Controlled Synthesis of “Reverse Pluronic”-Type Block Copolyethers with High Molar Masses for the Preparation of Hydrogels with Improved Mechanical Properties

Abstract

Hydrogels based on Pluronics (EOn/2-POm-EOn/2, EO = ethylene oxide, PO = propylene oxide) have been frequently investigated, yet key limitations still remain, including a propensity for quick erosion and insufficient mechanical robustness. This issue can be alleviated by creating “reverse Pluronics” (POn/2-EOm-POn/2), which is proposed to enable the formation of physical cross-links via a micellar network. Until recently, however, efforts in this direction were aggravated by synthetic difficulties, specifically prohibiting the realization of poly(propylene oxide) (PPO)-moieties with a high DP. In this study, an organocatalytic polymerization method is employed to synthesize “reverse Pluronics,” resulting in highly defined polymers (ÐM ≤ 1.02–1.07, Mn up to 35 000 g mol−1) with exceptionally long PPO blocks. The higher molar mass and the reverse constitution of the polyether combine to enable the generation of thermoresponsive hydrogels with a storage modulus that is increased tenfold relative to reference samples. Gelation temperature and maximum storage modulus (G′max) are readily influenced by the choice of the polyether (down to 5 wt%). The improved mechanical properties are accompanied by an increased resistance toward erosion in water. Isotactic enrichment is presented as an additional tuning parameter for hydrogel properties.