A ruthenium-catalyzed hydrosilane-induced polymerization of 3-alkyl-3-hydroxymethyloxetane derivatives: Facile access to functionalized polyoxetanes by virtue of organosilyl groups

Article abstract of DOI:10.1246/bcsj.20100155

Ring-opening polymerization of 3-alkyl-3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes is catalyzed by a triruthenium cluster, [Ru ₃{μ₃-(η₂,η₃, η₅-C₁₂H₈)}(CO)₇], in the presence of trialkylsilanes, providing a novel accessible method for functionalized polyoxetanes of M_n = 10₃-10₅. Oxetanes having alkoxy-, fluoroalkoxy-, triethyleneglycoloxy-, and trialkylsiloxy functions undergo polymerization and copolymerization. Consumption rates of two monomers in the copolymerization of 3-benzyloxymethyl- and 3-trimethylsiloxymethyl-3-alkyloxetanes are almost the same, indicating formation of random copolymers. The organosilyl group in the polymer and copolymers with siloxymethyl side chains is converted to CH₃OH or CH₂OCOR groups by hydrolysis or silyl/acyl exchange. These protocols give the way to access polymers or copolymers bearing OH and OCOR side chains. A ruthenium-catalyzed reaction of 3-ethyl-3- hydroxymethyloxetane with trialkylsilanes results in dehydrogenative silylation to give 3-ethyl-3-siloxymethyloxetane, which is followed by ring-opening polymerization. Combination of tandem dehydrogenative silylation/ring-opening polymerization/the silyl/acyl exchange realizes one-pot synthesis of polymers with CH₂OCOR side chains from 3-ethyl- 3-hydroxymethyloxetane. DSC analyses of the formed polymers provided T_g and T_m data, which are a good example showing that the polymer properties are controlled by appropriate selection of functional groups at the side chain.

Full text of DOI:10.1246/bcsj.20100155

26
Bull. Chem. Soc. Jpn. Vol. 84, No. 1, 26–39 (2011)
© 2011 The Chemical Society of Japan
BCSJ Award Article
A Ruthenium-Catalyzed Hydrosilane-Induced Polymerization
of 3-Alkyl-3-hydroxymethyloxetane Derivatives: Facile Access
to Functionalized Polyoxetanes by Virtue of Organosilyl Groups
Nari-aki Harada,1 Jushiro Yasuhara,1 Yukihiro Motoyama,2 Osamu Fujimura,3
Tetsuro Tsuji,4 Takeshi Takahashi,4 Yoshiaki Takahashi,2 and Hideo Nagashima*2
1Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580
2Institute for Materials Chemistry and Engineering, Kyushu University, Kasuga, Fukuoka 816-8580
3Organic Functional Material Research Laboratory, Corporate Research & Development,
UBE INDUSTRIES, LTD., Ichihara, Chiba 290-0045
4Chemicals Development Center, Production & Technology Division, UBE INDUSTRIES, LTD.,
Ube, Yamaguchi 755-8633
Received June 3, 2010; E-mail: nagasima@cm.kyushu-u.ac.jp
Ring-opening polymerization of 3-alkyl-3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes is catalyzed by a
triruthenium cluster, [Ru3{®3-(©2,©3,©5-C12H8)}(CO)7], in the presence of trialkylsilanes, providing a novel accessible
method for functionalized polyoxetanes of Mn = 103-105. Oxetanes having alkoxy-, fluoroalkoxy-, triethyleneglycoloxy-,
and trialkylsiloxy functions undergo polymerization and copolymerization. Consumption rates of two monomers in the
copolymerization of 3-benzyloxymethyl- and 3-trimethylsiloxymethyl-3-alkyloxetanes are almost the same, indicating
formation of random copolymers. The organosilyl group in the polymer and copolymers with siloxymethyl side chains is
converted to CH2OH or CH2OCOR groups by hydrolysis or silyl/acyl exchange. These protocols give the way to access
polymers or copolymers bearing OH and OCOR side chains. A ruthenium-catalyzed reaction of 3-ethyl-3-
hydroxymethyloxetane with trialkylsilanes results in dehydrogenative silylation to give 3-ethyl-3-siloxymethyloxetane,
which is followed by ring-opening polymerization. Combination of tandem dehydrogenative silylation/ring-opening
polymerization/the silyl/acyl exchange realizes one-pot synthesis of polymers with CH2OCOR side chains from 3-ethyl-
3-hydroxymethyloxetane. DSC analyses of the formed polymers provided Tg and Tm data, which are a good example
showing that the polymer properties are controlled by appropriate selection of functional groups at the side chain.
A discovery by Chalk in 1970 of the ring-opening polymer-
(CO)2
ization of THF by combination of Et3SiH and [Co2(CO)8],1
which was later expanded by Crivello and co-workers by using
RSiH3,2 was the start of a series of hydrosilane-induced
polymerization of cyclic ethers and vinyl ethers catalyzed by
transition-metal catalysts. The polymerization of these mono-
mers usually proceeds by the action of cationic initiators,
however, the Chalk-Crivello polymerization is initiated
smoothly by a species generated from neutral hydrosilanes
and [Co2(CO)8]. A ruthenium carbonyl cluster, [Ru3{®3-
(©2,©3,©5-C12H8)}(CO)7] (1) (Chart 1), discovered in our
laboratory has several advantages over [Co2(CO)8] as the
catalyst for the hydrosilane-induced polymerization:3 (1)
Handling of [Co2(CO)8] is not easy due to its air- and
temperature sensitivity. The ruthenium complex 1 is stable to
air and moisture and can be stored under aerobic conditions
over years: (2) The complex 1 produces highly active species
Ru
Ru(CO)2
CO
Ru
(CO)2
[Ru3{µ3-(η2,η3,η5-C12H8)}(CO)7] (1)
Chart 1.
in contact with R3SiH, which shows good catalytic activity
toward the polymerization of cyclic ethers, a cyclic siloxane,
and vinyl ethers with R3SiH: (3) a R3Si- group, which has
potential for further chemical transformation of the formed
polymers, was introduced at one of the polymer ends.
In our efforts to apply the ruthenium-catalyzed, hydrosilane-
induced polymerization to highly functionalized polymers, we
Published on the web December 25, 2010; doi:10.1246/bcsj.20100155

N. Harada et al.
OR'
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
27
R
the linear polymer in the reaction medium; (5) one-pot
synthesis of polymer and copolymers with CH2OCOR side
chains from 3-ethyl-3-hydroxymethyloxetane was achieved
by three tandem reactions consisting of the dehydrogenative
silylation, the ring-opening polymerization, and the silyl/acyl
exchange. By virtue of these, the present method is able to
produce polyoxetane with a variety of pendant functional
groups. As an example of a property controllable by the
pendant group, DSC analyses were performed.
R
OR'
O
1
+
H–SiR''3
H
SiR''3
n
O
Me
OR'
Et
OR'
R'
O
O
H
MHO-H
EHO-H
CH2Ph
SiMe3
MHO-Bn
EHO-Bn
EHO-SiMe3
Results and Discussion
Polymerization of 3-Alkyl-3-alkoxymethyloxetane and
3-Alkyl-3-siloxymethyloxetane. The ruthenium complex 1
is stable under aerobic conditions, but produces a highly active
species in contact with trialkylsilanes.3 In a typical example,
generation of active species by treatment of 1 with excess
PhMe2SiH (100 equiv to 1) was followed by addition of 3-
ethyl-3-benzyloxymethyloxetane [EHO-Bn; 1000 equiv to 1]
at room temperature. Exothermic reaction took place and all
of the monomer was polymerized in minutes. As shown in
Entry 1, Table 1, the corresponding polyoxetane with Mn =
4.9 © 104, Mw/Mn = 2.0 was isolated in 88% yield after
precipitation from methanol. Besides the signals due to the
SiPhMe2
MHO-SiPhMe2
MHO-EG
EHO-SiPhMe2
[(CH2)2O]2Me
[(CH2)2O]3Me
CH2CF2CF3
EHO-TEG
EHO-Rf
MHO-Rf
Scheme 1. Hydrosilane-induced polymerization of 3-alkyl-
3-alkoxyoxetanes.
were interested in 3-alkyl-3-hydroxymethyloxetanes, which are
easily prepared by dehydration of trihydroxymethylalkanes and
even available from commercial sources.4 Although polymer-
ization of 3-alkyl-3-hydroxymethyloxetanes is expected to be
promoted by Brønsted or Lewis acid with ease, reports in the
literature are not straightforward: polymerization of 3-alkyl-3-
hydroxymethyloxetanes initiated by strong Lewis acid does not
give the corresponding linear polymer but branched or hyper-
branched polyoxetanes.5 Although the cationic polymerization
operating at low temperature reportedly contributes to reduce
the number of polymer branches, completely linear polymer
has never been synthesized from 3-alkyl-3-hydroxymethyl-
oxetanes to our best knowledge.5g,5j,5n,5o Several 3-alkyl-3-
alkoxymethyloxetanes were subjected to cationic polymeriza-
tion and copolymerization to give the linear polymers and
copolymers, however, molecular weight of the formed polymer
is Mn of several thousands.6
1
phenyl group, five H resonances due to CH2Ph, CH2-OBn,
CH2-O of the polymer chain, C-CH2CH3, and C-CH2CH3
appeared at ¤ 4.39 (s), 3.30 (s), 3.25-3.16 (broad AB pattern),
1.39 (q), and 0.79 (t) in CDCl3, of which integral ratio was
2:2:4:2:3. The 13C NMR spectrum showed two signals at ¤ 71.8
and 43.6 which are assignable to methylene and quaternary
carbons of the polymer chain. Signals derived from the pendant
groups were observed at ¤ 73.4 (CH2Ph), 71.5 (CH2-OBn),
23.4 (C-CH2CH3), and 7.82 (C-CH2CH3) besides the phenyl
carbons. These spectroscopic data are consistent with those
expected from poly(EHO-Bn) with a linear polymer chain.
Since signals due to the terminal PhMe2SiO group were visible
1
in H NMR, the number of the repeated monomer units was
In this paper, we wish to report that these oxetane monomers
are polymerized by contact with hydrosilanes and the ruthe-
nium complex 1 (Scheme 1). Notable features compared with
the cationic polymerization are: (1) Silane-induced polymer-
ization of a series of 3-alkyl-3-alkoxymethyloxetanes shown in
Scheme 1 successfully took place to give the corresponding
polyoxetanes of Mn = 103-105; (2) copolymerizations of two
different oxetanes were investigated by two experiments; there
is significant difference in reactivity between two monomers in
the copolymerization of a fluorinated monomer and a monomer
having a glycol unit, whereas reaction profiles of two
monomers in copolymerization of a 3-ethyl-3-benzyloxy-
methyloxetane (EHO-Bn) and 3-ethyl-3-trimethylsiloxymethyl-
oxetane (EHO-SiMe3) are almost the same to give a completely
random polymer; (3) the organosilyl group in the polymer and
copolymers bearing siloxymethyl side chains undergoes acid-
promoted hydrolysis or silyl/acyl exchange by treatment with
acyl chlorides or anhydrides. This gives a way for further
transformation of the polymers or copolymers obtained: (4)
Polymerization of 3-alkyl-3-hydroxymethyloxetanes was pre-
ceded by dehydrogenative silylation of the hydroxy group by
catalysis of 1 to form 3-alkyl-3-siloxymethyloxetanes, which
subsequently underwent silane-induced polymerization to form
estimated by comparison of the integral ratio of the peak due to
the Si-CH3 moiety and the peaks derived from the polymer.
1H NMR spectra of poly(EHO-Bn) of Mn = 2.7 © 104 deter-
mined by GPC (Mw/Mn = 2.3) showed two sharp singlets due
to the Si-CH3 groups at ¤ 0.31 and 0.29 in CDCl3. Since the
polymerization is not stereospecific, it is likely that dual Si-
CH3 peaks appeared. The number of repeated monomer units
was calculated to be 47, which corresponds to Mn
(NMR) = 9.7 © 103. In contrast, that of poly(EHO-Bn) (Mn
(GPC) = 1.4 © 104, Mw/Mn = 1.8) gave a broad signal around
0.60-0.33 ppm in CDCl3, and the number of repeated monomer
units was calculated to be 18, which corresponds to Mn
(NMR) = 3.7 © 103. Although the molecular weights deter-
mined by NMR contain large experimental error, they are
approximately one of third of Mn (GPC) in both cases; similar
tendency was also reported in the silane-induced polymeriza-
tion of THF.3a,7
The polymerization of EHO-Bn is followed by a mechanism
proposed in the ruthenium-catalyzed ring-opening polymeriza-
tion of THF as described in the final part of this paper.3a
Although catalyst 1 is stable to air and moisture, highly active
¹
species R3Si+£[Ru3H] is generated in contact with excess
PhMe2SiH; the R3Si+ species initiates the ring-opening

