Diblock copolymers, anchoring polymer particles

Anchoring of Diblock Copolymers of Polystyrene and Poly(dimethyl siloxane) on Polymer Particles... 

The interfacial properties of chain-like molecules in many polymeric and colloidal systems are dependent on the conformation of the chains adsorbed at the interface (.1). Chains adsorbed at the solid-liquid interface may be produced by anchoring diblock copolymers to particles in a polymer dispersion. Such dispersions are conveniently prepared by polymerizing in the presence of a preformed AB diblock copolymer a monomer dissolved in a diluent which is a precipitant for the polymer. The A block which is... 

Much work on the preparation of nonaqueous polymer dispersions has involved the radical polymerization of acrylic monomers in the presence of copolymers having the A block the same as the acrylic polymer in the particle core 2). The preparation of polymer dispersions other than polystyrene in the presence of a PS-PDMS diblock copolymer is of interest because effective anchoring of the copolymer may be influenced by the degree of compatibility between the PS anchor block and the polymer molecules in the particle core. The present paper describes the interpretation of experimental studies performed with the aim of determining the mode of anchoring of PS blocks to polystyrene, poly(methyl methacrylate), and poly(vinyl acetate) (PVA) particles. 

With chains anchored to the surface, either by a chemical grafting or an insoluble block, good solvent conditions always produce a repulsion. Consequently, copolymers, e.g., diblock, comb, or graft, tend to comprise the most effective stabilizers. Direct grafting to the particle is feasible but requires chemistry specific to the particle (e.g., Green et al., 1987). Advances in synthetic polymer chemistry continue to increase the types of polymers available for this application (e.g., Reiss et al., 1987). 

Chain architecture also plays a role in determining the adsorption characteristics of copolymers. For instance, if we consider triblock ABA-type copolymers the relative positions of the anchor and buoy blocks become important. When there are two buoy blocks and a central anchor block, the copolymers show diblock AB-type behavior (see Fig. 9 and 10). If, however, there are two anchor blocks and a central buoy block, surface precipitation of the polymer molecule at the particle surface is generally observed. This precipitation (or multilayer formation) process is due to strong interaction between the anchor blocks themselves and manifests itself in the form of an ever-increasing adsorption isotherm (i.e., there is no plateau) of the type shown in Figure 11. When compared with... 

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