Effect of sodium dodecyl sulfate on shape-memory properties of side-chain crystalline hydrogel via micellar copolymerization

A chemical shape-memory hydrogel containing crystalline structure is prepared via micellar copolymerization of hydrophilic monomer acrylamide (AM) and hydrophobic monomer octadecyl acrylate (C18) in a sodium dodecyl sulfate (SDS) solution. The influence of SDS on the shape-memory behavior of hydrogel investigated by differential scanning calorimetry (DSC) and Temperature-dependent X-ray indicate that the melting and crystallization peaks derived from the thermal properties of C18 units is different from peaks corresponding to the pure SDS. In addition, the microstructure evolution information of hydrogels dose not change upon heating process, regardless of the presence or absence of SDS. Therefore, only the hydrophobic associations formed by C18 blocks play a decisive role in the shape memory function of hydrogel system. The difference between the transition process (from temporary shape to permanent shape) of hydrogel with and without SDS at different temperature is because that the hydrophobic region of side chain crystallization of SDS-free hydrogel may escape the restriction of SDS and become more sensitive to temperature, they can preferentially return to their initial shape under the same time and temperature than SDS-containing gels. Whether SDS exists only affect the speed of shape memory behavior, but not the microstructure evolution of hydrogel system.