Thermally induced twin polymerization of 4H-1,3,2-benzodioxasilines

Article abstract of DOI:10.1002/chem.201400038

The twin monomer 2,2′-spirobi[4H-1,3,2-benzodioxasiline] (1) can be polymerized to nanostructured SiO₂/phenolic-resin composite material by thermally induced twin polymerization. Thermally induced twin polymerization represents a way to produce

Full text of DOI:10.1002/chem.201400038

DOI: 10.1002/chem.201400038
Full Paper
&
Polymerization
Thermally Induced Twin Polymerization of 4H-1,3,2-
Benzodioxasilines
[
a]
[a]
[b]
[a]
[c]
Patrick Kempe, Tina Lçschner, Alexander A. Auer, Andreas Seifert, Gerhard Cox, and
[a]
Stefan Spange*
Abstract: The twin monomer 2,2’-spirobi[4H-1,3,2-benzo-
dioxasiline] (1) can be polymerized to nanostructured SiO2/
phenolic-resin composite material by thermally induced twin
polymerization. Thermally induced twin polymerization rep-
resents a way to produce nanocomposites simply by thermal
induction of twin monomers. Besides 1, the thermal reaction
of several related salicylic (2-oxybenzylic) silicon molecules
has been investigated. The thermal cleavage of the mole-
cules is studied by using several trapping reagents (e.g.,
vinyl compounds). A significant occurrence of quinone me-
thide adducts indicates that the thermal mechanism pro-
ceeds not only by a ring opening at the oxymethylene posi-
tion, but also with the ortho-quinone methide as a central or
alternative intermediate. This is supported by product analy-
ses of thermally initialized reactions of 1 and its substituted
analogues as well as by quantum chemical calculations.
Introduction
separation is prevented, the molecular combination in one mo-
nomer offers the possibility to synthesize composite materials
that possess single polymer phases that interfuse on the nano-
scale. This strategy is often interfered when byproducts are
formed that disturb a homogeneous distribution of both
phases. Phase separation occurs when both polymers have no
chemical linkage and do not show any attractive forces. If the
use of solvents is mandatory, their removal can have unfavora-
ble effects on the composite structure and a collapse of the
Composite materials represent a material class that we cannot
dispend in modern ages. Their application is manifold as well
as the combination scope of different material classes (dental
composites, fiber reinforced plastics, disk brake pads, ferrocon-
crete, etc.). Composites were already used in ancient times
(macroscopic: bricks of straw and mud; microscopic: concrete)
because of their advantageous properties due to the combina-
tion of two single materials. The principle of composite materi-
al is also found in nature (wood: cellulose/lignin, bones: hy-
droxyapatite/collagen fibers). The composite structure can
exist on different size scales from macroscopic to microscopic
[1]
material is possible. Novak and co-workers used alkenols to
synthesize alkenyloxysilanes as hybrid monomers. The organic
part can undergo chain-polymerization or ring-opening poly-
merization (ROP) and form the organic polymer, and the inor-
ganic silicon moiety can be polymerized by using a sol–gel
[
1]
level.
[2]
Prior-known strategies required to mix different monomers
and to adjust all reaction parameters until an almost simulta-
neous polymerization takes place. The improved method of
using inorganic/organic hybrid monomers is a well-known
process. Adversely, both polymerizations are not dependent
on each other and appropriate reaction conditions must be
found to achieve a simultaneous polymerization of both
phases to create the nanocomposite material. Additionally,
water is needed for the sol–gel process, which limits the
choice of the organic parts and the solvents because of immis-
[
2]
strategy for the production of composite materials. If phase
[2]
cibility and unfavorable reactions. This concept was extended
to other central atoms besides silicon, for example, titanium-
[a] P. Kempe, Dr. T. Lçschner, Dr. A. Seifert, Prof. Dr. S. Spange
Department of Polymer Chemistry
Chemnitz University of Technology
Strasse der Nationen 62, 09111 Chemnitz (Germany)
Fax: (+49) 371-531-21239
E-mail: stefan.spange@chemie.tu-chemnitz.de
[2]
oxopolyacrylate composites, and may also be applicable to
other inorganic oxide/polymer composites. Well-defined aryl-
or alkyl-bridged silanes or silsesquioxanes have been used to
produce type II composites (covalently bonded phases) with
[b] Prof. A. A. Auer
[2]
dimensions of 0.5 to 2 nm.
Department of Molecular Theory and Spectroscopy
MPI for Chemical Energy Conversion
Stiftstrasse 34–36, 45470 Mꢀlheim an der Ruhr (Germany)
[c] Dr. G. Cox
Department of Material Physics and Analytics
BASF SE, Carl-Bosch Strasse 38
6
7056 Ludwigshafen (Germany)
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201400038.
Scheme 1. Idealized TP Equation for 1.
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Advanced strategies such as a twin polymerization (TP) were
necessary to overcome the mentioned problems (Scheme 1).
The twin monomers form the basis of TP, which are specially
constructed inorganic/organic hybrid monomers with an ade-
quate reaction character. In contrast to former concepts, twin
monomers like 1 do not need additional molar amounts of
water to liberate the alcohol and to form reactive silanols and
silanolates as in a common sol–gel process. The formation of
silanol and silanolates happens intrinsically after cleavage of
the oxymethylene group at the same moment when the acti-
vated benzylic function is reacting and adds to the next phen-
oxy ring. Therefore, the organic and inorganic polymerizations
depend on each other. Additionally, the remaining SiꢀOꢀaryl
bonds suppress phase separation during the initial phase of TP.
In addition, as a further advantage, no water is released in
molar amounts, silanols react with twin monomers and create
SiOSi bonds, while phenolic OH is formed and is found in the
organic product phase (phenolic resin).
Figure 1. HAADF STEM images of glassy transparent composite material,
which was obtained by thermal TP of 1 in melt at 2308C (expt. II). The Fig-
ures show a composite material with homogenously distributed phases.
Domain sizes of 2–3 nm become visible on the nm scale (ChapterC2 in the
Supporting Information).
The improved TP process allows the synthesis of nanocom-
posite materials in a convenient polymerization process with
[
3]
no further requirements on reaction control. The TP can pro-
ceed catalyzed by electrophiles and nucleophiles at lower tem-
peratures or uncatalyzed at elevated temperatures as de-
scribed here (ChapterC1 in the Supporting Information). The
acid/electrophilic-catalyzed process is already described and
[
3,4]
the initial step of reaction is well explored.
The first step
after electrophilic attack—the cleavage of the benzyl–oxygen
bond and the electrophilic attack of benzyl to another elec-
tron-rich aromatic—is comparable to the known Friedel–
Crafts-benzylation reaction with benzyloxysilanes under acidic
Scheme 2. Twin monomers 1, 2, and related molecules researched in this
work.
[
5]
catalysis.
Here we report on the behavior of different 4H-1,3,2-benzo-
dioxasilines under non-catalyzed thermal conditions. The possi-
bility of thermal polymerization of twin monomers was discov-
ered during the research on 2,2’-spirobi[4H-1,3,2-benzodioxasi-
line] (1), which forms a glassy transparent nanocomposite ma-
terial upon heating to 2308C just like under acidic conditions
in melt or concentrated solution at low temperatures (Fig-
seemed possible (ChapterC3 in the Supporting Informa-
[4]
tion). Computational studies delivered further insights of the
thermal reaction behavior of 1.
To draw mechanistic conclusions for the thermal polymeri-
zation we used trapping agents (vinyl compounds) that were
supposed to react with thermally activated twin monomers or
with intermediate species of the thermal TP.
[
3d]
ure 1).
