Studies on the synthesis and thermal properties of alkoxysilane-terminated organosilicone dendrimers

Article abstract of DOI:10.1002/aoc.1615

Silicone core dendrimers bearing terminaldialkoxy andtrialkoxy silane groups were prepared in a three-step synthesis. Initially, the Si-H terminated multifunctional silicone dendrimer, i.e. tetrakis(dimethylsiloxy)silane, was prepared by the reaction of tetraethoxysilane and dimethylethoxysilane. Tetrakis(dimethylsiloxy)silane on reaction with allylglycidylether in the presence of Speier's catalystunderpressure (100 psi) yieldedepoxy- terminateddendrimerin veryhigh yield (95%).Theepoxy-terminated dendrimer was reacted with aminopropylalkoxysilanes to yield the next-generation dendrimer bearing dialkoxy and trialkoxy silane groups. The dendrimers were characterized by the usual physico-chemical techniques, i.e. elemental analysis, FT-IR, ¹H, ¹³C and ²⁹Si NMR. Thermal studies (Thermogravimetric analysis and Thermomechanical analysis) of the alkoxy terminated dendrimers and its cured products were also carried out. Copyright

Full text of DOI:10.1002/aoc.1615

Full Paper
Received: 30 July 2009
Revised: 25 November 2009
Accepted: 29 November 2009
Published online in Wiley Interscience: 5 January 2010
(
www.interscience.com) DOI 10.1002/aoc.1615
Studies on the synthesis and thermal
properties of alkoxysilane-terminated
organosilicone dendrimers
∗
Kanak Saxena, C. S. Bisaria and A. K. Saxena
Siliconecoredendrimersbearingterminaldialkoxyandtrialkoxysilanegroupswerepreparedinathree-stepsynthesis. Initially,
the Si–H terminated multifunctional silicone dendrimer, i.e. tetrakis(dimethylsiloxy)silane, was prepared by the reaction of
tetraethoxysilane and dimethylethoxysilane. Tetrakis(dimethylsiloxy)silane on reaction with allylglycidylether in the presence
ofSpeier’scatalystunderpressure(100 psi)yieldedepoxy-terminateddendrimerinveryhighyield(95%).Theepoxy-terminated
dendrimer was reacted with aminopropylalkoxysilanes to yield the next-generation dendrimer bearing dialkoxy and trialkoxy
silane groups. The dendrimers were characterized by the usual physico-chemical techniques, i.e. elemental analysis, FT-IR,
1
13
29
H, C and Si NMR. Thermal studies (Thermogravimetric analysis and Thermomechanical analysis) of the alkoxy terminated
dendrimers and its cured products were also carried out. Copyright ꢀc 2010 John Wiley & Sons, Ltd.
Keywords: silicone; Speier’s catalyst; dendrimer; tetraethoxysilane
Introduction
substrates for crosslinking reagents.[1,10,30,32] Hence they are used
as coating materials and resin matrices for FRP composites.
Aswehavecontinuedinterestinthesynthesisofmultifunctional
The design and architecture of any macromolecule and polymer
depends on the requirement of the properties and end use
application of the material. With the realization of the fact
that the branching of the polymer chain and functional group
mainly determines the properties of the materials, several
organosilanes,[
33–37]
it has been considered worthwhile to
synthesizeandcharacterizedendrimersbearingasiliconecoreand
exterior hydrolysable alkoxysilane functionalities. As alkoxysilane
groups are susceptible to moisture and hydroxyl groups present
on metal and glass surfaces, these dendrimers may act as very
good coating and coupling reagents for the preparation of FRPs,
RTVs and HTVs.
hyper-branched[
1–5]
[1,6–10]
and dendritic polymers
have been
prepared. For the synthesis of these building blocks, in general,
classical organic and organometallic synthetic methods are
used.[ The synthesis of dendrimers requires multiple steps,
so obtaining high-purity materials is difficult, yet few reports
are available to synthesize very high purity and quantitative
1]
Experimental
[
11]
yields of the dendrimers up to the third generation.
