 26.8., 18.4, 18.1, 0.0. IR (cm-1): 3402 (br), 2956, 1434,
1241, 904, 849. MS (m/z): 431 (M + 1), 448 (M + 18) (calcd
430.24). Calcd for C25H38O2SSi (%): C, 69.71; H, 8.89; found:
C, 69.79; H, 9.16.
1
Yield: 8.72 g (81% based on 4a). H NMR (CDCl3), δ (ppm):
7.00 (d, J ) 2.2 Hz), 2H, Ar-H; 6.74 (d, J ) 2.2 Hz), 2H, Ar-
H; 3.92 (s), 6H, OCH3; 2.17 (s), 6H, Ar-CH3; 1.38 (s), 18H,
t-Bu. 13C{1H} NMR (CDCl3), δ (ppm): 156.4, 143.2, 133.2,
130.8, 128.7, 127.2, 61.4, 35.1, 30.9, 21.0.
t-Butylthiacalix[4]arene (7).28 A 250 mL round-bottom
flask was charged with a stirbar, 63.42 g of 4-t-butylphenol
(422 mmol), 26.50 g of elemental sulfur (827 mmol atomic
sulfur), 19 mL of tetraethylene glycol dimethyl ether, and 8.60
g of sodium hydroxide (215 mmol). A nitrogen stream flowed
over the surface of the slurry to help remove hydrogen sulfide,
and the effluent gas was bubbled through a concentrated
solution of sodium hypochlorite. The reaction temperature was
slowly raised to 200 °C over about 4 h, heated at 210-240 °C
for an additional 6 h, and then allowed to cool slowly. The very
dark red solid was broken up in a mixture of toluene and ether
at a volume ratio of 1:1. To the slurry was then added 350 mL
of an 0.5 mol/L solution of sulfuric acid in water. The organic
fraction was separated and the aqueous portion washed with
100 mL of a toluene/ether mixture of a volume ratio of 1:1.
The combined organic fractions were reduced by rotary
evaporation and vacuum pump to a thick, dark red liquid, to
which were added 150 mL of hexanes. This precipitated a
cream-colored powder, which was filtered on medium glass frit
and air-dried, yielding 10.6 g (14% based on sulfur). 1H NMR
(CDCl3), δ (ppm): 9.58 (s), 4H, OH; 7.62 (s), 8H, Ar-H; 1.21
(s), 36H, t-Bu. MS (m/z): 720 (M - 1).
Bis(3-t-butyl-2-hydroxy-5-methylphenyl)sulfoxide (8).
Compound 8 was prepared by the reaction of 4a with 1 equiv
of 3-chloroperbenzoic acid according to literature procedures.29
2,4-Bis-t-butyl-6-[(2,6-dimethylphenyl)thio]phenol (9).
Under N2, 2.225 g of m-xylene-2-sulfenyl chloride (12.9 mmol)
was dissolved in 25 mL of hexanes. Under air, a 100 mL three-
necked round-bottom flask was charged with a stirbar and 2.64
g of 2,4-di-t-butylphenol (12.8 mmol); then, a reflux condenser
with vacuum adapter and addition funnel were attached. The
phenol was dried in vacuo for 20 min, placed under N2, and
immersed in an oil bath set at 100 °C. The solution of
m-xylene-2-sulfenyl chloride was then added via addition
funnel, and the reaction mixture was refluxed overnight.
Solvent had evaporated by morning, probably through a leaky
joint. The resulting brown solid was ground up in a mortar
and pestle and recrystallized from ethanol, yielding 2.170 g
of cream-colored solid that melted at 101-102 °C. A second,
somewhat darker crop of 0.434 g was recovered from the
mother liquor. Combined yield: 59% (based on 2,4-di-t-
butylphenol). M.p. 81.67 °C. 1H NMR (CDCl3), δ (ppm): 7.07-
7.13 (m), 4H, Ar-H; 6.82 (d, J ) 2.4 Hz), 1H, Ar-H; 6.28 (s),
1H, OH; 2.41 (s), 6H, CH3; 1.38 (s), 9H, t-Bu; 1.13 (s), 9H, t-Bu.
