A Review on Various Methods for the Cross-linking of Polymers

Abstract

Cross-Linking the carbon atoms suffices to transform such material intoa superior material that may be resistant to temperature, pressure, corrosion, and that can be used in a variety of applications. Cross Linking is a stabilization process in polymer chemistry which leads to multidimensional extension of polymeric chain resulting in network structure. Cross-link is a bond which links one polymer chain to other. It can be ionic or covalent. Cross Linking changes a liquid polymer into ‘solid’ or ‘gel’ by restricting the ability of movement. When polymer chains are linked together by cross-links, they lose some of their ability to move as individual polymer chains. A liquid polymer (where the chains are freely flowing) can be turned into a ‘solid’ or ‘gel’ by cross-Linking the chains together. Cross Linking increases the molecular mass of a polymer. Cross-linked polymers are important because they are mechanically strong and resistant to heat, wear and attack by solvents. Cross-link property has been used to improve the insolubility, mechanical strength, stiffness, and rigidity of polymer microbeads having potential applications in solid-phase synthesis, solid-phase extraction, and biomedical fields. Hydrogels represents a class of high-water content polymers with physical or chemical crosslinks. Their physical properties are similar to soft tissues. A popular approach to attaining controlled drug delivery from polymer-based systemsinvolves the use of cross-linkers. In order to improve the properties of polymers specific toothier applications, they can be modified by either physical cross-linkers (high pressure, irradiation) or chemical cross-linkers (glutraldehyde, genipin).Therefore, synthesis of polymer with desired cross-linker (hydrophilic/hydrophobic/rigid/flexible) and concentration of cross-linker (cross-link density) is an important.Polyethylene (PE) once cross linked is advantageously employed in the fabrication of blanket insulation for electrical and telephone wires, pipes for the transport of cold and hot liquids, prostheses for the human body. In the present review, chemical cross-Linking by free-radical, condensation, UV radiation, and small-molecule cross-Linking are discussed in details.