Despite,
Chemicals
the several high tech. applications of dendrimers like chemical
[
12,13]
[14]
[15,16]
sensors,
catalysts,
molecular devices
and chemo-
Benzene (LR grade, Ranbaxy) and hexane (LR grade, E. Merck) were
delivery in biology,[
17]
these new classes of materials have
[38]
purified and dried before use, as reported.
Dimethylethoxysi-
failed to make any commercial impact. Moreover, as compared
with organic hyperbranched polymers and dendrimers, inorganic
hyperbranched polymers and dendrimers have been less studied.
Most of the building blocks of dendrimers are prepared
using widely studied class of reactions like hydrosilylation,
Grignard reactions, dehydrocoupling, alcoholysis and alkenylation
reactions, either by divergent or convergent method.[1,18–27] The
lane (95%, Acros), tetraethoxysilane (98%, E. Merck) and al-
lylglycidylether (99%, Aldrich) were used after distillation. 3-
Aminopropyldiethoxymethylsilane (97%, Lancaster), dibutyltin
dilaurate (Technical grade, Fluka), 3-aminopropyltriethoxysilane
(
96%, Fluka) and silica gel (60–120 mesh LR grade, SD Fine
Chemicals) were used as such.
first silicon-containing dendrimer was reported by Aziz Muzafarov
Equipment and Analytical Measurements
et al. in 1989,[
28]
and the first commercially available silicon-
containing dendrimer was PAMAMOS.[ Since then, several such
29]
Perkin Elmer FT-IR Spectrometer RX1 was used to record IR spectra
using KBr pellets, Bruker Avance 400 MHz NMR spectrometer
was used for NMR studies using deutrated chloroform as solvent
[
1,10,11,18–27]
dendrimers have been reported in the literature.
A
number of applications of organosilicone dendrimers based on
the terminal functional groups and polysiloxycarbosilane core
[
1,10,30,31]
have also been enumerated in the literature.
Globular
∗
geometries, internal void spaces and high number of chain ends
of the dendrimers make them more soluble in solvent systems,
havinglesserbulkviscosityascomparedwithequivalentmolecular
weight linear polymers, which make silicon dendrimers potential
Correspondence to: A. K. Saxena, DMSRDE, Applied Chemistry Division,
DMSRDE, DRDO, Kanpur-208013, India. E-mail: arvsaxena@gmail.com
Defence Materials and Stores, Research and Development Establishment,
Kanpur 208013, India
Appl. Organometal. Chem. 2010, 24, 251–256
Copyright ꢀc 2010 John Wiley & Sons, Ltd.

K. Saxena, C. S. Bisaria and A. K. Saxena
and TMS as external reference. Vario EL III CHNOS elemental
analyzer was used for elemental analysis. Thermal properties were
measured using a Hi-Res TGA 2950 thermogravimetric analyzer
4H, –CHOH–), 3.42 (d, 8H, –O–CH2 –CHOH–), 3.75 (q, 16H,
1
3
–O–CH2 –CH3), 4.03 (t, 8H, –CH2 –CH2 –O–); C NMR (CDCl3)
δ (ppm) 0.1 [–Si–(CH3)2, –Si(OCH2CH3)2 –CH3)], 10.5 (–Si–CH2 –),
14.1 (–Si–CH2 –), 18.0 (–CH2 –CH3), 23.5 (–CH2 –CH2 –CH2 –), 44.1
(–CHOH–CH2 –NH–), 52.1 (–NHCH2CH2 –), 59.1 (–O–CH2 –), 63.4
(
TAInstruments, USA)andaTMA2940thermomechanicalanalyzer
◦
at a heating rate of 10 C/min under a N2 atmosphere.
(
–CHOH–), 70.1 (–OCH2 –CHOH–), 74.5 (–CH2 –CH2 –O–); 29Si
NMR (CDCl3) δ (ppm) −108 [Si(OSi)4], −17 [SiCH3(OEt)2CH2], 7.1
Si(OSi)(CH3)2CH2]; elemental analysis (%) C 49.54, H 9.86, O 20.65,
Typical Procedure and Product Characterization
[
Synthesis of tetrakis(dimethylsiloxy)silane dendrimer
Si 16.32, N 3.59 (calcd 49.55, 9.88, 20.64, 16.31, 3.61 respectively).
