Copolymer demixing

In a somewhat wider sense, one can define amphiphiles as molecules in which chemically very different units are linked together. For example, the structures formed by A B block copolymers in demixed A and/or B homopolymer melts and their phase behavior are very similar to those of classical amphiphiles in water and/or oil [13,14]. Copolymers are used not only to disperse immiscible homopolymer phases in one another, but also to create new, mesoscopically structured materials with unusual and interesting properties [15]. 

Some remarks can be made about the evolutions in the presence of Ca2+, although it is difficult to think that some brine could contain only this type of cations without monovalent cations. Before any aging, a copolymer of 17% of acrylate content begins to demix for CaCl2 > 2.5 10 2 M/l and this limit is lower for higher... 

Fig. 15 Cooling curves of crystallinity (solid line) and demixing parameter of comonomers (dashed line). The latter is defined as the mean fraction of neighboring sites occupied by other comonomers around each comonomer. The cooling program is a stepwise increase of Ep/(k T) from zero with a step length of 0.002 and a step period of 300 Monte Carlo cycles, a The slightly alternating copolymer with a comonomer mole fraction 0.36 b the heterogeneous copolymer with a comonomer mole fraction of 0.36 [52]...

Application. Using the copolymer-Ig conjugate, we developed a novel polymer-based immunoassay utilizing the demixing behavior of polyNIPAAM at or above the LCST as the separation technique. 

It is well-known that one can reduce the droplet size of a demixed polymer blend by adding a well-chosen block-copolymer at given p and T, and achieve interesting improvements of the blend s mechanical properties. 

EOS models were derived for polymer blends that gave the first evidence of the severe pressure - dependence of the phase behaviour of such blends [41,42], First, experimental data under pressure were presented for the mixture of poly(ethyl acetate) and polyfvinylidene fluoride) [9], and later for in several other systems [27,43,44,45], However, the direction of the shift in cloud-point temperature with pressure proved to be system-dependent. In addition, the phase behaviour of mixtures containing random copolymers strongly depends on the exact chemical composition of both copolymers. In the production of reactor blends or copolymers a small variation of the reactor feed or process variables, such as temperature and pressure, may lead to demixing of the copolymer solution (or the blend) in the reactor. Fig. 9.7-1 shows some data collected in a laser-light-scattering autoclave on the blend PMMA/SAN [46],... 

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... 

Until recently, very little quantitative information was available on blends of block copolymers. The literature is summarized in Table 6.3. Hoffman et al. (1970) reported microscopic demixing of blends of PS-PB diblocks, with two maxima in the domain size distribution, but with no evidence tor macrophase separation. These findings must be treated with caution in the light of more recent results. Hadziioannou and Skoulios (1982) used SAXS and SANS to investigate the morphology of binary blends of PS-PI diblocks, and binary PS-PI/PS-PI-PS or PS-PI/PI-PS-PI blends or blends of the two types of triblock. They found that the blends were microphase separated, and that the sharpness of the interface was not reduced in blends compared to neat copolymers. The transition between a lamellar and a cylindrical structure was shown to depend primarily on blend composition. In contrast, the transition from a lamellar to a disordered phase at... 

Kuhn R (1983) Characterization of polymer blends, block copolymers, and graft copolymers by fractionation procedures using demixing solvents. Polym Sci Technol 20 45-58. 

Noolandi J, Hong KM. Effect of block copolymers at a demixed homopolymer interface. Macromolecules 1984 17 1531-1537. 

Figure 9.19 CCD profiles for PMMA-g-PDMS copolymers of low PDMS content (17wt% PDMS) prepared anionically using 20,000 molecular weight PDMS grafts (top) supercritical chlo-rodifluoromethane fractionation (bottom) solvent demixing fractionation (DeSimone et al., 1988b).

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