Hydrophobically-Modified PEG Hydrogels with Controllable Hydrophilic/Hydrophobic Balance

This work reports on a novel method to synthesize hydrophobically-modified hydrogels by curing epoxy monomers with amines. The resulting networks contain hydrophilic poly(ethylene glycol) (PEG) segments, poly(propylene glycol) (PPG) segments, and C-18 alkyl segments. By varying the content of C-18 segments, networks with different hydrophilic-lipophilic balance (HLB) are obtained. All networks show an amphiphilic behavior, swelling considerably both in organic solvents and in aqueous media. In the latter they display a thermosensitive behavior, which is highly affected by the network HLB and the pH of the solution. A decrease in HLB results in an increment of the polymer weight content (w(p)) due to hydrophobic association. Furthermore, a reduction in HLB induces a remarkable increase in initial modulus, elongation at break and tensile strength, especially when w(p) becomes greater than about 10%. Low field nuclear magnetic resonance (LF-NMR) experiments evidence that, when HLB decreases, a sudden and considerable increase in hydrogel heterogeneity takes place due to occurrence of extensive physical crosslinking. Available data suggest that in systems with w(p) greater than or similar to 10% a continuous physical network superimposes to the pre-existing chemical network and leads to a sort of double network capable of considerably improving hydrogel toughness.

Automated summary

This work presents a novel method to synthesize hydrophobically-modified hydrogels, which exhibit thermosensitive behavior and enhanced properties when the HLB decreases, especially when wp exceeds 10%. The decrease in HLB results in an increase in polymer weight content and improvement in mechanical properties due to the occurrence of physical crosslinking.