Poly(silsesquioxanes) derived from the hydrolytic condensation of organotrialkoxysilanes containing hydroxyl groups

Article abstract of DOI:10.1016/S0022-328X(03)00377-2

Organotrialkoxysilanes containing secondary hydroxyl groups were synthesized by reacting 1 mole of (3-aminopropyl)triethoxysilane (APS) with 1 or 2 mole of phenylglycidylether (PGE). Resulting products, APS-PGE and APS-PGE₂, respectively, were subjected to hydrolytic condensation at 50 °C during 24 h. For APS-PGE, the reaction was performed using a molar ratio [H₂O]/Si=3, without addition of an external catalyst. For APS-PGE₂, the reaction was catalyzed by HCOOH or NaOH. Resulting poly(silsesquioxanes) (PSSO) were characterized by size exclusion chromatography, Fourier-transformed infrared spectroscopy and matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS). PSSO derived from APS-PGE and APS-PGE₂, catalyzed by HCOOH, exhibited a relatively narrow distribution of polyhedral structures. This constitutes a simple one-step synthesis of polyhedral oligomeric silsesquioxanes (POSS) functionalized with amine and/or hydroxyl groups. The directionality of the reaction pathway towards the formation of polyhedral structures was ascribed to the formation of intramolecular Si-O-C bonds through the reaction of SiOEt or SiOH groups with secondary hydroxyl groups. Intramolecular Si-O-C bonds were found in the structures of APS-PGE and APS-PGE₂, and in most of the species of the PSSO obtained from the NaOH-catalyzed reaction of APS-PGE₂. A small fraction of surviving Si-O-C bonds was also found in the polyhedral structures of the PSSO derived from the hydrolytic condensation of APS-PGE and APS-PGE₂ catalyzed by formic acid. By usual organic reactions transforming hydroxyl groups into other functional groups, it is possible to generate narrow distribution of multi-functionalized POSS starting from an OH-functionalized organotrialkoxysilane.

Full text of DOI:10.1016/S0022-328X(03)00377-2

Journal of Organometallic Chemistry 686 (2003) 42ꢀ51
/
www.elsevier.com/locate/jorganchem
Poly(silsesquioxanes) derived from the hydrolytic condensation of
organotrialkoxysilanes containing hydroxyl groups
Ignacio E. dell’ Erba a, Diana P. Fasce a, Roberto J.J. Williams a,*,
Rosa Erra-Balsells b, Yuko Fukuyama c, Hiroshi Nonami c
a Institute of Materials Science and Technology (INTEMA), University of Mar del Plata and CONICET, J.B. Justo 4302, 7600 Mar del Plata,
Argentina
b CIHIDECAR-CONICET, Department of Organic Chemistry, University of Buenos Aires, Pab. 2, Ciudad Universitaria, 1428 Buenos Aires, Argentina
c Plant Biophysics, Biochemistry Research Laboratory, College of Agriculture, Ehime University, Matsuyama 790-8566, Japan
Received 13 February 2003; received in revised form 17 April 2003; accepted 17 April 2003
Abstract
Organotrialkoxysilanes containing secondary hydroxyl groups were synthesized by reacting 1 mole of (3-aminopropyl)triethox-
ysilane (APS) with 1 or 2 mole of phenylglycidylether (PGE). Resulting products, APSꢀ
subjected to hydrolytic condensation at 50 8C during 24 h. For APSꢀPGE, the reaction was performed using a molar ratio [H2O]/
Siꢁ3, without addition of an external catalyst. For APSꢀPGE2, the reaction was catalyzed by HCOOH or NaOH. Resulting
/
PGE and APSꢀ/PGE2, respectively, were
/
/
/
poly(silsesquioxanes) (PSSO) were characterized by size exclusion chromatography, Fourier-transformed infrared spectroscopy and
matrix-assisted ultraviolet laser desorption/ionization time-of-flight mass spectrometry (UV-MALDI-TOF MS). PSSO derived from
APSꢀ
/
PGE and APSꢀPGE2, catalyzed by HCOOH, exhibited a relatively narrow distribution of polyhedral structures. This
/
constitutes a simple one-step synthesis of polyhedral oligomeric silsesquioxanes (POSS) functionalized with amine and/or hydroxyl
groups. The directionality of the reaction pathway towards the formation of polyhedral structures was ascribed to the formation of
intramolecular SiÃ
OÃC bonds were found in the structures of APSꢀ
NaOH-catalyzed reaction of APSꢀPGE2. A small fraction of surviving SiÃ
of the PSSO derived from the hydrolytic condensation of APSꢀPGE and APSꢀ
/
OÃ
/
C bonds through the reaction of SiOEt or SiOH groups with secondary hydroxyl groups. Intramolecular SiÃ
PGE and APSꢀPGE2, and in most of the species of the PSSO obtained from the
OÃC bonds was also found in the polyhedral structures
PGE2 catalyzed by formic acid. By usual organic
/
/
/
/
/
/
/
/
/
reactions transforming hydroxyl groups into other functional groups, it is possible to generate narrow distribution of multi-
functionalized POSS starting from an OH-functionalized organotrialkoxysilane.
