412
Y. Bolbukh et al.
is a complex molecular structure containing cross-linked polymers of phenolic
monomers especially p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
It is well known that amino-silica-based stationary phase is widely utilized to
carbohydrate separation. The interaction is primarily due to the reactivity of amino
group and can be implemented via hydroxyl groups of the polymer. In the presence
of carboxyl or carbonyl groups, the reaction with amino groups proceeds under mild
conditions to form silica/polymer bonds. The choice of the silicon hydride group is
primarily due to the possibility of chemically grafting the polymer as a result of the
reaction of the silicon hydride group with the C=C groupings of the polymer. In
addition, at a pH above 7, the hydrogen of the silicon hydride group is cleaved to
form an active site on silicon atom. The presence of methyl groups provides a change
in the hydrophobic/hydrophilic characteristics of the surface, which in turn provides
a change in the structure of the surface layer of the polymer and the orientation of the
macromolecules near the surface and inside the layer. The combination of amino and
hydride groups, along with a change in the hydrophobic/hydrophilic characteristics
of the filler surface, was expected to allow the chemical immobilization of lignin
under mild conditions.
So, silica surface chemistry (Table 26.1) can determine the structure of the
composite material. Interaction of the polymer with functional groups on the
silica surface determines the mechanism of macromolecule immobilization, namely,
physical adsorption or chemisorption as well as structure of polymer layer due to
influence on a macromolecule orientation relative to each other and to the silica
particles.
The infrared spectra (FTIR) of silica with the relatively chemically inert or with
chemically active groups in the surface layer are represented in Fig. 26.1a. Pristine
(unmodified) silica contains on surface isolated hydroxyl groups (3745 cm −1 ,
stretching vibrations of O–H in silanol groups), the OH groups perturbed with
hydrogen bonds (3660 cm −1 ), as well as physically adsorbed and strongly bound
water with a broadband with maximum absorption at 3450 cm −1 . The presence of
adsorbed water is additionally evidenced by the band at 1639 cm −1 . The bands at
1126 and 820 cm −1 are assigned to the stretching symmetric (ν s ) and asymmetric
(ν as ) vibrations of Si–O–Si grouping, band 980 cm −1 is attributed to the stretching
symmetric vibrations of Si-OH, and absorption at 474 cm −1 is attributed to the
bending vibrations (δ) of Si–O bonds. For the silica with substitution of surface
silanols with trimethylsilyl groups (SiO 2 CH 3 ), the band of hydroxyl group at
3745 cm −1 disappeared, and bands of stretching vibrations of methyl groups at 2970
and 2935 cm −1 are present (Fig. 26.1a, spectrum 2). The presence of silicon hydride
groups on the silica surface is confirmed by the band of the stretching vibrations of
Si–H bonds at 2250 cm −1 (Fig. 26.1a, spectrum 3). For the silica with bifunctional
surface layer (SiO 2 CH 3 SiH), the spectra revealed the presence of methylsilyl and
silicon hydride groupings (Fig. 26.1a, spectrum 4). As known, grafted aminopropyl
radicals can form bridge-like structures via interaction of amine groups with protons
of surface hydroxyl groups or adsorbed water molecules. Because of this the surface
layer of aminosilica (SiO 2 NH 2 ) contains NH 2 groups with different protonation
degrees (1643 and 1560 cm −1 ).
Y. Bolbukh et al.
is a complex molecular structure containing cross-linked polymers of phenolic
monomers especially p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol.
It is well known that amino-silica-based stationary phase is widely utilized to
carbohydrate separation. The interaction is primarily due to the reactivity of amino
group and can be implemented via hydroxyl groups of the polymer. In the presence
of carboxyl or carbonyl groups, the reaction with amino groups proceeds under mild
conditions to form silica/polymer bonds. The choice of the silicon hydride group is
primarily due to the possibility of chemically grafting the polymer as a result of the
reaction of the silicon hydride group with the C=C groupings of the polymer. In
addition, at a pH above 7, the hydrogen of the silicon hydride group is cleaved to
form an active site on silicon atom. The presence of methyl groups provides a change
in the hydrophobic/hydrophilic characteristics of the surface, which in turn provides
a change in the structure of the surface layer of the polymer and the orientation of the
macromolecules near the surface and inside the layer. The combination of amino and
hydride groups, along with a change in the hydrophobic/hydrophilic characteristics
of the filler surface, was expected to allow the chemical immobilization of lignin
under mild conditions.
So, silica surface chemistry (Table 26.1) can determine the structure of the
composite material. Interaction of the polymer with functional groups on the
silica surface determines the mechanism of macromolecule immobilization, namely,
physical adsorption or chemisorption as well as structure of polymer layer due to
influence on a macromolecule orientation relative to each other and to the silica
particles.
The infrared spectra (FTIR) of silica with the relatively chemically inert or with
chemically active groups in the surface layer are represented in Fig. 26.1a. Pristine
(unmodified) silica contains on surface isolated hydroxyl groups (3745 cm −1 ,
stretching vibrations of O–H in silanol groups), the OH groups perturbed with
hydrogen bonds (3660 cm −1 ), as well as physically adsorbed and strongly bound
water with a broadband with maximum absorption at 3450 cm −1 . The presence of
adsorbed water is additionally evidenced by the band at 1639 cm −1 . The bands at
1126 and 820 cm −1 are assigned to the stretching symmetric (ν s ) and asymmetric
(ν as ) vibrations of Si–O–Si grouping, band 980 cm −1 is attributed to the stretching
symmetric vibrations of Si-OH, and absorption at 474 cm −1 is attributed to the
bending vibrations (δ) of Si–O bonds. For the silica with substitution of surface
silanols with trimethylsilyl groups (SiO 2 CH 3 ), the band of hydroxyl group at
3745 cm −1 disappeared, and bands of stretching vibrations of methyl groups at 2970
and 2935 cm −1 are present (Fig. 26.1a, spectrum 2). The presence of silicon hydride
groups on the silica surface is confirmed by the band of the stretching vibrations of
Si–H bonds at 2250 cm −1 (Fig. 26.1a, spectrum 3). For the silica with bifunctional
surface layer (SiO 2 CH 3 SiH), the spectra revealed the presence of methylsilyl and
silicon hydride groupings (Fig. 26.1a, spectrum 4). As known, grafted aminopropyl
radicals can form bridge-like structures via interaction of amine groups with protons
of surface hydroxyl groups or adsorbed water molecules. Because of this the surface
layer of aminosilica (SiO 2 NH 2 ) contains NH 2 groups with different protonation
degrees (1643 and 1560 cm −1 ).