Photon Factory Activity Report 2014 #32 (2015) B

BL-10C/2014G011

Crystallization of Both-ends-tethered, One-end-tethered, and Untethered
Polymer Chains Confined in Lamellar Nanodomains
Shintaro Nakagawa, Koshun Kawazu, and Shuichi Nojima*
Department of Organic and Polymeric Materials, Graduate School of Science and Engineering,Tokyo Institute of Technology, H-125, 2-12-1 Ookayama, Meguro-ku Tokyo 152-8552, Japan
1 Introduction
Block copolymers consisting of a crystalline block anda glassy amorphous block exhibit interesting
crystallization behavior since the crystalline blocks are
spatially confined in nanodomains formed by microphaseseparation of block copolymers. Crystallization behavior
in such cases is significantly affected not only by theshape and size of nanodomains but also by the chain-ends
fixed at nanodomain interfaces (chain-end tethering). We
have recently studied the effect of chain-end tethering on
crystallization by comparing one-end-tethered (OT) anduntethered (UT) chains both spatially confined in
identical nanodomains [1]. In the present study, weinvestigate the crystallization behavior of both-endstethered (BT) chains as well as OT and UT chains tocomprehensively understand the effects of chain-end
tethering on the crystallization under spatial confinement.
2 Experiment
Samples. We synthesized two lamella-forming
polystyrene-block-poly(-caprolactone)-block-polystyrene(PS-b-PCL-b-PS) triblock copolymers having identicalcomposition and molecular weight (SCS and SC’S in Fig.
1a). SCS has two photocleavable o-nitrobenzyl groups(ONBs) in interblock junctions while SC’S has only one
ONB. SCS and SC’S both have BT PCL chains confinedin lamellar nanodomains. Upon photocleaving ONBs byUV irradiation, BT chains in SCS and SC’S are converted
to UT and OT chains, respectively (S/C/S and S/C’S inFig. 1a). It is then possible to directly compare thecrystallization behavior of BT, OT, and UT chainsconfined in identical lamellar nanodomains.
Measurements. The size and shape of nanodomains
were determined by SAXS at BL-10C in PF-KEK using
PILATUS3 2M detector. The isothermal crystallization
behavior was investigated using time-resolved infrared
spectroscopy (TR-IR) and differential scanningcalorimetry (DSC).
3 Results and Discussion
SAXS curves of SCS, SC’S, S/C/S, and S/C’S incrystallized state are shown in Fig. 1b. All the samples
exhibit multiple scattering peaks whose relative positions
are 1:2:3, indicating the presence of well-ordered lamellar
nanodomains. It is also clear that all the samples before
and after UV irradiation have identical nanodomains
since their primary peak positions are completelymatched. From the primary peak position and the volume
fraction of PCL chains, the thickness of lamellar

nanodomains containing PCL chains was calculated to beca. 11 nm for all the samples.
Fig. 2 shows the crystallization half-time t1/2 of thePCL chains in the samples evaluated from TR-IR andDSC results, where larger t1/2 means the lower
crystallization rate. It can be seen that the temperatures atwhich t1/2 is 10 min follow the relation SCS = SC’S <<S/C’S < S/C/S, indicating that chain-end tetheringmoderately retards the crystallization, though the effect of
one-end-tethering is not as profound as that of both-endstethering.

Fig. 1:(a) Schematic illustration showing the sample
preparation method used in this study.
(b) SAXS curves of the crystallized samples.

Fig. 2: Crystallization half-time plotted against
crystallization temperature.
Acknowledgment
Authors thank Prof. T. Ishizone at Tokyo Tech andProfs. K. Yamaguchi and S. Nakahama at Kanagawa Uni.
for their help in synthesizing the samples.
References[1] S. Nakagawa et al., Polymer 55, 4394-4400 (2014).
* snojima@polymer.titech.ac.jp