28
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
Table 1. Homopolymerization of 3-Ethyl-3-benzyloxymethyloxetane (EHO-Bn) Using
Various Hydrosilanesa)
Et
OBn
Et
OBn
O
1
+
H–SiR''3
H
n SiR''3
rt
O
d)
Mn
d)
Entry Hydrosilane
Time
Conv./%b) Yield/%c)
Mw/Mn
¹3
(©10
)
1
2
3
Me2PhSiH
Me2EtSiH
Me2(EtO)SiH
1 min
5 min
5 min
92
92
88
88
73
75
73
84
0
88
79
87
76
73
67
73
83
0
49
2.0
2.0
2.2
2.0
2.5
2.1
2.8
2.3
®
59
52
77
42
99
23
55
®
4
Me3SiOSiMe2SiHMe2 10 min
5e)
6e)
7e)
8e)
9e)
10e)
11e)
MeEt2SiH
(Me3Si)3SiH
Et3SiH
10 min
10 min
6 h
23 h
100 h
100 h
3 h
50
44
45
40
100
26
1.9
2.2
a) All reactions were carried out in the presence of the catalyst (3.3 ¯mol), the silane
(0.33 mmol), and EHO-Bn (3.3 mmol), and 1,4-dioxane (56 ¯L) under an argon
atmosphere at room temperature. b) Determined by 1H NMR. c) Isolated yield of the
polymer after precipitation. d) Determined by GPC (polystyrene standard). e) Among
several experiments we performed, two or three extreme examples are listed.
¹
polymerization of cyclic ethers whereas the [Ru3H] terminates
the propagation by hydride transfer to the carbocation at the
polymer end. As shown in Entries 1-4, Table 1, PhMe2SiH,
EtMe2SiH, Me2(EtO)SiH, and Me3SiOSiMe2SiHMe2 effective-
ly initiated the polymerization of EHO-Bn to give poly(EHO-
Bn) of Mn = 104-105. Since sterically more hindered hydro-
silanes have difficulty in generating active species from 1, the
reaction was not very reproducible. There were three cases
observed for the nonreproducible polymerization with hindered
hydrosilanes; the first case was unsuccessful generation of the
active species leading to no reaction. In the second case, the
reaction of 1 with the hydrosilane was slow and the polymer-
ization was initiated with low concentration of active species;
this provided higher monomer/active species ratio and slower
termination, giving rise to formation of poly(EHO-Bn) with
relatively higher molecular weights. The third case is polymer-
ization giving similar results to that observed for polymeriza-
tion with PhMe2SiH; this occurs especially when monomers
and solvents are highly purified, and the catalyst is activated
very carefully to generate enough amounts of the active species
prior to the addition of the monomer. Among several experi-
ments with Et2MeSiH, Et3SiH, and (Me3Si)3SiH under the
same conditions, two extreme examples in each case selected
are listed in Entries 5-11. The results with Et2MeSiH or
(Me3Si)3SiH giving significant differences in molecular
weights of the formed polymer suggest not steady generation
of active species from 1 and these hydrosilanes (cases 2 and 3).
We experienced all of the above three cases in the reactions
with Et3SiH as shown in Entries 9-11.
8.4 © 104. Attempted polymerization in a ratio of 1/PhMe2-
SiH/monomer = 1:10:5000 was unsuccessful; this is presum-
ably due to the deactivation of the catalyst species in diluting
the catalyst solution by large amounts of monomers (Entry 1).
In a ratio of PhMe2SiH/1 = 100:1, active species was
reproducibly generated to give the polymer in high yields as
shown in Entries 3-5. The reactions were complete in minutes
in the experiments shown in Entries 3 and 4, whereas addition
of larger amounts of the monomer caused decreased concen-
tration of the catalyst leading to the longer reaction time as
shown in Entry 5. The molecular weight is likely to be affected
by the ratio of the active species with the monomer, with larger
amounts of monomer providing polymer with higher molecular
weight [Mn; 1.0 © 104 (Entry 3) < 4.9 © 104 (Entry 4) <
9.6 © 104 (Entry 5)]. The molecular weight is not precisely
controllable by changing the ratio of 1/PhMe2SiH/EHO-Bn
due to the difficulties in quantitative generation of the active
species as well as the temperature control of the exothermic
reaction. Nevertheless, it should be noted that the ratio of active
species with the monomer shown in these experiments is a
rough but successful control factor for the molecular weight in
a range of 103-106. In Entries 6-9 are listed the results of
solution polymerization by increase of the amount of the
solvent from 56 ¯L (other entries) to 670 ¯L. In diluted
solutions, the reaction required longer reaction time for
completion. The temperature of 0 °C was too low to initiate
the active species in a dilute solution, whereas the reaction
smoothly occurred at 30, 40, and 60 °C. The molecular weight
seemed to decrease at higher temperature; but the effect was not
significant.
Above results showed that PhMe2SiH is a good hydrosilane
for the polymerization. In Table 2 are summarized representa-
tive results of polymerization of EHO-Bn with PhMe2SiH.
In a ratio of 1/PhMe2SiH/monomer = 1:10:1000 (Entry 2),
the reaction took place to give poly(EHO-Bn) with Mn =
In Table 3 is summarized polymerization of several 3-alkyl-
3-alkoxymethyl- or 3-alkyl-3-siloxymethyloxetanes with a
1/PhMe2SiH/monomer ratio of 1:100:1000. In the cases of
benzyloxy or siloxy derivatives, the reaction rapidly proceeded