Similarly, G1B was synthesized by the reaction of G0B dendrimer
A solution of tetraethoxysilane (TEOS; 12.48 g, 0.06 mol) and
dimethylethoxysilane (31.20 g, 0.30 mol) in benzene (200 ml) was
taken in a dropping funnel, added slowly in a beaker containing
water (500 ml) and magnetic stirrer and further stirred for 2 h
(7.84 g, 0.01 mol) and 3–aminopropyltriethoxysilane (3-APTES;
8
.84 g, 0.04 mol). The yield of the product (G1B dendrimer,
−
1
C68H160O24Si9N4) was quantitative. IR (cm ) 1092 (–SiOSi–),
3361 (–NH), 3475 (–C–OH); H NMR (CDCl ) δ (ppm) 0.07
1
◦
3
at 38–40 C. Afterwards the organic layer was separated using
[
s, 24H, –Si–(CH3)2], 0.56 [t, 8H, –Si(CH3)2 –CH2], 1.07 (m, 4H,
CH2 –NH–CH2), 0.64 (t, 8H, –Si–CH2), 1.59 (t, 36H, –O–CH2CH3),
.81 (m, 16H, CH2 –CH2 –CH2), 2.56 (m, 8H, –NH–CH2 –CH2)
a separating funnel in the presence of brine solution. The
solution was distilled on a water bath to remove benzene. The
tetrakis(dimethylsiloxy)silane (G0A) dendrimer (C8H28O4Si5) was
1
◦
2.62 (t, 8H, –CHOH–CH –NH), 3.15 (m, 4H, –CHOH), 3.20
2
distilled as colorless liquid, yield 13.50 g, 69%, b.p. 190–192 C (lit.
◦
[39]
−1
1
(d, 4H, –CHOH), 3.41(d, 8H, –O–CH –CHOH–), 3.75 (q, 24H,
2
b.p. 190 C ). IR (cm ) 1080 (–SiOSi–), 2131 (–SiH); H NMR
CDCl3) δ (ppm), 0.22 (d, 24H, –Si–CH3), 4.74 (m, 4H, –Si–H);
NMR(CDCl3)δ (ppm)0.2(–Si–CH3); SiNMR(CDCl3)δ (ppm)−108
Si(OSi)4], 8.5 [Si(OSi)H(CH3)2]; elemental analysis (%) C 29.23, H
.56, O 19.48, Si 42.74 (calcd 29.21, 8.58, 19.47, 42.73 respectively).
1
3
1
3
2 3 2 2
–O–CH –CH ), 4.01 (m, 8H, –CH –CH –O–); C NMR (CDCl3)
(
C
2
9
3 2 2
δ (ppm) 0.1 (–Si–CH ), 10.4 (–Si–CH ), 14.1 (–Si–CH ), 18.1
(
5
–CH2 –CH3), 23.6 (–CH2 –CH2 –CH2), 44.1 (–CHOH–CH2 –NH–),
2.1 (–NH–CH2 –CH2 –), 59.0 (–O–CH2), 63.5 (–CHOH), 70.1
[
8
2
9
(
(
–OCH2 –CHOH–), 74.6 (–CH2 –CH2 –O–); Si NMR (CDCl3) δ
ppm) −108 [Si(OSi)4], −40 [Si(OEt)3CH2], 7.1 [Si(OSi)(CH3)2CH2];
Synthesis of G0B dendrimer
elemental analysis (%) C 48.87, H 9.64, O 22.98, Si 15.14, N 3.34
(calcd 48.86, 9.66, 22.99, 15.13, 3.35 respectively).
