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In polymer chemistry "cross-linking" usually refers to the use of cross-links to promote a change in the polymers' physical properties. When "crosslinking" is used in the biological field, it refers to the use of a probe to link proteins together to check for protein–protein interactions , as well as other creative cross-linking methodologies.
At a given point of time, degree distribution (), is the probability that a randomly chosen monomer has connected neighbours. The central idea of the random graph theory of gelation is that a cross-linked or branched polymer can be studied separately at two levels: 1) monomer reaction kinetics that predicts () and 2) random graph with a given degree distribution.
A cross-linked polyethylene (PEX) pipe. Cross-linked polyethylene, commonly abbreviated PEX, XPE or XLPE, is a form of polyethylene with cross-links.It is used predominantly in building services pipework systems, hydronic radiant heating and cooling systems, domestic water piping, insulation for high tension (high voltage) electrical cables, and baby play mats.
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.
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.
Cross-linking can be introduced using N,N-methylenebisacrylamide. Some crosslinked materials are swellable but not soluble, i.e., they are hydrogels. Partial hydrolysis occurs at elevated temperatures in aqueous media, converting some amide substituents to carboxylates. This hydrolysis thus makes the polymer particularly hydrophilic.
Cross-linked Hydrogel The reaction scheme below is a terpolymerization to form a cross-linked hydrogel . The reactant ammonium persulfate (APS) is used in polymer chemistry as a strong oxidizing agent that is often used along with tetramethylethylenediamine (TMEDA) to catalyze the polymerization when making polyacrylamide gels .
Cross-linked polymers: Wide-meshed cross-linked polymers are elastomers and cannot be molten (unlike thermoplastics); heating cross-linked polymers only leads to decomposition. Thermoplastic elastomers , on the other hand, are reversibly "physically crosslinked" and can be molten.