N. Harada et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
Table 2. Homopolymerization of 3-Ethyl-3-benzyloxymethyloxetane (EHO-Bn) Using
29
a)
HSiPhMe2
Et OBn
Et
OBn
O
1
+
H–SiPhMe2
H
SiPhMe2
n
O
e)
Mn
e)
Entry 1/Si-H/monomer T/°C
Time Conv./%c) Yield/%d)
Mw/Mn
¹3
(©10
)
1
2
3
4
1/10/5000
1/10/1000
1/100/100
1/100/1000
1/100/5000
1/100/1000
1/100/1000
1/100/1000
1/100/1000
rt
rt
rt
rt
rt
3 d
10 min
5 min
1 min
18 h
6 h
trace
80
94
92
80
0
69
89
90
®
78
88
88
78
®
67
84
77
®
®
2.1
1.7
2.0
2.1
®
84
10
49
96
®
38
34
28
5
6b)
7b)
8b)
9b)
0
30
40
60
3 h
1 h
1 h
2.1
2.2
2.2
a) All reactions were carried out in the presence of the catalyst (3.3 ¯mol), H-SiPhMe2,
EHO-Bn, and 1,4-dioxane (56 ¯L: Entries 1-5). b) The amount of 1,4-dioxane was
1
670 ¯L. Entries 6-9 under an argon atmosphere. c) Determined by H NMR. d) Isolated
yield of the polymer after precipitation. e) Determined by GPC (polystyrene standard).
a)
Table 3. Homopolymerization of Various 3-Alkyl-3-alkoxymethyloxetanes Using HSiPhMe2
R1
OR2
R1
OR2
O
1
+
H–SiPhMe2
H
n SiPhMe2
O
d)
Mn
d)
Entry
R1
R2
CH2Ph
T/°C
Time
Conv./%b) Yield/%c)
Mw/Mn
¹3
(©10
)
1
2
3
4
5
6
7
8
9
Me
Me
Me
Me
Et
Et
Et
Et
Et
MHO-Bn
MHO-SiMe2Ph
MHO-EG
MHO-Rf
EHO-Bn
EHO-SiMe2Ph
EHO-SiMe3
EHO-TEG
EHO-Rf
rt
rt
rt
rt
rt
rt
rt
rt
80
30 min
5 min
1 h
97
96
78
92
83
78
86
88
95
72
71
42
66
15
97
49
57
31
19
35
2.6
3.6
2.1
2.0
2.0
2.4
2.9
2.1
2.3
SiMe2Ph
[(CH2)2O]2Me
CH2CF2CF3
CH2Ph
SiMe2Ph
SiMe3
99
87
4 h
1 min
5 min
5 min
5 h
92
95
>99
96
[(CH2)2O]3Me
CH2CF2CF3
8 h
95
a) All reactions were carried out in the presence of the catalyst (3.3 ¯mol), PhMe2SiH (0.33 mmol), and monomer
1
(3.3 mmol), and 1,4-dioxane (56 ¯L) under an argon atmosphere. b) Determined by H NMR. c) Isolated yield of the
polymer after precipitation. d) Determined by GPC (polystyrene standard).
to give the corresponding polymer of Mn = 4.0 © 104-
6.0 © 104 with regardless of alkyl group at the 3-position
being methyl or ethyl as shown in Entries 1, 2, and 5-7.
Oxetanes having CH2O(CH2CH2O)2CH3 or CH2OCH2CF2CF3
moieties at the 3-position polymerized slower than their
benzyloxy homologs. The rate was sensitive to the 3-alkyl
group; 3-methyl derivatives underwent the polymerization
within several hours, whereas 3-ethyl derivatives were appa-
rently slower.
Two-Step Conversion of 3-Alkyl-3-hydroxymethyl-
oxetanes to Polymers and Copolymers Bearing Siloxy
Pendants. An OH bearing monomer, MHO-H and EHO-H,
is different from alkoxy derivatives in giving hyperbranched
polymers with the aid of BF3¢OEt2.5 Thus, linear polymeriza-
tion to form polyoxetanes with OH groups at the side chains
is difficult to achieve by cationic initiators. The ruthenium-
catalyzed, silane-induced polymerization is able to solve this
problem, since 1 is a good catalyst for dehydrogenative
silylation of alcohols, which is faster than the ring-opening
polymerization. In a typical example, EHO-H was treated with
PhMe2SiH (2.0 equiv) in the presence of 1 in dioxane or THP
(Table 4, Entries 1 and 2). The reaction showed vigorous
evolution of H2 gas at the initial stage, being complete after
1 h to give poly(EHO-SiPhMe2) of Mn = ca. 2.0 © 104 and
Mw/Mn = around 2.5. 1H and 13C NMR of the formed polymer
were identical to those of poly(EHO-SiPhMe2) prepared by
the ruthenium-catalyzed polymerization of EHO-SiPhMe2; this
suggests that there was no side reaction leading to hyper-
branched polymers.8 As shown in the scheme in Table 4, the
results can be explained by rapid dehydrogenative silylation
of EHO-H to EHO-SiPhMe2, which is preceded by the ring-
opening polymerization.

30
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
Table 4. Homopolymerization of 3-Ethyl-3-hydroxymethyloxetane (EHO-H)a)
Et
OH
Et
OSiPhMe2
H–SiPhMe2
H–SiPhMe2
Et
OSiPhMe2
O
1
1
H
n SiPhMe2
-60 °C
rt
O
O
H–SiPhMe2, 1, rt
T/°C
d)
Mn
d)
Entry
1/Si-H/monomer
Solvent
Time/min
Conv./%b)
Yield/%c)
Mn/Mw
¹3
(©10
)
1
2
3
4
5e)
1:2000:1000
1:2000:1000
1:1100:1000
1:1100:1000
1:1100:1000
dioxane
THP
dioxane
THP
rt
rt
rt
rt
60
60
15
15
45
99
99
93
96
89
96
81
91
78
83
18
22
14
18
55
2.5
2.6
4.3
3.7
2.3
THP
¹60 ¼ rt
a) All reactions were carried out in the presence of the catalyst (3.3 ¯mol) dissolved in 1,4-dioxane or tetrahydropyran (56 ¯L) under an
argon atmosphere. b) Determined by 1H NMR. c) Isolated yield of the polymer after precipitation. d) Determined by GPC (polystyrene
standard). e) The reaction temperature was slowly raised from ¹60 to 11 °C. Dehydrogenative silylation of hydroxy groups was
completed after 8.5 h. When the mixture was warmed to room temperature, polymerization was started and complete after 45 min.
H–SiPhMe2
1 (x = 1 x 10-3)
Me
ORf
Me
OEG
Me
ORf
O
Me
54
OEG
O
+
H
SiPhMe2
40 °C, 1 h
O
O
46
:
(97% conv.)
n
MHO-Rf
(1
MHO-EG
1)
82% yield
Mn = 3.4 x 104; Mw/Mn = 2.8
:
Scheme 2. Copolymerization of MHO-EG and MHO-Rf.
Copolymerization Studies. Copolymerization behavior of
3-alkyl-3-alkoxymethyloxetane is an interesting subject in
considering the effect of side chains. Since the 3-position of
oxetane is remote from the oxygen atom of oxetanes which can
be activated by proton or Lewis acid to initiate the polymer-
ization, it is not likely that substituents at the 3-position
strongly affect the initiation. There is a possibility of
interaction of the alkoxymethyl group at the 3-position with
the cationic polymer terminus waiting for another molecule of
oxetane monomer; however, molecular modeling studies do not
suggest such interactions. Nevertheless, Wynne and co-workers
reported that there is substantial difference in reactivity
between MHO-EG and MHO-Rf.6i In contrast, Feng and co-
workers examined the copolymerization of 3-methyl-3-(meth-
oxyethoxyethoxyethoxymethyl)oxetane [MHO-(CH2CH2O)3-
CH3] and 3-methyl-3-(2-cyanoethoxy)methyloxetane (MHO-
CH2CH2CN).6j They reported that the monomer component
ratio in the polymer obtained was similar to the charged
monomer ratio. This implies that there is little difference
in reactivity between MHO-(CH2CH2O)3CH3 and MHO-
CH2CH2CN.
100
50
MHO-EG
MHO-Rf
0
1
2
3
4
time/h
Figure 1. Copolymerization behavior of MHO-EG and
MHO-Rf at room temperature.
at 40 °C. After 1 h, conversion of the monomers reached >97%
to give poly(MHO-EG-co-MHO-Rf) (MHO-EG/MHO-Rf =
54:46) (Scheme 2). At room temperature, the reaction was
slower, and conversion of the monomer vs. reaction time is
depicted in Figure 1. The monomer reactivity of MHO-
EG > MHO-Rf is similar to that observed in literature.6i
In contrast to the significant difference in monomer
reactivity between MHO-EG and MHO-Rf, PhMe2SiH-induced
homopolymerization of benzyloxy monomers, MHO-Bn and
EHO-Bn, and siloxy monomers, MHO-SiPhMe2, EHO-
SiPhMe2, and EHO-SiMe3 showed similar polymerization
Studies on the ruthenium-catalyzed, silane-induced copoly-
merization of MHO-EG and MHO-Rf revealed that substantial
difference in the reactivity of comonomers as deduced from the
reaction rate of homopolymerization of these monomers as
shown in Table 3. A 1:1 mixture of MHO-EG and MHO-Rf
(5 equiv each to PhMe2SiH) was treated with PhMe2SiH in
the presence of a catalytic amount of 1 (1 mol % to PhMe2SiH)