A solution of G0A dendrimer (9.84 g, 0.03 mol), allylglycidylether
[
40]
(17.1 g, 0.15 mol) and Speier’s catalyst
(0.03 mol%) was taken
in a pressure reactor (100 psi) under argon. The reaction mixture
was stirred (750 rpm) at 100 C for 3 h and allowed to cool to
Curing of G1 dendrimers
◦
room temperature. The excess amount of allylglycidylether was
removed under vacuum (3 torr, 40 C) leaving behind the colorless
liquid. The colorless liquid was column chromatographed on silica
using hexane as eluting agent. The hexane solution was distilled
on a water bath leaving behind a colorless liquid which was
identified as G0B dendrimer (C32H68O12Si5), yield 22.25 g, 95%. IR
(i) Curing of G1A dendrimer using TEOS in presence of dibutyltin
dilaurate (DBTDL): G1A dendrimer (1.55 g, 0.001 mol), TEOS
(0.42 g, 0.002 mol) and DBTDL (15 mol% of TEOS) as catalyst
were properly mixed and poured into a mold. The mixture
was left exposed to air for 24 h followed by sequential heating
◦
◦
◦
◦
at 40 C for 1 h, 50 C for 1 h and finally at 60 C for 3 h. A
sheet of cured material was obtained (CD1). Similarly, G1B
dendrimer was processed to afford cured dendrimer (CD3).
(ii) Curing of G1A dendrimer using (DBTDL): G1A dendrimer
(1.55 g, 0.001 mol) and DBTDL (15 mol% of TEOS) were
properly mixed and poured into a mold. The mixture was
left exposed to air for 24 h followed by sequential heating at
−
1
(
cm ) 913 (epoxy ring, asy), 1080 (–SiOSi–), 3050 (epoxy ring,
1
sym); H NMR (CDCl3) δ (ppm,) 0.07 (s, 24H, –Si–CH3), 0.54 (t,
H, –Si–CH2 –), 1.82 (m, 8H, –CH2 –CH2 –CH2 –), 2.59 (t, 4H, epoxy
ring, –CH2 –, trans), 2.77 (t, 4H, epoxy ring, –CH2 –, cis), 3.13 (m,
H, epoxy ring, –CH–), 3.37 (t, 4H, –O–CH2 –epoxy ring, cis), 3.71
8
4
(
t, 4H, –O–CH2 –epoxy ring, trans), 4.01 (t, 8H, –CH2 –CH2 –O–);
1
3
◦
◦
◦
C NMR (ppm, CDCl3): δ = 0.1 (–Si–CH3), 14.1 (Si–CH2 –), 23.5
–CH2 –CH2 –CH2 –), 44.6 (epoxy ring, –CH2 –), 50.9 (epoxy ring,
CH–), 70.9 (–O–CH2 –epoxy ring), 74.5 (–CH2 –CH2 –O–). 29Si
40 C for 1 h, 50 C for 1 h and finally at 60 C for 3 h. A sheet of
cured material was obtained (CD2). Similarly, G1B dendrimer
was processed to afford cured dendrimer (CD4).
(
–
NMR (CDCl3) δ (ppm) −108 [Si(OSi)4], 7.2 [Si(OSi)(CH3)2CH2];
elemental analysis (%) C 48.91, H 8.72, O 24.48 Si 17.90 (calcd
4
8.92, 8.73, 24.46, 17.89 respectively).
Results and Discussion
For the preparation of high-performance FRP composite and other
thermally stable structural material, such resin matrix and curing
agents are required which give high char yield and highly cross-
linked structures, so that better mechanical and thermo-oxidative
stablepropertiescanbeachieved.Organosiliconeshavebeenused
extensivelyasresinmatrices, coupling agents, cross-linkingagents
and reactive diluents for organic resins to tailor the properties of
composites, but such studies with dendrimers are very limited.
Therefore, we have prepared dendrimers and studied their curing
behavior and thermal properties as potential future materials for
composites and other cross-linked structures.
Synthesis of G1 dendrimers
G0B dendrimer (7.84 g, 0.01 mol) and 3-aminopropyldiethoxy-
methylsilane (3-APDES; 7.64 g, 0.04 mol) were taken into a three-
neckedflaskandstirredfor5 hat38–40 Cunderinertatmosphere
◦
to afford dendrimer G1A (C64H152O20Si9N4) in quantitative yield.
