The Hydrolysis/Condensation Behaviour of Methacryloyloxyalkylfunctional Alkoxysilanes: Structure-Reactivity Relations

Article abstract of DOI:10.1007/s00706-003-0615-y

Various methacryloyloxymethylalkoxysilanes have been synthesized by nucleophilic substitution reactions starting from chloromethylalkoxysilanes under phase transfer catalysis conditions. The compounds thus obtained show an exceptionally high degree of reactivity with regard to hydrolysis and condensation both under acidic as well as under basic conditions compared to the established 3-methacryloyloxypropyltrimethoxysilane. A mechanistic model for this high reactivity by intramolecular activation is discussed.

Full text of DOI:10.1007/s00706-003-0615-y

Monatshefte f€ur Chemie 134, 1081–1092 (2003)
DOI 10.1007/s00706-003-0615-y
The Hydrolysis=Condensation Behaviour
of Methacryloyloxyalkylfunctional
Alkoxysilanes: Structure-Reactivity Relations
ꢀ
¨
Stefan Altmann and Jurgen Pfeiffer
Wacker-Chemie GmbH, Werk Burghausen, D-84480 Burghausen, Germany
Received February 3, 2003; accepted February 5, 2003
Published online June 12, 2003 # Springer-Verlag 2003
Summary. Various methacryloyloxymethylalkoxysilanes have been synthesized by nucleophilic
substitution reactions starting from chloromethylalkoxysilanes under phase transfer catalysis condi-
tions. The compounds thus obtained show an exceptionally high degree of reactivity with regard to
hydrolysis and condensation both under acidic as well as under basic conditions compared to the
established 3-methacryloyloxypropyltrimethoxysilane. A mechanistic model for this high reactivity by
intramolecular activation is discussed.
Keywords. Acrylics; Hydrolysis; Kinetics; NMR spectroscopy; Organofunctional silanes.
Introduction
Organofunctional silanes, characterized by both organic functional groups and an
inorganic reactive center prone to hydrolysis, are commercially used since the
1950’s and demand is growing steadily (Fig. 1).
Major application fields of organofunctional silanes are filler=material treat-
ment and utilization as adhesion promoters or crosslinkers, respectively. This wide
range of applications relies on the bifunctionality of the organofunctional silanes,
giving rise to the possibility to form chemical bonds to both inorganic and organic
substrates and also between two organofunctional silane molecules [1].
For example, an aminoalkylfunctional silane can react with an inorganic mate-
rial bearing surface-bonded hydroxy groups and with an organic resin bearing e.g.
epoxy groups, thus forming a permanent link between the two different matrices
(Fig. 2).
In this context, methacryloyloxyalkylfunctional silanes bearing hydrolyzable
groups on the silicon atom are of special interest for
ꢀ
Corresponding author. E-mail: juergen.pfeiffer@wacker.com

1082
S. Altmann and J. Pfeiffer
Fig. 1. General formula of an organofunctional silane
Fig. 2. Formation of a chemical link between an organic and an inorganic matrix engaging a silane
coupling agent
*
*
the modification of organic polymers by co-polymerization or grafting (to give
moisture curable co-polymers),
the treatment of inorganic materials like metal surfaces, fillers, or glass fibre to
give strong adhesion between organic and inorganic substrates by e.g. radical
reactions or Michael-type additions.