13C{1H} NMR (CDCl3), δ (ppm): 151.2, 143.6, 142.8, 142.6,
135.5, 129.5, 128.8, 128.3, 126.1, 123.5, 35.3, 34.4, 31.6, 29.7,
22.2, 21.7. IR (cm-1): 3413 (br), 2959, 1461, 1440, 771. MS
(m/z): 343 (M + 1), 360 (M + 18) (calcd 342.20). Calcd for
C22H30OS (%): C, 77.14; H, 8.83; O, 4.67; found: C, 73.99; H,
8.14; O, 3.74.
2,4-Di-t-butyl-6-[(3,5-di-t-butyl-2-methoxyphenyl)thio]-
phenol (5d). To a slurry of 2.17 g of sodium t-butoxide (22.6
mmol) in 50 mL of THF was added a solution of 10.023 g of
4b‚0.5 MeCN (21.6 mmol) in 45 mL of THF over a period of
17 min while the mixture was heated to reflux. To the resulting
clear solution was added a solution of 4.06 g of methyl
p-toluenesulfonate (21.8 mmol) dropwise over 1 h followed by
overnight stirring with continued reflux. The resulting thick,
yellow slurry was allowed to cool and then was taken up with
200 mL of diethyl ether and 200 mL of water. The organic
fraction was separated and washed twice with water, while
the aqueous fraction was washed twice with ether after the
addition of 4.8 g of NaCl to facilitate separation. The organic
fractions were combined and dried over anhydrous sodium
sulfate, filtered, and reduced in vacuo to a deep golden oil.
Hexanes (150 mL) were added and quickly removed in vacuo
to complete the removal of polar solvent. Crystals were
obtained by the addition of ethanol (50 mL) and standing at 0
°C. After drying in air, 7.147 g (72%) were obtained. M.p.
1
100.24 °C. H NMR (CD2Cl2), δ (ppm): 7.46 (m), 2H, Ar-H;
7.19 (m) 1H, Ar-H; 7.11 (s), 1H, OH; 6.59 (m), 1H, Ar-H; 4.04
(s), 3H, O-CH3; 1.43, 18H, t-Bu; 1.32, 9H, t-Bu; 1.12, 9H, t-Bu.
13C{1H} NMR (CDCl3), δ (ppm): 154.2, 154.0, 146.7, 143.0,
142.6, 135.9, 131.5, 130.1, 126.8, 123.2, 122.6, 116.0, 61.9, 35.7,
35.5, 34.7, 31.8, 31.4, 31.4, 29.7. IR (cm-1): 3395 (br); 2961,
1468, 1442, 1362, 1244, 1105. MS (m/z): 457 (M + 1), 474 (M
Bis(3-t-butyl-2-(diethylaluminoxy)-5-methylphenyl)-
sulfide (10). An exemplary synthesis is described. Under

332 Wasserman et al.
Macromolecules, Vol. 38, No. 2, 2005
nitrogen, 2.03 g of 4a (5.4 mmol) was dissolved in 15 mL of
dry hexanes. To this solution was slowly added 7 mL of
triethylaluminum solution (10.8 mmol); the resulting solution
was allowed to stir at ambient temperature overnight. Clear,
colorless crystals suitable for X-ray analysis were obtained by
slow evaporation of solvent over an extended period at ambient
temperature. 1H NMR (toluene-d8), δ (ppm): 7.23 (d), 2H, Ar-
H; 7.16 (d), 2H, Ar-H; 2.09 (s), 6H, Ar-CH3; 1.44 (s), 18H,
t-Bu; 1.21 (br s), 6H; 0.9 (br s), 6H; 0.26 (br s); 8H. 13C{1H}
NMR (toluene-d8), δ (ppm): 156.5, 142.0, 133.9, 133.5, 131.7,
121.4, 36.2, 20.9, 9.4, 1.6; the last two peaks being ∼0.5 ppm
fwhm. Calcd for C30H48Al2O2S (%): C, 68.41; H, 9.18; found:
C, 67.09; H, 9.34.
water and 50 mL of methanol was added. After removal of
residual monomer by nitrogen sparge, the polymer slurry was
collected and dried in a vacuum oven at 50 °C. Yield: 27.2 g.
A similar procedure, only quenched with a mixture of 5 mL of
48% hydrobromic acid/water and 50 mL of methanol, yielded
43.5 g of polymer.