The glassy transparent nature already indicates the presence
of an amorphous composite with homogeneously distributed Results and Discussion
phases with domain sizes smaller than the wavelengths of visi-
Thermal homopolymerization
ble light (ChapterC2 in the Supporting Information). In addi-
tion to the aforementioned advantages of TP compared to the
sol–gel processes and hybrid monomer strategies, the thermal
TP of 1 demonstrates that TP requires no additional catalyst if
a suitable twin monomer is chosen.
As is known from acidic catalysis, the spiro monomer 1 is more
reactive to the initial ring-opening reaction than 2 (ChapterC4
[4]
in the Supporting Information). A comparison of 1 and 2 was
also made for the thermal polymerization. Experiments on
a multigram scale showed that 2 is volatile at elevated temper-
atures and finally boils at ꢁ2308C. Contrary to our assump-
tion, compound 2 does not tend to polymerize thermally. After
heating at reflux at 2308C for 3 h under an argon atmosphere,
compound 2 remained unchanged as evidenced by NMR spec-
troscopy.
Compound 1 and three related molecules were chosen for
a mechanistic study (Scheme 2). 2,2-Dimethyl-[4H-1,3,2-benzo-
dioxasiline] (2) was also tested for thermal TP. The thermal re-
action behavior of the substituted analogue compounds of 1:
2
,2’-spirobi[6,8-dimethyl-4H-1,3,2-benzodioxasiline] (3), and
,2’-spirobi[8-tert-butyl-6-methyl-4H-1,3,2-benzodioxasiline] (4)
2
were also tested. Although the formation of phenolic resin is
impeded for 3 and 4 (due to blocked ortho- and para posi-
tions), their reaction should deliver additional mechanistic in-
formation, at least the formation of silica-like structures
The NMR spectroscopic data proves that 2 possesses a less-
polarized oxymethylene unit than 1, which confirms the higher
stability of
2 under non-catalyzed reaction conditions:
1
13
1
13
d (CD Cl , H/ C, CH O)=5.22/66.9 ppm; d (CD Cl , H/ C,
1
2
2
2
2
2
2
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CH O)=4.96/64.3 ppm. The inductive effect of the
2
methyl groups and the less-polarized oxymethylene
group afford a higher proton concentration for 2
than for 1 relative to the number of rings in the acid-
catalyzed TP to show full conversion to the TP prod-
ucts. The central Si atom of 1 is surrounded by four
oxygen atoms resulting in a higher polarization of
the oxymethylene group (ChapterC5 in the Support-
ing Information). The lower stability of 1 allows ther-
mal non-catalyzed TP at 2308C. Because of the lower
reactivity of 2, a higher reaction temperature is nec-
essary for 2 than for 1 under non-catalyzed thermal
TP. Unfortunately, compound 2 has a boiling point of
ꢁ
2308C that is too low, and the activation tempera-
ture for thermal TP is not reached at standard pres-
sure (ChapterC6 in the Supporting Information). DSC
analysis of 1 shows an endothermic melt peak and Figure 3. TGA (10 Kmin , under He flow) and DTGA (dashed curve) of 1.
an exothermic polymerization peak. Compound 2
ꢀ
1
(
liquid at 258C) shows only an endothermic evapora-
tion peak. The effect of additional reactivity of 1 is evident
Figure 2). Another effect that distinguishes both monomers in
about the evaporating side products (ChapterC6 in the Sup-
porting Information). NMR spectroscopic analyses of experi-
ments on a multigram scale (Table 1, expt. I–V) showed that
the material, which evaporates from the reaction mixture and
condenses to the upper regions of the reaction flask and at
the reflux condenser, consists mainly of aromatic compounds
(ChapterC7 in the Supporting Information). These represent
the main mass loss during the thermal polymerization of 1;
water was not detected.
(
their polymerization behavior is the additional autocatalytic
acidity of formed silica-like structures during the TP of 1.
According to the DSC results, the initial reaction of 1 starts
upon reaching 1858C at a heating rate of 10 Kmin . A small
shoulder (ꢁ2008C) may indicate that a more reactive spiro
structure is consumed first, followed by the reactions of the re-
ꢀ
1
The thermal TP of 1 in melt (Table 1, expt. I, II) leads to the
Table 1. Data of thermal TP experiments of 1 in melt and in DIPN. Last
column: C content of the nanocomposites after CHCl
3
extraction.
Expt. No
T
t
[h]
c
1
C
ꢀ1
[
8C]
[molL
]
[wt.%]
I
II
III
IV
V
230
230
230
230
230
1
melt
melt
DIPN 0.27
DIPN 0.11
DIPN 0.55
ꢁ62
ꢁ61
ꢁ58
ꢁ57
ꢁ57
0.5
0.5
2
2
formation of glassy transparent monolithic materials, which
were homogeneous nanocomposites of phenolic resin and
a silica-like phase as typical for a twin polymer (ChapterC2 in
ꢀ1
2
Figure 2. DSC (10 Kmin , under N flow) of 1 and 2.
[3d]
the Supporting Information). The obtained monoliths are
nearly insoluble in aprotic solvents. A mass loss was hardly de-
tectable when 1 was polymerized in melt, only a very thin
layer of low-weight compounds condensed in the upper
colder regions of the flask. The yield was close to 100%, which
means the mass of the composite material was nearly equal to
the applied mass of 1. Contrary to the DSC and TGA results
with their small sample volumes and high sample surface area,
a multigram-scale polymerization of 1 possesses a smaller sur-
face area, a gas flow of inert gas cannot take away significant
masses of 1 or of side products, and there is a higher probabil-
ity that cleaved low-weight side products are consumed in the
maining 4H-1,3,2-benzodioxasiline ring structures. Also, a faster
reaction of the organic phase may be considered, which results
[
3d]
in a shoulder.
A third explanation is an endothermic character of evaporat-
ing low-weight side products under the nitrogen flow, which
leads to a deformation of the exothermic peak. TGA results of
1
support the latter argumentation, because of a main mass
loss at the same temperature of ꢁ2008C, which is ꢁ30 K
below the applied reaction temperature (Figure 3). The TGA-
coupled mass spectrometry of 1 delivered no clear information
Chem. Eur. J. 2014, 20, 1 – 15
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reaction medium before evaporating from it (ChapterC7 in the
Supporting Information).
The consumption rate of all reactive moieties depends on
the reaction time, the concentration, and the applied tempera-
ture (here: 2308C). It should be considered that at higher tem-
peratures (>3008C) the TP process changes slowly into a car-
bonization reaction of the composite material (ChapterC2 and
C6 in the Supporting Information). To determine the full con-
version of 1 to phenolic resin and SiO in the TP process is dif-
2
ficult. In every case, all of the benzyloxy groups should be con-
sumed. Also, in a narrower sense, all the silanol groups (SiOH)
and aryloxy-silyl bonds (aryl-OꢀSi) must have reacted to give
phenols (aryl-OH) and SiꢀOꢀSi to fulfil the idealized reaction
equation of TP (Scheme 1). The product samples were ana-
13
lyzed by C solid-state NMR spectroscopy, which shows the
2
9
1
3
conversion state of the benzyloxy groups and Si solid-state
NMR spectroscopy gives information about the condensation
degree of the inorganic phase.