The progress of the reaction was monitored using FT-IR. IR
−
1
1
(
cm ) 1090 (–SiOSi–), 3364 (–NH), 3472 (–C–OH); H NMR
(CDCl3) δ (ppm) 0.07 [s, 24H, –Si–(CH3)2], 0.13 (s, 12H, –Si–CH3),
0
0
1
.55 [t, 8H, –Si(CH3)2 –CH2 –], 1.08 (m, 4H, –CH2 –NH–CH2 –),
.64 (t, 8H, –Si–CH2 –), 1.57 (t, 24H, –O–CH2 –CH3), 1.82 (m,
6H, –CH2 –CH2 –CH2 –), 2.57 (m, 8H, –NH–CH2 –CH2 –) 2.61
Although the tetrakis(dimethylsiloxy)silane (G0A dendrimer)
has been prepared by the reaction of (LiO)4Si and
(t, 8H, –CHOH–CH2 –NH–), 3.15 (m, 4H, –CHOH–), 3.21 (d,
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Copyright ꢀc 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 251–256

Alkoxysilane terminated organosilicone dendrimers
H
H C
3
Si
CH3
CH3
C H O
2
5
CH3
OC H
C H O
2
5
4
Si
O
2
5
H
H C
O
Si
3
H
Si
C H O
CH3
Si
2
5
Si
OC H
2
5
hydrolysis
O
H C
H
3
Tetraethoxysilane
O
H C Si
3
CH3
CH3
H
G A dendrimer
0
Scheme 1. Synthesis of tetrakis(dimethylsiloxy)silane (G0A) dendrimer.
chlorodimethylsilane[39] and also by the reaction of tetramethyl-
product δ CH2CH3 protons of ethoxy group, which were present in
[
41]
13
disiloxane, isopropanol and tetraethoxysilane,
we tested an
tetraethoxysilane and dimethylethoxysilane, did not appear.
C
alternative route to prepare it by the reaction of tetraethoxysi-
lane and dimethyethoxysilane in one pot, which gave 69% yield
NMR gave only one peak at δ 0.2 ppm, which may be assigned
2
9
to δ CH3. Si NMR showed two peaks at δ −108 and δ 8.5 ppm.
(
1
7
Scheme 1). The other byproducts formed were identified as
The peak at higher field may be assigned to structural species
◦
4
,1,3,3-tetramethyldisiloxane (3.65g, 19%), b.p. 71–72 C (lit. b.p.
Q [Si(OSi)4] and corresponds to a silicon atom attached to four
◦
[44,45]
2–73 C), along with highly viscous silicones and silica.
silicon species via oxygen bridges.
Similarly, the peak at lower
1
The G0B dendrimer was also synthesized by the reaction of
field may be assigned to structural species M [Si(OSi)H(CH3)2] and
G0A dendrimer and allylglycidylether under high temperature
and pressure in very high yield (95%) and in a much shorter
time (3 h) as compared with the earlier reported method.[
The G0B dendrimer was reacted with 3-aminopropylalkoxysilanes
under inert atmosphere at 38–40 C for 5 h to afford alkoxy
group-terminated G1 dendrimer (Scheme 2).
corresponds to a silicon atom attached to one silicon atom via an
Therefore, it may be concluded that the G0A
dendrimer synthesized successfully.
oxygen bridge.[
44,45]
6,42,43]
The progress of the hydrosilylation reaction of G0A dendrimer
and allylglycidylether was monitored with the disappearance of δ
◦
1
SiH proton at 4.74 ppm and δ H2C CH2 at ∼5–6 ppm. H NMR
When the G1 dendrimer was reacted with TEOS in the presence
of DBTDL, it yielded a high char yield resin matrix (Scheme 3). The
G1 dendrimer also crosslinked intermolecularly in the presence
of DBTDL, but the char yield of the cured materials was lower
comparedwithpreviousones. Insuchcases, curingoccursthrough
hydrolysis of alkoxy groups followed by condensation of hydroxyl
groups.[
of G0B dendrimer showed characteristic signals for an oxirane
ring at δ 2.59 ppm (CH2, trans), 2.77 ppm (CH2, cis) and 3.13 ppm
(CH). The δ SiCH3 appeared as a singlet at 0.07 ppm whereas δ
SiCH2 appeared as a triplet at 1.17 ppm due to coupling with
protons of the nearby –CH2 group. The signals of δ –CH2 of the
Si–CH2 –CH2 –CH2 – group appeared as a multiplet at 1.82 ppm,
which may be assigned to the coupling of protons of the –CH2
group with the protons present on either side carbon atom, δ
CH2, which joins the ether linkage to the oxirane ring appearing
at 3.37 ppm (cis) and 3.71 ppm (trans), both appearing as triplets
due to coupling with the proton present on the same carbon
atom as well as protons attached to the next carbon atom of the
oxirane ring. The δ CH2 of the CH2 –CH2 –O– group appeared at
4.01 ppm as a triplet, which showed coupling with the protons of
44]
IR Studies
FT-IR spectra of dendrimers were studied in the range
−
1
4
00–4000 cm using KBr pellets. The G0A dendrimer showed
−
1
the presence of νSi–O–Si absorption at 1080 cm
131 cm . The νSi–CH3 absorption was not characteristic as both
and νSi–H at
−
1
2
1
3
the reactants showed the same absorption for νSi–CH3 groups.
