Due to low intensity or interference with other absorption lines, FTIR bands
characteristic for carbon–carbon multiple bonds in hydrocarbon groups connected
to Si atoms (C–H: doublet at 958 and 1006 cm
−1 , bands at 3016, 3056 cm
−1 and
C=C: 1598 cm
−1 [22]) are of limited utility in the studies of hydrosilylation. Their
presence in the spectrum of the reaction product shows, however, that conversion of
alkene derivative during the process has not been complete.
Hydrosilylation of carbon–carbon double bonds is accompanied by the formation of ethylene (–CH 2 CH 2 –) linkages between Si atoms (Fig. 12.1). The bands due
to C–H bonds of these moieties are located in FTIR spectra of the reaction products
at 1140, 2850, and 2900 cm
−1 [22].
Additionally, in all FTIR spectra of polysiloxanes, oligomeric silsesquioxanes,
and spherosilicates modified by hydrosilylation, a strong band due to Si–O–Si
vibrations in the range of 1000–1200 cm
−1 [22] is always visible.
In the studies of hydrosilylation processes or their products, FTIR spectroscopy
is very often complemented by NMR, particularly
1 H and
29 Si NMR techniques.
1 H
NMR spectra, similarly to FTIR, make it possible to follow the progress of
hydrosilylation by monitoring the changes in intensity of the line due to protons of
Si–H groups, located at d = 4.7–4.8 ppm [26]. Completeness of the reaction can be
also established by the disappearance of the signals in the range of d = 5–6 ppm
attributed to protons of vinyl/allyl groups [26]. Moreover,
1 H NMR spectra allow
discriminating between b and a adducts formed in hydrosilylation (Fig. 12.1) as
they give rise to the signals at d = 1.63 ppm (Si–CH(CH 3 ) and 1.03 ppm (Si–CH
(CH 2 )), respectively. Integral intensities of the appropriate lines visible in the
1 H
NMR spectra provide information on the degree of the initial compound functionalization or on the selectivity of the hydrosilylation process.
The signals corresponding to the units containing Si–H bond in the
29 Si NMR
spectra are observed at d = −35 ppm ([CH 3 Si(O 2 )H] units in polysiloxanes) , at
d = −85 ppm ([SiO 3 H] units in cage silsesquioxanes), and at d = 0.5 ppm ([(CH 3 ) 2
SiO(H)] units in spherosilicates) [27]. Formation of the hydrosilylation product is
confirmed by the appearance of the lines at d = −20 to −24 ppm ([CH 3 Si(O 2 )CH 2 ]
units in polysiloxanes), d = −65 ppm ([Si(O 3 )CH 2 ] units in cage silsesquioxanes),
or d = 10–11 ppm ([(CH 3 ) 2 Si(O)CH 2 ] units in spherosilicates).
29 Si NMR spectra
are also applied to verify if the cage structure of spherosilicates is preserved after
functionalization. Its retention is manifested by the clear line at d = −108–110 ppm
([SiO 4 ] units [27]).
12.4 Polysiloxanes Modified by Organic
Functional Groups
There are three classes of polysiloxanes modified by organic functional groups. In
the first one, organic moieties are attached to Si atoms of the polymer backbone;
these are the so-called side group-functionalized or pendant group polysiloxanes.
12 Application of Spectroscopic Methods in the Studies …
365
characteristic for carbon–carbon multiple bonds in hydrocarbon groups connected
to Si atoms (C–H: doublet at 958 and 1006 cm
−1 , bands at 3016, 3056 cm
−1 and
C=C: 1598 cm
−1 [22]) are of limited utility in the studies of hydrosilylation. Their
presence in the spectrum of the reaction product shows, however, that conversion of
alkene derivative during the process has not been complete.
Hydrosilylation of carbon–carbon double bonds is accompanied by the formation of ethylene (–CH 2 CH 2 –) linkages between Si atoms (Fig. 12.1). The bands due
to C–H bonds of these moieties are located in FTIR spectra of the reaction products
at 1140, 2850, and 2900 cm
−1 [22].
Additionally, in all FTIR spectra of polysiloxanes, oligomeric silsesquioxanes,
and spherosilicates modified by hydrosilylation, a strong band due to Si–O–Si
vibrations in the range of 1000–1200 cm
−1 [22] is always visible.
In the studies of hydrosilylation processes or their products, FTIR spectroscopy
is very often complemented by NMR, particularly
1 H and
29 Si NMR techniques.
1 H
NMR spectra, similarly to FTIR, make it possible to follow the progress of
hydrosilylation by monitoring the changes in intensity of the line due to protons of
Si–H groups, located at d = 4.7–4.8 ppm [26]. Completeness of the reaction can be
also established by the disappearance of the signals in the range of d = 5–6 ppm
attributed to protons of vinyl/allyl groups [26]. Moreover,
1 H NMR spectra allow
discriminating between b and a adducts formed in hydrosilylation (Fig. 12.1) as
they give rise to the signals at d = 1.63 ppm (Si–CH(CH 3 ) and 1.03 ppm (Si–CH
(CH 2 )), respectively. Integral intensities of the appropriate lines visible in the
1 H
NMR spectra provide information on the degree of the initial compound functionalization or on the selectivity of the hydrosilylation process.
The signals corresponding to the units containing Si–H bond in the
29 Si NMR
spectra are observed at d = −35 ppm ([CH 3 Si(O 2 )H] units in polysiloxanes) , at
d = −85 ppm ([SiO 3 H] units in cage silsesquioxanes), and at d = 0.5 ppm ([(CH 3 ) 2
SiO(H)] units in spherosilicates) [27]. Formation of the hydrosilylation product is
confirmed by the appearance of the lines at d = −20 to −24 ppm ([CH 3 Si(O 2 )CH 2 ]
units in polysiloxanes), d = −65 ppm ([Si(O 3 )CH 2 ] units in cage silsesquioxanes),
or d = 10–11 ppm ([(CH 3 ) 2 Si(O)CH 2 ] units in spherosilicates).
29 Si NMR spectra
are also applied to verify if the cage structure of spherosilicates is preserved after
functionalization. Its retention is manifested by the clear line at d = −108–110 ppm
([SiO 4 ] units [27]).
12.4 Polysiloxanes Modified by Organic
Functional Groups
There are three classes of polysiloxanes modified by organic functional groups. In
the first one, organic moieties are attached to Si atoms of the polymer backbone;
these are the so-called side group-functionalized or pendant group polysiloxanes.
12 Application of Spectroscopic Methods in the Studies …
365