N. Harada et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
31
Table 5. Copolymerization of EHO-SiMe3 and EHO-Bna)
e)
Mn
e)
Entry
m/nb)
t/min
Conv./%c)
Yield/%d)
Mw/Mn
PhCH2/Me3Sif)
Tg/°C
¹3
(©10
)
1
2
3
4
5
8:2
6:4
5:5
4:6
2:8
5
5
15
5
98
99
99
98
97
98
98
97
92
87
22
22
22
24
17
2.4
2.3
2.2
2.5
2.2
80:20
61:39
50:50
43:57
24:76
¹24.9
¹25.1
¹24.5
¹25.4
¹25.0
5
a) All reactions were carried out in the presence of the catalyst (3.3 ¯mol), H-SiPhMe2 (0.33 mmol), and monomers (EHO-Bn + EHO-
SiMe3 = 3.3 mmol), and 1,4-dioxane (56 ¯L) at room temperature under an argon atmosphere. b) Charged molar ratio of two
1
monomers. c) Determined by H NMR. d) Isolated yield of the polymer after precipitation. e) Determined by GPC (polystyrene
1
standard). f) Ratios of two monomer components in the polymer determined by H NMR.
Et
OBn
O
Et
OBn
O
AcCl (10 equiv)
H
H
n SiPhMe2
n COCH3
benzene
rt, overnight
(>99% conv.)
90% yield
Mn = 2.7 x 104; Mw/Mn = 2.2
Mn = 2.7 x 104; Mw/Mn = 2.3
Scheme 3. Chemical transformation of the poly(EHO-Bn).
of copolymerization of a 1:1 mixture of EHO-SiMe3 and EHO-
1
100
50
Bn indicates that there is no difference in the consumption rate
of two monomers regardless of the reaction time. Similarly, the
component ratio of an EHO-SiMe3 unit with an EHO-Bn
moiety in the formed copolymer was 1:1, which is independent
on the reaction time. These clearly indicates that monomer
reactivity ratio between EHO-SiMe3 and EHO-Bn was close to
one, giving a random copolymer.
X
X
X
X
1
X
0.5
Acylation of the Siloxy Group.10,11 As reported earlier,
the hydrosilane-induced polymerization of cyclic ethers is
effectively catalyzed by 1 to form the polyether, R3SiO-
[(CH2)nO]m-H.3a There is an R3SiO group derived from the
hydrosilane, R3SiH, as an end group of the polymer, which is
assigned by NMR spectroscopy. The polyoxetane described in
this paper also has a PhMe2SiO group at the polymer terminus;
0
0
2
3
4
5
time/h
Figure 2. Copolymerization behavior of EHO-Bn and
EHO-SiMe3: conversion of EHO-Bn ( ) and EHO-SiMe3
( ), and EHO-Bn component in the polymer ( ).
1
in a typical example, poly(EHO-Bn) showed a H and a 13C
resonances at ¤ 0.31 and 0.29 for SiCH3 and ¤ ¹1.84 (br) for
SiCH3 in CDCl3, respectively. The terminal PhMe2Si group
can be transformed to an acetyl moiety by treatment with AcCl
(Scheme 3).10 For instance, a benzene solution of poly(EHO-
Bn) bearing a OSiMe2Ph terminus [Mn (GPC) = 2.7 © 104,
Mw/Mn = 2.3] was treated with AcCl (10 equiv to the PhMe2Si
behavior by catalysis of 1, suggesting not very different
monomer reactivity in the copolymerization of either of two
monomers. As a representative example, we carried out the
copolymerization of EHO-Bn and EHO-SiMe3 in detail.
Treatment of a 1:1 mixture of EHO-Bn and EHO-SiMe3
(5 equiv each to PhMe2SiH) with PhMe2SiH and a catalytic
amount of 1 (x = 1 © 10¹2 to PhMe2SiH) resulted in formation
of the corresponding copolymer in several minutes at room
temperature. In Table 5 are summarized the results of copoly-
merization changing the ratio of two monomers from 1:4-4:1.
In all cases, the copolymers have Mn = 1.7-2.4 © 104, Mw/
1
group) at room temperature overnight. H and 13C resonances
due to the AcO group appeared in regions expectable
[1H NMR: ¤ 1.93 (CH3), 13C NMR: ¤ 20.8 (CH3) and 170.9
(C=O)], and a typical ¯C=O absorption was observed at
1742 cm¹1. GPC profiles before and after the acetylation did
not change. The yield of the acetoxy-terminated polymer was
90% [Mn (GPC) = 2.7 © 104, Mw/Mn = 2.2].7
1
Mn = 2.2-2.5. H NMR and 13C NMR spectra of the copoly-
mer, poly(EHO-SiMe3-co-EHO-Bn) are in coincidence with
sum of those of poly(EHO-Bn), poly(EHO-SiMe3).9 All of the
copolymerization proceeded quantitatively, and the component
ratios of two monomer units in the produced polymers are close
to the charged ratios of two monomers. The reaction was
slowed by diluting with dioxane [EHO-SiMe3 (1.65 mmol)
and EHO-Bn (1.65 mmol) in 670 ¯L of dioxane]; this made
possible observation of the reaction profile seeing consumption
rate of the monomers as shown in Figure 2. The reaction profile
In similar fashion, the siloxy groups at the side chain of the
polyoxetane were converted to the acyloxy group with ease
(Scheme 4). Treatment of a benzene solution of poly(EHO-
SiPhMe2) (Mn = 3.3 © 104, Mw/Mn = 3.2) with AcCl (3.0
equiv) at room temperature for 24 h gave poly(EHO-Ac)
(Mn = 2.6 © 104, Mw/Mn = 2.6) in 82% yield. As a synthetic
method for polyoxetanes having acetoxymethyl side chains,
treatment of insoluble poly[3,3-bis(hydroxymethyl)oxetane]
with large excess of Ac2O at high temperature was reported.6b

32
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
AcCl
(3 equiv)
Et
OCOCH3
O
H
n COCH3
benzene
rt, 24 h
(>99% conv.)
82% yield
Mn = 2.6 x 104; Mw/Mn = 2.6
Et
OSiPhMe2
O
H
n SiPhMe2
Mn = 3.3 x 104; Mw/Mn = 3.2
(CF3CO)2O
(2 equiv)
Et
OCOCF3
O
H
n COCF3
CH2Cl2
rt, 12 h
(>99% conv.)
80% yield
Mn = 3.6 x 104; Mw/Mn = 2.1
Scheme 4. Chemical transformations of poly(EHO-SiPhMe2).
1 (x = 1 x 10-3)
Et
OH
Et
OSiPhMe2
Et
OSiPhMe2
O
HSiPhMe2 (1.1 equiv)
H
n SiPhMe2
dioxane
0 °C, 30 min
(43% conv.)
rt, 15 min
O
O
>99% conv.
Mn = 3.1 x 104; Mw/Mn = 3.0
Et
H
OCOCF3
O
(CF3CO)2O (2 equiv to OSiPhMe2)
nCOCF3
Tg = -23.2 °C
m = 25–40 °C
CH2Cl2
rt, overnight
(>99% conv.)
T
72% yield
Mn = 3.3 x 104; Mw/Mn = 2.1
Scheme 5. Synthesis of poly(EHO-COCF3) from EHO-H.
The procedure presented in this paper is apparently more useful
than the previous method in the points that hydrosilane-induced
polymerization provides soluble siloxypolyoxetane and the
subsequent PhMe2Si/Ac exchange proceeds under mild con-
ditions using a small amount of AcCl. Trifluoroacetylation
was also possible; poly(EHO-SiPhMe2) (Mn = 3.3 © 104,
Mw/Mn = 3.2) was treated with (CF3CO)2O (2 equiv to the
polymer) in CH2Cl2 at room temperature for 12 h to give a
polymer showing typical signals of CF3CO groups [19F NMR:
¤ ¹78.3 (CF3), IR: ¯C=O 1787 cm¹1] in 80% yield.11
The utility of dehydrogenative silylation/ring-opening poly-
merization of EHO-H described above was emphasized by
combination with the OSi/OCOR exchange of the formed
siloxy polymers. For example, a tandem procedure consisting
of dehydrogenative silylation of EHO-H (1/Si-H/mono-
mer = 1:1100:1000) at 0 °C, polymerization at room temper-
ature, and trifluoroacetylation in CH2Cl2 gave poly(EHO-
COCF3) (Mn = 3.3 © 104, Mw/Mn = 2.1) in 72% yield based
on the charged EHO-H (Scheme 5).
One-Pot Synthesis of Acyloxy/Benzyloxy Copolymers.
By taking advantage of almost identical reactive monomer ratio
of EHO-Bn and EHO-SiPhMe2, random copolymers of EHO-
Bn and EHO-COR were also synthesized in one-pot starting
from a mixture of EHO-Bn and EHO-H. The component ratio
of EHO-Bn and EHO-COR was precisely controlled by the
charged ratio of EHO-Bn and EHO-H. In a typical example, a
1:1 molar ratio of EHO-Bn and EHO-H was treated with a
slightly excess amount of PhMe2SiH to EHO-H at 0 °C then
room temperature followed by trifluoroacetylation or acetyla-
tion to give poly(EHO-Bn-co-EHO-COCF3) (71% isolated
yield; EHO-Bn/EHO-COCF3 = 50:50) or poly(EHO-Bn-co-
EHO-COCH3) (88% isolated yield; EHO-Bn/EHO-COCH3 =
49:51) as shown in Scheme 6.
Hydrolysis of Silyl Groups and Its Application to
Synthesize Hydroxy/Benzyloxy Copolymer. As described
above, chemical transformation of siloxy groups by acyl groups
has made possible preparation of polyoxetane with acyloxy
pendants. An alternative chemical transformation of siloxy
groups is hydrolysis, which can produce polyoxetane polyols
(Table 6). As typical examples, poly(EHO-SiMe3) and poly-
(EHO-Bn-co-EHO-SiMe3) were subjected to acid-promoted
hydrolysis (Table 6). In a typical example, poly(EHO-Bn-co-
EHO-SiMe3) (EHO-Bn/EHO-SiMe3 = 50:50, Mn = 2.6 © 104,
Mw/Mn = 2.1) dissolved in toluene was treated with HCl/
MeOH at room temperature overnight. After removal of the
solvent, the residue was purified by precipitation twice from
THF/hexane to give poly(EHO-Bn-co-EHO-H) (EHO-Bn/
EHO-H = 47:53) in 92% yield (Entry 3). The GPC profiles
before and after the hydrolysis are almost identical; this
indicates that no side reaction involving degradation of the
polyoxetane chain occurred. NMR analyses of copolymers
before and after the hydrolysis showed that signals due to the
organosilyl groups disappeared, and change of chemical shifts
suggesting CH2OSi ¼ CH2OH was observed [1H NMR: ¤ 3.40
to 3.51 (CH2); 13C NMR: ¤ 63.2 to 67.6-64.5 (CH2)].
Hydrolysis of the homo- and copolymers shown in Table 6
showed that polarity of the polymer chain was apparently
increased by conversion of OSiMe3 moieties to OH groups; this
is typically seen in solubility of the polymers to organic
solvents. Typically, poly(EHO-H) shown in Entry 6 is not