Figure 4. C Solid-state NMR (CPMAS) spectra of the monolithic composite
materials from melt (expt. I, II) and the filtered and extracted composite par-
ticles (III–V) of the thermal TP of 1 in solution at 2308C. Beside the signals of
phenolic resin, additional signals in some of the solid-state NMR spectra con-
firm the presence of trimers of ortho-quinone methide (ToQM) in the com-
Diisopropylnaphthalene (DIPN) was used as solvent for ther-
mal polymerization of 1 in solution because of its high boiling
point (>2808C) and inertness. Thermal polymerization of 1 in
DIPN (Table 1, expt. III–IV) yielded precipitated composite parti-
cles that also showed a homogeneous distribution of both
phases on the nanoscale (ChapterC2 in the Supporting Infor-
mation). The yield of filtered and extracted composite was low-
ered to 60–70% of the theoretical maximum mass. Reasons for
the yield loss were attributed to the difficult handling of the
obtained small particles, which were very dusty and electro-
static (especially when dry), and the small particles adhered to
the filter or even passed the filters. Centrifuging was no more
convenient because of the large volume of the reaction mix-
ture. Multiple centrifuging, extracting, and decanting suffer
from similar problems. Low-molecular-weight side products
were isolated from the filtrate and the extract of the precipitat-
ed material (ChapterC7 in the Supporting Information). Their
combined total mass was <5 wt.% of the applied mass of 1.
The C content of the composite material obtained from melt
was close to the C content of 1 (61.75 wt.%) as expected
when almost no substances cleave and evaporate. In the case
of the obtained particles from solution in DIPN some organic
material was not cross-linked to the composite and is found in
the filtrates and extracts; the C content of the particles is
slightly lowered (Table 1).
1
3
posite structure. The high-resolution C NMR spectrum of ToQM in CDCl is
shown for comparison. Spinning rates and number of scans (NS) are depict-
ed; [*]=spinning side bands are assigned.
3
13
field-shifted C NMR phenoxy signal (Figure 4, signal a, Dd
ꢁ1 ppm) may indicate non-cleaved silicon. The formation of
phenolic resin is clearly confirmed by the diarylmethylene
signal, the center of the broad signal at dꢁ31 ppm indicates
a dominant ortho–ortho-linkage of the phenolic resin (o–p-link-
age: dꢁ35 ppm). The aromatic signals with a low ratio of
signal b (Figure 4) support this statement.
29
Figure 5 shows the Si solid-state NMR spectra of the ob-
tained composite materials. No signal for 1 (d=ꢀ78 ppm, Q )
0
was detected, its thermal conversion lead to a condensed
silica-like phase with a high content of Q and Q signals be-
3
4
sides the phenolic resin.
13
In Figure 4 the C solid-state NMR spectra of the obtained
monoliths (expt. I, II) and the filtered and extracted precipitates
(III, IV, V) are depicted. In all cases 1 was consumed completely
because no narrow monomer signal appeared at d=66 ppm
13
in the C solid-state NMR spectra, also the prior-separated ex-
tracts contained no more 1 (ChapterC7 in the Supporting In-
formation). A broad signal at dꢁ64 ppm indicates an incom-
plete reaction of the organic moieties with remaining 4H-1,3,2-
benzoxasiline cycles or open benzyloxysilane groups (ꢀOꢀ
arylꢀCH ꢀOꢀSiꢀ) or benzyl alcohol groups (ꢀOꢀarylꢀCH ꢀOH).
2
2
2
9
Figure 5. Si MAS NMR spectra of the monolithic composite material from
melt (expt. I), the filtered and extracted composite particles (expt. III) from
DIPN, the obtained composite material after reaction of 1 with TD (expt. XI),
These moieties still interlink silicon to the organic phase, if the
phenoxy-O or the benzyl-O is condensed to Si. Experiment II
shows that a reaction time that is too short leads to an incom-
plete conversion of the benzyloxy groups, also a slightly low-
29
and Si CPMAS NMR of the finally obtained material of expt. XII (1+PB). In
CPMAS experiments the intensities of Q and Q peaks are overrated.
2 3
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Side products
mentioned side products are redox reactions of the oQM-inter-
mediate, H-donors and -acceptors are found in the phenol
structures and side products themselves (ChapterC7 in the
1
3
Small signals in the C solid-state NMR spectra (Figure 4,
expt. II–V) indicate a substructure. These characteristic signals
[6]
Supporting Information). The proof of these condensates in
the reaction mixture is more difficult because of their low con-
centration, and their consumption in the reactive mixture
(ChapterC7 in the Supporting Information). Methyl, methylol,
and aldehyde groups can also form in the polymer structure in
1
3
were also found in the C NMR spectrum of an extracted side
product: the trimer of the ortho-quinone methide (ToQM, see
Scheme 3, and 7). Hence, this trimeric structure is assumed to
[6]
low concentrations.
In the filtrates and extracts of the thermal TP in DIPN several
side products were found: ToQM, 1,2-bis(2-hydroxyphenyl)-
ethane (BPE), calixarenes, and oligomers of phenolic resin rep-
resent the major side products. Additionally, traces of bis(2-hy-
droxybenzyl) ether, the redox-chain members salicyl aldehyde,
salicyl alcohol, ortho-cresol, and the acetal of salicyl aldehyde
and salicyl alcohol were found (Scheme 3). Their combined
total mass was below 5 wt.% of the applied mass of 1 (Chap-
terC7 in the Supporting Information).
A release of formaldehyde from bis(2-hydroxybenzyl) ether
is also possible yielding phenolic resin (diarylmethylene); very
1
13
weak H/ C NMR signals indicate even oligo(oxymethylene) is
released in trace amounts. However, this reaction is negligible,
because firstly, only small amounts of benzylic alcohols as salic-
yl alcohol were detected, secondly, these small amounts must
cleave formaldehyde or condense to dibenzylic ethers and
cleave formaldehyde afterwards. No significant amounts of di-
benzyl ether were found, only trace signals were attributed to
it. Even when formaldehyde is liberated it can react again with
the reaction media and remain in the phenolic resin structur-
e (ChapterC7 in the Supporting Information).
Scheme 3. Isolated compounds from the filtrates and extracts of the precipi-
tated composite material of the thermal polymerization of 1 in DIPN (ex-
pt. III–V). Characterization and further details are collected in the Supporting
Information (ChapterC7 in the Supporting Information). Their combined
total mass was <5 wt.% of the applied mass of 1. Extracted oligomeric
phenolic resin, calixarenes, ToQM, and BPE represent the main part beside
further side products.
[
6]
Mechanistic considerations
be part of the phenolic resin in a small extent. The electron-
rich phenoxy-structures of ToQM can be substituted at their ac-
tivated ring positions and be chemically bonded to the phe-
nolic resin. The existence of this substructure and ToQM itself
shows that probably the thermal activation of 1 leads to the
formation of ortho-quinone methides (oQM) or quinoidal struc-
tures, which react with themselves to oQM-[4+2]-adducts or
with other phenoxy-structures to a phenolic resin.
In particular, the existence of ToQM, BPE, and the three redox
partners indicates a more complicated mechanism than in the
acid-catalyzed TP at low temperatures. Additional reactions
occur at elevated temperatures. There are different mechanistic
scenarios possible. A reactive polarized benzyloxymethylene
group that reacts in a concerted mechanism results in a diaryl-
methylene and a silanol group. In addition, one can consider
a reactive benzyl cation or radical from heterolytic or homolyt-
ic cleavage. A homolytic cleavage is less probable, because the
benzyl radical is only stabilized by the aromatic system, not by
the phenoxy oxygen. The benzyl cation is additionally stabi-
lized by the mesomeric effect of the phenoxy oxygen (+M-
effect), and a quinone-like structure forms (Scheme 4). The re-
action of the benzyl cation with a 1 yields the same product as
in the concerted mechanism described first.
