Qingyu Xu

Graphene oxide-based composite hydrogels with self-assembled macroporous structures

The self-assembly technique provides a new and simple route for designing porous hydrogels. At present, most of the studies in graphene oxide (GO)–polymer hydrogels are concentrated on mechanical reinforcement. Developing a self-assembled GO-based porous hydrogel along with swelling and mechanical merits is still challenging, yet very interesting and desirable for practical applications. Herein, we report self-assembled GO-based macroporous composite hydrogels by integrating GO sheets and chitosan-based hydrogel networks. GO sheets, containing adequate hydrophilic functional groups, can be dispersed well and thereby they form self-assembled supramolecular structures with polymer chains by effective intermolecular interactions (e.g., hydrogen bonding, electrostatic attraction or covalent bonding). Surprisingly, an extremely low amount (0.05–0.30 wt%) of GO can remarkably affect the architecture of hydrogel networks, leading to the formation of macroporous composite hydrogels. On the whole, the GO-based polymer composite hydrogels possess both macroporous structures (10–100 μm) and enhanced mechanical performance, yet can still retain the similar swelling properties of their parent polymeric hydrogel. Therefore, this study provides a simple route for fabricating porous hydrogels, which could find some potential applications in wastewater treatment or biomedical engineering.

Understanding the effects of carboxylated groups of functionalized graphene oxide on the curing behavior and intermolecular interactions of benzoxazine nanocomposites

Novel benzoxazine (BOZ)/carboxylated graphene oxide (GO-COOH) composites were prepared via in situ intercalative polymerization. The curing behaviour, morphology and intermolecular interactions of GO-COOH based nanocomposites were investigated and compared with those of a graphene oxide (GO) blend system to clarify the influence of carboxylic groups. Compared to GO, GO-COOH with a large amount of carboxylic groups, relatively higher thermal stability, and exfoliated sheet morphology might be more easily dispersed and reacted in the BOZ matrix. The GO-COOH nanoplatelet based composites possessed a different polymerization path from that of the GO based system, implying that carboxylic groups not only provided catalytic effects but also participated in the grafting polymerization reactions between carboxyl groups of GO-COOH and phenolic hydroxyl groups of BOZ. A significant improvement of both the glass transition temperature (Tg) and crosslinking network density of the GO-COOH blend system further confirmed that covalent bonding occurred between filler and polymer chains, indicating that the GO-COOH nanoplatelets had a stronger influence on the thermal property improvement of the nanocomposites than that of the GO blend system. Surprisingly, a very low amount (1 wt%) of GO-COOH can affect the thermal properties of the composite remarkably, leading to a more than 30 °C increase of Tg in comparison with pure benzoxazine.

A facile method for the preparation of aliphatic main-chain benzoxazine copolymers with high-frequency low dielectric constants

The designed aliphatic main-chain benzoxazine copolymer oligomers were synthesized by the Mannich reaction. It should be noted that increasing the ratio and polarity of a polar solvent is an effective strategy to prepare an aliphatic main-chain copolymer oligomer with a relatively satisfactory dispersity index (2.63). Accordingly, a copolymer prepared under the optimized toluene/N,N-dimethylformamide heterogeneous solvent conditions has the highest glass transition temperature (195 °C) and the minimum high-frequency dielectric constants (2.65, 5 GHz; 2.54, 10 GHz). Therefore, this work not only provides a simple route for improving the processing and high-frequency dielectric properties of main-chain benzoxazine but also gives some insight into the effects of the polar solvent on the formation of copolymers.