Thus, it may be tentatively concluded that G0A dendrimer formed.
The FT-IR spectra of G0B dendrimer showed the appearance
of characteristic absorption peaks of oxirane ring at 913 and
the next CH2 group. C NMR spectra showed that the signals for
δ SiCH3 appeared at 0.1 ppm, for δ SiCH2 at 14.1 ppm, δ –CH2 of
the Si–CH2 –CH2 –CH2 – group appeared at 23.5 and 74.5 ppm, δ
SiCH2 of the oxirane ring at 44.6 ppm, δ CH2 of the O–CH2 –oxirane
−
1
−1
29
3
054 cm and disappearance of νSi–H peak at 2131 cm , which
ring at 70.9 and δ CH of the epoxy ring at 50.9. Si NMR spectra
4
was very prominent in the G0A dendrimer. The olefinic bond of
showed the two peaks at δ −108 ppm and δ 7.2 ppm for Q
−
1
1
allylglycidylether at 1649 cm also disappeared in the product.
Therefore, it may be inferred that the hydrosilylation reaction of
G0A and allylglycidylether took place.
species [Si(OSi)4] and M species [Si(OSi)(CH3)2CH2], respectively,
andtherewashardlyanychangewiththeG0A. Therefore, itmaybe
concluded that the G0B dendrimer was synthesized successfully.
The formation of dendrimer G1A and G1B was also confirmed by
In the reaction product of G0B and 3-aminopropylalkoxysilanes,
−
1
1
the oxirane ring absorption peaks at 913 and 3054 cm disap-
NMR spectra. H NMR spectra of dendrimer G1A and G1B showed
−
1
peared and secondary –OH peaks apperared at ∼3475 cm . The
a peak at ∼3.21 ppm as a doublet for protons of the hydroxyl
group and at 1.08 ppm as a multiplet for the amine group proton;
splitting of peaks occurred due to the coupling with the nearby
protons. The peak for δ OCH2 and δ CH2CH3 of the ethoxy group
appeared at 3.75 ppm as quartet due to the coupling with –CH3
groupprotonsandat1.57 ppmasatripletduetothecouplingwith
−
1
νNH2 absorption peaks at ∼3420 cm disappeared and a broad
−
1
peak appeared at ∼3361 cm , which may be due to overlapping
of νOH and νNH peaks. Therefore, it may be concluded that epoxy
group reacted smoothly with 3-aminopropylalkoxysilanes and G1
dendrimers formed.
–
OCH2 protons. The spectra also showed additional peaks at 0.13
1
3
for Si–CH3 in the case of 3-aminopropyldiethoxymethylsilane.
C
NMR Studies
NMR spectra of dendrimer G1A and G1B showed peaks for δ CHOH
at 63.4 ppm. The peak for δ OCH2 appeared at 59.0 ppm and for δ
1H NMR spectra of G0A dendrimer showed multiplet for δ SiH at
2
9
4.74 ppm due to coupling with SiCH3 protons and doublet for δ
CH2CH3 at 18.1 ppm. Si NMR spectra of dendrimer G1A and G1B
4
SiCH3 at0.22 ppmduetocouplingwithprotonsofSiHgroup.Inthe
showed peaks at −108 ppm for Q species [Si(OSi)4] and 7.1 ppm
Appl. Organometal. Chem. 2010, 24, 251–256
Copyright ꢀc 2010 John Wiley & Sons, Ltd.