# 2003 Elsevier Science B.V. All rights reserved.
Keywords: Poly(silsesquioxanes); Polyhedral oligomeric silsesquioxanes (POSS); UV-MALDI-TOF MS; OH-functionalized organotrialkoxysilanes;
SiÃ
/
OÃC bonds
/
1. Introduction
organicꢀ
in a PSSO may vary from perfect polyhedra of formula
(RSiO1.5)n (nꢁeven number ]6), denoted as Tn or as
polyhedral oligomeric silsesquioxanes (POSS), to par-
tially condensed (but completely hydrolyzed) products
/
inorganic hybrid materials [2]. Species present
The hydrolytic condensation of organotrialkoxysi-
?
lanes, RSi(OR3), performed in the presence of water
/
/
and an acid or base as catalysts, leads to products that
are generically called poly(silsesquioxanes) (PSSO), or
silsesquioxanes [1]. These polymers have acquired in-
creasing importance for the synthesis of functionalized
of generic formula Tn(OH)m, where Tꢁ/RSiO1.5ꢂm/2n.
The maximum value of m is equal to 2ꢃn, representing
/
a linear/branched chain devoid of intramolecular cycles.
The structure of a particular n-mer may thus vary from
a linear/branched chain (open structure) to a polyhe-
dron (closed structure). A distinctive parameter that
characterizes the structure of a particular PSSO is the
average fraction of intramolecular cycles (f) present in
* Corresponding author. Tel.: ꢃ
481-0046.
E-mail address: williams@fi.mdp.edu.ar (R.J.J. Williams).
/
54-223-481-6600; fax: ꢃ54-223-
/
0022-328X/03/$ - see front matter # 2003 Elsevier Science B.V. All rights reserved.
doi:10.1016/S0022-328X(03)00377-2

I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ
/51
43
their species [3]. For a generic n-mer, f is given by:
f ꢁ(2ꢃnꢂm)=(2ꢃn) (for nꢁeven)
or
to give, respectively, APSꢀ
/
PGE and APSꢀ
/
PGE2. The
reaction was carried out in bulk, at 50 8C under vacuum,
during 24 h. In these conditions the reaction attained
complete conversion [5]. Scheme 1 shows the structure
of APS and the two reaction products. The product
f ꢁ(2ꢃnꢂm)=(1ꢃn) (for nꢁodd)
denoted as APSꢀPGE is in fact a mixture of the three
/
The average fraction of intramolecular cycles present
in a particular PSSO depends on the nature of the
organic substituent and on the conditions of the
synthesis [3,4]. We recently reported that the hydrolytic
condensation of an organotrialkoxysilane with a bulky
organic group bearing hydroxyl functionalities, in the
presence of both acid and basic catalysts, led to a
narrow distribution of perfect and imperfect polyhedra:
T8, T9(OH), and T10, with traces of T7(OH) and
T11(OH) [5]. The starting silane was the reaction product
silanes. Assuming an equal reactivity of primary and
secondary amino groups, the reaction product of
equimolar amounts of APS and PGE will consist of
25% APS, 50% APSꢀ
The hydrolytic condensation of both APSꢀ
APSꢀPGE2 was performed by dissolving 1 g of the
/
PGE and 25% APSꢀ/PGE2.
/PGE and
/
corresponding silane in 1.5 ml tetrahydrofuran (THF),
adding water and eventually a catalyst, and heating at
50 8C during 24 h, allowing continuous evaporation of
volatiles. For APSꢀ
used, and the reaction was catalyzed by the amino
groups of the silane. For APSꢀPGE2, the hydrolytic
condensation was catalyzed by HCOOH 85 wt.% (molar
ratios: [HCOOH]/Siꢁ3, [H2O]/Siꢁ1.35), or by NaOH
(molar ratios: [NaOH]/Siꢁ0.05, [H2O]/Siꢁ3). Formic
/
PGE, a molar ratio [H2O]/Siꢁ
/3 was
of
(AEAPS) with 3 mole of phenylglycidylether (PGE):
AEAPSꢀPGE3, with 3 secondary hydroxyl groups in its
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane
/
/
structure. The precise directionality of the reaction path
towards the generation of three main species was
ascribed to the presence of a bulky organic substituent
(steric effect promoting intramolecular condensation).