PO Homopolymerization. The PPO oligomer was pre-
pared using the same apparatus as in the EO polymerizations.
In this case, the catalyst was a hexane solution containing a
mixture of ligand 4a (5 mmol) and TiBA (10 mmol). PO (20
mL) was added in one portion to ca. 300 mL of hexanes
followed by the catalyst solution. The reaction was maintained
at 29-30 °C for 2h, at the end of which period, a mixture of 5
mL of 37% hydrochloric acid/water and 50 mL of methanol
was added. After removal of residual monomer by nitrogen
sparge, the polymer slurry was collected and allowed to air-
dry, and 5.5 g of a viscous, deep yellow polymer was recovered.
Crystallography. Data tables are presented in the body
of the paper, while the details of data collection and analysis
are to be found in the Supporting Information.
NMR Spectroscopy. Ligand analyses were done using a
Bruker AMX-300 (300 MHz) spectrometer. Catalyst and
polymer NMR spectra were obtained on a 400 MHz instrument
(Varian). Catalysts and mixtures of catalysts with 1,2-epoxy-
hexane were prepared in toluene-d8 (vacuum distilled from
sodium-potassium alloy) after first removing any proteated
solvents used in catalyst synthesis. The poly(ethylene oxide)
samples were dissolved in CDCl3 and analyzed by 13C NMR.
Gel-Permeation Chromatography (GPC). The number-
average and weight-average molecular weights were measured
using a Polymer Liquids PL Aquagel-OH, 16 mm column using
0.05% NaN3 as the mobile phase, at a rate of 0.8 mL/min and
an injection size of 200 mL. A Water 590 HPLC isocratic pump
was used together with a Waters 717Plus Autosampler and
dual detection on a Wyatt Technology Dawn DSP Laser
Photometer and a Water 2410 refractive index detector. The
results were interpreted by use of WTC-Astra 4.72 software.
Mass Spectrometry. Spectra of compounds 5b, 5c, 5d, and
9 were collected using a Finnigan TSQ-7000 mass spectrom-
eter with a headpressure of 1 psi, a source temperature of 150
°C, an emission current of 800 µA, an electron lens voltage of
130, and an electron multiplier at 1300 eV. Ammonia was used
as the chemical ionization gas and caused the appearance of
M + 18 peaks in addition to those identifiable as M + 1.
Compound 7 was analyzed by electron impact using a solids
probe. This sample was dissolved in o-dichlorobenzene, and a
small amount was transferred to a probe crucible and inserted
into the probe, which was then inserted into the source of the
spectrometer. The probe was then heated at 20 °C/min to 300
°C.
(3-t-Butyl-2-diethylalumino-5-methylphenyl)(3-t-butyl-
2-methoxy-5-methylphenyl)sulfide (11). To a solution of
2.008 g (5.4 mmol) of 5a in 15 mL of dry hexanes was added
dropwise a hexane solution of trimethylaluminum (5.4 mmol)
in hexane (8 mL). After being stirred for 2 h at ambient
temperature, all volatiles were removed. Colorless crystals
were obtained by storage of a toluene/pentane solution at -25
to -30 °C. The NMR spectrum revealed the presence of one
equivalent of toluene as the solvent of crystallization. The
crystal structure of this compound lacked this solvent, how-
ever. 1H NMR (toluene-d8), δ (ppm): 7.21 (s), 1H, Ar-H
(phenolic); 7.15 (s), Ar-H (phenolic); 7.06 (t), 2H, J ) 7.2 Hz,
Ar-H (toluene); 6.98 (d), 1H, J ) 7.2 Hz, Ar-H (toluene); 6.94
(t), 1H, J ) 7.6 Hz, Ar-H (toluene); 6.89 (s), 1H, Ar-H
(phenolic); 6.82 (s), 1H, Ar-H (phenolic); 3.62 (s), 3H, OCH3;
2.11 (s), 3H, Ar-CH3; 2.09 (s), 3H, Ar-CH3; 1.72 (s), 3H, Ar-
CH3; 1.45 (s), 9H, t-Bu; 1.29 (s), 9H, t-Bu; -0.41 (s), 6H, Al-
CH3. 13C{1H} NMR (toluene-d8), δ (ppm): 159.9, 154.5, 142.7,
139.8, 137.7, 132.7, 131.2, 131.1, 129.6, 129.2, 128.4, 125.6,
65.1, 35.5, 35.4, 31.5, 29.6, 22.7, 20.8, 14.2, -9.0. Calcd for
C25H37AlO2S (%): C, 70.06; H, 8.70; found: C, 68.44; H, 8.66.