The small amount of material that condensed to the upper
regions of the flask and reflux condenser in the thermal TP of
1
(in melt and solution) shows mainly characteristic NMR spec-
troscopic signals of salicyl aldehyde, salicyl alcohol, and ortho-
cresol (redox chain). The formation of salicyl aldehyde because
of an oxidative reaction due to an O -leakage is not likely, be-
2
cause it does not explain the existence of ortho-cresol, which is
the product of a reductive process. Salicyl alcohol (generally
benzyl alcohol groups) represents the center of the redox
chain and can be formed by hydrolysis steps in small amounts,
it is probably the starting point of the redox processes. Litera-
ture describes that at elevated temperatures salicyl alcohol
tends to condense to the corresponding dibenzyl ether, further
heating can lead to scission of the ether function under dispro-
portionation to a methyl and an aldehyde function leading to
The unique character of the TP becomes obvious when in
the concerted or benzyl-cationic mechanism a diarylmethylene
bridge is formed (organic polymerization) and at the same
time a silanol group is formed (active species of the inorganic
polymerization) and the aryloxysilane group is still unchanged,
which prevents a phase separation in the initial phase of TP.
Furthermore, the release of reactive oQM takes place (indi-
cated by the presence of ToQM and BPE), which can react as
an electrophile, a nucleophile, and takes part in [4+2]-cycload-
[
6]
ortho-cresol and salicyl aldehyde. A further source of the
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[
6]
Scheme 6. Liberation of ortho-quinone methide. The liberation can start
from 1 or hydrolyzed forms of 1 and also from bis(2-hydroxybenzyl) ether.
Scheme 4. Thermal activation of the benzyl-O bond and its theoretical reac-
tions: the concerted mechanism, the unfavored homolytic, and the favored
heterolytic dissociation.
Scheme 5. The mesomeric structures of oQM and the aromatic diradical
structure clarify the versatile reactivity (nucleophilic/electrophilic, [4+2], radi-
calic).
ditions, and redox reactions with H-shifts and partial radical
mechanisms (Schemes 5–7).
Scheme 7. Ortho-quinone methide trimerizes through a radical mechanism
and/or a [4+2]-cycloaddition. Redox processes lead to BPE.
When the phenolic OH is not condensed to Si, the formation
of o-quinone methide is even promoted, hence a proton-cleav-
[
6]
[
6]
age is necessary. Its liberation may happen directly from the
monomer, but if we regard an isolated monomer like 1, an im-
probable species with Si=O double bonds would remain, thus,
a reaction partner is necessary. If once a silanol has formed
Quantum chemical calculations
For compound 1 and 2 the proton-catalyzed activation has
been calculated at the B3-LYP-D3/def2-TZVP+COSMO level of
theory. For compound 1 the activation energy is calculated to
(Scheme 4) the inorganic polymerization (silanol attack at the
Si center) leads to phenol-OH formation, then the cleavage of
oQM is promoted. oQM can also cleave from the product phe-
nolic resin or from other side products and intermediates at
elevated temperatures (Scheme 6). The liberation of oQM from
salicyl derivatives is known, for instance from an analogue
ꢀ
1
be in the order of 22 kJmol with a reaction energy of
ꢀ
1
ꢀ27 kJmol . For compound 2 the barrier and reaction energy
ꢀ
1
are calculated to be 26 and ꢀ16 kJmol , respectively. Thus,
the reactivity of the two compounds mostly differs due to
their reaction energies rather than the barriers.
[
6]
boron compound.
The formation of ToQM and BPE can be explained starting
Quantum chemical calculations at the B3-LYP-D3/def2-
TZVP+COSMO level of theory indicate that in contrast to the
proton-catalyzed activation the thermal non-catalyzed activa-
tion by bond cleavage is highly endothermic. Although in the
presence of protons a cationic species converts into the active
polymerizing compound with a barrier that is estimated to be
from oQM by [4+2]-cycloadditions or radical intermediates
(
Scheme 7). Because of the absence of other possible [4+2]-ad-
ducts, Turner rationalized that the mechanism may comprise
[
6]
radical intermediates. The formation of BPE comprises an un-
expected direct bonding of two methylene groups that are
electropositively polarized in the oQM. An explanation is to
consider that oQM is in equilibrium with a diradical (radicalic
at phenoxy and methylene position), which recombines at the
methylenes and accepts two hydrogens. Or that the oQM-
ꢀ
1
ꢀ1
22 kJmol and a reaction energy of ꢀ27 kJmol , the forma-
tion of a zwitterionic active species is endothermic by more
ꢀ
1
than 200 kJmol .
A detailed charge analysis shows that the intermediate that
could be formed by heterolytic cleavage of the oxymethylene
bond during the thermal activation is indeed a zwitterionic
[
4+2]-adduct cleaves homolytically to the same intermediate
and accepts two hydrogens and forms BPE.
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the vinyl compound. Also, the already postulated presence of
oQM can be evidenced by these trapping agents (Scheme 8).
If a reaction with vinyl compounds proceeds, there may be
a direct addition of 1 to the vinyl carbons. Reactive intermedi-
Figure 6. Electrostatic potential of 1 (left), the protonated active species
bottom right) and the zwitterionic active species (top right).
(
Scheme 8. Considered reactive structures in the thermal TP (thermally acti-
vated twin monomer and its possible hetero- and homolytic scission prod-
ucts and oQM). Their reaction with different vinyl compounds delivers mech-
anistic information.
species in which the negative charge is mostly located on the
oxygen atom, whereas the positive charge is delocalized over
the phenyl ring (Figure 6).
The computational study of the thermal activation also ex-
hibits the reaction path for forming the side product oQM.
Bond cleavage of the benzylic CO yields a transition state that
can either convert to a local minimum by internal rotation or it
can undergo a second bond cleavage resulting into fragmenta-
tion. However, the latter process has an overall reaction energy
ate structures like benzyl cations or benzyl radicals or phenoxy
radicals (Scheme 7) additionally can initialize a polymerization
of adequate vinyl compounds. After the addition of a benzyl
cation or radical, an intermediate structure has the possibility
of further transformation, for example, through a H-shift, to
the most stable ring size before the ring is closed by the
second addition of the siloxy site. But these radical or carbo-
cationic intermediates would afford to surmount a high energy
barrier. Also, the formation of oQM from 1 or an intermediate
has to surmount such a barrier. The adduct formation itself is
entropically slightly unfavored, because of the formation of
one molecule out of two at high temperatures. The high tem-
perature is necessary to activate 1 and to surmount the de-
scribed energy barriers. On the other hand, the cleavage of the
double bond and the formation of two new single bonds
should thermodynamically favor this addition reaction.
ꢀ
1
of over 300 kJmol and is thus, in agreement with the experi-
mental findings, a highly unfavored reaction path that should
only yield traces of this side product. Furthermore, unrestricted
calculations clearly indicate that the formation of radical spe-
cies by bond cleavage of 1 is unlikely; all the resulting species
are found to be of singlet multiplicity with higher spin states
like biradical species being much higher in energy (at least
ꢀ
1
1
00 kJmol ).
It has to be noted that the calculations refer to the isolated
monomer and the bond dissociation energies given above re-
flect a possible reaction path for a single molecule in a field
that resembles the averaged influence of the solvent. In the
presence of further monomers, however, other reaction paths
might be accessible for which energy barriers for reactions ulti-
mately yielding the polymeric product might be much lower
All trapping compounds were tested first without twin mon-
omers at the applied reaction temperatures to exclude self-ini-
tiation or other side reactions (blank tests). The chosen reac-
tion temperatures depended on the boiling points of the trap-
ping agents and monomers; if possible a maximum tempera-
ture of 2308C was applied. All mentioned trapping compounds
in Table 2 do not alter during the blank tests at the used reac-
tion temperatures for 2.5 h. To obtain information about possi-
ble mechanisms we applied the trapping agents in excess
(Scheme 4). This might also be the case for the oQM forma-
tion, which may occur at alternative intermediate stages
during the reaction (Schemes 6 and 7.)
(
Table 2).
