Photon Factory Activity Report 2022 #40 (2023)

BL-10C/2021G569

Corner-Opened Cage-Silsesquioxane
as a Directional Template for Tripodal Poly(methyl methacrylate)
Ryota TANAKA1, Amato IGARASHI1, Taihei HAYASHI1, Hideaki TAKAGI2, Nobutaka SHIMIZU2,Noriyuki IGARASHI2, Shinichi SAKURAI1, Hiroaki IMOTO1, and Kensuke NAKA1
Graduate School of Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan2
Photon Factory, Institute of Materials Structure Science,High Energy Research Organization, 1-1 Oho, Tsukuba, Ibaraki 305-0801, Japan

1 Introduction
The branched structures of polymers, such as stars,brushes, hyperbranches, and dendrimers, exhibit properties
that are different from those of linear polymers.[1,2]Among them, star polymers have attracted significant
attention because of the diversity in their synthetic
methods and structures. In this study, the structure andproperties of the incompletely condensed polyhedraloligomeric silsesquioxanes (IC-POSS) containing threepoly(methyl methacrylate) chains at the open corners of
the cubic siloxane core have been studied.
2 Experiment
The small-angle X-ray scattering (SAXS) measurements
were performed at BL-10C beamline of photon factory(PF) of high-energy research organization (KEK), Japan,
with the wavelength of 0.10 nm and the size of the incident
X-ray beam being 182µm (H) ×346µm (V). The distance
between the specimen and the 2-dimensional detector(PILATUS3 2M, DECTRIS, Switzerland) was set at 2.5 m.
The exposure time of the one-shot measurement was 30s.
3 Results and Discussion
To obtain clear evidence of the aggregation of the POSS
moieties, we performed SAXS, as shown in Figure 1. Themeasured SAXS profiles [I(q), the scattering intensity I asa function of q] for 1a and 1b indicate a power-law
behavior as I(q) ~ q-4, which is well known as Porod’s law.
On the contrary, those for 3a and 3b exhibit a shoulder anda peak around q = 0.77 nm-1, respectively, providing a clear
indication of aggregation of corner-opened POSS moieties.
We conducted the fitting by assuming a spherical particle
scattering function for the SAXS profile to evaluate theparticle size distribution in the specimen. The resulting
particle size distributions are shown in Figure 2 for 3a and3b (as-cast and annealed), which were annealed at 110 °Cfor 12 h. The particle size is monodisperse for almost all
the specimens studied herein, except for the annealed 3b.
In particular, the diameter of the particles in as-cast 3b was
the lowest at 3 nm. Considering the 1-nm diameter of thecorner-opened POSS moiety, approximately 27 (= 33)
moieties were included in this aggregation of the POSS
moieties. For this specimen, peak fitting (see SupportingInformation) revealed 7.24 nm as the distance between two
neighbouring particles. Owing to the phase separation
between the POSS and PMMA moieties, a core-shellstructure can be assumed. Then, from the value of 7.24 nm,
the thickness of the outer PMMA layer (shell) can be
estimated as 2.12 nm (= (7.24–3)/2) if we consider thedirect contact between the two neighbouring particles.
Thus, the structure of the core-shell particle is deduced
from the SAXS results for the as-cast 3b; the core diameterof 3.0 nm and the PMMA layer thickness of 2.1 nm arereasonable from the chemical structure of the molecule.
By contrast, as-cast 3a exhibits monodisperse featureswith a diameter of 6 nm, which is twice as large as that ofas-cast 3b. It is interesting to find this contrasting result
even though the difference between 3a and 3b exists in thenumbers of PMMA chains attached to the corner-opened
POSS and its molecular weight while maintaining the same
volume percentage of the composition (for a more detailed
discussion on the particle size, see the supporting
information). Furthermore, the particles of 3a do notexhibit a lattice peak, as shown in Figure 1. This implies
that the particles of 3a do not have direct contact with eachother and, which in turn, implies the existence of ahomogeneous dispersion of the molecules without
aggregation. The fact that the size distribution of theparticles for 3a (Figure 2) did not change significantly
upon thermal annealing confirms the robustness of theaggregation. This is in contrast to 3b 1b, which exhibited abroadening of the particle size distribution upon thermalannealing. However, notably, the average diameter is 5.5
nm for both specimens (3a and 3b). Therefore, larger
particles are formed upon annealing for 3b, suggesting thecoalescence and merging of particles. As the lattice peak
for annealed 3b is still clearly observed in Figure 1, theoriginal particles with a diameter of 3 nm, which are in
direct contact with neighbouring particles, remained uponannealing.
* shin@kit.ac.jp
10

scattering intensity, I(q) / a.u.

110101010101010105

as cast
1a1b4

3

3a3bannealed
1a3a1b3b2

10-1-2-3
678 90.1

234q / nm

5678 912-1Fig. 1 SAXS profiles of 1a, 1b, 3a,and 3b (as-cast and annealed).
Annealing was conducted at 110 °Cfor 12 h.

Fig. 2 Distribution of theparticle size in 3a and 3b (ascast and annealed). Annealing
was conducted at 110 °C for 12h.