Phase behavior, random copolymers

In the absence of polymer the sediment volume of silica depends on the non-solvent fraction of the medium as shown in Figure 6. The sediment volume assessment of steric stabilization behavior of the copolymers is illustrated in Figures 7a to 7c. At low styrene contents, both the random and block copolymers show a steady increase in sediment volume as the non-solvent content is raised up to the phase separation value. With polystyrene and random copolymers of high styrene content, the sediment volume stays largely constant with alteration in the non-solvent fraction until the theta-point is approached and then continues to become larger as the limit of solubility is reached. In Figure 7b only the data points of RC 86 are shown, RC 94 giving almost identical values. 

This article reviews the phase behavior of polymer blends with special emphasis on blends of random copolymers. Thermodynamic issues are considered and then experimental results on miscibility and phase separation are summarized. Section 3 deals with characteristic features of both the liquid-liquid phase separation process and the reverse phenomenon of phase dissolution in blends. This also involves morphology control by definite phase decomposition. In Sect. 4 attention will be focused on flow-induced phase changes in polymer blends. Experimental results and theoretical approaches are outlined. 

Phase Behavior of Blends with Random Copolymers. 43... 

In conclusion, the mean-field theory outlined above turns out to be a powerful tool for rationalizing the complex phase behavior of polymer blends, especially of random copolymer based blends, in terms of interaction, ftee-volume and size effects. 

Homopolymer (A)/random copolymer (B) blends, poly(1)/poly(2-ran-3). Phase behavior may be discussed in terms of the interaction parameter XAB which is given in the mean-field approximation by [2, 3]... 

Unlike the random copolymers, block and graft copolymers separate into two phases, with each phase exhibiting its own Tg (or TM).40 The modulus-temperature behavior of a series of... 

Based on the pioneering work of Molau [64], it is evident that phase separation can occur in blends of two or more copolymers produced from the same monomers when the composition difference between the blend components exceeds some critical value. The mean field theory for random copolymer-copolymers blends has been applied to ES-ES blends differing in styrene content to determine the miscibility behavior of blends [65,66]. On the basis of the solubility parameter difference between PS and PE, it was predicted that the critical comonomer difference in styrene content at which phase separation occurs is about 10 wt% S for ESI with molecular weight around 105. DMS plots for ES73 and ES66 copolymers and their 1 1 blend are presented in Figure 26.8. 

Random copolyesters based on bromoterephthalic acid, methyl hydroquinone, and hexane diol have been synthesized. Their mesophase properties were studied by differential scanning calorimetry, optical microscopy, realtime X-ray diffraction and melt rheology. At low molecular weight these copolymers exhibit triphasic behavior, where two mesomorphic phases coexist with an isotropic phase. Fractionation based on solubility in THF enables the identification of two components. Simple statistical arguments are employed to model the polymerization reaction and account for the observed phase behavior. 

As a last example of the application of HPTMC, we calculate the phase behavior of block copolymers and random copolymers. Again, lattice models are used in these calculations. For block copolymers, we study the influence of the number of blocks on the phase behavior for random copolymers, we examine the effect of sequence length. We use a one-dimensional Ising model to represent the random copolymer. Sequence length is statistically determined by the temperature of the one-dimensional Ising model. When this temperature approaches infinity, the sequence of the copolymer is completely random when the temperature approaches zero, the random copolymer becomes a diblock copolymer. For all calculations, the chain length isn = 1000. 

Figure 15 shows the phase diagram of block copolymers and random copolymers. For comparison, the phase diagram of a homopolymer having the same molecular weight is also shown in the figure. As we can see, the number of blocks on the polymer has a dramatic effect on the phase behavior. The... 

Thermodynamic equations are formulated for the isomorphic behavior of A-B type random copolymer systems, in which both A and B comonomer units are allowed to cocrystallize in the common lattices analogous to, or just the same as, those of the corresponding homopolymers poly(A) or poly(B). It is assumed that, in the lattice of poly (A), the B units require free energy relative to the A units and vice versa. On the basis of the derived thermodyn-amie equations, phase diagrams are proposed for the A-B random copolymers with cocrystallization. The melting point versus comonomer composition curve predicted by this diagram is very consistent with that experimentally observed for the P(3HB-co-3HV) copolymers, as shown in Fig. 21.1. It is suggested that the minor comonomer unit with a less bulky structure cocrystallize thermodynamically simpler than that with a more bulky structure. 

Bulk Properties. Block polymers can show mechanical properties in the bulk state that are superior to those that can be achieved with the corresponding homopolymers or random copolymers. This improvement in behavior is made possible by the segregated phase structure in block polymers. Of primary interest have been structures possessing both soft and hard phases. These polymers may range from the thermoplastic elastomers in which the hard phase is dispersed in a soft phase matrix, to toughened (i.e., high impact strength) thermoplastics in which the soft phase is dispersed in a... 

A considerable amount of work has focused on the design and synthesis of macromolecules for use as emulsifiers for lipophilic materials and as polymeric stabilizers for the colloidal dispersion of lipophilic, hydrocarbon polymers in compressed CO2. It has been shown that fluorinated acrylate homopolymers, such as PFOA, are effective amphiphiles as they possess a lipophilic acrylate-like backbone and C02-philic, fluorinated side chains, as indicated in Figure 4.5-1 [100]. Furthermore, it has been demonstrated that a homopolymer which is physically adsorbed to the surface of a polymer colloid precludes coagulation due to the presence of loops and tails [110]. These fluorinated acrylate homopolymers can be synthesized homogeneously in CO2 as described in an earlier section. The solution properties [111,112] and phase behavior [45] of PFOA in SCCO2 have been thoroughly examined. Additionally, the backbone of these materials can be made more lipophilic in nature by incorporating other monomers to make random copolymers [34]. 

Jain S, Dyrdahl MHE, Gong X, Scriven LE, Bates FS (2008) Lyotropic phase behavior of poly(ethylene oxide)-poly(butadiene) diblock copolymers evolution of the random network morphology. Macromolecules 41 3305-3316... 

SHA Sharma, S.C., Acharya, D.P., Garcia-Roman, M., Itami, Y., and Kunieda, H., Phase behavior and surface tensions of amphiphilic fluorinated random copolymer aqueous solutions, Coll. Surfaces A, 280, 140, 2006. 

MA2 Maeda, Y. and Yamabe, M., A unique phase behavior of random copolymer of N-isopropylacrylamide and W-diethylaciylamide in water. Polymer, 50, 519, 2009. 

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