However, these previous studies also showed the pre-
/
/
/
/
acid acts both as a catalyst and as reactant, promoting
the condensation through the formation of sililformates
as intermediate species [6].
sence of SiÃ
/
OÃ
/
C bonds in the starting OH-functiona-
lized organotrialkoxysilane, produced through reaction
of SiOMe groups with secondary hydroxyl groups [5].
2.2. Characterization of poly(silsesquioxanes)
The reversible formation of SiÃ
/
OÃ
/
C bonds may also
Size exclusion chromatography (SEC) was performed
with a Waters 510 device, provided with three Styragel
columns (HR 3, HR 1 and HR 0.5), and a UV detector
(Waters Lambda-Max 481, at 254 nm). THF was used
as a carrier at a rate of 1 ml minꢂ1. A solution of about
20 mg of the PSSO in 10 ml THF was prepared, and 0.1
ml were injected in the chromatograph.
Fourier-transformed infrared spectra (FTIR) were
recorded with a Genesis II-Mattson device, in the
transmission mode, making coatings on NaCl windows.
Matrix-assisted UV-MALDI-TOF MS, was per-
formed using an Applied Biosystems Voyager DE-STR
take place during the synthesis of the PSSO, through
reaction of SiOH groups and OH groups of the organic
branches. Extensive intramolecular cyclization through
intermediate SiÃ
/
OÃ
/
C bonds would favor the formation
of cage structures in the resulting PSSO.
The aim of this study was to analyze if the hydrolytic
condensation of an OH-functionalized organotrialkox-
ysilane, with an organic group less bulky than the one
used in the previous work [5], could also lead to a
narrow distribution of silsesquioxane cages. For this
purpose, AEAPS was replaced by (3-aminopro-
pyl)triethoxysilane (APS) as the starting silane. Hydrox-
yl groups were generated by reacting APS with 1 or 2
mole PGE. PSSO obtained by the hydrolytic condensa-
tion of these organotrialkoxysilanes were analyzed by
matrix-assisted ultraviolet laser desorption/ionization
time-of-flight mass spectrometry (UV-MALDI-TOF
MS), to characterize their average fraction of intramo-
lecular cycles.
device, equipped with a pulsed nitrogen laser (lꢁ
/
337
nm; pulse widthꢁ3 ns). The selected matrix was 2,5-
/
dihydroxybenzoic acid (gentisic acid, GA; Sigma).
Samples were irradiated just above the threshold laser
power to obtain molecular ions. Measurements were
performed in linear positive-ion modes. Usually 50
spectra were accumulated. Spectra were calibrated using
insulin, aprotinin, and a-, b-, and g-cyclodextrin.
2. Experimental
3. Results and discussion
2.1. Synthesis of the poly(silsesquioxanes)
3.1. Reaction between APS and PGE
Organotriethoxysilanes containing hydroxyl groups
were synthesized by reacting 1 mole of APS (Sigma, 98%
purity), with 1 or 2 mole of PGE (Aldrich, 99% purity),
The reaction of 1 mole of APS with 2 mole of PGE, at
50 8C, was followed by SEC. After 24 h, the monomer
and the monoreacted intermediate had completely

44
I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ51
/
Scheme 1. Chemical structures of the organotriethoxysilanes.
disappeared and APSꢀ
/
PGE2 was the main reaction
product. However, a small fraction of higher molar mass
(c) The dimer present in largest concentration was
characterized by peaks at 906.4 and 928.2 Da. These
masses may be assigned to the species formed by the loss
species was also recorded. This was ascribed to the
formation of dimers, trimers, etc., of APSꢀPGE2
through the following reaction:
/
of 3 mole of EtOH from 2 APSꢀ
/
PGE2 mole (Scheme 2;
theoretical massꢁ
/
906.1 Da, ionized with Hꢃ, and
928.1 Da, ionized with Naꢃ). This means that once a
loop is formed there is a high trend to form subsequent
loops. It may be speculated that the eight-member ring
is formed first leaving the possibility for the other
SiÃ(OEt)ꢃCÃ(OH)ꢁSiÃOÃCꢃEtOH
An UV-MALDI MS of the reaction product revealed
the following facts.
