Block copolymer/homopolymer binary blends

Macrophase separation after microphase separation has been observed in an AB block copolymer/homopolymer C blend (Hashimoto et al 1995). Blends of a PS-PB starblock copolymer (75wt% PS) and PVME homopolymer were prepared by solvent casting. Binary blends of PS and PVME exhibit a lower critical solution temperature (LCST), i.e. they demix at high temperatures. The initial structure of a 50% mixture of a PS-PB diblock and PVME shown in Fig. 6.20(a) consists of worm-like micelles. Heating led to macrophase separation as evident... 

This chapter is organized as follows. Section 6.2 is concerned with experiments on binary block copolymer/homopolymer blends, Section 6.3 deals with experiments on ternary blends containing a block copolymer and in Section 6.4 experiments on binary blends of block copolymers are reviewed. Theory for the corresponding type of blend is discussed successively in Sections 6.5 to 6.7. Finally, experiments on thin films are discussed in Section 6.8, separately from the work on bulk blends, in keeping with earlier chapters. 

Experiments on binary block copolymer/homopolymer blends... 

Table 6.1 Experimental studies of binary block copolymer/homopolymer blends. Adapted and extended from Roe and Rigby (1987)...

A number of classes of polymer blends containing block copolymers have been studied. Namely, binary blends of a block copolymer with a homopolymer, ternary mixtures of a block copolymer with two homopolymers and blends of two block copolymers. Experimental and theoretical studies of all these mixtures are the subject of Chapter 6. 

In binary blends of A homopolymer and AB diblock copolymer, the interplay between microphase separation and macrophase separation is controlled mainly by the relative length of the chains, in addition to the composition of the mixture. Homopolymers shorter than the corresponding block tend to be solubilized within the corresponding domain of a microphase-separated structure. As the homopolymer molecular weight increases to approach that of the corresponding... 

The phase behaviour of a binary blend of a block copolymer and a homo-polymer is primarily governed by the length of the homopolymer chain compared to the copolymer. Experiments by the groups of Hashimoto and Winey have led to the identification of three regimes, depending on the degree of polymerization of the homopolymer A, NAti, and that of the same component of the copolymer, NAc. 

The temperature dependence of the total interaction parameter shows that there exists an optimum condition for the composition at a given temperature (Fig. 3). Binary blends of PEO/PS and PEO/PAA are immiscible and miscible, respectively, at room temperature. The shape of curves implies that the homopol-ymer/homopolymer blends will exhibit UCST behaviors. A drastic effect of the sequence distribution on the miscibility can be found in Fig. 4. As the AA content in SAA increases from 5 mol% (Fig. 4a) to 7 mol% (Fig. 4b) to 10mol% (Fig. 4c), the blend becomes more miscible. The blend with random copolymers becomes miscible at a composition between 5 and 7 mol%, which agrees well with the experimental results [15]. At 7 mol%, the blend with block copolymers shows positive x> while the blend with random copolymers has negative y. This is very interesting because the miscibility could be controlled only by the change of copolymer sequence distributions. 

Since the 1980s, phase behaviors of A-homopolymer/A-B diblock copolymer binary systems have been investigated experimentally [14—22] and theoretically [23-25], where the EG /Si CsEOn systems that we focus on in this study are also their counterpart. The phase behaviors of binary blends of homopolymer and block copolymer are affected not only by o, , and ( NAE but also by a= where... 

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