As evidenced, compound 2 was not activated thermally to
polymerize even at its boiling point of ꢁ2308C. However, com-
Trapping experiments
We found different vinyl compounds as adequate trapping
agents that allow mechanistic conclusions of the thermal TP
and its intermediates. Vinyl compounds offer p-nucleophilicity
to the positively polarized benzyl-function similar to electron-
rich phenoxy structures of other twin monomers in a common
TP when the phenolic resin is formed.
Table 2. Experimental data of trapping experiments. The trapping agents
were used in molar excess to the monomers (m).
Expt. No
m
Trapping agent
Molar excess
of vinyl
T
[8C]
t
[h]
As it is the case in the acidic TP, the oxymethylene unit was
supposed to be the most labile bond, which will cleave first by
thermal activation. At elevated temperatures the cleavage of
the benzyl–oxygen bond can occur by a concerted (activated
polarized benzyl-O bond), ionic/heterolytic (benzyl cation), or
less probably radicalic/homolytic (benzyl radical) mechanism,
finally yielding a new benzyl–carbon bond after addition to
VI
2
2
2
2
1
1
1
cis-cyclooctene
1-dodecene
cyclohexyl vinyl ether
n-dodecyl vinyl ether
n-dodecyl vinyl ether
1-tetradecene
20
20
10
10
15
15
–
150
220
150
230
230
230
230
2.0
2.5
2.0
2.0
1.0
1.0
1.0
VII
VIII
IX
X
XI
XII
poly(butadiene)
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pound 2 was tested together with the trapping agents in the
case that a combination leads to a reaction due to a decrease
of the activation barrier by electronic interactions. We used
common alkenes of increasing boiling points (Table 2, expt. VI,
VII), and we applied electron-rich vinyl ethers with increasing
boiling points (Table 2, expt. VIII, IX). Heating 2 with these trap-
ping agents also showed no reaction, all educts stood un-
changed. The trapping agents did not lower the energy barrier
for the thermal reaction of 2.
As the presence of the trapping agents does not lower the
activation barrier, trapping experiments with 1 were conducted
solely at 2308C. In experiment X (Table 2), NMR spectroscopic
data show only a moderate conversion of 1 in an excess of n-
dodecyl vinyl ether (DoVE) and the formation of an unexpect-
ed acetal and a small ratio of probably an oQM-[4+2]-vinyl-
adduct (ChapterC8 in the Supporting Information). A signifi-
cant polymerization of the vinyl ether was not observed, as it
was expected when cationic intermediates occur after thermal
activation of 1. Probably DoVE forms micellar structures and
1
3
Figure 7. C CPMAS NMR spectrum of the precipitating composite material
from experiment XI (1+TD) measured at 12.5 kHz; [*]=spinning side bands
1
3
are assigned. For better comparison the C NMR spectra (measured in
CDCl ) of TD and the quinone methide adduct are depicted. The composite
was treated with MeOH and chloroform, after drying (908C, vacuum) the
C NMR spectrum still shows a methoxy-signal of remaining MeOH or esteri-
ficated MeOH (aryl-O-Me). Not all benzyloxy groups are consumed yet
3
1
3
1
is found in the apolar alkyl-chain region. Therefore, the reac-
tion of 1 with the polar head group of DoVE is hampered and
the reaction of 1 with other spiro monomers is slow because
of the dilution in DoVE. In contrast, polar products (such as R-
OH) are preferably reacting with the polar head group of DoVE
leading to acetals beside oQM-adducts.
(
dꢁ64 ppm).
More striking results delivered experiment XI (Table 2);
during the experiment a white solid precipitated. The prepara-
tive product separation revealed a composition of several
products besides non-consumed 1-tetradecene (TD). Firstly,
a solid nanocomposite material consisting of a silica-like phase
and a phenolic resin phase with tetradecyl moieties is obtained
(40 m%C, Figures 5 and 7). Secondly, an oQM-[4+2]-adduct
1
13
with TD is present (Figure 7; ChapterC9 in the Supporting In-
formation). Furthermore, a fraction of tetradecyl species was
isolated, which is not volatile at 2308C/0.1 mbar and consists
of oligo(tetradecene) and oQM-substituted species of the
oQM-TD-adduct (Figure 8; ChapterC10 in the Supporting Infor-
mation).
Figure 8. H (left) and C NMR (right) spectra of the non-volatile product
fraction of expt. XI. A high ratio of oligo(tetradecene) and a small ratio of
multiple oQM-substituted oQM-TD-adducts were detected (ChapterC10 in
the Supporting Information).
The following product distribution was found for all benzylic
compounds: 53 mol% of the benzyl groups from 1 are com-
prised in the oQM-TD-adduct, 2 mol% in salicyl alcohol, the re-
maining benzyl moiety is found in the composite material as
phenolic resin, which seems to contain some tetradecyl chains,
probably bonded in an oQM-adduct structure or an oligo-tetra-
decyl structure. An oligomerization of TD may be initialized by
phenoxy radicals.
solely polymerized to phenolic resin. This is also indicated by
the signals around d1H =4.11 ppm, which belong to an adduct
structure of oQM and the double bonds of PB. This is con-
1
13
firmed by H/ C 2D-NMR spectroscopy (Figure 11); the specific
1
13
H/ C-correlation of d1
=4.11/77.2 ppm corresponds to the
H/13C
chemical shifts of the oQM-TD-[4+2]-adduct, a [4+2]-addition
of oQM with PB occurred. By treatment with several solvents,
a slightly ductile solid material was precipitated, filtrated, and
extracted. NMR spectroscopic analyses show that the material
is composite of PB/phenolic resin/silica (61 m%C).
As proven, an adduct formation of the organic phase of the
TP with olefins is possible. Combinations of different twin
monomers with different monomeric olefins and alkynes but
also with polymers that contain double and triple bonds seem
interesting for further research. As preliminary test for a combi-
nation of a twin monomer and such a polymer serves experi-
ment XII (Table 2), a thermal reaction of 1 in poly(butadiene)
From these additional results with vinyl compounds we con-
clude that the thermal TP mechanism follows a reaction of the
thermally activated and polarized benzyl–oxygen bond in
a concerted mechanism (Scheme 4, first row), the positive po-
larization is compensated by the +M-effect of the phenoxy-
oxygen, the benzylcationic mechanism by heterolytic dissocia-
tion can be considered as border case. But additionally the for-
mation of oQM from 1, reaction products, and intermediates is
promoted at 2308C (Scheme 6).
(PB). The corresponding NMR data are depicted (Figures 5, 9,
and 10) and show the complete consumption of 1 (no remain-
1
13
29
ing signal at d( H/ C/ Si)=5.2/66/ꢀ81 ppm), but the narrow
1
aryl signals in the H NMR spectrum indicate that 1 is not
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1
Figure 9. H NMR spectra of expt. XII. After the reaction mixture of 1 in PB is
heated to 2308C for 1 h, compound 1 is converted completely (the signal at
dꢁ5.2 ppm disappeared, the aryl signals shifted to high-field). An oQM-PB-
adduct structure is formed (compare with Figure 10 and 11). Shaded areas
belong to PB NMR signals and do not vary significantly.
1
13
Figure 11. H/ C 2D NMR (HMQC) of the reaction mixture of expt. XII after
heating to 2308C for 1 h. 1 is consumed completely and a quinone methide
adduct structure has formed besides phenolic resin.
1
3
Figure 10. C CPMAS NMR spectrum of the precipitating composite material
from experiment XII (1+PB) measured at 12.5 kHz. The signals of the residu-
al after washing with several solvents show the presence of PB and phenolic
resin structures.
Substituted analogue compounds of 1
Figure 12. TGA and DSC of 3 and 4.
We extended our research to monomers 3 and 4, which are
substituted analogues of 1. The ability to form phenolic resin
is extinguished due to blocked ortho- and para positions of
the phenolic rings, but their thermal reaction behavior delivers
additional mechanistic information.
the mass loss at 2858C is significantly higher than in the case
of 1. TGA-MS did not show any signals of water.