N. Harada et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
33
Et
Et
OBn
OH
Et
Et
OBn
O
+
O
+
Et
OBn
O
Et
OSiPhMe2
O
a)
b)
H
SiPhMe2
OSiPhMe2
n
>99% conv.
Mn = 2.1 x 104; Mw/Mn = 2.1
O
O
(EHO-Bn/EHO-H = 1:1)
(CF3CO)2O
(2 equiv to OSiPhMe2)
Et
OBn
O
Et
OCOCF3
O
H
(eq 1)
COCF3
CH2Cl2
rt, overnight
(>99% conv.)
50
:
50
n
71% yield
Mn = 2.4 x 104; Mw/Mn = 1.8
Tg = -27.0 °C
Et
Et
OBn
OH
Et
Et
OBn
O
+
O
+
Et
OBn
O
Et
OSiPhMe2
O
a)
b)
H
SiPhMe2
OSiPhMe2
53
Et
:
47
n
O
O
90% conv.
(EHO-Bn/EHO-H = 1:1)
AcCl
(3 equiv to OSiPhMe2)
Et
OBn
O
OCOCH3
H
(eq 2)
COCH3
O
toluene
rt, 10 h
49
:
51
n
(>99% conv.)
88% yield
Mn = 3.1 x 104; Mw/Mn = 2.2
Tg = -19.4 °C
Conditions: a) 1 (x = 1 x 10-3)/PhMe2SiH (0.6 equiv)/dioxane/0 °C/30 min ( 50–60% of EHO-H was converted
to EHO-SiPhMe2); b) rt/15 min (both dehydrogenative silylation of EHO-H and polymerization proceeded)
Scheme 6. One-pot synthesis of acyloxy/benzyloxy copolymers.
Table 6. Hydrolysis of Poly(EHO-Bn-co-EHO-SiMe3) to Poly(EHO-Bn-co-EHO-H)a)
Before hydrolysis
After hydrolysis
EHO-Bn
/EHO-SiMe3
Entry
Conv./%b)
Yield/%
b)
Mn (©10
)
Mw/Mn
EHO-Bn/EHO-Hb) Mn (©10
)
Mw/Mn
c)
¹3
c)
c)
¹3
c)
1
2
3
4
5
6
80:20
59:41
50:50
40:60
23:77
0:100
>99
>99
>99
>99
>99
>99
88
90
92
87
85
90
29
26
26
29
17
17
2.3
2.2
2.1
2.3
2.2
2.1
80:20
59:41
47:53
40:60
24:76
0:100
27
22
21
23
14
®
2.7
2.3
2.2
2.3
2.4
d)
d)
®
a) The polymers listed in this Table were treated with HCl/MeOH (5 equiv to O-SiMe3) in toluene at room temperature overnight.
1
b) Determined by H NMR. c) Determined by GPC in THF calibrated by the polystyrene standard. d) GPC failed due to the low
solubility of the polymer.
soluble in polar organic solvents or water presumably due to
strong interchain hydrogen bonding. As described above, there
is essentially no difference in monomer reactivity between
EHO-Bn and EHO-SiMe3; this gives a good preparative way to
random copolymers of which component ratio is controllable
by the charged monomer ratio. Combination of this copoly-
merization with the hydrolysis achieves preparation of copoly-
mers in which the nonpolar component EHO-Bn and the highly
polar component EHO-H, of which ratio can be controlled, is
randomly distributed.

34
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
DSC Studies of the Homopolymers and Copolymers. As
described above, a feature of the polymers and copolymers of
substituted oxetanes formed by hydrosilane-induced polymer-
ization catalyzed by 1 is facile introduction of siloxy or alkoxy
groups as substituents of the polyoxetane side chain. It is
important that the siloxy group can be transformed to either
acyloxy or hydroxy group; this emphasizes the utility of the
silane-induced polymerization as a preparative method for
polyoxetane having a variety of pendant groups. The pendant
groups are expected to give interesting properties to the
polymers. As introductory experiments to access desired
properties of polyoxetanes, we carried out DSC analyses of
the homo- and copolymers synthesized in this study. DSC
measurements of several polyoxetanes have appeared in
literature.12,13 Parent polyoxetane with no side chains report-
edly shows a change of DSC curve with a reflection point at
¹71 °C, an exothermic peak at ¹30 °C, an endothermic peak at
20 °C at heating rate of 10 °C min¹1, which are assignable to Tg,
cold crystallization, and Tm, respectively.12 DSC analyses of
poly(3,3-dialkyloxetane), where alkyl = Me, Et, n-Pr, n-Bu,
and t-Bu, showed glass transition in temperature range from
¹50 to ¹4 °C;13 the Tg values of these polyoxetanes are higher
when the alkyl groups in the side chain are bulky. As DSC
studies on polymers of EHO and MHO derivatives, homo- and
copolymers of MHO-(CH2O)3OCH3 and MHO-CH2CH2CN
were investigated; Tg of these were observed in a temperature
range of ¹52 to ¹18 °C.6j Tg of the copolymers are according
to the Fox equation (Tg(cal)¹1 = w1Tg1¹1 + w2Tg2¹1).14 In DSC
of the homo- and copolymers of MHO-(CH2O)2OCH3 and
MHO-Rf (Rf = CH2CF2CF3), Tg was observed from ¹67.3 to
¹43.5 °C (heating rate: 20 °C min¹1).6i
In Figure 3 and Table 7 are summarized DSC data (heating
rate: 10 °C min¹1) of homopolymers of EHO and MHO
prepared by the present method. A change of DSC curve with
a reflection point assignable to Tg was observed on DSC of
homopolymers, in which Tg was dependent on the func-
tional groups of the side chain; Tg of polyEHO; R2 = CH2Ph
and SiMe3 (ca. ¹20 °C) > SiMe2Ph and CH2CF2CF3 (ca.
¹35 °C) > TEG (¹77.2 °C). There was no significant differ-
ence in Tg between polyEHO and polyMHO as long as the
functional group of the side chain is identical. In contrast to
the fact that the siloxy or alkoxy polyoxetanes did not show
a peak suggesting melting point, the polymers having OH,
OCOCH3, and OCOCF3 groups showed a strong endothermic
peak assignable to Tm. DSC of poly(EHO-H) showed a broad
strong endothermic peak at 132 °C assignable to Tm besides
two small changes of DSC curve with a reflection point at
46.9 and 87.9 °C. Poly(EHO-Ac) is interesting in showing
only one strong Tm peak at 66.7 °C. In several runs of DSC
measurements of poly(EHO-COCF3), a change of DSC curve
with a reflection point at ¹23.2 °C, presumably due to Tg,
always appeared, whereas a weak peak which may be
assignable to Tm seen at 25-40 °C was observed (not always
reproducible). These features in DSC can be roughly
explained by considering the interaction of functional
group-functional group between polymer chains. The high
melting point observed for poly(EHO-H) may be explained
by the interpolymer chain hydrogen bonding of OH groups,
while weak polar acetoxy-acetoxy interaction may be the
poly(EHO-Ac)
Exothermic
poly(EHO-TEG)
poly(EHO-Bn)
Endothermic
-150
-100
-50
0
50
100
Temperature/°C
Figure 3. DSC curves of poly(EHO-Ac), poly(EHO-TEG),
and poly(EHO-Bn). The measurements were done by
raising the temperature from ¹100 to 100 °C with the
¹1
heating rate of 10 °C min
.
Table 7. DSC Data of EHO- and MHO-Derived Homopolymers
Mn
a)
Entry R1 R2
Mw/Mn
Tg/°C
Tm/°C
¹3 a)
(©10
)
b)
1
2
3
4
5
6
7
8
9
Et CH2Ph
27
25
31
10
35
®
26
36
42
66
2.3
3.6
2.9
3.2
2.3
¹24.7
¹33.8
¹22.3
¹77.2
¹36.6
®
®
b)
SiMe2Ph
SiMe3
TEG
CH2CF2CF3
H
COCH3
COCF3
b)
®
®
b)
b)
®
c)
c)
®
46.9, 87.9 131.9
b)
2.6
2.1
2.6
3.6
3.1
2.0
®
66.7
¹23.2 25-40d)
b)
Me CH2Ph
¹22.7
¹34.3
¹74.1
¹46.6
®
®
®
®
b)
b)
b)
10
11
12
SiPhMe2
EG
CH2CF2CF3
8.7
97
a) Mn, Mw/Mn of copolymer was calculated by GPC (solvent
was THF; polystyrene standard). b) Not detected. c) GPC was
not measurable because of low solubility of the formed
polymer in THF. d) Tm changed in the range from 25 to 40 °C
in some measurements.
reason for the Tm of poly(EHO-Ac). In the case of
poly(EHO-COCF3), the polar interaction due to the
£
¤+C=O¤¹ ¤+C=O¤¹ is mitigated by CF3-CF3 repulsion to
give Tg instead of Tm.
The DSC studies on copolymers are summarized in
Tables 8 and 9. Poly(EHO-Ac-co-EHO-Bn) (EHO-Ac/EHO-
£
Bn = 50:50) showed Tg at ¹19 °C. The ¤+C=O¤¹ ¤+C=O¤¹
interaction giving strong interpolymer chain interaction is
mitigated by introduction of Bn groups. Poly(EHO-COCF3-co-
EHO-Bn) (EHO-COCF3/EHO-Bn = 50:50) showed Tg at
¹27 °C. The data of poly(MHO-Rf-co-MHO-TEG) (heating
rate: 10 °C min¹1) are similar to those reported by Wynne
(heating rate: 20 °C min¹1) in considering the difference in the
heating rates. They are also in accord with Tg (¹61.4 °C)
calculated from the Fox equation.14 The DSC data of copoly-
mers, poly(EHO-Bn-co-EHO-H), are dependent on the copoly-
mer ratio; as expected, the increased ratio of OH resulted in

