Physical cross-links interaction

In B. mori silk, the main repeating motif GAGAGS forms the [3-sheets, with Gly facing one side and Ala the other side, as depicted in Figure 3c. The small 3D crystallites are stacks of [3-sheets. This stacking combined with the hydrophobic interaction between the [3-sheets locks the molecules in place. These small crystallites are regarded as the physical cross-links that... 

Furthermore, crystalline polymers do obey the rules even at room temperature in so far as swelling behaviour is concerned. This again is a demonstration that crystalline regions serve as physical cross-links. Some crystalline polymers with strong hydrogen bonding groups can be made to dissolve at room temperature. But in these cases a very specific interaction between polymer and solvent must occur. For example, cellulose is soluble in 70% sulphuric acid and in aqueous ammonium thiocyanate nylon 6.6 is soluble in phenol and in a 15% calcium chloride solution in methanol. 

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.

The physical cross-linking in these amphiphilic polymers is based on hydrophobic interactions between side chains which counterbalances the electrostatic repulsions between cationic chitosan chains in acidic condition [154],... 

Keywords Aerogels Cellulose Derivatives Graft copolymers Hydrogels Physical cross-linking Supramolecular interactions... 

It is well known that thermoset polymers such as epoxy, vinyl ester, polyester, phenolic, etc., are chemically or physically cross-linked polymers (chemical bonds between polymer chains, intermolecular van der Waals bonds, dipole-dipole interactions, and molecular entanglement). These cross-links serve as molecular anchorages, which prevent molecular motion of the... 

Some of the early examples describing covalent main-chain macromolecules with UPy units attached include copolymers based on poly(l-hexene) 11 and poly (alkyl methacrylate) 12, reported by the groups of Coates and Long, respectively (Figure 12). In the latter example, tensile testing and melt rheology were used to show that the extent of interchain interactions (physical cross-links),... 

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