Methacryloyloxyalkylfunctional Alkoxysilanes
1083
Despite of the high efficiency of organofunctional silanes for improving e.g. the
mechanical properties or chemical resistance of organic=inorganic composite
materials, several factors governing the reaction behaviour are still not fully
understood.
In addition, as environmental requirements become more and more important,
new organofunctional silanes have to be developed which are equally efficient in
the mentioned application fields but do not show the disadvantages of known
organofunctional silanes like liberation of volatile organic or toxic compounds.
In the light of these requirements, we investigated the reactivity of various
methacryloyloxyalkylsilanes in comparison to the nowadays most important organ-
ofunctional silanes bearing an unsaturated functionality, namely vinyltrimethoxy-
silane and 3-methacryloyloxypropyltrimethoxysilane.
Results and Discussions
Basic Reactivity of Organofunctional Silanes
The reactivity as well as the reaction types possible at the organofunctional termi-
nus of an organofunctional silane strongly depend on the functional group as well
as the substrate to be reacted with. On the other hand, commercially important
reactions at the organosilicon moiety of these compounds can be mainly divided
into two categories, namely hydrolysis and condensation (Fig. 3) [2]. These reac-
tions are both reversible, many of them being equilibria with substantial concen-
trations of both products and reactants present under typical conditions unless
by-products liberated are removed from the equilibrium or the products separate
from the reaction medium, e.g. by precipitation. In addition, the reaction scheme is
complicated by the fact that both hydrolysis and condensation can occur at the
same time with comparable reaction rates.
The rate with which the respective equilibrium is reached strongly depends on
various parameters, e.g. pH, temperature, etc. In general, the following simplified
statements can be made, with exceptions depending on the specific structure of the
silane investigated:
*
*
In neutral medium, the hydrolysis rate of alkoxysilanes displays a minimum.
Under basic conditions below pH 10, hydrolysis of the first alkoxy group is the
rate determining step and data obtained suggests a SN2 –Si mechanism (above
ꢀꢀ
pH 10, ionization of the SiOH group has major influence on the mechanism).
Fig. 3. Key reactions of alkoxysilanes (in the condensation the two silanols are not necessarily
identical, one may, e.g., be a surface-SiOH group)

1084
S. Altmann and J. Pfeiffer
*
In acidic medium, hydrolysis of the first alkoxy group is fast compared to hy-
drolysis of further alkoxy groups present in the molecule. The hydrolysis rate
strongly depends on the kind of leaving group with the hydrolysis rate decreas-
ing in the order MeO ! EtO ! MeOCH2CH2O–. Data obtained implies a SN2
mechanism on a protonated alkoxysilane.
*
*
The rate of condensation of silanols strongly depends on the substitution pattern
at silicon: Trisilanols show a condensation rate minimum at about pH 4, whereas
disilanols are most stable at about pH 6. Finally, monosilanols show a rate
minimum at about pH 6.5–7.
Under acidic conditions, hydrolysis in most cases is faster than condensation. In
contrast, in basic medium condensation of partially hydrolyzed alkoxysilanes
may occur prior to complete hydrolysis.
For industrial applications of organofunctional silanes, both the hydrolysis (as a
prerequisite for condensation) as well as the condensation reaction are of funda-
mental importance.
1
In the present study, hydrolysis was investigated by H NMR, whereas 29Si
NMR was used to observe and analyze the condensation behaviour of various
methacryloyloxyalkylfunctional alkoxysilanes which are depicted in Fig. 4. In ad-
dition, vinyltrimethoxysilane 6 as well as the saturated analogues 4a, 4b, and 5
were investigated as model substances for silane modified co-polymers.
Hydrolysis of the various unsaturated silanes was studied in the presence of a
30-fold excess of water with acetone as co-solvent at pH 4 (0.001 M HCl) as
well as at pH 9 (buffer solution boric acid=potassium chloride=sodium hydroxide).
Due to the high reactivity of the investigated methacryloyloxymethylsilanes,
Fig. 4. Molecules investigated in the present study

Methacryloyloxyalkylfunctional Alkoxysilanes
1085
Fig. 5. Comparison of hydrolysis rates of 3a (a) k ¼ 1.59 hÀ 1 and 1a (b) k ¼ 21.8 hÀ 1 under acidic
conditions (pH ¼ 4, 30-fold excess water)
condensation observed by 29Si NMR was performed at pH 6.5 in order to slow
down the condensation relative to the time required to obtain the NMR spectra.
Surprisingly, all methacryloyloxyfunctional silanes bearing a methylene spacer
connecting the methacrylic functionality and the silane moiety were found to ex-
hibit exceptionally high hydrolysis rates under the experimental conditions. As an
example, the plots for the acidic hydrolysis of the first methoxy group of 3-meth-
acryloyloxypropyltrimethoxysilane 3a and methacryloyloxymethyltrimethoxysi-
lane 1a are depicted in Figs. 5a and 5b. The reactions were found to proceed
according to the expected pseudo first order rate law in the silane [3], but compared
to 3a, the hydrolysis of 1a is faster by a factor of 13.6. In Table 1 the rate constants
obtained for all investigated substances are summarized.
In summary, four conclusions can be drawn from the data obtained:
1. Hydrolysis of the methylene spacer bearing methacryloyloxyfunctional silanes
is up to 60 times faster than that of 3-methacryloyloxypropyltrimethoxysilane
both in case of methoxy and ethoxy derivatives under acidic or basic conditions.