Thermally induced reactions of 3 and 4 in experiments on
a multigram scale delivered transparent brownish products
(Table 3). The C contents of the untreated products obtained
The thermal behavior was analyzed with DSC and TGA. As
depicted in Figure 12 they also show an endothermic melt
peak in the DSC followed by an exothermic reaction curve. The
exothermic reaction is accompanied with mass loss as can be
seen in the TGA. The mass loss arises from evaporating prod-
ucts; this endothermic process deforms the exothermic reac-
tion peak. The strong deformation of the exothermic DSC
peaks suggests a higher content of evaporating products and
at 2008C were comparable to those of the educts
3
(65.83 wt.%) and 4 (69.86 wt.%). Again the results of TGA/DSC
and experiments on a multigram scale differed due to the
volume effect. At least the lower C content of expt. XV
(Table 3) confirmed the evaporation of low-weight products
(Table 3). The C content of the extract of expt. XIII (Table 3) was
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[
a]
Table 3. Thermally induced reactions of monomers (m) 3 and 4.
Expt.
No
m T
t
C
product
m
[wt%]
C
insoluble
C
extract
[wt%]
[8C] [h] [wt%]
[wt%]
XIII
XIV
XV
3
4
4
200
200
250
3
3
3
ꢁ66
ꢁ69
ꢁ65
52
100
74.5
47
–
46
80
ꢁ69
74
[a] The 5th column displays the C content of the untreated products. The
6
th column displays the mass loss after extraction with CH Cl . The 7th
2
2
and 8th columns display the C content of the remaining insoluble materi-
al and the extract, respectively.
80 wt.%, which implies that almost no silicon species were dis-
solved. The remaining insoluble material was a composite of
a SiO -like phase with organic material (C: 47 wt.%). The or-
2
ganic phase is insoluble because of chemical bonds to SiO2
and because of strongly interlacing of both phases with low-
ered accessibility for solvents.
After thermal reaction of 3, the NMR spectroscopic analysis
29
confirmed its full consumption. Si solid-state NMR spectrosco-
1
py evidenced the presence of a silica-like phase. H and
13
C NMR spectroscopy showed that the formation of a phenolic
resin was suppressed due to the methyl-substituted phenoxy
rings. In the case of 3 the solid transparent product was solu-
ble in high portions (52 wt.% mass loss) and the liquid-state
NMR spectrum showed nearly the same signals as in the solid-
state NMR spectrum, but the narrow signals indicate the for-
mation of significant quantities of low-molecular-weight prod-
ucts. The products were analyzed after distillation by GC-MS
and NMR spectroscopic experiments and were identified as
2,4,6-trimethylphenol, methyl-substituted BPE, and small
amounts of 3,5-dimethyl salicyl aldehyde and traces of 4,6-di-
methyl-2-(hydroxymethyl)phenol (d1H ꢁ4.8 ppm; Figure 13;
ChapterC7 in the Supporting Information)). The exclusive for-
mation of these low-weight products occurs by the reaction of
the corresponding dimethyl-oQM and redox processes with H-
shifts, whereas the formation of phenolic resin is hindered. No
signals of [4+2]-adducts were found in the NMR spectra. Addi-
tionally, it is known that methyl groups can take part in the
thermal reactions; they can donate hydrogens, especially in
[6]
the presence of reactive substances like quinone methides.
The formed benzyl or phenoxy radicals and quinone methides
can form BPE derivatives.
1
13
29
When 4 was heated to 2008C under argon for 3 h (Table 3,
expt. XIV) a transparent red-brownish material formed. But
contrary to 3 it seemed to be fully soluble or at least it was
completely disassembling not regarding that non-visible micro-
Figure 13. H (top), C (middle), and Si NMR (bottom) spectra of the ther-
mal reaction of 3. In expt. XIII, compound 3 is consumed completely. The
2
9
13
Si solid-state NMR spectrum shows a silica-like phase and the C solid-
state NMR spectrum shows mainly signals of the methyl-substituted ana-
logue compound of BPE. Further side products were found. [*]=spinning
side bands.
scopic SiO -particles could be present. By applying a reaction
2
temperature of 2508C (Table 3, expt. XV) a partial soluble mate-
rial formed, a mass loss of ꢀ75 wt.% occurred by extraction.
The extract had a C content of ꢁ74 wt.%. The insoluble re-
1
13
The H and C NMR product spectra of expt. XIV (Figure 14)
show clearly characteristic signals of an analogue ToQM with
tert-butyl and methyl substitution as it is the case for 4. These
signals do not appear in the NMR spectra of the material ob-
tained at 2508C (expt. XV, Figure 14). At this temperature
a retro-[4+2]-reaction is promoted (!substituted oQM and its
mainder had a C content of 46 wt.% and represents a SiO -rich
2
phase with organic moieties that are either directly bonded or
are heavily interlaced with the inorganic phase, which hinders
extraction. NMR spectroscopic analyses reveal that even at
2508C for 3 h not all benzyloxy groups are converted.
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conclude the presence of remaining SiꢀOꢀC bonds. From the
results of blocked molecules 3 and 4 we conclude the thermal
reaction is mainly accompanied by a cleavage of substituted
oQM species from the starting molecules or intermediates as
described in Scheme 6. The reaction products represent com-
pounds that are normally formed as side products when un-
blocked 1 is used (ChapterC7 in the Supporting Information).
Conclusion
In this work we studied the thermal reaction of twin mono-
mers 1 and 2, which are condensed hybrid monomers of sili-
con and salicyl alcohol. The thermal TP of spiroidal 1 is compa-
rable to the known acid-catalyzed TP. Starting from one twin
monomer (1) in melt, a transparent glassy nanocomposite is
formed after thermal activation. Domains of single phases
become detectable on the nanoscale (dꢁ2–3 nm); side prod-
ucts are not detected in molar amounts. When the procedure
was driven in high-boiling solvents like DIPN, precipitated par-
ticles of the same composition were obtained.
Although 1 and 2 are known to be capable of an acid-cata-
lyzed TP, compound 2 is not accessible to thermal induction at
2308C contrary to 1. The reactivity for the initial reaction of
1
is greater than of 2, confirming results from the acid-cata-
lyzed TP. This reappoints that the molecular composition of
twin monomers influences their reactivity within the TP pro-
cess; in particular, the initial reaction is influenced by this
structure–reactivity effect. Spiro structures such as 1 favor
[5]
ring-opening reactions; the stronger bond polarizations of
1
compared with 2 (CH ꢀO bond polarization: 1>2) lead to
2
a higher reactivity. A polymerization without additional catalyst
becomes possible, for the thermal TP the required reaction
temperature depends on this reactivity. Additionally, the phe-
nolic resin product phase and the silica-like product phase of
1
have an acidic autocatalytic effect.
A possible polymerization of a vinyl ether (DoVE) in a mixture
with 1 did not occur in a significant manner. Although a reac-
tion temperature of 2308C is not very favorable for vinyl poly-
merizations, a high content of free benzyl cations should have
led to a polymerization of DoVE. Or at least an addition of
such benzyl cation species to the vinyl group should have oc-
curred. We rationalize from these results that 1 is not cleaved
heterolytic to an energy-rich zwitterion and no other cationic
benzyls are present in significant amounts. A homolytic cleav-
age of 1 to an energy-rich diradical is also excluded.
TD in combination with 1 yielded a high ratio of an oQM-
TD-[4+2] adduct. In fact, the liberation of oQM seems to play
a role at the thermal TP of 1. The liberation directly from isolat-
ed 1 seems improbable because a remaining species with an
unfavored Si=O bond must form; but in contact with reaction
partners and starting from described intermediates the oQM-
liberation is expectable and proven.