(a) The main species was APSꢀ
by the presence of peaks at 522.5 Da (theoretical
valueꢁ
522.6 Da, ionized with Hꢃ), and 544.9 Da
(theoretical valueꢁ
544.6 Da, ionized with Naꢃ).
(b) No peaks assignable to the loss of 1 or more EtOH
moles from APSꢀPGE2 were observed, meaning that
SiÃ(OEt) was not involved in the formation of intra-
molecular loops with CÃOH groups pertaining to the
organic moiety bonded to the same Si atom.
/
PGE2, characterized
organic branch to form new SiÃ
intramolecular or intermolecular condensations (dimers
with one or two SiÃOÃC bonds were not present in
/
OÃ/C bonds through
/
/
/
/
significant concentrations). The intramolecular conden-
sation through a 16-member ring is indeed possible as
shown by the optimized geometry (Scheme 2b). But a
second eight-member ring can not be closed due to steric
reasons. Trimers and larger molar mass species were
/
/
/

I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ
/51
45
Scheme 2. Chemical structure of the dimer formed during the synthesis of APSꢀ/PGE2; (a) schematic representation, (b) optimized geometrical
structure (MM program of Molecular Mechanics).
ꢃ
/
also detected in small concentrations, meaning that
intermolecular condensations do also take place.
POSS, functionalized with both hydroxyls and amino
groups. These may be used as building blocks in several
types of polymerization reactions.
The hydrolytic condensation of unmodified APS,
under the same experimental conditions, led to a typical
broad distribution of structures (in Tn(OH)m, several
values of m were present for a particular n value),
extending to the range of large masses. Instead, the
The formation of intramolecular cycles through SiÃ
OÃC bonds seems to be a characteristic of organotrialk-
oxysilanes bearing hydroxyl groups. In the presence of
C bonds will be
/
/
water and an adequate catalyst, SiÃ
/
OÃ
/
hydrolyzed leading to a PSSO through condensation of
the resulting SiOH groups.
hydrolytic condensation of APSꢀPGE led to polyhedral
/
structures with a relatively narrow distribution of n
values. The dramatic change in the reaction path is
ascribed to the presence of hydroxyl groups in the
3.2. PSSO derived from APSꢀPGE
/
Fig. 1 shows an UV-MALDI-TOF mass spectra of
the PSSO obtained by hydrolytic condensation of APSꢀ
structure of APSꢀPGE, rather than to the increase in
/
/
the size of the organic moiety. It is possibly that SiOH
groups participate in reversible reactions with COH
groups pertaining to the organic part attached to
PGE. Although low-molar-mass products were also
present, most of the species were observed in the (m/z)
range comprised between 2000 and 4000 Da. Assign-
ment of main peaks is shown in Table 1. Species present
in this particular PSSO were perfect polyhedra: T8, T10,
imperfect polyhedra: T9(OH), T11(OH), and other
structures exhibiting a large fraction of intramolecular
cycles: T9(OH)3, T10(OH)2. For every one of these
species there is distribution of molar masses that
depends on the number of moles of PGE that are
covalently bonded to the 3-aminopropyl group. As a 1:1
molar ratio of PGE with respect to APS was used in the
another Si atom, forming SiÃ
/
OÃ
/
C bonds. After hydro-
lysis of these bonds, the reaction between two neighbor-
ing SiOH groups should be favored thus promoting the
formation of closed (polyhedral) structures. An experi-
mental fact supporting this hypothesis may be obtained
by analyzing the species present in minor concentrations
in the UV-MALDI MS shown in Fig. 1. Among these
species we found T8(OH)2, T9(OH)ꢂ
H2O, T12, T12(OH)2, T13(OH)ꢂH2O, T13(OH), T14,
T14(OH)2, T15(OH)ꢂH2O, T15(OH) and T15(OH)3.
Four of these species (Tn(OH)ꢂH2O), are imperfect
/
H2O, T11(OH)ꢂ
/
/
/
synthesis of APSꢀPGE, the most probable number of
/
/
PGE moles in a generic species Tn(OH)m, is equal to n.