1086
S. Altmann and J. Pfeiffer
Table 1. Summarized rate constants for the hydrolysis of the first alkoxy group found for the
investigated compounds 1–6 under acidic and basic conditions
Compound
Hydrolysis rate at pH 4 hÀ 1
Hydrolysis rate at pH 9 hÀ 1
1a
1b
1c
2a
2b
2c
3a
3b
4a
4b
5
21.8
24.0
67.9
17.5
1.2
14.4
a)
b)
27.2
a)
9.5
2.2
1.6
c)
1.2
0.5
31.5
4.9
27.7
1.6
5.2
0.6
6
13.7
6.4
a)
Hydrolysis of compounds 1c and 2c, respectively, was extremely fast; after 60 seconds, only the
silanol could be observed besides liberated methanol; b) The rate constant for the first hydrolysis step
of compound 2a could not be determined due to excessive overlap of the signals under the chosen
conditions; c) Hydrolysis of compound 3b was found to be extremely slow under acidic conditions;
almost no reaction was found to proceed within 1 h
Under basic conditions the ethoxy silanes 2a and 2c hydrolyze at rates com-
parable to 3a (except the difunctional 2b), whereas the methoxy compounds
1a–1c still exhibit an extremely high rate of hydrolysis.
2. Dialkoxymethyl silanes bearing the methacryloyloxymethyl group hydrolyze at
a rate comparable to the corresponding trialkoxy silanes under acidic conditions
(and at a somewhat higher rate under basic conditions). This is in contrast to the
behaviour of 3-methacryloyloxypropyl(dimethoxy)methylsilane, the hydrolysis
of which is much slower than that of its trimethoxy counterpart.
3. Under acidic conditions ethoxy substituted methacryloyloxymethylsilanes hy-
drolyze at rates comparable to those of the corresponding methoxy silanes.
This again is in contrast to the propylene spacer bearing analogues: 3-meth-
acryloyloxypropyltriethoxysilane is known to hydrolyze extremely slow com-
pared to the methoxy derivative [4], making it attractive for e.g. dental
applications which require relatively long shelf-lifes.
4. The saturated butanoic acid derivatives 4a and 4b of the silicon containing
methacrylic acids esters 1a and 3a hydrolyze at rates comparable to the unsat-
urated compounds under both acidic and basic conditions. This indicates that in-
corporation of these substances into co-polymers with standard unsaturated
monomers (e.g. styrene, acrylic acid, methyl methacrylate, etc.) does not slow
down the hydrolysis rate. In contrast, the saturated analog of vinyltrimethoxy-
silane 6 (which shows a hydrolysis reactivity comparable to the methacryloyl-
oxymethylsilanes), namely propyltrimethoxysilane 5, shows a much lower
reaction rate.
The surprisingly high reactivity of the methacryloyloxymethylsilanes 1a–1c
and 2a–2c may be explained in terms of an electronic influence of the ester group

Methacryloyloxyalkylfunctional Alkoxysilanes
1087
on the electron density at the silicon atom. In principle, three different possibilities
may be assumed, namely
*
*
*
intermolecular interactions between the silicon atom of a first molecule with the
ester group of a second molecule (Fig. 6a),
intramolecular activation of the silicon atom by interaction with the carbonyl
group by forming a silatrane analog five-membered ring (Fig. 6b), and
intramolecular activation of the silicon moiety by electron transfer from the ester
group via the methylene group either through space, via the s-bonds, or by hyper-
conjugation (Fig. 6c).
The first possibility is unlikely, because this effect should also play a significant
role in case of methacryloyloxyalkylsilanes bearing a propylene spacer. Evidence
for one of the latter two models can be drawn from the comparison of the 29Si NMR
data of compounds 1a, 1b, 2a, and 2b with 3a and 3b (Table 2).
This data reveals that all methacryloyloxyalkylsilanes bearing a methylene
spacer show a high-field shift of 8–14 ppm compared to their counterparts bearing
a propylene spacer. This indicates a partial electron transfer from one of the oxygen
Fig. 6. Possible electronic influence explaining the high reactivity of the methacryloyloxymethyl-
alkoxysilanes
Table 2. Comparison of the 29Si NMR data of the investigated compounds
Compound
Chemical shift
Chemical shift
Compound
1a
2a
1b
2b
6
À 53.3
À 56.6
À 11.4
À 14.9
À 56.0
À 42.8
3a
À 3.1
3b
5
À 41.5