2,2′-Thiobis(6-t-butyl-4-methylphenoxy)(ethyl)alumi-
num Diethyl Etherate (12). To a solution of 2.018 g of 4a in
40 mL of dry diethyl ether was slowly added 3.65 mL of
triethylaluminum solution (5.62 mmol) at ambient tempera-
ture. After stirring overnight, the volume was reduced by
evaporation to about 10 mL. Clear, colorless crystals were
obtained by cooling a mixture of this solution with pentane at
-25 to -30 °C. The NMR of this compound showed a slight
1
excess of diethyl ether. H NMR (toluene-d8), δ (ppm): 7.45
(d), 2H, J ) 2.0 Hz, Ar-H; 7.07 (d), 2H, J ) 2.0 Hz, Ar-H;
3.91 (br q), 5H, CH3CH2O; 2.10 (s), 6H, Ar-CH3; 1.45 (s), 18H,
t-Bu; 1.39 (t), 3H, J ) 8.0 Hz, CH3CH2Al; 1.05 (t), 8H, J ) 7.2
Hz, CH3CH2O; 0.41 (q), 2H, J ) 8.0 Hz, CH3CH2Al. 13C{1H}
NMR (toluene-d8), δ (ppm): 137.8, 133.1, 130.0, 126.8, 123.4,
65.6, 35.2, 29.7, 13.9, 9.9. Calcd for C28H43AlO3S (%): C, 69.10;
H, 8.91; found: C, 68.73; H, 9.15.
EO Polymerizations. Polymerizations were carried out in
a glass slurry reactor composed of a jacketed reactor kettle
fitted with an air-powered mechanical stirrer, thermometer,
jacketed addition funnel, coldfinger condenser, and gas-disper-
sion tube. A generalized description of the polymerization
procedure is as follows. To a dry, N2-flushed reactor was
charged 275 mL of hexane. A hexane solution of catalyst was
injected via oven dried syringe followed by condensation/
addition of 50-100 mL of EO to the jacketed addition funnel.
The polymerization was initiated by addition of 3 mL of EO,
followed by dropwise addition over 2 h. The reaction was
stopped after 3-6 h total reaction time by addition of 2-pro-
panol to inactivate the catalyst and removal of excess EO to
scrubbers under positive CO2 pressure. The polymer was
discharged, washed with hexane, and dried in vacuo overnight.
To prepare the EO oligomers whose analyses are presented
in Figures 10-13, the above general procedure was followed,
with the following specific conditions. The catalyst was pre-
pared by mixing 3.7 g (10 mmol) of 5a with 10 mmol of TiBA
(solution in hexane) overnight with additional hexane. The
catalyst solution was added to ca. 300 mL of hexanes in the
jacketed glass reactor. EO (50 mL) was added over a period of
1 h, and the reaction was allowed to proceed for 4.25 h. The
reaction temperature was kept at 27-30 °C for 4 h, at the end
of which period, a mixture of 5 mL of 37% hydrochloric acid/
MALDI-TOF mass spectrometry on polymeric samples was
performed on a Bruker Biflex III time-of-flight mass spectrom-
eter, operated in the linear and reflectron modes. The matrix
was 10% water in THF saturated with 2-(4-hydroxyphenylazo)-
benzoic acid (HABA). Samples were prepared as approximately
2000 ppm solutions in 10% water/THF. Sample and matrix
solutions were combined 1:1 and briefly vortex-mixed. Ap-
proximately 1 µL of this preparation was spotted directly onto
a stainless-steel target disk. Spectra were acquired by averag-
ing a few hundred laser shots. Mass calibration was performed
using oligomer peaks from poly(ethylene glycol) (PEG) 3350
and 8000 in the same matrix. Parent ions were mainly M‚
Na+ cations, formed from sodium salt in the matrix.
