Photon Factory Activity Report 2005 #23 Part B (2006)
Materials Science

10C/2004G093

SR-SAXS studies on morphology formation in a binary blend of crystallineamorphous diblock copolymer and crystalline homopolymer. 2.
Michiaki AKABA 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
Introduction
We have investigated the process of morphology
formation in a binary blend of crystalline homopolymerand crystalline-amorphous diblock copolymer. Here, wequantitatively analyze the experimental results1-3, andclarify the mechanism of morphology formation as afunction of characteristic length of composition variation
ξ induced by macroscopic phase separation and also
crystallization temperature Tc.
Experimental Section
Samples We used poly(ε-caprolactone)-block-polybutadiene (PCL-b-PB) as a block copolymer and poly(εcaprolactone) (PCL) as a crystalline homopolymer.
SAXS measurements The SR-SAXS experiment wasperformed at beam line BL-10C. The accumulation timewas 10 sec for each measurement. The backgroundscattering and Lorentz factor were taken into account, andfinally the relative intensity was obtained as a function ofwave number s (= (2/λ)sin θ, 2θ: scattering angle). To
evaluate the angular position and relative intensity of eachscattering peak accurately, we used the Lorenz function
for each scattering peak and the Debye-Bueche equation
for the increasing intensity at lower s. The peak position(or spacing) and peak intensity were finally evaluated as afunction of crystallization time tc at each ξ and Tc.
Results and Discussion
The spacing from the microdomain structure is
gradually replaced with two kinds of spacing, one fromthe lamellar morphology formed in the crystallized PCLb-PB region and the other from the crystallized PCL

Fig. 1 Half-time of crystallization t1/2 for PCL ( ) and PCL-b-PB( ) regions plotted against ξ for the blend with φPCL = 0.6. The
closed symbols stand for t1/2 of neat PCL ( ) and PCL-b-PB ( ).

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region, at the middle of tc. However, the tc dependence ofthe normalized intensity depends significantly on ξ and Tc.
For example, the normalized intensity from two regions
make one master curve at Tc = 35 oC while they deviate at
Tc > 40 oC, indicating that the crystallization rates of PCLoand PCL-b-PB are equivalent at Tc = 35 C but they differoconsiderably at Tc > 40 C.
The half-time of crystallization t1/2, which is a measureof crystallization rate, can be evaluated from the tc
dependence of each SAXS peak, and is plotted in Figs 1and 2 against ξ and Tc. Fig 2 shows that when ξ is lessthan 500 nm the crystallization rate of PCL and PCL-bPB regions is identical and intermediate between those ofneat polymers, but the difference becomes significant
when ξ goes beyond 500 nm and they approach to thecrystallization rate of neat polymers. Fig. 3 shows that at
Tc = 35 oC the values of t1/2 for PCL-b-PB and PCL are
identical but they deviate significantly with increasing Tc.
In addition, t1/2 for the quenched blend with a smaller ξtakes a middle position between those for PCL and PCLb-PB in the phase-separated blend. These Figures clearlyshow that the combination of ξ and Tc drives thecrystallization behavior of this blend.
References[1] M. Akaba and S. Nojima Polym. J., 37, 464 (2005).
[2] M. Akaba and S. Nojima Polym. J., 37, 584 (2005).
[3] M. Akaba and S. Nojima Polym. J., 38, xxx (2006).
*snojima@polymer.titech.ac.jp

Fig. 2 Tc dependence of t1/2 for PCL-b-PB ( ) and PCL ( )in the phase-separated blend with ξ = 2.5 µm. represents
the result for the quenched blend, where t1/2 is equivalent for
PCL and PCL-b-PB.