N. Harada et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
35
Table 8. DSC Data of Copolymers
R1
R2
R3
R2/R3 a)
Mn (©10
)
Mw/Mn
Tg/°C
Tm/°C
b)
¹3
b)
Entry
c)
1
2
3
4d)
Et
Et
Me
Me
COCH3
COCF3
CH2CF2CF3
CH2CF2CF3
CH2Ph
CH2Ph
EG
51:49
50:50
46:54
50:50
31
24
34
2.2
1.8
2.8
¹19.4
¹27.0
¹65.2
¹56.9
®
®
c)
c)
®
®
c)
EG
3.7-4.5
1.9-2.8
1
a) Determined by H NMR. b) Mn, Mw/Mn of copolymer was calculated by GPC (solvent was THF; polystyrene standard). c) Not
detected. d) Ref. 6i.
Table 9. DSC Data of Poly(EHO-Bn-co-EHO-H)a)
Mn
(©10
c)
Exothermic
Entry EHO-Bn/EHO-Hb)
Mw/Mn
Tg/°C Tm/°C
¹3 c)
)
Bn/H = 8:2
d)
1
2
3
4
5
6
7
100:0
80:20
59:41
47:53
40:60
24:76
0:100
27
27
22
21
23
14
®
2.3
2.7
2.3
2.2
2.3
2.4
¹24.7
¹15.2
0.9
2.2
12.4
35.3
®
®
®
®
®
d)
d)
d)
d)
Bn/H = 1:1
131.0
46.9, 87.9 131.9
e)
e)
®
Endothermic
Bn/H = 0:1
150 200
a) The measurements were done from ¹100 to 220 °C
(10 °C min¹1). b) Determined by H NMR. c) Mn, Mw/Mn of
copolymer was calculated by GPC (solvent was THF;
polystyrene standard). d) Not detected. e) Low solubility of
the formed polymer in THF made GPC difficult.
1
-100
-50
0
50
100
Temperature/°C
Figure 4. DSC curves of poly(EHO-Bn-co-EHO-H)
copolymers. The measurements were done by raising the
temperature from ¹100 to 220 °C with the heating rate of
species are necessary for reproducible polymerizations in dilute
solutions and those of lower 1/Si-H ratio. The molecular
weight of the formed polymer is dependent on the concen-
¹1
10 °C min
.
¹
increase of Tg as shown in Figure 4 and Table 9, Entries 1
(EHO-Bn/EHO-H = 100:0)-5 (40:60). Copolymers of (EHO-
Bn/EHO-H = 24:76) showed Tm at 131 °C. Similar to the
result of poly(EHO-Ac-co-EHO-Bn), interchain hydrogen
bonding in poly(EHO-Bn-co-EHO-H) possibly gives Tm;
however, it was not seen in poly(EHO-Bn-co-EHO-H) of
(EHO-Bn/EHO-H = 80:20-40:60) because the hydrogen
bonding is prevented by benzyloxy groups in the copolymer.
tration of R3Si+ species as the initiator and that of [Ru3H] as
the terminator. The propagation is competitive with the hydride
¹
transfer from the [Ru3H] species; however, it is fast enough
to produce the polymer of Mn = 103-105 under the standard
conditions. The results shown in Entries 3-5 of Table 2 suggest
that the molecular weight would become higher in increas-
ing the monomer concentration, if uniform amounts of
¹
R3Si+£[Ru3H] species can be generated in the reaction
Mechanistic Consideration.
As noted earlier, the
medium. Since the polymerization is not living, precise control
of the molecular weight by appropriate choice of the monomer,
the hydrosilane, and the catalyst is impossible. The molecular
weight was determined by the concentration of the active
species, which is affected by both initiation and termination
steps, and by that of monomer. In an ideal case, in which active
species equal to the amount of the catalyst is generated, the rate
of the initiation and termination would be stable. Thus, the
monomer concentration is a key to determine the molecular
weight. In a real system, the active species is generated by
treatment of the Ru3 cluster and the hydrosilane. The Ru3
cluster is stable and the reaction with the hydrosilane is slow
even if large excess amounts of hydrosilane is used for the
initiation. Under the circumstances, the concentration of the
active species is not always the same at the initiation of
polymerization. Thus, the molecular weight of the polymer is
roughly controllable by changing the ratio of the monomer
and the hydrosilane, but contains large experimental errors.
At present stage, the molecular weight control is roughly
accomplished by the choice of 1/R3SiH/monomer ratio;
however, the results implicate that discovery of the catalyst
polymerization mechanism for the ruthenium-catalyzed ring-
opening polymerization of hydrosilanes was proposed in our
previous papers.3 As evidenced by isolation of intermediary
ruthenium clusters having Ru-Si and Ru-H bonds, the reaction
of 1 with R3SiH results in activation of the Si-H bond to give a
catalytically active species, R3Si[Ru3H], which generates ion
¹
pair, R3Si+£[Ru3H] , in solution. The R3Si+ species activates
the oxetane monomer to initiate the polymerization. The
termination occurs by hydride transfer from the [Ru3H] to the
¹
cationic species at the polymer end (Figure 5). The catalyst 1 is
a stable solid and can be stored over years under aerobic
conditions. In contact with excess R3SiH, air- and moisture-
sensitive R3Si[Ru3H] was generated in dioxane, which pro-
motes exothermic polymerization of the oxetane under the
standard conditions. The stability of 1 has the advantage of
easy handling, but is not good for instant and quantitative
generation of the active species, especially when sterically
hindered compounds are used as a hydrosilane. Since the active
species is sensitive toward air and moisture, purification of the
monomer and the solvent and careful generation of the active

36
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
R1
OR2
monomer
O
[Ru3–H]
monomer
SiR3
R3Si–H
R1
OR2
(excess)
…
[Ru3–H]
1
R3Si
O
R3Si
(Catalyst Precursor)
O
[Ru3–H]
R3Si–H
R2O
R1
[Ru3]
R1
OR2
monomer
O
polyoxetane
R3Si
n
O
[Ru3–H]
R2O
R1
Figure 5. Proposed catalytic cycle.
precursor which generates the active species quantitatively as
soon as contact with the hydrosilane leads to more precise
control of the molecular weight.
obtained were investigated, showing that this polymerization is
an interesting and useful entry to polyoxetane-based polymer
materials.15
Conclusion
Experimental
The present polymerization procedure initiated by hydro-
silane and a catalytic amount of a triruthenium cluster 1 has
provided a convenient and reliable method for synthesis of
polyoxetane with a variety of pendant functional groups. In
contrast to the fact that conventional cationic polymerization
of EHO-R and MHO-R (R = alkyl group) gives polymer of
relatively low molecular weight, the present method gave
polymer of Mn = 103-105. Application of the present reaction
to polymerization of EHO-H gave a linear polymer EHO-SiR3;
this is interesting in that cationic polymerization of EHO-H
gives hyperbranched polymers. An interesting result was
obtained from copolymerization of EHO-Bn and EHO-SiMe3,
in which there is no difference in monomer reactivity ratio to
give random copolymers with a component ratio identical to
the charged monomer ratio. This is particularly important in
producing copolymers with interesting properties in combina-
tion with facile chemical transformation of organosilyl func-
tional groups to others. Typical two examples are OSiR3/
OCOR exchange by treatment with RCOCl and hydrolysis
of OSiR3 moieties to OH groups. Nonpolar OSiR3 group is
converted to polar OCOR or OH groups by this chemical
transformation. These polar polymers and copolymers can be
prepared in one-pot connecting the silane-induced polymer-
ization and chemical transformation of OSiR3 groups. The
results described in this paper suggest that chemists can
synthesize polyoxetanes having a variety of properties which
are available by appropriate design of the pendant functional
groups. As the simplest examples of design of polymer
property, DSC analyses of the polymers and copolymers
1H, 13C, 19F, and 29Si NMR spectra were measured on a
JEOL GSX-270 (270 MHz), ECA 400 (396 MHz), and ECA
600 (600 MHz) spectrometers. Chemical shifts for 1H NMR are
described in parts per million downfield from tetramethylsilane
as an internal standard (¤ = 0) in CDCl3, unless otherwise
noted. Chemical shifts for 13C NMR are expressed in parts per
million in CDCl3 as an internal standard (¤ = 77.1), unless
otherwise noted. Chemical shifts for 19F NMR are described
in parts per million downfield from trifluoroacetic acid as
an external standard (¤ = ¹79 ppm). Chemical shifts for
29Si NMR were described in parts per million downfield from
tetramethylsilane as an external standard. IR spectra were
measured on a JASCO FT/IR-4200 spectrometer. GPC analy-
sis was performed with a JASCO-GPC system consisting of
DG-1580-53 degasser, PU-980 HPLC pump, UV-970 UV-vis
detector, RI-930 RI detector, and CO-2065-plus column oven
(at 40 °C) using two connected Shodex GPC-KF-804L columns
in THF (sample concentration: w = 1 © 102; flow rate = 1.0
mL min¹1). The molecular weight was calibrated with a
commercially available polystyrene (Shodex: SM-105); seven
standard solutions, of which Mn range from 1.31 © 103 to
7.36 © 105 (Mw/Mn = 1.07). A DSC 6220 (Seiko Instruments
Inc.) was used for analyses of the thermal behavior of the
polymers. The polymer samples (5-15 mg) were pretreated at
100 °C under reduced pressure (0.05 Torr) overnight and cooled
to ¹100 °C by liquid nitrogen. The measurements were done
from ¹100 to 100 °C in aluminum pans under N2 flow (13-
¹1
50 mL min¹1) with a heating rate of 10 °C min
unless
otherwise noted. [Ru3{®3-(©2,©3,©5-C12H8)}(CO)7] (1) was

