Hydrogels compression-strain measurements

The cross-linking density cannot be estimated from the stoichiometric relation between monomer and cross-linker, e.g., NlPAAm and MBAAm, since the possibility of cychzation during NlPAAm polymerization is high (see Sect. 2, in chapter General properties of hydrogels ). A more realistic number of net chains can be determined by compression or stress-strain measurements, preferred on a gel swollen in organic solvent. 

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