Competitive Effects of Hydrogen Bonds and Molecular Weights on the Phase and Crystallization Behaviors of Binary Block Copolymers

Tough Polyurethane Hydrogels with a Multiple Hydrogen-Bond Interlocked Bicontinuous Phase Structure Prepared by In Situ Water-Induced Microphase Separation

Hydrogels with mechanical performances similar to load-bearing tissues are in demand for in vivo applications. In this work, inspired by the self-assembly behavior of amphiphilic polymers, polyurethane-based tough hydrogels with a multiple hydrogen-bond interlocked bicontinuous phase structure through in situ water-induced microphase separation strategy are developed, in which poly(ethylene glycol)-based polyurethane (PEG-PU, hydrophilic) and poly(ε-caprolactone)-based polyurethane (PCL-PU, hydrophobic) are blended to form dry films followed by water swelling. A multiple hydrogen bonding factor, imidazolidinyl urea, is introduced into the synthesis of the two polyurethanes, and the formation of multiple hydrogen bonds between PEG-PU and PCL-PU can promote homogeneous microphase separation for the construction of bicontinuous phase structures in the hydrogel network, by which the hydrogel features break strength of 12.9 MPa, fracture energy of 2435 J m-2, and toughness of 48.2 MJ m-3. As a biomedical patch, the outstanding mechanical performances can withstand abdominal pressure to prevent hernia formation in the abdominal wall defect model. Compared to the commercial PP mesh, hydrogel can prevent tissue/organ adhesion to reduce inflammatory responses and promote angiogenesis, thereby accelerating the repair of abdominal wall defects. This work may provide useful inspiration for researchers to design different gel materials through solvent-induced microphase separation.

Compositional asymmetry in a crystalline-amorphous block copolymer influences the phase and crystallization behaviors of its blend with an amorphous block copolymer

This study determined the phase and crystallization behaviors of blends composed of asymmetric polystyrene-block-poly(ethylene oxide) (PS-PEO) and symmetric polystyrene-block-poly(methyl methacrylate) (PS-PMMA). The PS blocks in the various binary block copolymers exhibited nearly identical molecular weights, whereas the molecular weight ratios of PEO and PMMA varied. The compatibility of the PEO and PMMA chains aided the binary block copolymers in co-ordering in a lamellar microdomain morphology, with the PEO and PMMA blocks sharing a common microdomain. Adding short tethered PMMA chains to long tethered PEO chains led to a decrease in the common microdomain spacing and an increase in the grafting density. These behaviors increased PEO chain stretching, causing macrophase separation. The mismatch in PEO and PMMA block lengths divided the common PEO/PMMA microdomain into two sections: the coexisting PEO/PMMA section close to the microdomain interface and the neat PEO section far away from it. The high-glass-transition-temperature PMMA reduced PEO chain mobility, inhibiting PEO crystallization in the coexisting PEO/PMMA section but not in the neat PEO section. When the block length ratio of PEO to PMMA decreased, the neat PEO section narrowed. The increase in the extent of PEO confinement led to a reduction in PEO crystallizability.