N. Harada et al.
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011)
37
prepared according to a method reported previously.16 Hydro-
silanes listed in Table 1 and HCl/MeOH reagent (ca. 5-10%
HCl) are purchased from Tokyo Chemical Industry Co., Ltd. or
Chisso. Monomers, EHO-H, EHO-Bn, MHO-H, and MHO-Bn
were donated from Ube Industries. Other monomers shown in
Scheme 1 were prepared from MHO-H or EHO-H as summa-
rized in the Supporting Information. All reactions were carried
out in a reaction vessel dried by heat gun under vacuum just
before use under an argon atmosphere.
Dehydrogenative Silylation Followed by the Silane-
Induced Polymerization of 3-Ethyl-3-hydroxymethyl-
oxetane (Table 4, Entry 3). In a 20 mL two-necked flask,
1 (2.15 mg, 3.3 ¯mol) was dissolved in dioxane (60 ¯L). To this
solution, PhMe2SiH (495 mg, 3.63 mmol) was added and the
mixture was stirred at ambient temperature for 30 min. At this
point, the initial orange color of the solution darkened. Then,
EHO-H (383 mg, 3.3 mmol) was added dropwise and the
mixture was stirred at room temperature. The reaction was
exothermic and vigorous evolution of H2 gas was observed at
the initial stage. The viscosity of the reaction mixture gradually
increased. After 15 min, the reaction was complete. The
reaction mixture was dissolved in benzene (6 mL). The benzene
solution was poured into MeOH (20 mL) to precipitate the
polymer. Yield 91% (760 mg); Mn = 1.4 © 104, Mw/Mn = 4.3;
1H NMR (396 MHz, CDCl3): ¤ 7.54-7.49 (m, 2H, Ph), 7.34-
7.26 (m, 3H, Ph), 3.43 (s, 2H, CH2-OSi), 3.19-3.09 (m, 4H,
CH2-O of polymer chain), 1.32 (q, J = 7.7 Hz, 2H, C-
CH2CH3), 0.76 (t, J = 7.7 Hz, 3H, C-CH2CH3), 0.29 (s, 6H,
Si-CH3); 13C NMR (99.5 MHz, C6D6): ¤ 139.0 (ipso-Ph), 134.3
(o-Ph), 130.3 ( p-Ph), 128.6 (m-Ph), 72.5 (CH2-O of polymer
chain), 64.6 (CH2-OSi), 45.0 (C-Et), 23.9 (C-CH2CH3), 8.8
(C-CH2CH3), ¹1.1 (Si-CH3).
A Typical Procedure for the Silane-Induced Polymeriza-
tion of 3-Alkyl-3-alkoxymethyloxetane. In a 20 mL two-
necked flask, 1 (2.15 mg, 3.3 ¯mol) was dissolved in a
minimum amount of dioxane (typically, 60 ¯L). To this
solution, PhMe2SiH (50 ¯L, 0.33 mmol) was added, and the
mixture was stirred at ambient temperature for 30 min. The
initial orange color of the solution was darkened. Then, the
monomer EHO-Bn (681 mg, 3.3 mmol) was added dropwise
and the mixture was stirred at room temperature. The reaction
was exothermic and viscosity of the reaction mixture was
gradually increased. After the reaction was complete, the
reaction mixture was dissolved in benzene (6 mL). The benzene
solution was poured into MeOH (20 mL) to precipitate the
polymer. Filtration followed by removal of the solvent
remained in vacuo gave poly(EHO-Bn) in 86% yield
Chemical Transformation of the Copolymer, Poly(EHO-
SiMe3-co-EHO-Bn). Hydrolysis: Silylated polymers are
subjected to protodesilylation with HCl in MeOH. In a typical
example, the copolymer, poly(EHO-SiMe3-co-EHO-Bn)
(EHO-SiMe3/EHO-Bn = 50:50, Mn = 2.6 © 104, Mw/Mn =
2.1; 575 mg, 2.91 mmol, 1.46 mmol of SiMe3 group) dissolved
in dry toluene (12 mL) was treated with HCl/MeOH (5-10%
HCl; 5.31 g) at room temperature overnight. After removal
of the solvent, the residue was dissolved in THF (5 mL). To
the THF solution, hexane (20 mL) was added to precipitate
poly(EHO-H-co-EHO-Bn). Yield 92% (431 mg; EHO-H/
1
(586 mg). Mn = 4.9 © 104, Mw/Mn = 2.0; H NMR (396 MHz,
CDCl3): ¤ 7.37-7.16 (m, 5H, Ph), 4.39 (s, 2H, CH2Ph), 3.30 (s,
2H, CH2-OBn), 3.25-3.16 (brs, 4H, CH2-O of polymer chain),
1.39 (q, J = 7.7 Hz, 2H, C-CH2CH3), 0.79 (t, J = 7.7 Hz, 3H,
C-CH2CH3); 13C NMR (99.5 MHz, CDCl3): ¤ 139.2 (ipso-Ph),
128.3, 127.29 (o- and m-Ph), 127.26 ( p-Ph), 73.4 (CH2Ph),
71.8 (CH2-O of polymer chain), 71.5 (CH2-OBn), 43.6 (C-Et),
23.4 (C-CH2CH3), 7.82 (C-CH2CH3).
A typical example for the copolymerization is as follows:
In a 20 mL Schlenk tube, 1 (2.15 mg, 3.3 ¯mol) was dissolved
in dioxane (60 ¯L). To this solution, PhMe2SiH (50 ¯L,
0.33 mmol) was added and the mixture was stirred at room
temperature for 30 min. A mixture of EHO-Bn (340 mg,
1.65 mmol) and EHO-SiMe3 (311 mg, 1.65 mmol) was added
and the mixture was stirred at room temperature. The reaction
was exothermic and viscosity of the reaction mixture gradually
increased. After the reaction was complete, the reaction mixture
was dissolved in benzene (6 mL). The benzene solution was
poured into MeOH (20 mL) to precipitate the polymer.
Filtration followed by removal of the solvent remained in
vacuo gave poly(EHO-SiMe3-co-EHO-Bn) in 97% yield
(631 mg; EHO-SiMe3/EHO-Bn = 50:50 by 1H NMR). Mn =
2.2 © 104, Mw/Mn = 2.2; 1H NMR (396 MHz, CDCl3): ¤ 7.38-
7.17 (m, 5H, Ph), 4.42 (brs, 2H, CH2Ph), 3.40 (brs, 2H, CH2-
OSi), 3.32 (brs, 2H, CH2-OBn), 3.28-3.07 (m, 8H, CH2-O of
polymer chain), 1.46-1.24 (m, 4H, C-CH2CH3), 0.86-0.74 (m,
6H, C-CH2CH3), 0.10-0.01 (m, 9H, Si-CH3); 13C NMR
(67.8 MHz, CDCl3): ¤ 139.3 (ipso-Ph), 128.3 (Ph), 127.4
(Ph), 127.3 (Ph), 73.4 (CH2Ph), 71.9, 71.7, 71.6 (CH2-O of
polymer chain and C-OBn), 63.3 (C-OSi), 43.9 (C-Et derived
from EHO-SiMe3), 43.7 (C-Et derived from EHO-Bn), 23.5
(C-CH2CH3 of EHO-Bn moiety), 23.0 (C-CH2CH3 derived
from EHO-SiMe3), 8.0 (C-CH2CH3), ¹0.4 (Si-CH3);
29Si NMR (119 MHz, CDCl3): ¤ 16.8-16.6 (O-SiMe3), 6.8-
6.6 (OSiMe2Ph of the polymer end).
EHO-Bn = 53:47); Mn = 2.1 © 104, Mw/Mn = 2.2; IR (film):
1
¯
3434 cm¹1; H NMR (600 MHz, CDCl3): ¤ 7.36-7.20 (br,
OH
5H, Ph), 4.49-4.39 (m, 2H, CH2Ph), 3.51 (brs, 2H, CH2OH),
3.39-3.15 (m, 10H, CH2-O of polymer chain and CH2-OBn),
1.44-1.24 (m, 4H, C-CH2CH3), 0.81 (brs, 6H, C-CH2CH3);
13C NMR (99.5 MHz, CDCl3): ¤ 139.2-138.4 (m, ipso-Ph),
128.2 (o- or m-Ph), 127.7-126.8 (m, o- or m-Ph and p-Ph),
74.5-70.5 (m, CH2-O of polymer chain, CH2Ph and C-OBn),
67.6-64.5 (m, CH2OH), 43.8-42.8 (m, C-Et), 23.7-22.7 (C-
CH2CH3), 7.7 (brs, C-CH2CH3); Tg = 2.2 °C.
Organosilyl/Acyl Exchange; Terminal Silyl Group: The
following is a typical example: poly(EHO-Bn) (294 mg)
prepared by a procedure described above, of which Mn was
estimated as 2.7 © 104 (GPC) and 9.7 © 103 (1H NMR),
contained 30.3 ¯mol of PhMe2SiO group. This was dissolved
in benzene (5 mL), and treated with acetyl chloride (22 ¯L,
0.30 mmol) at room temperature for 18 h. After removal of the
volatiles, the residue was dissolved in ether (50 mL). The ether
solution was washed with aqueous NaHCO3. The aqueous
layer was extracted five times with ether. The combined
extracts were dried over MgSO4 and the solvent was removed
under reduced pressure. Then the residue was dissolved in a
mixture of ether (3 mL) and MeOH (15 mL) and the solution
was stored at ¹30 °C for 24 h to give the polymer as a
precipitate. Yield 90% (265 mg); Mn = 2.7 © 104, Mw/Mn =

