Photon Factory Activity Report 2018 #36 (2019)

BL-6A & 10C/2017G084

Structural Dynamics of Substituted Poly(lactic acid) with sec-Butyl Side Chains
Revealed by Synchrotron SAXS/WAXD Simultaneous Measurements
Hironori MARUBAYASHI,* Ryo MIZUKAMI, Yuji HAMADA, and Shuichi NOJIMA
School of Materials and Chemical Technology, Tokyo Institute of Technology,
2-12-1 Ookayama, Meguro-ku, Tokyo 152-8552, Japan
1 Introduction
Recently, the side-chain-substituted poly(lactic acid)s(SPLAs) have attracted much attention to overcome
weakness of poly(L-lactic acid) (PLLA), one of therepresentative bio-based plastics [1,2]. Poly[(2S,3S)-2hydroxy-3-methylpentanoic acid] [P(L-2H3MP)] is one of
the crystalline SPLAs [2]. We found that P(L-2H3MP)
showed a complicated multiple melting behavior bythermal analysis. However, its mechanism is still unclear.
In this study, we investigated the dynamics of higherorder and crystal structures of P(L-2H3MP) during aheating process by using time-resolved synchrotron
SAXS/WAXD simultaneous measurements.
2 ExperimentP(L-2H3MP) with Mn = 70 kg/mol was synthesized byring-opening polymerization of cyclic dimers of the L-αhydroxy acid derived from L-isoleucine [1–3]. The meltcrystallized sample was prepared by thermal annealing(210 °C, 1 min → 165 °C, 3 h → LN2 quench).
SAXS/WAXD simultaneous measurements wereperformed at KEK PF BL-6A and 10C (λ = 0.1500 and0.1488 nm, respectively) using an FP84HT TA Microscopy
Cell (METTLER) for heating from 30 to 210 °C at20 °C/min, during which the data acquisition and intervaltimes were set to 2.5 and 0.5 seconds, respectively. Thetemperature of samples packed in a washer was measured
by a resistance temperature detector. SAXS/WAXD
analyses were done using the handmade software [4].
3 Results and Discussion
Fig. 1 shows the changes of Lorentz-corrected SAXS
profiles during the heating process for P(L-2H3MP) which
had been isothermally-crystallized at 165 ℃. In SAXS
profiles below 150 °C (blue), peaks at lower and higher q
would be ascribed to the alternating structure composed ofthicker lamellar crystals and amorphous layers, and that ofthinner lamellae and amorphous layers, respectively. The
high-q peak shifted to lower q with increasing temperature,
and when temperature reached 150 °C, this peak was nolonger observed. In SAXS profiles above 150 °C (red),
only the low-q peak was seen until melting. In the
differential scanning calorimetry (DSC) curve, three
endothermic peaks were observed: the annealing peaktemperature (Ta) < Tm1 < Tm2. The Ta peak was seen justabove 165 °C, indicating that the high-q SAXS peak wasresponsible for the annealing peak. The WAXD data
showed no changes in the crystal structure during theheating process. Therefore, the annealing peak on the DSC
curve should be explained by the melting of thin (andprobably disordered) lamellar crystals. However, the originof Tm1 and Tm2 (distribution in lamella thickness and/or
melt-recrystallization-remelt) is still an open question.

Fig. 1: Changes of Lorentz-corrected SAXS profiles
during the heating process at 20 °C/min for P(L-2H3MP)
which had been isothermally-crystallized at 165 ℃. SAXS
profiles below/above 150 °C are shown in blue/red.
Acknowledgement
This work was financially supported by the “Planting
Seeds for Research” program from Tokyo Tech (2014–2015), Mizuho Foundation for the Promotion of Sciences(2015–2017), JSPS KAKENHI Grant-in-Aid for Young
Scientists (B) 17K12836 (2017–2019), and Kanamori
Foundation Research Grant (2018–2019).
References[1] H. Marubayashi and S. Nojima, Macromolecules 49,5538 (2016).
[2] H. Marubayashi et al., Polym. Degrad. Stab. 153, 318(2018).
[3] H. Marubayashi et al., Macromol. Chem. Phys. 214,2546 (2013).
[4] H. Marubayashi et al., Polym. Degrad. Stab. 146, 174(2017).
* hironori.marubayashi.d7@tohoku.ac.jp