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In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural polymers (such as proteins ).
Gelation occurs when a polymer forms large interconnected polymer molecules through cross-linking. [1] In other words, polymer chains are cross-linked with other polymer chains to form an infinitely large molecule, interspersed with smaller complex molecules, shifting the polymer from a liquid to a network solid or gel phase.
For example, in the synthesis of PET, a small fraction of the ethylene glycol can be replaced by glycerol which has three alcohol groups. This trifunctional molecule inserts itself in the polymeric chain and bonds to three carboxylic acid groups forming a branch point. Finally, the formation of cross-linked polymers involves tetrafunctional ...
In polymer science Flory–Rehner equation is an equation that describes the mixing of polymer and liquid molecules as predicted by the equilibrium swelling theory of Flory and Rehner. [1] It describes the equilibrium swelling of a lightly crosslinked polymer in terms of crosslink density and the quality of the solvent.
The use of non-covalent interactions such as hydrogen bonding, pi-stacking or crystallization that lead to physical cross-links between polymer chains is one way of introducing dynamic cross-linking. The thermoreversible nature of the physical cross-links results in polymer materials with improved mechanical properties without losing ...
In polymer chemistry, branching is the regular or irregular attachment of side chains to a polymer's backbone chain. It occurs by the replacement of a substituent (e.g. a hydrogen atom ) on a monomer subunit by another covalently-bonded chain of that polymer; or, in the case of a graft copolymer , by a chain of another type.
Like the peptidoglycan found in bacterial cell walls, pseudopeptidoglycan consists of polymer chains of glycan cross-linked by short peptide connections. However, unlike peptidoglycan, the sugar N-acetylmuramic acid is replaced by N-acetyltalosaminuronic acid , [ 42 ] and the two sugars are bonded with a β ,1-3 glycosidic linkage instead of β ...
The cross-linked polymers absorb water to form hydrogels, which are responsive to temperature changes, expanding to a limit defined by the cross-link density below a critical solution temperature, but contracting above that temperature. This is the basis of controlled permeability membranes.