1088
S. Altmann and J. Pfeiffer
atoms to silicon. This is also true for vinyltrimethoxysilane 6, which exhibits a
high-field shift of 14.5 ppm compared to propyltrimethoxysilane 5. A comparable
effect was found, for example, for substituted diphenylsilanes: The chemical shift
of diphenylmethylchlorosilane was found to be 10.6 ppm. Introduction of a
methoxymethyl substituent at the ortho-position of the phenyl group was accom-
panied by a high-field shift of about 7 ppm to 3.4 ppm by intramolecular coordi-
nation [5]. A decision, whether the influence on the electronic structure of silicon is
due to intramolecular ring formation (Fig. 6b) or hyperconjugation (Fig. 6c) cannot
be made based on the present data. The data obtained for the rate constants may be
explained by the following mechanistic assumptions:
a) Acidic conditions: Protonation of an alkoxy oxygen is the first reaction step
under acidic conditions and is becoming slower from mono- to di- to trialkox-
ysilanes. This trend is enhanced by intramolecular coordination of the ester
group. Steric crowding should play only a minor role in this state of the reac-
tion. After protonation nucleophilic displacement of the protonated alkoxy
group by a water molecule occurs. This step is fast for trialkoxysilanes and
becomes slower for di- and monoalkoxysilanes due to the electron-withdrawing
effect of the alkoxy groups (which is in accordance with the slow hydrolysis of
3b compared to 3a). Intramolecular coordination should slow down the rate of
this reaction step in all three cases. On the other hand, due to steric reasons,
attack on the protonated monoalkoxysilanes might be accelerated relative to the
di- and trialkoxysilane analogues. The balance between these two competiting
effects might be an explanation for the rate constants observed for the first
hydrolysis step under acidic conditions.
b) Basic conditions: Under basic conditions, formation of a pentacoordinate inter-
mediate is presumed to be the rate determining step. Due to electronic reasons
(electron withdrawing influence of alkoxy groups), this reaction step is faster
for trialkoxysilanes than for di- and monoalkoxysilanes. Due to coordination of
the ester oxygen, the electron density at silicon is enhanced, slowing down the
formation of the pentacoordinate intermediate. On the other hand, steric crowd-
ing might lower the reaction rate from mono- to di- to trialkoxysilanes. These
competiting effects might explain the reactivity maximum observed for the
dialkoxysilanes 1b and 2b in the row tri-, di-, and monofunctional.
Condensation of the silanols resulting from the hydrolysis of the silanes 1–6
has been investigated in a qualitative manner by 29Si NMR spectroscopy under
neutral conditions (pH 6.5). No products resulting from hydrolysis or condensation
were observed in case of the methacryloyloxymethylsilanes 2a–2c, as well as in
case of 3a, 3b, 4b, 5, and 6 within 12 hours at room temperature. In contrast, a
dramatic reactivity enhancement was found for the methacryloyloxymethylsilanes
1a–1c and the saturated counterpart 4a. In case of 1a and 4a, complete con-
sumption of the starting compound was observed within 90 minutes leading to
T-structures without the observation of silanol intermediates.
In case of 1b, the monosilanol and the disilanol could be observed along with
the formation of M- and D-structures. After 12 hours, approximately 50% of the
starting compound have been consumed. In case of 1c, about 90% of the starting

