Structure and Properties of the POSS-Containing Nanocomposites …
493
on the angular position (2θ m ) of the apex of the amorphous halo (2θ m ≈ 19,6
o ), the
period (d) of the near ordering of molecular chain fragments between the cross-links
in the volume of PU, according to the Bragg equation [43]:
d = λ(2sinq m )
−1
,
is equal to 0.45 nm.
Investigation of the native POSS by WAXS have shown (Fig. 4, curve 6) the existence of two discrete diffraction maxima which are significantly different in intensity,
with the diffraction maximum of significant intensity having Miller’s indices (001)
and low intensity having Miller’s indices (002). These two diffraction maxima indicate the existence of a two-level layered structure in the volume of the native POSS
sample. The formation of such a structure of POSS is due to the bicyclic structure
of its molecules, and the grafted aliphatic chain with two hydroxyl groups at the
end. The Bragg’s distance between the centers of molecular layers of the first level
(d 001 ), according to the angular position of the diffraction maximum of greater intensity (2θ 001 = 8.2
o ), is 1.07 nm, and the distance between the centers of the layers
(d 002 ), according to the less intensity diffraction maximum position (2θ 002 = 11.2
o )
is 0.79 nm. In addition to the layered structure, the POSS sample has also a crystalline
structure. This is indicated by the presence of a singlet diffraction maximum at the
curve of POSS (Fig. 4, curve 6) at 2θ m = 19.4
o and the multiplet maximum at 2θ m
~ 26.8
o .
Comparing the WAXS X-ray diffractograms of the native PU and the nanocomposites containing POSS, it was found that the apex of the amorphous halo of the
polyurethane matrix at 1 wt% of POSS insignificantly rises above the part of the
amorphous halo below 17.2° (Fig. 4, curves 1, 2). With an increase of POSS content
in the volume of PU up to 3 wt%, the apex of the amorphous halo becomes even more
(than at 1 wt% POSS) raised above the part of the amorphous halo (Fig. 4, curves
2, 3). Also at this concentration of POSS the low-intensity discrete maximum (001)
(at 2θ m = 8.2
o ) and barely noticeable the maximum (002), reflecting the two-level
layered structure of the nanofiller, could be observed.
With a further increase of POSS content up to 5 and 10 wt% in the volume of PU,
unlike PU samples containing 1 and 3 wt% of POSS, the peak of the amorphous halo
becomes less diffuse, that is, more sharpened (Fig. 4, curves 1–3 and 4, 5). At the
same time, the intensity of the diffraction peaks (001) and (002), which characterize
the layered structure of POSS, gradually increases.
The detected changes in the apex of the amorphous halo of the PU matrix at the
introduction of a different amount of POSS into the reaction mixture during the PU
synthesis may indicate that at least one terminal hydroxyl group of the aliphatic
chain of POSS may participate in the urethane formation reaction, and therefore the
POSS may be implanted into the chain between cross-links of PU. Consequently,
the detected changes in the apex of the amorphous halo of PU matrix in the POSScontaining nanocomposites with different POSS content can be explained precisely
by the grafting of a certain number of POSS molecules to the molecular chains
between cross-links of PU.
493
on the angular position (2θ m ) of the apex of the amorphous halo (2θ m ≈ 19,6
o ), the
period (d) of the near ordering of molecular chain fragments between the cross-links
in the volume of PU, according to the Bragg equation [43]:
d = λ(2sinq m )
−1
,
is equal to 0.45 nm.
Investigation of the native POSS by WAXS have shown (Fig. 4, curve 6) the existence of two discrete diffraction maxima which are significantly different in intensity,
with the diffraction maximum of significant intensity having Miller’s indices (001)
and low intensity having Miller’s indices (002). These two diffraction maxima indicate the existence of a two-level layered structure in the volume of the native POSS
sample. The formation of such a structure of POSS is due to the bicyclic structure
of its molecules, and the grafted aliphatic chain with two hydroxyl groups at the
end. The Bragg’s distance between the centers of molecular layers of the first level
(d 001 ), according to the angular position of the diffraction maximum of greater intensity (2θ 001 = 8.2
o ), is 1.07 nm, and the distance between the centers of the layers
(d 002 ), according to the less intensity diffraction maximum position (2θ 002 = 11.2
o )
is 0.79 nm. In addition to the layered structure, the POSS sample has also a crystalline
structure. This is indicated by the presence of a singlet diffraction maximum at the
curve of POSS (Fig. 4, curve 6) at 2θ m = 19.4
o and the multiplet maximum at 2θ m
~ 26.8
o .
Comparing the WAXS X-ray diffractograms of the native PU and the nanocomposites containing POSS, it was found that the apex of the amorphous halo of the
polyurethane matrix at 1 wt% of POSS insignificantly rises above the part of the
amorphous halo below 17.2° (Fig. 4, curves 1, 2). With an increase of POSS content
in the volume of PU up to 3 wt%, the apex of the amorphous halo becomes even more
(than at 1 wt% POSS) raised above the part of the amorphous halo (Fig. 4, curves
2, 3). Also at this concentration of POSS the low-intensity discrete maximum (001)
(at 2θ m = 8.2
o ) and barely noticeable the maximum (002), reflecting the two-level
layered structure of the nanofiller, could be observed.
With a further increase of POSS content up to 5 and 10 wt% in the volume of PU,
unlike PU samples containing 1 and 3 wt% of POSS, the peak of the amorphous halo
becomes less diffuse, that is, more sharpened (Fig. 4, curves 1–3 and 4, 5). At the
same time, the intensity of the diffraction peaks (001) and (002), which characterize
the layered structure of POSS, gradually increases.
The detected changes in the apex of the amorphous halo of the PU matrix at the
introduction of a different amount of POSS into the reaction mixture during the PU
synthesis may indicate that at least one terminal hydroxyl group of the aliphatic
chain of POSS may participate in the urethane formation reaction, and therefore the
POSS may be implanted into the chain between cross-links of PU. Consequently,
the detected changes in the apex of the amorphous halo of PU matrix in the POSScontaining nanocomposites with different POSS content can be explained precisely
by the grafting of a certain number of POSS molecules to the molecular chains
between cross-links of PU.