Morphological Confinement on Crystallization in Blends of Poly(oxyethylene-block-oxybutylene) and Poly(oxybutylene)

Abstract

Three poly(oxyethylene-block-oxybutylene) diblock copolymers, E76B38, E114B56, and E155B76, were blended with poly(oxybutylene) homopolymer, B14 and B28, such that lamellae (lam), gyroid (gyr), hexagonally packed cylinders (hex), and body-centered-cubic (bcc) spheres were obtained in the melt. The nonisothermal crystallization on cooling of the blends was investigated with synchrotron smallangle X-ray scattering (SAXS) and differential scanning calorimetry (DSC). In general, two classes of behavior are observed. In confined crystallization the morphology of the melt is retained, and crystals have limited dimensions. In breakout crystallization the melt morphology is destroyed, and a new lamellar morphology is formed. The morphological state (confinement in or breakout of melt morphology) during crystallization was evaluated by the change of the position of the first-order peak (q*) in SAXS and the crystallization temperature (T c). Breakout of morphology was observed in all E76B38/B14 blends and E114B56/ B28 and E155B76/B28 blends with lam morphology, while confined crystallization occurred in E155B76/B28 blends with hex and bcc morphologies and E114B56/B28 blends with bcc morphology. Confined crystallization was also observed in low E content E114B56/B28 blends with hex morphology. These findings lead to two conclusions: (i) the tendency of confined crystallization varies with morphology and decreases in the order bcc > hex > lam, and (ii) confinement on crystallization tends to increase with the extent of segregation between the two blocks. The DSC results show that the crystallization temperature of the blends varies with morphology and chain length of the block copolymers. A much lower T c was observed for the blends exhibiting confined crystallization behavior, and this phenomenon is explained by a homogeneous nucleation mechanism. The morphology over a larger scale was also examined by polarized light microscopy, and spherulite formation was only observed in the blends where the morphology was easily broken out during crystallization.

Ellipsometry as a probe of crystallization kinetics in thin diblock copolymer films

“…Studies have shown that when the matrix is rubbery as opposed to glassy, crystallization can break out and destroy the phase-separated melt morphology. 2,[11][12][13][14] However, if the blocks are strongly segregated, this may not be the case, and the phase-separated morphology can be preserved upon crystallization. 9 Chen et al 10 found that they could increase confinement by blending poly(butadiene-b-ethylene oxide) (PB-PEO) with a lowmolecular-weight polybutadiene (PB) homopolymer.…”

“…2,7,9,10,[14][15][16] Atomic force microscopy (AFM) studies by Reiter et al 8 have allowed for the direct visualization of nucleation within individual spherical domains of thin PB-PEO films. The use of AFM was particularly insightful because the random distribution of nucleated domains verified that crystallization was occurring in each sphere, independently of neighboring sites.…”

Melting–Recrystallization of Block Copolymer Crystals in Confined Environments

“…[1][2][3][4][5][6][7][8][9][10][11] Crystallization in confined environments is usually initiated by homogeneous nucleation at large supercooling. 2,10,12 Thus the crystals formed are highly imperfect and have lower crystallinity, 5,11 compared with the crystals formed under normal crystallization conditions. As a result, the possibility of reorganization of these less perfect crystals into more ordered crystals is of great interest.…”

“…As revealed in our previous work, confined crystallization occurs in both blends at such a cooling rate. 10 To examine the ability of reorganization of the PEO crystals formed in these two blends, a slower heating rate of 0.5 C/min was applied to the blends after cooled at a rate of 10 C/min and the melting traces are illustrated in Figure 2. There was nearly no change in the shape of DSC trace for E155-83 and the shoulder melting peak at lower temperature was observed as well at such a slow heating rate.…”

“…Both samples undergo non-isothermal crystallization at a cooling rate of 10 C/min from 70 to À50 C. Our previous results showed that in this process both samples exhibit confined crystallization behavior, since the position of the first-order SAXS peak, q à , shows a continuous change instead of a stepwise change after the PEO block crystallizes. 10 The samples were heated to 40 C at rate of 10 C/min and heated from 40 to 65 C at a rate of 0.5 C/min. The changes of q à in the second heating step are shown in Figure 3.…”