Polymer Physics: Nongelling associating polymers

This chapter presents some important nongelling binary associating mixtures. Throughout this chapter, we assume the pairwise association of reactive groups, the strength of which can be expressed in terms of the three association constants for A·A, B·B, and A·B association. We apply the general theory presented in Chapter 5 to specific systems, such as dimerization, linear association, side-chain association, hydration, etc. The main results are summarized in the form of phase diagrams. Dimer formation as associated block-copolymers The first system we study is a mixture of R{A 1 } and R{B 1 } chains, each carrying a functional group A or B at one end. Diblock copolymers are formed by the end-to-end association ( hetero-dimerization ). End groups A and B are assumed to be capable of forming pairwise bonds A·B by thermoreversible hetero-association. The hydrogen bond between acid and base pair is the most important example of this category. For such mixtures, composite diblock copolymers R{A 1 }- block -R{B 1 } with a temporal junction are formed (Figure 6.1). The system is made up of a mixture of diblock copolymers (1,1), and unassociated homopolymers of each species (1,0) and (0,1). It is similar to the mixture of chemically connected diblock copolymers dissolved in their homopolymer counterparts, but its phase behavior is much richer because the population of the block copolymers varies with both temperature and composition.