Photon Factory Activity Report 2016 #34 (2017)

BL-15A2/2015G572

Frank-Kasper  Phase Boundary of
Polybutadiene-poly(-caprolactone)/homopolymer BlendsHideaki Takagi1,*1
Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan
1 Introduction
Recently, quasicrystals have been discovered in soft
matter system, such as dendrimers, multi block
copolymers and block copolymer solutions [1]. The allquasiperiodic structure observed in dendric and polymericmaterials has 12-fold symmetry, while the temperatureinduced transition from the face-centered cubic phase to
the 12-fold and 18-fold symmetry phases occurred inblock copolymer solutions. Frank-Kasper  phase which
is well known as a crystalline approximant of adodecagonal quasicrystal have been also observed in suchsystems. The Frank–Kasper  phase has P42/mnm
symmetry and 30 spheres in a unit cell.
Theoretical studies on thermodynamic stability of the phase in block copolymers have been studied intensively
in the last few years. Self-consistent field theory (SCFT)
predicts that the appearance of the  phase is theconformational asymmetry  = vAaA2/(vBaB2), where v anda are the molecular volume and the statistical segmental
length, respectively [2]. The  phase as a stable phaseappears in a narrow region between the body-centeredcubic (BCC) and hexagonally packed cylinders (HEX) at
 > 1.5.
In a pure polymer system without any solvents, the phase was observed in a novel linear or miktoarm multi
block copolymer composed of three or more blocks.
Recently, we reported that the  phase was found in block
copolymer/homopolymer blends [3]. In this report, inorder to investigate the concentration effect of added
homopolymer to the appearance of the  phase, the phase
diagram of block copolymer/homopolymer blends wasconstructed.
2 Experiment
Polybutadiene-poly(-caprolactone) block copolymer(PB-PCL) and polybutradiene (PB) homopolymer weresynthesized by anionic polymerization under a highvacuum. The number -average molecular weight (Mn) and
its heterogeneous index (Mw/Mn) of PB-PCL were 6,400
kg/mol and 1.02, respectively. The volume fraction ofPCL was 0.27. The Mn of the synthesized PB
homopolymer (PB5k) was 4,500, and the Mw/Mn was 1.03.
Blend samples were obtained by solvent casting fromtoluene solution of the blend sample. The weight fractionof added homopolymer was 0.29.
The small angle X-ray scattering (SAXS)
measurements were conducted at BL-15A2 in PF. The
detector was set at a position of 3.5 m apart from sample
position. The energy of X-ray was 5.7 keV.

3 Results and Discussion
Figure 1 shows the phase diagram for PB-PCL/PB5k
blends. The horizontal axis represents the weight fractionof added PB5k (PB5k) and the vertical axis represents themorphology observed at each temperature. The orderedstructures observed were HEX (triangles), coexisting of
BCC and HEX (squares), BCC (circles), Frank-Kasper phase (pluses) and disordered state (crosses). Filled
diamonds represent non-equilibrium lattice disordered
micelles, which is observed after melting of thecrystalline-amorphous alternating lamellar structure [4].
As depicted in Figure 1, HEX was seen in the lower PB5kregion (PB5k ≤ 17 wt%). On the other hand, at higher
PB5k region (PB5k ≥ 41 wt%), BCC phase was onlyobserved. Frank-Kasper  phase appeared between BCCand HEX phase in the narrow range 29 ≤ PB5k ≤ 33.
Theoretical studies predict that  phase is observed in anarrow region between HEX and BCC [2]. Thus, ourresults were in good agreement with theoretical ones.

Fig. 1: The phase diagram for PB-PCL/PB5k blends.
Phase notation is as follows: triangles (HEX), squares(coexisting of HEX and BCC), circles (BCC), pluses (phase), diamonds (transient disordered micelles) andcrosses (disordered state).
References[1] T. Dotera, J. Polym. Sci. Part B 50, 155 (2012).

Photon Factory Activity Report 2016 #34 (2017)[2] N. Xie, et al., ACS Macro Lett. 3 906 (2014).
[3] H. Takagi, et al., J. Phys: Condens. Matter 29, 204002(2017).
[4] H. Takagi, et al., Colloid Polym. Sci. 294, 993 (2016).
* takagih@post.kek.jp