For example, for T11(OH), Table 1 shows the presence
of a distribution of species containing from 8 to 15 PGE
residues. As an example, Scheme 3 shows an isomer of a
T8 species containing 8 PGE units covalently bonded to
the amine groups.
polyhedra with their only silanol group reacted with a
COH group, with the loss of 1 mole of water. This
proves that SiÃ
/
OÃ
/
C bonds are in fact present in some of
the species of the PSSO.
The FTIR spectra of the PSSO in the range of 800ꢀ
/
1250 cmꢂ1 is shown in Fig. 2 (curve a). Peaks at 1120
Therefore, the one-step hydrolytic condensation of
APSꢀ/PGE led to a relatively narrow distribution of
and 1079 cmꢂ1 are characteristic of nas SiÃ
/
OÃ/Si in

46
I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ51
/
Fig. 1. UV-MALDI-TOF MS of the PSSO obtained by hydrolytic condensation of APSꢀPGE.
/
polyhedra and imperfect polyhedra [7], in agreement
with the assignments of the mass spectrum.
Table 1
Assignment of peaks of UV-MALDI-TOF mass spectra for the PSSO
obtained by hydrolytic condensation of APSꢀ
/PGE
3.3. PSSOs derived from APSꢀPGE2
/
m/z (exp.)
Species
m/z (theor.)
n PGE
2051.4
2083.0
2154.0
2202.7
2223.0
2232.7
2302.8
2352.7
2373.0
2382.7
2422.2
2453.4
2503.0
2523.8
2603.6
2652.6
2674.3
2722.5
2753.8
2773.5
2823.7
2872.7
2903.2
2923.4
3024.8
3173.6
3323.7
3474.2
T9(OH)
T8
T10
2052.9
2083.9
2154.1
2203.1
2221.1
2234.1
2304.3
2353.3
2371.3
2384.3
2423.4
2454.4
2503.4
2521.4
2604.6
2653.6
2671.6
2723.8
2754.8
2772.8
2821.8
2874.0
2905.0
2923.0
3024.2
3174.3
3324.5
3474.7
7
8
Size exclusion chromatograms for the PSSOs ob-
tained by the hydrolytic condensation of APSꢀPGE2
/
7
catalyzed by HCOOH or NaOH, are shown in Fig. 3.
The PSSO synthesized in the presence of HCOOH
exhibited a relatively narrow distribution of reaction
products in the region of large masses (low elution
times). The NaOH-catalyzed product showed the pre-
sence of a narrow peak at large masses, together with a
series of peaks corresponding to low-molar mass species.
The hydrolytic condensation was clearly less efficient in
the presence of NaOH, for the selected concentrations
and reaction conditions.
FTIR spectra provide a confirmation of SEC results
(Fig. 2, curves b and c). The PSSO synthesized with
HCOOH showed the presence of an intense absorption
band at 1127 cmꢂ1, together with a band of medium
intensity at 1080 cmꢂ1, which are characteristic of
polyhedral structures [7]. For the NaOH-catalyzed
PSSO, the more intense band in this region was a
double peak located at 1047 and 1067 cmꢂ1, with a less
intense band at 1128 cmꢂ1. This reveals the presence of
a different structure for the species present in this PSSO.
Unsymmetrical structures containing internal cyclotrisi-
T9(OH)
T9(OH)3
T8
8
8
9
T10
8
T9(OH)
T9(OH)3
T8
9
9
10
8
T11(OH)
T10
9
T9(OH)
T9(OH)3
T10
10
10
10
11
11
10
11
11
12
11
12
12
12
13
14
15
T9(OH)
T9(OH)3
T11(OH)
T10
T10(OH)2
T9(OH)3
T11(OH)
T10
T10(OH)2
T
11(OH)
11(OH)
T
T11(OH)
T11(OH)
loxane rings exhibit characteristic nas SiÃ
/
OÃ
/
Si bands
near 990 and 1065 cmꢂ1, in addition to others in the
m/z, Da; theoretical values correspond to ionization with Hꢃ
.

I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ
/51
47
Scheme 3. Chemical structure of a particular isomer of an octahedron (T8), with 8 PGE residues, present in the PSSO obtained from the hydrolytic
condensation of APSꢀPGE.
/
Fig. 3. SEC chromatograms of PSSOs obtained by hydrolytic
condensation of APSꢀPGE2, catalyzed by HCOOH or NaOH.
/
absence of bands at 958 and 1168 cmꢂ1 indicates
complete hydrolysis of EtO groups [8]. However, the
absence of a band at 930 cmꢂ1 evidences that SiOH
groups are not present in significant concentrations [8].
