Copolymer blends solubility parameter theory

Fig. 3. Calculation of interaction parameters for blends of a homopolymer with a copolymer using solubility parameter theory.

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. 

This is a three-part book with the first part devoted to polymer blends, the second to copolymers and glass transition tanperatme and to reversible polymerization. Separate chapters are devoted to blends Chapter 1, Introduction to Polymer Blends Chapter 2, Equations of State Theories for polymers Chapter 3, Binary Interaction Model Chapter 4, Keesome Forces and Group Solubility Parameter Approach Chapter 5, Phase Behavior Chapter 6, Partially Miscible Blends. The second group of chapters discusses copolymers Chapter 7, Polymer Nanocomposites Chapter 8, Polymer Alloys Chapter 9, Binary Diffusion in Polymer Blends Chapter 10, Copolymer Composition Chapter 11, Sequence Distribution of Copolymers Chapter 12, Reversible Polymerization. 

Simple theory says that a blend of A + B should be compatibilized by a block copolymer of A-B. Where this is not readily available, theorists generally concede that the blocks of the compatibilizer need not be identical with A and B, so long as they are miscible or at least compatible with A and B [6, 7, 9, 10, 31]. For example, typical estimates conclude that the solubility parameters of the blocks in the compatibilizer must be within 0.2 1.0 units of those in A and B [6, 7]. In practice, most researchers compromise between the two extremes, using a block copolymer A to com-patibilize a blend of A + B, by choosing block C for compatibility with B. 

Note that in order to describe the xsans(F) data for ten binary sPB blends, we employ only three adjustable parameters, while the analysis of Graessley et al. [28-30] requires a separate set of temperature-dependent solubility parameters for each individual copolymer species (i.e., 20 sets of solubility parameters in all). Despite the huge contraction of the 8 T) and 8i T) values into just the three parameters (saa. bb. and y) of the BLCT, the slopes x of xsans(F) vs. 1/T, however, differ considerably between theory and experiment. Some decrease in this discrepancy can be obtained by introducing different chain stiffness for the two blend components or by allowing y to differ slightly for the 1,2 and 1,4 monomer imits, but given the experimental... 

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