Microstructural features and their effect on properties

Characteristics of polymer dispersions that influence product properties 

Copolymer composition has a direct effect on the Tg of the polymer, which determines the minimum film forming temperature (MFFT) of the latex and the application. Thus, a 95/5 wt/wt butyl acrylate/methyl methacrylate is an adhesive, whereas a 50/50 copolymer of the same monomers is a binder for paints. Copolymer composition affects properties such as resistance to hydrolysis [4] and weatherability. In situ formed blends of random copolymers of different compositions may be beneficial for application properties [5]. Conventional free-radical polymerization, which is the process used to manufacture almost all commercial emulsion polymers, does not allow the production of block and gradient copolymers (accessible by means of controlled radical polymerization [6], Section 3.3). Nevertheless, graft copolymers are frequently formed, and the extension of grafting largely determines the application properties. Thus, grafting determines the size of the rubber domains in ABS polymers, and the toughness of these polymers increases with rubber size. 

Polymer architecture plays a crucial role in final properties. Thus, in papers coated with carboxylated styrene-butadiene latexes, blister resistance decreases and dry pick increases 

The application properties of many latexes are strongly affected by the chemistry of the surface of the polymer particles. Relatively small amounts (1-2 wt% based on monomers) of acidic monomers (e.g., acrylic acid, AA) are frequently used in the manufacture of latexes. Because this monomer is water-soluble, upon polymerization, most of the AA-rich polymer chains are located at the surface of the polymer particles. The presence of AA at the surface of the polymer particles is beneficial for both the stability of the latex [11] and the application properties (e.g., both the shear strength of the adhesives [ 12] and the pick strength of coated paper [9] increase with the AA content). In addition, the type and amount of surfactant affects application properties such as colloidal stability and water sensitivity of the film [13]. 

In most of the applications of the synthetic polymer dispersions (e.g., paints and coatings, adhesives and paper coatings), the commercial product is a complex formulation. Table 6.3 presents an example of a coating formulation. In these formulations, the latex is the key ingredient, but the application properties are also affected by the other components of the formulation. Product formulation is out of the scope of this booL 

---