Mass spectra provide additional information which is
necessary to elucidate the structures of both PSSOs. Fig.
Fig. 2. FTIR spectra in the range of 800ꢀ
obtained by hydrolytic condensation of: (a) APSꢀ
PGE2 in the presence of HCOOH, (c) APSꢀ
NaOH.
/
1250 cmꢂ1, of the PSSO
PGE, (b) APSꢀ
/
/
/
PGE2 in the presence of
range of 1080ꢀ
/
1115 cmꢂ1 [7]. This type of structure
might be present in the NaOH-catalyzed PSSO. The

48
I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ51
/
4 shows an UV-MALDI-TOF MS of the PSSO obtained
by hydrolytic condensation of APSꢀPGE2, in the
presence of HCOOH. Table 2 shows the assignment of
main peaks, which are present in the region of m/z
comprised between 3000 and 5000 Da, in decreasing
order of intensities.
Table 2
Assignment of main peaks present in the UV-MALDI-TOF mass
spectra of the PSSO obtained by hydrolytic condensation of APSꢀ
PGE2 in the presence of HCOOH
/
/
m/z
(exp.)
Species
m/z (the-
or.)
n PGE
Main species present in the PSSO obtained in the
3703.2
4104.9
4123.6
3581.1
4506.3
4525.3
4001.1
3982.8
4086.9
4403.0
4384.5
T9(OH)
T10
T10(OH)2
3704.9
4106.4
4124.4
3582.7
4508.0
4526.0
4002.2
3984.2
4088.4
4403.8
4385.8
18
20
20
17
22
22
19
19
20
21
21
presence of HCOOH are polyhedral structures with 8ꢀ
11 Si atoms, as in the case of the hydrolytic condensa-
tion of APSꢀPGE. Again, the presence of OH groups in
/
T9(OH)(ꢃ
T11(OH)ꢂ
11(OH)
T10(OH)2(ꢃ
T10(ꢃHCOOHꢂ
T10(OH)2ꢂ2H2O
11(OH)(ꢃHCOOHꢂ
T11(OH)ꢂH2O(ꢃHCOOHꢂ
H2O)
10(OH)2ꢂ
H2O)
/
HCOOHꢂ
/
H2O)
/
/
H2O
the starting organotrialkoxysilane enabled the one-step
synthesis of a narrow distribution of POSS. Main
species were: T8, T9(OH) (the species present in the
T
/HCOOHꢂ
/
H2O)
/
/H2O)
/
highest concentration), T9(OH)ꢂ
T10(OH)2ꢂ2H2O, T11(OH) and T11(OH)ꢂ
T9(OH)ꢂH2O and T11(OH)ꢂH2O exhibit one intra-
molecular SiÃOÃC bond formed by reaction of the
SiOH group with an hydroxyl group of one of the
organic branches. In the case of T10(OH)2ꢂ2H2O, there
are two intramolecular SiÃOÃC bonds formed by
/H2O, T10, T10(OH)2,
T
/
/H2O)
/
/H2O. Both
/
/
/
/
/
3964.3
T
/
2H2O(ꢃ
/
HCOOHꢂ
/
3966.2
19
/
/
3684.7
3283.8
3161.7
3459.2
T9(OH)ꢂ
T8
/H2O
3686.9
3285.3
3163.1
3460.5
18
16
15
16
/
T8(ꢃ
/
HCOOHꢂ
/H2O)
/
/
T9(OH)(ꢃ
/2HCOOHꢂ2H2O)
/
reaction of both SiOH groups with hydroxyls of the
organic chains. It may be also noticed that although
species containing the stoichiometric PGE units were
present in the highest concentrations, species lacking 1
or 2 PGE units were also detected. This means that the
initial formulation had in fact a slight defect of PGE or
that the reaction was not carried out to 100% conversion
(although conversion was very close to this value). It is
interesting to note that every amino group that was not
previously reacted with PGE, formed an amide group by
reaction with HCOOH (eliminating 1 water molecule).
Fig. 5 shows the UV-MALDI-TOF MS of the PSSO
obtained by hydrolytic condensation of APSꢀPGE2, in
/
the presence of NaOH. In this case, the PSSO shows
clusters of oligomers containing a particular number of
Si atoms: from 2 Si atoms (maximum at 808.0 Da) to 12
Si atoms (maximum at 4890.3 Da). No monomer was
detected (peaks at m/z less than 600 Da are due to the
matrix or to z values equal to or higher than 2).
