Controlled Fabrication of Cross-Linked Nanoparticles/Polymer
... each other, each having a diameter of approximately 4 nm. Since some carboxyls are still bonded to the Pb ions on the particle surface after reacting with H2S, the compact polymer networks can prevent the PbS particles from growing further after nucleation, resulting in their small size and uniform ...
... each other, each having a diameter of approximately 4 nm. Since some carboxyls are still bonded to the Pb ions on the particle surface after reacting with H2S, the compact polymer networks can prevent the PbS particles from growing further after nucleation, resulting in their small size and uniform ...
Combustion and thermal degradation of polymers
... Figure 7. Examples of addition polymers. Condensation polymers (called stepwise reaction polymers) are the products of the reaction occurring between two polyfunctional molecules by eliminating a small molecule, for example, water. Examples of condensation polymers are given in ...
... Figure 7. Examples of addition polymers. Condensation polymers (called stepwise reaction polymers) are the products of the reaction occurring between two polyfunctional molecules by eliminating a small molecule, for example, water. Examples of condensation polymers are given in ...
eprint_5_24935_775
... peptide linkages to form polyamides or polypeptides. Polypeptides are often used by biologists to denote oligomers or relatively low molecular weight proteins. All α-amino acids found in proteins, except glycine (Gly), contain a chiral carbon atom and are Lamino acids. ...
... peptide linkages to form polyamides or polypeptides. Polypeptides are often used by biologists to denote oligomers or relatively low molecular weight proteins. All α-amino acids found in proteins, except glycine (Gly), contain a chiral carbon atom and are Lamino acids. ...
Free-radical polymerization
... Rate of initiation The rate of initiation of the chains and the dependence of this rate on the monomer concentration and temperature is quite different in photochemical initiator from the situation found in thermal initiation. Rate of initiation for thermal initiation ...
... Rate of initiation The rate of initiation of the chains and the dependence of this rate on the monomer concentration and temperature is quite different in photochemical initiator from the situation found in thermal initiation. Rate of initiation for thermal initiation ...
Polymer Properties and Structure
... Describe basic features of a polymer Name three steps in the addition polymerization process Distinguish between addition and condensation polymerization Describe essential features of condensation polymerization Identify polymerization process used on basis of polymer composition ...
... Describe basic features of a polymer Name three steps in the addition polymerization process Distinguish between addition and condensation polymerization Describe essential features of condensation polymerization Identify polymerization process used on basis of polymer composition ...
Emulsion polymerization
Emulsion polymerization is a type of radical polymerization that usually starts with an emulsion incorporating water, monomer, and surfactant. The most common type of emulsion polymerization is an oil-in-water emulsion, in which droplets of monomer (the oil) are emulsified (with surfactants) in a continuous phase of water. Water-soluble polymers, such as certain polyvinyl alcohols or hydroxyethyl celluloses, can also be used to act as emulsifiers/stabilizers. The name ""emulsion polymerization"" is a misnomer that arises from a historical misconception. Rather than occurring in emulsion droplets, polymerization takes place in the latex particles that form spontaneously in the first few minutes of the process. These latex particles are typically 100 nm in size, and are made of many individual polymer chains. The particles are stopped from coagulating with each other because each particle is surrounded by the surfactant ('soap'); the charge on the surfactant repels other particles electrostatically. When water-soluble polymers are used as stabilizers instead of soap, the repulsion between particles arises because these water-soluble polymers form a 'hairy layer' around a particle that repels other particles, because pushing particles together would involve compressing these chains.Emulsion polymerization is used to manufacture several commercially important polymers. Many of these polymers are used as solid materials and must be isolated from the aqueous dispersion after polymerization. In other cases the dispersion itself is the end product. A dispersion resulting from emulsion polymerization is often called a latex (especially if derived from a synthetic rubber) or an emulsion (even though ""emulsion"" strictly speaking refers to a dispersion of an immiscible liquid in water). These emulsions find applications in adhesives, paints, paper coating and textile coatings. They are often preferred over solvent-based products in these applications due to the absence of VOCs (Volatile Organic Compounds) in them.Advantages of emulsion polymerization include:High molecular weight polymers can be made at fast polymerization rates. By contrast, in bulk and solution free radical polymerization, there is a tradeoff between molecular weight and polymerization rate.The continuous water phase is an excellent conductor of heat, enabling fast polymerization rates without loss of temperature control.Since polymer molecules are contained within the particles, the viscosity of the reaction medium remains close to that of water and is not dependent on molecular weight.The final product can be used as is and does not generally need to be altered or processed.Disadvantages of emulsion polymerization include:Surfactants and other polymerization adjuvants remain in the polymer or are difficult to removeFor dry (isolated) polymers, water removal is an energy-intensive processEmulsion polymerizations are usually designed to operate at high conversion of monomer to polymer. This can result in significant chain transfer to polymer.Can not be used for condensation, ionic or Ziegler-Natta polymerization, although some exceptions are known.↑ ↑ ↑