www.interscience.wiley.com/journal/aoc

K. Saxena, C. S. Bisaria and A. K. Saxena
O
O
H C
3
Si
CH3
O
O
CH3
4
O
O
G0A
Dendrimer
O
O
(
hydrosilylation)
Si
CH3
Si
O
H C
Si
3
O
CH3
H C Si
3
CH3
O
O
O
O
G B dendrimer
0
R
R
Si
R'
HN
HO
O
H C
3
Si
4
NH (CH ) SiR R'
CH3
2
2 3
2
R
CH3
G B Dendrimer
Si
O
0
N
H
O
stirring
O
R'
Si
CH3
Si
5h
R
HO
Si
O
H C
3
O
CH3
H C Si
3
CH3
O
HO
HN
O
R'
Si
R
HO
R
HN
R
R'
R
Si
G
dendrimer
1
Scheme 2. Synthesis of G1 dendrimers, where for G1A, R = OCH2CH3, Rꢁ = CH3 and for G1B, R = Rꢁ = OCH2CH3.
O
O
O
OEt
Si
EtO
EtO
Si
O
Si
OEt
O
DBTDL
EtO
+
Si
OEt
O
O
OEt
Si Si
O
O
O
O
O
G Dendrimer
TEOS
Cured Dendrimer
1
Scheme 3. Synthesis of cured dendrimers.
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Copyright ꢀc 2010 John Wiley & Sons, Ltd.
Appl. Organometal. Chem. 2010, 24, 251–256

Alkoxysilane terminated organosilicone dendrimers
Table 1. Thermal analysis data for G1 and cured dendrimers
Cured
dendrimers
Char yield (%)
(800 C)
◦
◦
◦
◦
Tg ( C)
Td ( C)
Td ( C)
G1A
G1B
CD1
CD2
CD3
CD4
–
344
350
359
352
317
360
–
25
27
42
40
32
35
–
–
212
236
173
216
472
466
441
452
Tg, glass transition temperature; Td, crest temperature of first stage
degradation; Td, crest temperature of second stage degradation.
Figure 1. Thermomechanical analysis of cured dendrimers.
1
forM species[Si(OSi)(CH3)2CH2]. ThepeaksforTstructuralspecies
[
Si(OEt)3CH2] appeared at δ −40 ppm and for D structural species
[SiCH3(OEt)2CH2] at δ −17 ppm.
Thermal Analysis
TMA and TGA methods were carried out for the thermal property
studies of the cured and uncured dendrimers. Figure 1 shows
the TMA curves of all the cured dendrimers. All the TMA curves
indicated a single transition, giving the idea that there is uniform
cross-linking. Comparative study of different cured materials
showed that CD2 had the highest glass transition temperature
(
Tg) and CD3 had lowest Tg. The variation in Tg data of different
Figure 2. Thermogravimetric analysis of cured dendrimers.
cured dendrimers can be explained by the fact that Tg increases
with high cross-linking density. Among all the cured dendrimers,
CD2 had the highest Tg due to high cross-linking density as the
more peripheral cross linking sites were available in the dendritic
reactant used for its synthesis.
may be used as resin matrices for composites and also for RTVs
1
and HTVs. All the materials were characterized by FT-IR, NMR ( H,
1
3
29
C and Si) and elemental analysis.
The TGA data (Table 1) showed that the degradation of uncured
dendrimers occurred in one step with the crest temperature of
◦
∼
344 C, whereas in case of cured dendrimers, it occurred in two
Acknowledgments
◦
steps. The first step degradation started at ∼340 C with the crest
◦
Thanks are due to the Director, DMSRDE for necessary encourage-
ment and providing laboratory facilities to facilitate the work. We
temperature at ∼355 C, indicating mainly the decomposition of
ether linkage; simultaneously other groups attached remotely
to the silicon atom also decomposed. The second stage of
1
13
also extend our thanks to CAF Division, DMSRDE, for H, C NMR
and thermal studies. We are grateful to Dr F.A. Khan, IIT Kanpur,
◦
degradation with a crest temperature of ∼466 C corresponded
2
9
for carrying out Si NMR studies.
to the decomposition of groups nearer to the silicon atom. It
is obvious from the results that both cured as well as uncured
dendrimers are high temperature-resistant materials.
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