Fig. 4. UV-MALDI-TOF MS of the PSSO obtained by hydrolytic condensation of APSꢀPGE2, in the presence of HCOOH.
/

I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ
/51
49
Fig. 5. UV-MALDI-TOF MS of the PSSO obtained by hydrolytic condensation of APSꢀPGE2, in the presence of NaOH.
/
Table 3 shows the assignment of the main peak for
every cluster. The dimer present in the highest concen-
The presence of a significant amount of the comple-
tely dehydrated dimer gives evidence of: (a) the competi-
tion between the formation of SiÃ
bonds during the reaction catalyzed by NaOH, (b) the
stability of generated SiÃOÃC bonds. The reaction path
/
OÃ
/
Si and SiÃ
/
OÃ
/
C
tration had a mass that could be assigned to T2(OH)4ꢂ
4H2O. This corresponds to the formation of the four
possible SiÃOÃC bonds, meaning that this species has
/
/
/
/
/
seems to be a typical hydrolytic condensation of Si(OEt)
groups, arrested by the total consumption of SiOH
groups through intramolecular cyclization with COH
groups. The generated oligomers devoid of silanol
groups remain stable under the selected reaction condi-
tions.
no free SiOH or COH residual groups. Scheme 4 shows
a possible chemical structure for this dimer exhibiting
eight- and ten-member rings (the optimized geometry is
shown in Scheme 4b). Notice that SiOH groups have
reacted with COH groups pertaining to the organic
branch bonded to the other Si atom; this follows from
Every species present in the highest concentration in
the corresponding cluster, could be assigned to
the fact that no intramolecular SiÃ
/
OÃ
/
C bonds were
found in the monomer during the synthesis of APSꢀ
/
Tn(OH)m ꢂmH2O (Table 3). This means that all silanol
/
PGE2.
groups form intramolecular cycles with hydroxyl
groups, in agreement with results arising from the
FTIR spectrum. The number of free hydroxyl groups
is 2nꢂ
cycles is low for the tetramer (fꢁ
(fꢁ0.2), indicating the presence of an ‘open’ SiÃ
skeleton. But it increases significantly for the high-
molar-mass oligomers (e.g. fꢁ0.67 for the decamer and
fꢁ0.71 for the dodecamer). Table 3 also shows that
/
m. The fraction of intramolecular SiÃ
0) up to the octamer
OÃSi
/
OÃ
/
Si
Table 3
Assignment of the main peak of every cluster of species with 2ꢀ
atoms, present in the UV-MALDI-TOF mass spectra of the PSSO
/
12 Si
/
/
/
/
obtained by hydrolytic condensation of APSꢀ
NaOH (m/z, Da)
/
PGE2 in the presence of
/
m/z (exp.)
Species
m/z
(theor.ꢃ
m/z
(theor.ꢃ )
Naꢃ
/
/
Hꢃ
)
/
Naꢃ ionization was significant for the species contain-
ing a small number of residual hydroxyl groups (for the
dimer, the intensity of the peak corresponding to Naꢃ
ionization was higher than the peak arising from Hꢃ
ionization).
785.6; 808.0
T2(OH)4ꢂ
/
4H2O
3H2O
6H2O
5H2O
6H2O
5H2O
8H2O
3H2O
786.1
1205.6
1589.1
2008.7
2410.2
2829.7
3213.3
3668.8
808.0
1227.6
1611.1
2030.7
1205.3; 1227.7 T3(OH)3ꢂ
1588.5; 1611.1 T4(OH)6ꢂ
2008.4; 2030.5 T5(OH)5ꢂ
2409.7 T6(OH)6ꢂ
2829.4; 2851.0 T7(OH)5ꢂ
3212.8
3668.3
4069.6
4488.9
4890.3
/
/
/
/
/
2851.7
T8(OH)8ꢂ
T9(OH)3ꢂ
10(OH)4ꢂ
T11(OH)3ꢂ
12(OH)4ꢂ
/
/
4. Conclusions
T
/4H2O 4070.4
/3H2O 4489.9
The presence of hydroxyl groups in the organic part
of organotrialkoxysilanes has a significant influence on
T
/4H2O 4891.5

50
I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ51
/
Scheme 4. Chemical structure of the dimer formed during the hydrolytic condensation of APSꢀ/PGE2, in the presence of NaOH; (a) schematic
representation, (b) optimized geometrical structure (MM program of Molecular Mechanics).