Methacryloyloxyalkylfunctional Alkoxysilanes
1089
compounds remained unchanged after 12 hours, with the monosilanol and the di-
mer being present in a molar ratio of approximately 1:1.
This decrease in reactivity is in accordance with the well-known differences in
stability of mono-, di-, and trisilanols depending on the pH of the solvent. The lack
of reactivity of compounds 2a–2c, 3a, 3b, 4b, 5, and 6 under the choosen condi-
tions can presumably be explained by the slow hydrolysis of the compounds under
neutral conditions.
Conclusions
The performed analysis of the hydrolysis=condensation behaviour of several
methacryloyloxymethylalkoxysilanes has revealed a significant reactivity enhance-
ment changing from a propylene to a methylene spacer group. This change in
reactivity is most likely due to an intramolecular electronic influence of the ester
group on the silicon moiety via the methylene spacer. The high reactivity observed
makes the methacryloyloxymethylalkoxysilanes promising candidates for applica-
tions which require highly reactive alkoxysilyl groups.
Applications like glass fibre sizing, utilization as adhesion promoter for inor-
ganic substrates, e.g. glass, metals like iron, aluminum or steel, fillers like korun-
dum, silica, quarz, mica, etc. should be mentioned.
In addition, copolymerization with unsaturated acrylic monomers (acrylic or
methacrylic acid or their derivatives) or other unsaturated monomers like vinyl
acetate, styrene, or combinations thereof to give moisture curable compounds is
a highly promising application field for the investigated monomers. Thus, the
obtained materials can be used as basic materials for elastomers, coatings, adhe-
sives, sealants, or foams (e.g. in the automotive industry, wood coating applica-
tions, scratch resistant coatings, e.g. for automotive polycarbonate windshields,
food package material, wall paints, etc.), avoiding tin-based condensation catalysts
or avoiding liberation of toxic methanol by using ethoxysilanes.
Furthermore, incorporation of methacryloyloxymethylsilanes in polyolefins
like LDPE, LLDPE, HDPE, and PP as well as in olefin copolymers, e.g. EVAc
and EMA, by copolymerization or grafting gives moisture curable thermoplastics
which are very versatile for the manufacture of silane crosslinkable polyolefin
compositions for use in electric cables and wires as well as for the manufacture
of tubes and pipes. Economic advantage is provided especially by the high
crosslinking speed due to the high hydrolysis=condensation rate of the methacryl-
oyloxymethylsilanes compared to the established vinyl- and 3-methacryloyloxy-
propylsilanes, 3a and 6, respectively.
Due to the high reactivity of the methacryloyloxymethylsilanes, even the pro-
duction of fast-curing adhesives can be envisioned, replacing the established, toxic
cyanacrylate adhesives.
Experimental
All chemicals were used as purchased, compounds 1–4 were synthesized. 1H NMR spectra of the pure
silanes were recorded on a Bruker AVANCE DPX 360 (360.13 MHz) or DPX 400 (400.13 MHz).
29Si NMR spectra were measured on a Bruker AVANCE 300 (59.63 MHz) or DPX 360 (71.54 MHz)

