pH-Ionizable in Situ Gelling Poly(oligo ethylene glycol methacrylate)-Based Hydrogels: The Role of Internal Network Structures in Controlling Macroscopic Properties

Mechanical properties of temperature-responsive gels containing ethylene glycol in their side chains

The mechanical properties of temperature-responsive and biocompatible poly(oligo-ethylene glycol methyl ether methacrylate)-based gels were investigated using dynamic viscoelasticity measurements so as to find applications in tissue and biomedical engineering. The gels were copolymerized using two ethylene glycol methacrylate monomers with diethylene glycol side chains: diethylene glycol methacrylate (MeO₂MA), which contains two ethylene oxide units, and oligo-ethylene glycol methyl ether methacrylate (OEGMA) with either four or five ethylene oxide units. The storage (G') and loss (G'') moduli of these gels exhibit unique temperature-responsive behavior and depend on the copolymerization ratio. In MeO₂MA-rich gels, phase separation occurred with increasing temperature, resulting in a significant increase in G' and the disappearance of the frequency dependence of G''. Although phase separation of OEGMA-rich gels was also observed with increasing temperature, it resulted in only a slight increase in the storage modulus due to the steric hindrance of the side chain. The mechanical properties of these gels are thus found to be strongly affected by a slight difference in the number of ethylene oxide groups in their side chains.

Electrostatically Driven Guest Binding in a Self-Assembled Porous Network at the Liquid/Solid Interface

We present here the construction of a self-assembled two-dimensional (2D) porous monolayer bearing a highly polar 2D space to study guest co-adsorption through electrostatic interactions at the liquid/solid interface. For this purpose, a dehydrobenzo[12]annulene (DBA) derivative, DBA-TeEG, having tetraethylene glycol (TeEG) groups at the end of the three alternating alkoxy chains connected by p-phenylene linkers was synthesized. As a reference host molecule, DBA-C10, having nonpolar C₁₀ alkyl chains at three alternating terminals, was employed. As guest molecules, hexagonal phenylene-ethynylene macrocycles (PEMs) attached by triethylene glycol (TEG) ester and hexyl ester groups, PEM-TEG and PEM-C6, respectively, at each vertex of the macrocyclic periphery were used. Scanning tunneling microscopy observations at the 1,2,4-trichlorobenzene/highly oriented pyrolytic graphite interface revealed that PEM-TEG was immobilized in the pores formed by DBA-TeEG at higher probability because of electrostatic interactions such as dipole-dipole and hydrogen bonding interactions between oligoether units of the host and guest, in comparison to PEM-C6 with nonpolar groups. These observations are discussed based on molecular mechanics simulations to investigate the role of the polar functional groups. When a nonpolar host matrix formed by DBA-C10 was used, however, only phase separation and preferential adsorption were observed; virtually no host-guest complexation was discernible. This is ascribed to the strong affinity between the guest molecules which form by themselves densely packed van der Waals networks on the surface.