ꢃ
/
the course of its hydrolytic condensation. This is due to
the formation of SiÃOÃC bonds through the reaction of
SiOH (or SiOEt) groups with the hydroxyl functional-
ities of an organic moiety bonded to a neighboring Si
atom, producing intramolecular cycles. Depending on
presence of species exhibiting these cycles in the result-
ing PSSO (e.g. T11(OH)ꢂH2O represents an imperfect
polyhedron of 11 Si atoms with the only residual SiOH
/
/
/
group reacted with an hydroxyl, generating an intramo-
lecular SiÃ
/
OÃ
/
C bond).
the catalyst and reaction conditions, SiÃ
may be stable or may be hydrolyzed leading to more
stable SiÃOÃSi bonds. In the last case, the resulting
/
OÃ
/
C bonds
Under reaction conditions where SiÃ
/
OÃ/C bonds were
stable (for the NaOH-catalyzed reaction), the resulting
PSSO exhibited a distribution of low-molar-mass oligo-
mers with a large fraction of stable intramolecular cycles
/
/
PSSO exhibits a narrow distribution of polyhedral
structures, an interesting finding that makes it possible
the one-step synthesis of OH-functionalized POSS. The
directionality effect towards the generation of closed
structures, is possibly derived from the continuous
reversible formation of intramolecular cycles through
formed through SiÃ
/
OÃ
/
C bonds. In this case, the
SiOHꢃ
/
COH reaction became competitive with the
SiOHꢃ
/
SiOH reaction, provoking an arrest of the molar
mass increase due to depletion of SiOH groups.
The significance of this study is related to the possibility
of generating narrow distributions of functionalized
SiÃ
/
OÃ/C bonds. This argument was supported by the

I.E. dell’ Erba et al. / Journal of Organometallic Chemistry 686 (2003) 42ꢀ
/51
51
silsesquioxane cages, by the hydrolytic condensation of
OH-functionalized organotrialkoxysilanes. After the
synthesis, hydroxyl groups may be transformed into
different functional groups through typical organic
References
[1] R.H. Baney, M. Itoh, A. Sakakibara, T. Suzuki, Chem. Rev. 95
(1995) 1409.
[2] C. Sanchez, F. Ribot, B. Lebeau, J. Mater. Chem. 9 (1999) 35.
[3] (a) W.E. Wallace, C.M. Guttman, J.M. Antonucci, J. Am. Soc.
Mass Spectr. 10 (1999) 224;
reactions leading to
a variety of multifunctional
silsesquioxane cages. These products may be used as
building blocks of silsesquioxane-modified polymer net-
works.
(b) W.E. Wallace, C.M. Guttman, J.M. Antonucci, Polymer 41
(2000) 2219;
(c) P. Eisenberg, R. Erra-Balsells, Y. Ishikawa, J.C. Lucas, H.
Nonami, R.J.J. Williams, Macromolecules 35 (2002) 1160.
[4] (a) D.A. Loy, B.M. Baugher, C.R. Baugher, D.A. Schneider, K.
Rahimian, Chem. Mater. 12 (2000) 3624;
(b) J.K. Lee, H.J. Kim, J.B. Kim, E.S. Park, S.J. Park, D.Y. Yoo,
D.Y. Yoon, J. Am. Chem. Soc. 123 (2001) 12121.
[5] (a) D.P. Fasce, R.J.J. Williams, F. Me´chin, J.P. Pascault, M.-F.
Llauro, R. Pe´tiaud, Macromolecules 32 (1999) 4757;
(b) D.P. Fasce, R.J.J. Williams, R. Erra-Balsells, Y. Ishikawa, H.
Nonami, Macromolecules 34 (2001) 3534.
Acknowledgements
We gratefully acknowledged the financial support
from ANPCyT, CONICET and University of Mar del
Plata (Argentina). Mass spectrometry was performed as
part of the Academic Agreement between R.E.-B. and
H.N. with the facilities of the High Resolution Liquid
Chromatography-integrated Mass Spectrometer System
Laboratory of the United Graduate School of Agricul-
tural Sciences (Ehime University, Japan).
[6] K. Sharp, J. SolꢀGel Sci. Technol. 2 (1994) 35.
/
[7] (a) J.F. Brown, Jr., L.H. Vogt, Jr., J. Am. Chem. Soc. 87 (1965)
4313;
(b) J.F. Brown, Jr., J. Am. Chem. Soc. 87 (1965) 4317.
[8] C.H. Chiang, H. Ishida, J.L. Koenig, J. Colloid Interface Sci. 74
(1980) 396.