FT-IR Spectroscopy. Spectra were collected on a Nicolet
Magna 750 FT-IR spectrometer via transmission. The samples
were prepared as thin films cast from a methylene chloride
solution. Resolution was set at 4 cm-1, and 128 scans were
collected. Spectra were processed with triangular apodization.
Differential Scanning Calorimetry. Melting points were
obtained on a TA Instruments DSC 2920, heating from 30 to
180 °C in air at a rate of 5 °C/min.
Elemental Analysis. Analyses were performed by Quan-
titative Technologies, Inc., Whitehouse, NJ except for that of
compound 10, which was analyzed by Complete Analysis
Laboratories, Inc., Parsippany, NJ.

Macromolecules, Vol. 38, No. 2, 2005
Ethylene Oxide Polymerization 333
(9) World Pat. Publ. WO2002098559, Priority Appl. US 60/
294964 (20010531), to Union Carbide.
(10) Poor productivity (<1 g/mmol(Al)) was also observed with
triisobutylaluminum, methyl aluminoxane, and mixtures of
triethylaluminum, H2O, and acetylacetone (“Vandenberg’s
catalyst”; see: U.S. Patent No. 3,135,705, Priority Date
19590511, to Hercules Powder Co.).
Acknowledgment. The authors gratefully acknowl-
edge the efforts of Ms. I. Rabinovich in catalyst and
polymer synthesis. [J. Perry, J. O’Donnell, R. Walling-
ford] We would also like to thank Dr. R. Wehmeyer for
helpful discussions. The authors gratefully acknowledge
the efforts of Ms. I. Rabinovich in catalyst and polymer
synthesis. We would also like to thank Dr. R. Wehmeyer
for helpful discussions.
(11) Ohba, Y.; Ito, K.; Nagasawa, T.; Sakurai, S. J. Heterocycl.
Chem. 2000, 37, 1071-1076.
(12) Ohba, Y.; Ito, K.; Nagasawa, T. Heterocycl. Commun. 1998,
4, 529-534.
Supporting Information Available: Tables of crystal-
lographic data for 10, 11, and 12. This material is available
free of charge via the Internet at http://pubs.acs.org.
(13) Campbell, E. J.; Zhou, H.; Nguyen, S. Angew. Chem., Int. Ed.
2002, 41, 1020-1022.
(14) Taden, I.; Kang, H.-C.; Massa, W.; Spaniol; Okuda, J. Eur.
J. Inorg. Chem. 2000, 441-445.
(15) Trimethylaluminum was chosen over TEAl because com-
plexes of 5a with the latter do not yield crystals.
(16) Cooperative Lewis acid chemistry has been invoked as a goal
justifying efforts to synthesize dialuminum complexes of
conformationally rigid diphenolate-type ligands: Cottone, A.,
III; Scott, M. J. Organometallics 2000, 19, 5254-5256.
(17) Atwood, J. L.; Gardiner, M. G.; Jones, C.; Raston, C. L.;
Skelton, B. W.; White, A. H. Chem. Commun. 1996, 2487-
2488.
References and Notes
(1) Back, D. M.; Schmitt, R. L. Ethylene Oxide Polymers. In
Encyclopedia of Polymer Science and Technology, Online ed.;
John Wiley and Sons: New York, 2004; Section 9.
(2) Bailey, F. E., Jr.; Koleske, J. V. Poly(ethylene oxide): Aca-
demic Press: New York, 1976; pp 15-22.
(3) (a) Vandenberg, E. J. J. Polym. Sci. 1960, 149, 186-189. (b)
Vandenberg, E. J. Polym. Lett. 1964, 2, 1085-1088. (c)
Vandenberg, E. J. J. Polym. Sci. A-1, 1969, 7, 525-567.
(4) (a) Kuran, W.; Listos, T.; Abramczyk, M.; Dawidek, A. J.
Macromol. Sci., Pure Appl. Chem. 1998, A35, 427-437. (b)
Sarbu, T.; Beckman, E. J. ACS Polym. Div., Polymer Preprints
1999, 40(2), 903-904. (c) Liu, S.; Munoz-Hernandez, M.-A.;
Atwood, D. A. J. Organomet. Chem. 2000, 596, 109-114. (d)
Chisholm, M. H.; Navarro-Llobet, D.; Simonsick, W. J., Jr.
