Microphase separation and crystallization in mixtures of polystyrene–poly (methyl methacrylate) diblock copolymer and poly(vinylidene fluoride) Jong Kwan Lee a , Ji Seon Kim a , Hae Jin Lim a , Kwang Hee Lee a, * , Seong Mo Jo b , Toshiaki Ougizawa c a Department of Polymer Science and Engineering, Inha University, 253, Yonghyun-dong, Nam-gu, Incheon 402-751, South Korea b Polymer Hybrids Research Center, Korea Institute of Science and Technology, Seoul 136-791, South Korea c Graduate School of Science and Engineering, Tokyo Institute of Technology, Tokyo 152-8550, Japan Received 18 October 2005; received in revised form 16 March 2006; accepted 4 May 2006 Available online 13 June 2006 Abstract This study examined the microdomain structures and the crystallization behavior in binary blends consisting of an asymmetric block copolymer and a homopolymer using small-angle X-ray scattering, optical microscopy and differential scanning calorimetry. A polystyrene-block- poly(methyl methacrylate) copolymer (PS-b-PMMA) was mixed with a low molecular weight poly(vinylidene fluoride) (PVDF), where the PS-b- PMMA had a 0.30 wt fraction of the PMMA block. At a PVDF concentration of !13.0 wt%, the PVDF was completely miscible with the PMMA microdomains, and the blends had a cylindrical structure. The addition of PVDF altered the morphology from a PMMA-cylindrical structure to a lamellar structure and finally to a PS-cylindrical structure. When the PVDF concentration was !23.0 wt%, the PVDF was distributed uniformly within the PMMA microdomains. After adding more PVDF, some of the PVDF was locally dissolved in the middle of the PMMA microdomains. The addition of PVDF also affected the ordered microstructure in the blends, leading to a well-defined microdomain structure. However, PVDF crystallization significantly disturbed the pre-existing microdomain structure, resulting in a poorly ordered morphology. In the blends, PVDF had unique crystallization behavior as a result of the space constraints imposed by the microdomains. q 2006 Elsevier Ltd. All rights reserved. Keywords: Block copolymer; Microphase separation; Crystallization 1. Introduction In recent years, many studies have been carried out to determine the morphology of binary mixtures containing a block copolymer with a homopolymer [1–25]. The addition of a homopolymer to a block copolymer can cause changes in the microstructures and properties of the block copolymer. However, the choice of miscible homopolymers for mixing with block copolymers is limited on account of the poor miscibility of most polymer pairs. Most studies used homopolymers with repeat units identical to one of the blocks in the block copolymers [1–19]. Relatively, a few studies have considered blends where the homopolymer is different from either the segments of the block copolymer but is miscible with one of the blocks [20–25]. One important difference between a homopolymer/block copolymer blend and a homopolymer/homopolymer blend is that the homopolymer has limited solubility in the micro- domains of a block copolymer. It is expected that the solubility of a homopolymer in the microdomains of a block copolymer will depend on the molecular weight ratio of the homopolymer and the appropriate block of the block copolymer (M H /M B ), specific interactions between the homopolymer and the block copolymer, the microstructure geometry, and temperature. Various thermodynamic theories predict the solubility of a homopolymer in a block copolymer. Meier [6] reported that significant solubility of a homopolymer in a block copolymer occurs when M H /M B !1. The maximum solubility of homo- polymer A in the A-phase of an AB or ABA block copolymer is estimated to be approximately 14 vol% if the block copolymer microstructure is lamellar and the M H /M B Z1. However, it is possible to achieve a high solubility even when the M H /M B is O1 in a strong interaction system. Lei and Weiss [21] examined the phase behavior of the blends of a lightly sulfonated styrenic block copolymer and poly(caprolactone) (PCL). The blend had a lamellar microstructure and a Polymer 47 (2006) 5420–5428 www.elsevier.com/locate/polymer 0032-3861/$ - see front matter q 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.05.022 * Corresponding author. Tel.: C82 32 862 9507; fax: C82 32 865 5178. E-mail address: polylee@inha.ac.kr (K.H. Lee).