1
13
29
Figure 14. H (top), C (middle), and Si NMR (bottom) spectra of the ther-
mal reaction of 4. The spectra show clearly that no phenolic resin is formed,
only oQM-adducts and their transformed products are found ([4+2]-trimer,
substituted BPE).
[
4+2]-dimer). Because of the blocked aromatics the formation
of phenolic resin with the substituted oQM is impossible. But
the substituted [4+2]-dimer can transform to an analogue BPE.
This comprises a homolytic cleavage and H-transfer, for exam-
ple, from phenolic OH (Scheme 7 and Figure 14; ChapterC3 in
For the thermal non-catalyzed TP we conclude that 1 reacts
in a concerted mechanism (comparable to a Friedel–Crafts-
benzylation). But additionally, the oQM-formation is promoted
thermally under these conditions. Silanols, phenols, and SiO2-
29
the Supporting Information). The Si NMR product spectra
show a high content of Q and Q signals, the inorganic phase
2
3
is not condensed well and partial soluble parts are present. We
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like structures have an autocatalytic effect, which increases
during polymerization.
tero GmbH and dried with molecular sieves 3 ꢁ prior to use. Stan-
dard solvents were used after drying.
The oQM-formation increases when the polymerization to
phenolic resin is blocked by substituents at the aromatic
system. The formation of side products also increases; oQM is
a central intermediate of manifold transformation processes.
Additionally, some evidence suggests the presence of radi-
calic mechanisms with H-transfers that are reliant for redox
processes and the existence of low amounts of ortho-cresol
and salicyl aldehyde. This phenomenon is known in literature
of thermal preparation of phenolic resin and is also explained
by the presence of quinone methides as central intermediates
and their versatile reactivity. Commonly, H-donors are consid-
ered to be phenols (aryl-OH), beside other structures. Cleaving
H from benzyl alcohol delivers an aldehyde group. Bis(2-hy-
droxybenzyl) ether can disproportionate to ortho-cresol and
salicyl aldehyde or react to two oQM and water. But water was
never detected, because firstly, at least during the initial phase,
Analysis methods
NMR spectroscopy (liquid state): All NMR spectra were recorded
at 258C on a Bruker Avance 250. CDCl , CD Cl , and [D ]acetone
3
2
2
6
13
were taken as solvents and C-references, the residual H signals
1
1
13
were taken as H references: d(CDCl
,
3
H/ C)=7.26/77.0 ppm;
1
13
1
13
d(CD Cl ,
H/ C)=5.32/54.0 ppm; d((CD ) CO,
H/ C)=2.04/
2
2
3 2
2
9.9 ppm. Tetrakis(trimethylsilyl)silane (TTSS) was used as reference
29
for Si NMR: d(Si(CH ) )=ꢀ9.8 ppm).
3
3
NMR spectroscopy (solid state): Measurements were performed at
.4 T on a Bruker Avance 400 spectrometer equipped with double-
9
1
3
1
tuned probes capable of magic angle spinning (MAS). C{ H}
CPMAS NMR was accomplished in 4 mm rotors (ZrO ). Cross polari-
zation with contact times of 5.5 ms was used, the recycle delay was
2
2
9
1
d1 =6 s. Quantitative Si{ H} MAS NMR was performed in 7 mm
rotors. The recycle delay was set to d =300 s to get full T1 relaxa-
tion. Si CPMAS NMR was performed with a recycle delay of d
s. Cross polarization with a contact time of p =5.5 ms was used.
1
29
=
1
6
the hydroxy concentration (aryl-OH, arylCH OH, SiꢀOH) is low,
3
2
Mass spectrometry: Mass spectrograms have been recorded on
a Bruker Esquire with an ion trap detector using the electrospray
ionization method (ESI-MS) and the electron ionization (GC-EI-MS).
and secondly, even intermediate water would re-enter a reac-
tion with SiꢀOꢀC compounds or would be added to oQM. In
consequence of energy-rich intermediates as quinone me-
thides additional reaction paths are open (oQM can react elec-
trophilicly, nucleophilicly, radically, in redox reactions with H-
shift, and in [4+2]-cycloaddtions). This versatility explains also
further side products. Phenols (aryl-OH), benzyl alcohols (aryl-
CH OH), cresols (hydroxyaryl-CH ), and other products can
TGA: TGA was obtained on “TGA 7, PerkinElmer”. Samples were
measured in Al-cups under He with a standard heating rate of
ꢀ
1
1
2
0 Kmin . TGA-MS was measured on a Thermo-Micro-Balance TG
09 F1 Iris, a coupled mass spectrometer MS 403C Aꢂolos (Netzsch)
was used (“Quadrupol MS (QMA200)” with a mass range of 0–
300 amu, crossbeam ion source, channeltron (SEM) detector). The
sample was prepared under argon and the measurement was
2
3
serve as H-donors, further redox reactions are possible. All the
found side products correspond to side products that were
also found in the thermal curing process of phenolic resin (es-
ꢀ
1
done under helium flow (heating rate: 10 Kmin ).
DSC: DSC was performed on “DSC 30, Mettler” and “DSC 1 Stare
[
6]
System, Mettler Toledo” under nitrogen at a standard heating rate
pecially novolaks). The presence of radicalic redox reactions
with H-shifts explains the formation of an oligo(1-tetradecene),
which could be initialized by a phenoxy radical.
ꢀ
1
of 10 Kmin using Al-cups.
Quantum chemical calculations and NBO charge analysis: The
quantum chemical calculations have been carried out at the unre-
stricted B3-LYP/TZVPP level of theory using the TURBOMOLE pro-
gram package. To assess the effect of the solvent single-point cal-
culations have been carried out using the COSMO model as imple-
mented in the TURBOMOLE. Charge analysis have been carried out
on the basis of the NBO charges (ChapterC11 in the Supporting In-
formation).
The quinone methide character within the thermal TP can
be used to include olefins within the reaction. Generally
carbon–carbon double- and triple bonds should be applicable
no matter if they are located in a monomer (as shown for 1-
tetradecene, TD) or in a polymer structure (as shown for poly-
(butadiene), PB). Also a combination of 1 with carbonyl-con-
taining polymers (PMMA, polyamide) in complete melt or sur-
face reaction is interesting because of the reaction of oQM as
High angle annular dark-field scanning TEM: ((HAADF-STEM),
Tecnai F20 FEG TEM at 200 kV accelerating voltage): Images were
taken at the very thin areas at the edge of the microtome sec-
tioned slices (ultramicrotome Leica UZT Ultracut). The electron
spot size was set below 1 nm. Obtained high resolution contrast
images show very small bright clusters in the range from 2 to
[4+2]-reagent. A linkage between the TP composite and the
carbonyl containing polymer will arise.
Finally the nanocomposite material can be transformed to
microporous carbon and porous silica (ChapterC6 in the Sup-
porting Information).
3
nm. The signal in a HAADF STEM image is being collected by an
annular detector sensitive to electrons scattered into high angles.
It increases monotonically with the atomic number of the scatter-
ing atoms if the thickness in the area of interest does not change
rapidly. Since the composite samples were evenly thin slices cut by
ultramicrotomy, the clusters in the HAADF images represent Si-rich
areas. The structure sizes correlate with the used magnifications.
Experimental Section
Chemicals
DIPN (dry) was purchased from BASF SE. 1-Dodecene (b.p.
