Melting Behavior of Poly(ε-caprolactone)-block-Polybutadiene Copolymers

Abstract

The melting behavior of poly( -caprolactone)-block-polybutadiene (PCL-b-PB) copolymers, crystallized at various temperatures T c from the melt (homogeneous state or microphase-separated state), has been studied by small-angle X-ray scattering with synchrotron radiation (SR-SAXS). The strong SR-SAXS intensity peak changed into a sharp diffraction or a diffuse peak on heating, indicating a morphological transition from the lamellar morphology (an alternating structure consisting of crystallized lamellae and amorphous layers) into the microdomain structure or the homogeneous melt. The melting process of PCL-b-PB was extremely different from that of the poly( -caprolactone) (PCL) homopolymer; the long spacing of the lamellar morphology in PCL-b-PB, which depended significantly on Tc, remained constant or decreased slightly on heating, whereas that in PCL increased steadily. The morphological change in PCL-b-PB and PCL under the different thermal treatments was quantitatively investigated by SAXS and DSC. Details of the lamellar morphology initially formed in PCL-b-PB were determined mainly by the nonequilibrium crystallization of the PCL block at T c, as in the case of PCL, but the subsequent heating did not alter this morphology, owing probably to the competition between the lamellar thickening and the contraction of the PB block existing between PCL lamellae, resulting in the characteristic melting behavior of PCL-b-PB.

Significant increase in the melting temperature of poly(ɛ-caprolactone) blocks confined in the crystallized lamellar morphology of poly(ɛ-caprolactone)-block-polyethylene copolymers

“…Details of the equipment and instrumentation have already been described elsewhere. 9,26 The SAXS intensity was detected using an image plate system R-AXIS VII (Rigaku Co., Tokyo, Japan). The two-dimensional SAXS curves thus obtained were first converted into one-dimensional curves using a circular averaging program, and then corrected for background scattering.…”

“…This chain stretching of amorphous blocks in the crystallized lamellar morphology of crystalline-amorphous diblock copolymers is theoretically predicted 6,7 and also experimentally verified. [8][9][10] The crystalline-crystalline diblock copolymers with separate melting temperatures T m,1 and T m,2 (T m,1 cT m,2 ) behave as crystalline-amorphous diblocks at temperatures higher than T m,2 . [11][12][13][14][15] The lower panel in Figure 1 schematically shows the morphology formation in an asymmetric crystalline-crystalline diblock copolymer with an extremely minor higher-T m block.…”

Composition Dependence of Crystallization Behavior Observed in Crystalline-Crystalline Diblock Copolymers

“…Details of the equipment and the intensity correction procedure were already described elsewhere. [29][30][31] Accumulation time for each frame was 10 s, and the measurement was continued until an integrated intensity did not change any more. The SAXS curves were finally obtained as a function of s ¼ ð2=Þ sin , where is the wavelength of incident X-ray (¼ 0:1488 nm) and 2 the scattering angle.…”

“…It was found from these studies that the crystallization behavior of PCL blocks and also resulting morphology were significantly influenced by the crystallization temperature of PCL blocks T c ; at lower T c (< 30 C), PCL blocks crystallized within the existing PE lamellar morphology (an alternating structure consisting of thin PE crystals and amorphous PE + PCL layers) as a template, while at higher T c (> 35 C) it crystallized by deforming and/ or partially destroying the PE lamellar morphology. As a result, the final morphology depended intimately on T c , and the transition temperature T p was [30][31][32][33][34][35][36][37][38][39][40] C for selected PCL-b-PE copolymers.…”

Temperature Dependence of Crystallization Behavior in a Phase-Separated Blend of Poly(ε-caprolactone) Homopolymer and Poly(ε-caprolactone)-block-Polybutadiene Copolymer

“…Details of the optics and the instrumentation were described elsewhere. 25,26 The SR-SAXS measurements were continued until the integrated intensity did not change any more, and each time-sliced SAXS intensity during 10 sec was obtained as a function of wave number s (¼ 2 sin ; 2: scattering angle, : X-ray wave length (¼ 0:1488 nm)) after correcting background scattering. The SAXS curves thus obtained were very complicated because they consisted of three scattering peaks and also an increasing intensity toward s !…”