Photon Factory Activity Report 2016 #34 (2017)

BL-6A, BL-10C/2016G525

Thermotropic Order-Order Transition between FCC and HCP Latticein Sphere-forming Block Copolymer/Homopolymer blends
1

Hideaki Takagi1,*
Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan

1 Introduction
It is well known that block copolymers can form aspherical morphology when a composition asymmetry issignificantly large. In many cases, spherical micelles
composed of block copolymers are arranged into bodycentered cubic (BCC) lattice. It was reported that theclose-packed lattice exists outside theoretically as anordered phase in the phase diagram [1]. The
polybutadiene-poly(ethylene oxide) block copolymer was
reported to exhibit a face-centered cubic (FCC) lattice [2].
Theoretical studies on thermodynamic stability ofclose-packed lattice show that the free energy of FCC isonly slightly smaller than hexagonal close-packed (HCP)
lattice; i.e., the Helmholtz free energies of FCC and HCP
lattice differ by less than 0.05% [3].
Our research group has studied the phase behavior ofbinary mixtures of block copolymers and homopolymers
by using small angle X-ray scattering (SAXS) techniques.
In this report, we confirmed that thermotropic order-ordertransition form FCC to HCP was observed in block
copolymer/homopolymer blends.
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 7,600
kg/mol and 1.04, respectively. The volume fraction ofPCL was 0.41. The Mn of the synthesized PB
homopolymer (PB2k) was 1,700, and the Mw/Mn was 1.06.
Blend samples were prepared by solvent casting fromtoluene solution of the blend sample. The weight fractionof added homopolymer was 0.53.
SAXS measurements were conducted at BL-6A and
BL-10C in PF. The detector was set at a position of 2.5 m
at BL-6A and 3 m at BL-10C apart from sample position,respectively. The wavelength of X-ray was 1.5 Å at BL6A and 1.77 Å at BL-10C, respectively.
3 Results and Discussion
Figure 1 shows the SAXS profiles for PB-PCL/PB2k
obtained at 160 °C and 240 °C. Data are plotted as thelogarithmof the relative scattered intensity log I(q) versus themagnitude of scattering vector q = 4sin(/2)/, λ is thewavelength of the x-ray and θ is the scattering angle. The
profiles are shifted vertically to avoid overlapping. At160°C, the scattering peaks are observed at a relative qpeak position of 1:1.15:1.63:1.91:2:2.52:2.83:3.42 as
marked thick arrows. Here, theoretical relative q-peakpositions and reflection indexes for FCC and HCP are
shown in Table 1. It was found that scattering peaks
observed at 160 °C are good agreement with that of FCC.
When the temperature reaches 240 °C, the scatteringprofile was changed. The relativ q-peak position changes
to the 1:1.06:1.13:1.46:1.73:1.87:2.07:2.12:2.56:2.65:2.7
5:2.84 position (thin arrows). From Table 1, a series ofthe peak positions was consistent with that predicted asHCP, indicating that a phase transition from FCC to HCP
took place.

Fig. 1: The phase diagram for PB-PCL/PB2k blends. Thinarrows show scattering from HCP, and thick arrows
represent scattering peaks from FCC.
Table 1: Calculated relative peak positions and reflection
indexes of FCC and HCP

HCP(111)1(100)
1(200)
1.15(220)1.06(220)1.63(101)
1.13(311)
1.91(102)
1.46(222)2(110)
1.73(400)
2.31(103)
1.86(331)
2.52(112)
2.04(420)
2.58(201)2.07(422)
2.83(004)
2.12(333)
3(202)
2.26(440)
3.27(104)
2.34(531)
3.42(203)
2.56(442)
3.46(210)
2.65(533)
3.79(211)
2.7(444)4(114)
2.75

FCC

Photon Factory Activity Report 2016 #34 (2017)

References[1] M. W. Matsen,et al., Macromolecules 29, 1091 (1996).
[2] Y. Y. Haung, et al., Macromolecules 40 406 (2007).
[3] P. G. Bolhuis, et al A. Nature 388, 235 (1997).
* takagih@post.kek.jp