38
Bull. Chem. Soc. Jpn. Vol. 84, No. 1 (2011) BCSJ AWARD ARTICLE
2.2 (determined by GPC); Mn = 7.0 © 103 (determined by
polymer chain), 2.05-1.92 (m, 3H, CH3 of Ac), 1.38 (brs, 4H,
C-CH2CH3), 0.80 (brs, 6H, C-CH2CH3); 13C NMR (99.5 MHz,
CDCl3): ¤ 171.0-170.8 (C=O), 139.2-139.0 (ipso-Ph), 128.3-
128.2 (m, Ph), 127.4-127.2 (m, Ph), 73.4 (O-CH2Ph), 71.9-
71.2 (m, CH2-O of polymer chain), 65.6-65.1 (CH2-OAc),
43.6-43.5 and 42.5 (m, CH2-O of polymer chain and C-Et),
¹1
1H NMR); IR (film): ¯C=O 1742 cm
;
1H NMR (600 MHz,
CDCl3), signals due to the polymer chain: ¤ 7.31-7.16 (m, 5H,
Ph), 4.40 (s, 2H, CH2Ph), 3.30 (s, 2H, CH2-OBn), 3.25-3.16
(m, 4H, CH2-O of polymer chain), 1.38 (q, J = 7.3 Hz, 2H,
CH2 of Et), 0.79 (t, J = 7.3 Hz, 3H, CH3 of Et). Small peaks
due to the terminal acetyl group were visible at ¤ 2.01-1.89 (m,
CH3 of Ac); 13C NMR (99.5 MHz, CDCl3), signals due to the
polymer chain: ¤ 139.1 (ipso-Ph), 128.2 (o- or m-Ph), 127.3
(o- or m-Ph), 127.2 ( p-Ph), 73.4 (O-CH2Ph), 71.8 (CH2-O of
the polymer chain), 71.5 (C-OBn), 43.6 (C-Et), 23.5 (C-
CH2CH3), 7.9 (C-CH2CH3). Small peaks due to the terminal
acetyl group were visible at ¤ 170.9 (C=O), 20.9 (CH3 of
Ac).
23.5-23.2 (C-CH2CH3), 20.9 (CH3 of Ac), 7.92-7.62 (m,
¹1
C-CH2CH3); DSC (10 °C min
¹19.4 °C (Tg).
, ¹100 °C < T < 100 °C):
This work was supported by a Grant-in-Aid for Scientific
Research from the Ministry of Education, Culture, Sports,
Science and Technology, Japan.
Supporting Information
Conversion of Organosilyl Groups at the Polymer Side
Chain to an Acetoxy Moiety: In a similar manner to the
terminal acetylation, poly(EHO-SiPhMe2) (Mn = 3.3 © 104,
Mw/Mn = 3.2; 370 mg containing 1.48 mmol of Me2PhSi
groups) was dissolved in benzene (3 mL). To this solution,
acetyl chloride (0.32 mL, 4.44 mmol) was added and the
mixture was stirred at room temperature for 24 h. After removal
of the volatiles, the residue was dissolved in ether (25 mL). The
ether solution was washed with aqueous NaHCO3. The aqueous
layer was extracted five times with ether. The combined
extracts were dried over MgSO4 and the solvent was removed
under reduced pressure. The residue was dissolved in a mixture
of ether (3 mL) and hexane (7 mL) and the solution was kept at
¹30 °C for 24 h. The desired copolymer was precipitated. Yield
82% (192 mg); Mn = 2.6 © 104, Mw/Mn = 2.6; IR (film): ¯C=O
Detailed experimental procedures, characterization data of
both the substrates and the products. This material is available
free of charge on the web at http:// www.csj.jp/journals/bcsj/.
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One-Pot Synthesis of Poly(EHO-Ac-co-EHO-Bn) from
EHO-H and EHO-Bn. In a 20 mL Schlenk tube, 1 (4.3 mg,
6.6 ¯mol) was dissolved in dioxane (120 ¯L). To this solution,
PhMe2SiH (540 mg, 3.96 mmol) was added and the mixture
was stirred at ambient temperature for 30 min. The mixture
of EHO-H (192 mg, 1.65 mmol) and EHO-Bn (340 mg,
1.65 mmol) was placed in another 20 mL Schlenk tube. A half
amount of the catalyst solution described above was added
dropwise at 0 °C. The mixture was stirred at 0 °C for 30 min,
and then, gradually warmed to room temperature. Evolution of
H2 was observed, and the reaction was exothermic. Viscosity of
the reaction mixture was gradually increased. After 1 h, the
reaction mixture was dissolved in toluene (4 mL). To this
solution, acetyl chloride (389 mg, 4.95 mmol) was added and
the mixture was stirred at room temperature for 10 h. After
removal of volatiles, the residue was dissolved in a mixture of
toluene (7 mL) and methanol (50 mL) and the solution was kept
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6
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¯
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CO
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the linear polymer, whereas no signal due to the CH2OSiMe2
moiety was seen in the hyperbranched polymer. Similarly, the
integral ratio of the signal due to methylene protons of the ethyl
group vs. CH2 groups in the polymer chain are also good proof; an
ideal ratio is 1:2 in the linear polymer, whereas that is 1:3 in the
hyperbranched polymer. This clearly showed that hyperbranched
structure was not included in poly(EHO-SiMe2Ph) formed from of
EHO-H by the ruthenium-catalyzed dehydrogenative silylation and
subsequent ring-opening polymerization.
9
In general, NMR spectra of random copolymers are not the
precise sum of those of homopolymers. This results from magnetic
interaction between the comonomer units. In the copolymers
presented in this paper, two units derived from the comonomers,
-CH2C(R1)(CH2OR2)CH2- and -CH2C(R3)(CH2OR4)CH2-, were
separated by oxygen atoms; this reduce the magnetic interaction.
10 a) K. Tamao, T. Yamauchi, Y. Ito, Chem. Lett. 1987, 171. b)
A. G. Shipov, E. P. Kramarova, E. A. Mamaeva, O. A.
Zamyshlyaeva, V. V. Negrebetsky, Y. E. Ovchinnikov, S. A.
Pogozhikh, A. R. Bassindale, P. G. Taylor, Y. I. Baukov, J.
Organomet. Chem. 2001, 620, 139.
11 S. D. Stamatov, J. Stawinski, Eur. J. Org. Chem. 2008,
2635.
12 E. Pérez, M. A. Gómez, A. Bello, J. G. Fatou, Polym. Sci.
1983, 261, 571.
13 a) E. Pérez, A. Bello, J. M. Pereña, Polym. Bull. 1988, 20,
291. b) A. Bello, E. Perez, Thermochim. Acta 1988, 134, 155.
14 T. G. Fox, Bull. Am. Phys. Soc. 1956, 1, 123.
15 Polymers obtained by the present method are brownish
solids due to the ruthenium residues, which are not completely
removable by precipitation. Further treatment of the polymers with
activated carbon or activated clay makes them colorless.
16 Y. Motoyama, C. Itonaga, T. Ishida, M. Takasaki, H.
Nagashima, Org. Synth. 2005, 82, 188.
7
One of the reviewers suggested that we should check the
number of repeating units before and after the acetylation. Two
samples, PhMe2Si(EHO-Bn)47H [Mn (GPC) = 2.7 © 104, Mw/
Mn = 2.3] and PhMe2Si(EHO-Bn)18H [Mn (GPC) = 1.4 © 104,
Mw/Mn = 1.8], were subjected to the acetylation. Comparison of
1H resonances due to the Ac group and those due to the polymer
units suggested that the number of the repeating units were
calculated to be 40 and 11, respectively. They are relatively smaller
than those of the samples bearing a terminal PhMe2Si group. This
is due to the contamination of a small amount of acetic acid or
its derivatives derived from acetyl chloride, which was hardly
removable from the polar polyoxetane. The impurities contribute
to increase the integral value of the Ac peak to result in decrease
of Mn.
8
In the 1H NMR spectra of the polymer formed by the
reaction of EHO-H with PhMe2SiH described in the text, the
signals are exactly the same as those observed for poly(EHO-
SiPhMe2) formed by polymerization of EHO-SiPhMe2. The
integral ratio of the signal due to CH2OSiMe2 vs. that due to
CH2 groups in the polymer chain are good indication; it is 1:2 in