1090
S. Altmann and J. Pfeiffer
with chromium(III) acetylacetonate as relaxation accelerator under 1H inverse gated decoupling. The
1H NMR measurements for studying the hydrolysis behaviour of the silanes were performed on a
Bruker AVANCE DPX 400 spectrometer, the 29Si NMR spectroscopic analysis was carried out on a
Bruker AVANCE 300.
General Procedure for the Synthesis of 1–4
1 Mol 50% aqueous KOH solution and 300 g of toluene were placed into a 1 dm3 four-necked vessel
equipped with a mechanical stirrer, a thermometer, a dropping funnel, and a reflux condenser. From the
dropping funnel, 1 mol of methacrylic acid was slowly added while stirring the reaction mixture. After
addition was complete, the water was removed by azeotropic distillation, followed by removal of 270g
of toluene by distillation. To the thus obtained potassium methacrylate, a solution of 10mmol of tetra-n-
butylphosphoniumchloride and 5 mmol of 4,40-bismethylene(2,6-di-tert-butylphenol) in a mixture of
50g of toluene, 17 g of ethyl methyl ketone, and 1 mol of the corresponding chloroalkylalkoxysilane was
added. The suspension was heated for four hours to 110ꢁC under stirring, the potassium chloride formed
was filtered off and washed with toluene, and the products were isolated by column distillation under
reduced pressure. Yields were between 92 and 96% based on the chloroalkylalkoxysilane employed.
(Methacryloyloxymethyl)trimethoxysilane (1a, C8H15O5Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 1.70 (s, 3H, CH3), 3.30 (s, 9H, 3OCH3), 3.85 (s, 2H, SiCH2O), 5.09
(s, 1H, H(H)C¼), 5.98 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 71.54 MHz): ꢀ ¼ À 53.28.
(Methacryloyloxymethyl)dimethoxymethylsilane (1b, C8H15O4Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 0.23 (s, 3H, SiCH3), 1.93 (s, 3H, CH3), 3.44 (s, 6H, 2OCH3), 4.01
(s, 2H, SiCH2O), 5.31 (s, 1H, H(H)C¼), 6.21 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 59.63 MHz):
ꢀ ¼ À 11.42.
(Methacryloyloxymethyl)dimethylmethoxysilane (1c, C8H15O3Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 0.00 (s, 6H, Si(CH3)2), 1.77 (s, 3H, CH3), 3.18 (s, 3H, OCH3), 3.80
(s, 2H, SiCH2O), 5.13 (s, 1H, H(H)C¼), 6.05 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 71.54 MHz):
ꢀ ¼ 12.71.
(Methacryloyloxymethyl)triethoxysilane (2a, C11H22O5Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 1.24 (t, J ¼ 7.04Hz, 9H, 3CH2CH3), 1.96 (s, 3H, CH3), 3.92
(q, J ¼ 7.04Hz, 6H, 3OCH2CH3), 4.16 (s, 2H, SiCH2O), 5.33 (s, 1H, C¼C(H)H), 6.27 (s, 1H,
C¼C(H)H); 29Si NMR (C6D6, 71.54 MHz): ꢀ ¼ À 56.59.
(Methacryloyloxymethyl)diethoxymethylsilane (2b, C10H20O4Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 0.05 (s, 3H, SiCH3), 0.96 (t, J ¼ 7.04Hz, 6H, 2CH2CH3), 1.71
(s, 3H, CH3), 3.54 (q, J ¼ 7.04Hz, 4H, 2OCH2CH3), 3.81 (s, 2H, SiCH2O), 5.11 (s, 1H, C¼C(H)H),
5.99 (s, 1H, C¼C(H)H); 29Si NMR (C6D6, 71.54MHz): ꢀ ¼ À 14.95.
(Methacryloyloxymethyl)dimethylethoxysilane (2c, C9H18O3Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 0.01 (s, 6H, 2SiCH3), 0.98 (t, J ¼ 6.85Hz, 3H, CH2CH3), 1.71
(s, 3H, CH3), 3.46 (q, J ¼ 6.85 Hz, 2H, OCH2CH3), 3.72 (s, 2H, SiCH2O), 5.15 (s, 1H, C¼C(H)H),
6.02 (s, 1H, C¼C(H)H); 29Si NMR (C6D6, 71.54MHz): ꢀ ¼ 10.3.