Syntheses
ꢁ
2138C, 95%) and 1-tetradecene (b.p. ꢁ2508C) were purchased
[3d]
[7]
[4]
The syntheses of 1, 2, and 4 are already published.
from Merck KGaA. Cyclohexyl vinyl ether (98%, b.p. ꢁ1488C), n-do-
decyl vinyl ether (98%, b.p. ꢁ2708C), poly(butadiene) (average
4,6-Dimethyl-2-(hydroxymethyl)phenol: In water (10 mL), NaOH
(2.50 g 0.063 mol) was dissolved and 2,4-dimethylphenol (12.22 g,
0.100 mol) was added. At 0–58C formalin (37%, 0.135 mol, 10.96 g)
ꢀ
1
M =1530–2070 gmol ), cis-cyclooctene (95%, b.p.ꢁ1488C) were
n
purchased from Aldrich. CDCl (99.8%) was purchased from Deu-
3
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12
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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were added to the clear solution. The reaction vessel was closed
and stirred for 2 h at 0–58C, then 45 h at 258C. After addition of
filtrate and extract were distilled and fractionated. The analyses of
the solid and liquid product fractions are presented in the article.
water (30 mL), CO gas was introduced to neutralize the reaction
2
Thermally induced reaction of 1 in poly(butadiene) (PB): The re-
action flask was filled with 1 and TD under argon. The reaction
medium was stirred and heated (ꢁ3 Kmin ) to the final reaction
mixture. An oily orange precipitate formed. Afterwards the mixture
was shaken three times with diethyl ether (3ꢃ50 mL) in a separat-
ing funnel. The combined ether fractions were washed with water
ꢀ1
temperature and kept at this temperature. An unclear viscous fluid
was obtained. NMR spectroscopic analyses directly after reaction
confirm a complete conversion of 1 and an oQM-[4+2]-cycloaddi-
tion to the double bonds of PB. In case of experiment XII, PB
(14.215 g) and 1 (3.566 g) were applied. After reaction CHCl3
(50 mL) were added and stirred for 2 h, the medium stayed unclear.
The mixture was then dropped into MeOH (500 mL) and stirred for
15 h. An unclear MeOH-phase resulted and a precipitated viscous
(
50 mL), dried with MgSO , and filtered off. Then, diethyl ether was
4
evaporated and the crude product was re-crystallized in a hexane/
toluene mixture (ratio 9:1). Colorless crystals were obtained. Yield:
1
9
.40 g (0.062 mol)=61.8% of theory. H NMR (CD Cl , 5.32 ppm,
2
2
2
50 MHz): d=2.20 (s, 3H, ortho-CH ), 2.23 (s, 3H, para-CH ), 3.00
3
3
(
s(br), 1H, CH OH), 4.76 (s, 2H, CH ), 6.66 (s, 1H, meta), 6.90 (s, 1H,
2 2
13
meta), 7.3 ppm (s(br), 1H, aryl-OH); C NMR (CD Cl , 54.0 ppm,
2
2
1
1
00 MHz): d=15.7 (ortho-CH ), 20.5 (para-CH ), 64.8 (CH ), 124.4,
25.2, 126.3, 129.1, 131.5, 152.2 ppm (Caryl-OH).
3
3
2
substance. After filtration CHCl (200 mL) were added to the vis-
3
cous precipitate. Then, it was stirred and to the unclear dispersion
hexane (400 mL) was slowly added, finally a solid material was pre-
cipitating. After stirring for further 2 h the solvent was decanted
from the precipitate. Remaining solvents were evaporated, a last
2
,2’-spirobi[6,8-dimethyl-4H-1,3,2-benzodioxasiline] (3): 4,6-Di-
methyl-2-(hydroxy-methyl)phenol (10.97 g, 0.072 mol) was dis-
solved in toluene (70 mL) at 258C under argon. Tetramethylorthosi-
licate (6.58 g, 0.043 mol) was added followed by of 1m tetra-n-
butyl-ammonium fluoride solution (25 mL) in THF. At a distiller, the
reaction mixture was heated to 808C and the pressure is slowly re-
duced until MeOH distils off. After several hours (ꢁ8 h) no more
MeOH is formed and the reduction of pressure below 300 mbar
leads only to the distillation of toluene. The remaining solvents
were removed at low pressure (ꢁ10 mbar, 408C). The crude prod-
uct was redissolved in little toluene at 708C under argon and re-
time the material was extracted with CHCl , and dried at 25 mbar/
3
7
58C. A slightly ductile solid was obtained (1.97 g, elemental analy-
sis). Analysis are presented in the article, they reveal a composite
of PB, phenolic resin and a silica-like phase (61 m%C). All extracts
1
and filtrates do not show significant differences in the H NMR
spectra compared to the mixture obtained directly after reaction.
The slightly unclear appearance is due to remaining small compo-
site particles in the fluids.
crystallized. White crystals were obtained (yield: 5.56 g, M =
w
ꢀ1
3
28.43 gmol , n=0.017 mol, 47% of theory). M.p. 154–1568C;
1
H NMR (CD Cl , 5.32 ppm, 250 MHz): d=2.23 (s, 6H, 2ꢃCH ), 2.28 Acknowledgements
2
2
3
2
(
s, 6H, 2ꢃCH ), 5.14 (s(br), in fact: 2d, 4H, 2ꢃCH , J =14.0 Hz),
HA,HB
3
2
13
6
.71 (s, 2H), 6.96 ppm (s, 2H); C NMR (CD Cl , 54.0 ppm,
2 2
We thank Dr. S. Anders (TU Chemnitz, Prof. Dr. L. Kroll group)
for TGA-MS measurements, Dr. T. Rꢄffer (TU Chemnitz, Prof. Dr.
H. Lang group) for X-ray structure analysis, and Dr. I. Bauer (TU
Dresden) for mass-spectrometry measurements. Financial sup-
port by BASF SE and DFG (FOR 1497: AU 206/5-1, SP 392/34-1)
is gratefully acknowledged.
2
50 MHz): d=15.8 (2ꢃCH ), 20.7 (2ꢃCH ), 66.7 (2ꢃCH ), 124.3,
3 3 2
29
1
25.3, 128.1, 131.3, 131.6, 149.0 ppm (C-OSi); Si NMR (CD Cl /
2 2
TTSS, ꢀ9.8 ppm): d=ꢀ79.0 ppm.
Thermal reactions of compounds 1–4: Reaction conditions are
summarized in Tables 2 and 3. Reaction flasks were filled with the
salicylic silicon compounds 1–4 under argon. For reactions in solu-
tion dry solvents were added. The reaction medium was stirred
ꢀ1
and heated (ꢁ3 Kmin ) under argon to the final reaction temper-
Keywords: nanostructures · polymerization · ring-opening
polymerization · silicon · quinones
ature and kept at this temperature. In case of polymerization of
1
in substance the melt became increasingly viscous until the
magnet stirrer was caught in the hardening composite while the
colorless material turned slowly to a light-orange transparent ma-
terial. At the end of the reaction time a transparent glassy mono-
lith is obtained. Samples were extracted for several hours with
[
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Received: January 5, 2014
Faure, G. Thomas-David, R. Bartnik, Z. Cebulska, E. Graca, S. Lesniak, Bull.
Published online on && &&, 2014
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FULL PAPER
The twin monomer 2,2’-spirobi[4H-
&
Polymerization
1,3,2-benzodioxasiline] (1) can be poly-
P. Kempe, T. Lçschner, A. A. Auer,
A. Seifert, G. Cox, S. Spange*
merized to nanostructured phenolic-
resin/SiO composite material by ther-
2
mally induced twin polymerization (TP;
see figure). Thermally induced TP repre-
sents a way to produce nanocomposites
simply by thermal induction of twin
monomers. The thermal cleavage of the
molecules is studied by using several
trapping reagents in which ortho-qui-
none methide was found.
&
& – &&
Thermally Induced Twin
Polymerization of 4H-1,3,2-
Benzodioxasilines
Chem. Eur. J. 2014, 20, 1 – 15
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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&
These are not the final page numbers! ÞÞ