Macromolecules 2001, 34, 8851-8857. (e) Antelmann, B.;
Chisholm, M. H.; Iyer, S. S.; Huffman, J. C.; Navarro-Llobet,
D.; Simonsick, W. J.; Zhong, W. Macromolecules 2001, 34,
3159-3175. (f) Chakraborty, D.; Chen, E. Y.-X. Macromol-
ecules 2002, 35, 13-15. (g) Dagorne, S.; Lavanant, L.; Welter,
R.; Chassenieux, C.; Haquette, P.; Jaouen, G. Organometal-
lics 2003, 22, 3732-3741. (h) Braune, W.; Okuda, J. Angew.
Chem., Int. Ed. 2003, 42, 64-68.
(18) Hsueh, M.-L.; Huang, B.-H.; Lin, C.-C. Macromolecules 2002,
35, 5763-5768.
(19) Fokken, S.; Spaniol, T. P.; Kang, H.-C.; Massa, W.; Okuda,
J. Organometallics 1996, 15, 5069-5072.
(20) Software: NUTS NMR Utility Transform Software, Version
1,0,0,1, Acorn NMR, 2001.
(21) A similar downfield shift in proton NMR resonances was
observed for propylene oxide coordinated to triisobutylalu-
minum: Billouard, C.; Carlotti, S.; Desbois, P.; Deffieux, A.
Macromolecules 2004, 37, 4038-4043.
(22) Odian, G. Principles of Polymerization, 3rd ed.; John Wiley
and Sons: New York, 1991; p 87.
(23) (a) Windmueller, H. G.; Ackerman, C. J.; Engel, R. W. J. Biol.
Chem. 1959, 234, 895-899. (b) LaRochelle, R. W.; Trost, B.
M. J. Am. Chem. Soc. 1971, 93, 6077-6086.
(5) Akatsuka, M.; Aida, T.; Inoue, S. Macromolecules 1994, 27,
2820-2825.
(6) (a) Cameron, P. A.; Gibson, V. C.; Irvine, D. J. Angew. Chem.,
Int. Ed. 2000, 39, 2141-2144. (b) Bi, X.; Wang., D.; Wu, Z.
J. Mol. Catal. A.: Chem. 2002, 179, 53-57.
(24) Hicks, R. G.; Nodwell, M. B. J. Am. Chem. Soc. 2000, 122,
6746-53.
(25) Pastor, S. D.; Denney, D. Z. Phosph. Sulfur Relat. Elem. 1987,
32, 105-111.
(26) Jira´ckova´, L.; Posp´ısil, J. Collect. Czech. Chem. Commun.
1974, 39, 2792-2795.
(7) Ko, B.-T.; Lin, C.-C. Macromolecules 1999, 32, 8296-8300.
(b) Cameron, P. A.; Jhurry, D.; Gibson, V. C.; White, A. J. P.;
Williams, D. J.; Williams, S. Macromol. Rapid Commun.
1999, 20, 616-618. (c) Taden, I.; Kang, H.-K.; Massa, W.;
Spaniol, T. P.; Okuda, J. Eur. J. Inorg. Chem. 2000, 441-
445. (d) Ovitt, T. M.; Coates, G. W. J. Polym. Sci. A: Polym.
Chem. 2000, 38, 4686-4692. (e) Chen, H.-L.; Ko, B.-T.;
Huang, B.-H.; Lin, C.-C. Organometallics 2001, 20, 5076-
5083.
(27) Synthesis reported previously: Pastor, S. D.; Spivack, J. D.;
Steinhuebel, L. P. J. Heterocycl. Chem. 1984, 21, 1285-1287.
(28) Kumagai, H.; Hasegawa, M.; Miyanari, S.; Sugawa, Y.; Sato,
Y.; Hori, T.; Ueda, S.; Kamiyama, H.; Miyano, S. Tetrahedron
Lett. 1997, 38, 3971-72.
(29) (a) Chasar, D. W. Polym. Deg. Stab. 1980-1981, 3, 124-125.
(b) Johnson, C. R.; McCants, D., Jr. J. Am. Chem. Soc. 1965,
87, 1109-1114.
(8) Chisholm, M. H.; Navarro-Llobet, D.; Simonsick, W. J.
Macromolecules 2001, 34, 8851-8857.
MA049209D