Methacryloyloxyalkylfunctional Alkoxysilanes
1091
[3-(Methacryloyloxy)propyl]trimethoxysilane (3a, C10H20O5Si)
1H NMR (CDCl3, 400.13 MHz): ꢀ ¼ 0.66 (t, J ¼ 8.43 Hz, 2H, SiCH2), 1.76 (qui, J ¼ 7.66Hz, 2H,
CH2), 1.91 (s, 3H, CH3), 3.55 (s, 9H, 3OCH3), 4.09 (t, J ¼ 6.72Hz, 2H, CH2O), 5.52 (s, 1H, H(H)C¼),
6.07 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 59.62 MHz): ꢀ ¼ À 42.71.
[3-(Methacryloyloxy)propyl]dimethoxymethylsilane (3b, C10H20O4Si)
1H NMR (C6D6, 360.13MHz): ꢀ ¼ 0.00 (s, 3H, SiCH3), 0.51 (t, J ¼ 8.4 Hz, 2H, SiCH2), 1.64
(qui, J ¼ 7.66 Hz, 2H, CH2), 1.83 (s, 3H, CH3), 3.30 (s, 6H, 2OCH3), 4.03 (t, J ¼ 6.93Hz,
2H, CH2O), 5.22 (s, 1H, H(H)C¼), 6.11 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 71.54 MHz):
ꢀ ¼ 3.00.
(Butyryloxymethyl)trimethoxysilane (4a, C8H18O5Si)
1H NMR (C6D6, 360.13 MHz): ꢀ ¼ 0.80 (t, 3H, J ¼ 7.1 Hz, CH2–CH3), 1.48 (quin, 2H,
J ¼ 7.1 Hz, CH2CH2CH3), 2.18 (t, 2H, J ¼ 7.1 Hz, CH2C¼O), 3.30 (s, 9H, 3OCH3), 4.15 (s,
2H, SiCH2), 5.09 (s, 1H, H(H)C¼), 5.98 (s, 1H, H(H)C¼); 29Si NMR (C6D6, 71.54 MHz):
ꢀ ¼ À 53.02.
[3-(Butyryloxy)propyl]trimethoxysilane (4b, C10H22O5Si)
1H NMR (CDCl3, 400.13 MHz): ꢀ ¼ 0.66 (t, J ¼ 8.43Hz, 2H, SiCH2), 1.03 (t, 3H, J ¼ 7.1 Hz, CH2–
CH3), 1.70 (quin, 2H, J ¼ 7.1 Hz, CH2CH2CH3), 1.80 (quin, J ¼ 7.66Hz, 2H, CH2), 2.41 (t, 2H,
J ¼ 7.1 Hz, CH2C¼O), 3.77 (s, 9H, 3OCH3), 4.15 (t, J ¼ 6.72 Hz, 2H, CH2O); 29Si NMR (C6D6,
59.62 MHz): ꢀ ¼ À 42.2.
1
Procedure for Hydrolysis Study by H NMR
100 mm3 of buffer (or 0.001 N HCl, respectively) were added to 600mm3 of acetone-d6 (Merck,
99.8%) in a 5 mm NMR sample tube. After tuning and matching the probehead to this solvent mixture
the spectrometer was also shimmed to achieve good resolution and sensivity in the following aquisi-
tions. During this procedure the sample tube with the solvent mixture was preequilibrated to 303 K.
The NMR sample tube was ejected again and 50mm3 of silane were added with a syringe and mixed.
1
60s after the addition of the silane the first time dependent H NMR measurement of the locked
sample was started using an aquisiton time of 4.09 s and a sweep width of 8012 Hz. Only one scan per
spectrum was recorded with a 90ꢁ pulse width. By choosing suitable delays the time difference
between the beginning of two following measurements was adjusted to 32 and 96s, respectively. In
cases of slow reaction times, 16 scans had been accumulated at greater time intervals with a 30ꢁ pulse
width and a delay D1 of 4 s.
Procedure for Hydrolysis Study by 29Si NMR
Spectroscopic analysis was carried out after addition of 900 mm3 of silane to 0.3 cm3 of water (pH 7) in
1.8 cm3 of acetone-d6 with 3% chromium(III) acetylacetonate as relaxation accelerator in a 10 mm
NMR sample tube. During the first 12 hours every hour a spectrum was accumulated under inverse
gated decoupling (1280 scans; time domain: 64k; sweep width 11905Hz; 30ꢁ pulse width; relaxation
delay D1 0.1 s [6]). Afterwards, 29Si measurements were carried out with an relaxation delay of 4 s
accumulating 2048 scans.

1092
S. Altmann and J. Pfeiffer: Methacryloyloxyalkylfunctional Alkoxysilanes
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Pohl ER (1992) J Adhesion Sci Technol 6: 127
[3] Brand M, Frings A, Jenkner P, Lehnert R, Metternich HJ, Monkiewicz J, Schram J (1999) Chem
Sciences 54: 155
[4] Altmann S, Pfeiffer J, unpublished results
[5] Berlekamp UH, Mix A, Jutzi P, Stammler HG, Neumann B (2000) Oxygen, Phosphorus or Sulfur
Donor Ligands in Higher-Coordinated Organosilyl Chlorides and Triflates. In: Auner N, Weis J
(eds) Organosilicon Chemistry IV. Wiley-VCH, Weinheim, p 489
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[6] D1 of 0.1 s was chosen in analogy to Rodrıguez SA, Colon LA (2001) Applied Spectroscopy
55: 472