Chemical cross-links polycondensation

For the preparation of nano- and microstructures there are numerous examples of endo- and exo-templates that have been used for the synthesis of particle- and pore structures from the nanometer to the micrometer scale. Templates can be inorganic, organic, or biological materials as are the materials or casts produced therefrom. The hardening process can be physical (crystallization from the melt, glass formation) or chemical (cross-linking, polycondensation). Templates usually have to be extracted in order to obtain the desired material. 

Fig. 1 Representative methods of hydrogel formation. (A) Chemically cross-linked hydrogels are prepared from monomers, oligomers, or polymers in the presence of cross-linking agents. The chemical cross-linking proceeds via radical polymerization or polycondensation reaction. (B) Physically cross-linked hydrogels can be formed by ionic interactions, hydrophobic interaction, or hydrogen bonding.

Chemical Drying. Chemically drying paints contain binder components that react together on drying to form cross-linked macromolecules. These binder components have a relatively low molecular mass, so that their solutions can have a high solids content and a low viscosity. In some cases, solvent-free liquid paints are possible. Chemical drying can occur by polymerization, polyaddition, or polycondensation. 

The wall formation is a chemical and physical process.Under acidic condition, the amino resin prepolymer, which is methylol compound and water soluble, becomes more hydrophobic because of the etherification and methylene bridge formation. The hydrophilic and hydrophobic interactions drive the oligomer concentrated on the interface and create a primary wall on the oil droplet. And finally with the further polycondensation, the wall is cross-linked and the wall thickness is built up. The related chemistry is presented in Equations 16.1 through 16.4. ... 

Polyester is a group of polymers that contain the ester functional group in their chain. Esters are chemical compounds derived from a carboxyUc acid and a hydroxyl compound, nsnally an alcohol. Most esters are considered biocompatible since they are endogenous to the human metaboUsm and able to break down to natural metabohc products by simple hydrolysis. Elastomers composed of aliphatic polyester chains cross-linked with each other by ester bonds, snch as poly(diol citrates) and poly(glyc-erol sebacate) (PGS), have received mnch attention because they are soft, elastic, and biocompatible [26,27]. Yang et al. synthesized the first citrate-based biodegradable elastomer (CABE), poly(diol citrates), in 2004 nsing a convenient and cost-effective polycondensation reaction [26,28]. 

Before setting, reactive adhesives consist predominantly of reactive low molecular mass monomers and/or oligomers that, during curing, are converted by chemical reactions into high molecular mass, often three-dimensionally cross-linked polymers. Reactive adhesives can be divided into polymerization, polyaddition, and polycondensation adhesives. Vulcanizing reactive adhesives are a special group. 

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