Poly(ethylene-co-propylene)/poly(ethylene glycol) elastomeric hydrogels with thermoreversibly cross-linked networks

A series of elastomeric hydrogels with repeated processability were prepared in this work. These hydrogels were obtained by cross-linking of two common polymers, poly(ethylene-co-propylene) (ethylene-propylene rubber, EPR) and poly(ethylene glycol) (PEG), via dynamic covalent bonds, specifically, through firstly furyl functionalization of EPR at the side groups and maleimide modification of PEG at the chain ends, and followed by the Diels-Alder reaction between furan and maleimide to construct thermo-reversible EPR-PEG networks. The composition and microstructure of the network were adjustable in a wide range by facilely tuning the PEG feeding ratios and molecular weights (as the cross-linking agent). In the network the crystalline PEG and the elastic EPR endowed the material with strength and toughness respectively in the dry state, giving a fracture strength of 4-6 MPa and elongation at break of up to 380%; meanwhile, due to the hydrophilicity of PEG, the network could absorb water and form hydrogels, in which the hydrophobic EPR elastomer enhanced the hydrogels effectively. By tailoring the amount and the chain structure of the PEG moiety, the water absorption of the copolymer could reach as high as 356% in 1 hour, and the hydrogel elongation at break could achieve similar to 400%, which was comparable to that of pristine cross-linked EPR. The material displayed low cytotoxicity in MC3T3-L1 cells and was biocompatible.