Stabilizer polymer dispersions

Marie E, Landfester K, Antonietti M (2002) Synthesis of chitosan-stabilized polymer dispersions, capsules, and chitosan grafting products via miniemulsion. Biomacromolecules 3 475-481... 

These monomers provide a means for introducing carboxyl groups into copolymers. In copolymers these acids can improve adhesion properties, improve freeze-thaw and mechanical stability of polymer dispersions, provide stability in alkalies (including ammonia), increase resistance to attack by oils, and provide reactive centers for cross-linking by divalent metal ions, diamines, or epoxides. 

Internal surfactants, i.e., surfactants that are incorporated into the backbone of the polymer, are commonly used in PUD s. These surfactants can be augmented by external surfactants, especially anionic and nonionic surfactants, which are commonly used in emulsion polymerization. Great attention should be paid to the amount and type of surfactant used to stabilize urethane dispersions. Internal or external surfactants for one-component PUD s are usually added at the minimum levels needed to get good stability of the dispersion. Additional amounts beyond this minimum can cause problems with the end use of the PUD adhesive. At best, additional surfactant can cause moisture sensitivity problems with the PUD adhesive, due to the hydrophilic nature of the surfactant. Problems can be caused by excess (or the wrong type of) surfactants in the interphase region of the adhesive, affecting the ability to bond. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

All of these intermolecular forces influence several properties of polymers. Dispersion forces contribute to the factors that result in increased viscosity as molecular weight increases. Crystalline domains arise in polyethylene because of dispersion forces. As you will learn later in the text, there are other things that influence both viscosity and crystallization, but intermolecular forces play an important role. In polar polymers, such as polymethylmethacrylate, polyethylene terephthalate and nylon 6, the presence of the polar groups influences crystallization. The polar groups increase the intensity of the interactions, thereby increasing the rate at which crystalline domains form and their thermal stability. Polar interactions increase the viscosity of such polymers compared to polymers of similar length and molecular weight that exhibit low levels of interaction. 

Acrylic resins are generally well characterized by Py-GC/MS without the need for any derivatization reaction. However, in waterborne polymer dispersions it is common to have minor amounts of acrylic and/or methacrylic acid monomers added in the copolymerization to help the stability of the final latex. These monomers can also appear in the pyrolysis products, and it has been shown that with on-line derivatization they can be more efficiently revealed [85]. 

The steric stabilization of dispersed particles by both grafted chains and by physically adsorbed polymers has been much studied in recent years. In the present paper we extend earlier work on... 

To produce novel LC phase behavior and properties, a variety of polymer/LC composites have been developed. These include systems which employ liquid crystal polymers (5), phase separation of LC droplets in polymer dispersed liquid crystals (PDLCs) (4), incorporating both nematic (5,6) and ferroelectric liquid crystals (6-10). Polymer/LC gels have also been studied which are formed by the polymerization of small amounts of monomer solutes in a liquid crystalline solvent (11). The polymer/LC gel systems are of particular interest, rendering bistable chiral nematic devices (12) and polymer stabilized ferroelectric liquid crystals (PSFLCs) (1,13), which combine fast electro-optic response (14) with the increased mechanical stabilization imparted by the polymer (75). 

Figure 1.20 Encapsulation of microdroplets of liquid crystals in ORMOSIL matrices results in materials with better transparency and thermal stability than polymer-dispersed liquid crystals. Gel-glass dispersed liquid crystal device switched between the OFF and ON state (thickness 10 pm, 4 x 2 cm, Fp p = 90V). (Reproduced from ref. 45, with permission.)...

G.J. Fleer, J.M.H.M. Scheutjens and B. Vincent, The Stability of Dispersions of Hard Spherical Particles in the Presence of Nonadsorbing Polymer in Polymer Adsorption and Dispersion Stability, E.D. Goddard and B. Vincent (eds.), American Chemical Society, Washington DC, 1984, ACS Symposium Series 240, Chapter 16, pp. 245-263. 

The dispersion polymerization system is composed of monomer, solvent, initiator, and stabilizer. The combination of monomer, solvent, and stabilizer is essential for particle preparation. That is to say, the stabilizer is chosen to meet the demand of the monomer and solvent. In any system, the stabilizer has affinity or cohesive strength for both the medium and the polymer particles. In a dispersion polymerization, the medium and polymer particles both are organic compounds. Therefore, it is not rational to rely on dispersion stabilization, which comes from the electrostatic repulsion force between particles. The stabilizer for dispersion polymerization that makes interfacial energy low must have affinity for particles due to the same quality and solvation at the surface of particles. It is desired that the stabilizer be a polymer that indicates a steric stabilization effect on the surface (5). 

In many practical instances (see Vignette 1.5), electrostatic repulsion is not a convenient option. In such cases, a suitable polymer that adsorbs on the particle surfaces may be added to the dispersion. The resulting polymer layer masks the attraction and may also provide a repulsive force, partly due to pure steric effect, when the polymer layers on two interacting particles attempt to overlap with each other. This is what is known as polymer-induced stability. Polymer-induced stability is often referred to as steric stability for the above... 

Our primary focus in this chapter is on kinetic stability of dispersions arising due to either electrostatic forces or polymer-mediated forces. 

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