Synthesis And Characterization Of Ionic Hydrogels And The Research On Self-healing

Hydrogel is a kind of three-dimensional hydrophilic network structure material, for now, most of the ionic hydrogels are formed by the interaction of polymers and metal ions. But there are few reports on the formation of gels by ionic interaction only from polymeric macromolecules. Herein two kinds of macromolecular polymers were prepared by the reversible addition-fragmentation chain transfer (RAFT) polymerization, and the molecular chain end groups of the polymers were modified by functionalization. Then the cross-linking structure was constructed by quaternization reaction between the functional groups of the two polymer chains, and the ionic hydrogels with self-healing properties were prepared under UV light irradiation. The main contents of this paper are as follows:1. The synthesis of RAFT chain transfer agents, terminal carboxyl bifunctionalized polystyrene (HOOC-PS-COOH) and poly(4-vinylpyridine) (P4VP) which all contain trithiocarbonate groups (TTC). Two different structures of RAFT chain transfer agents(CTA)S,S’-bis-(α,α’-dimethyl-α"-acetic acid) trithiocarbonate (BDATC) and S-1-dodecyl-S’-(α,α’-dimethyl-α"-acetic acid) trithiocarbonate (DDMAT) were prepared. The two chain transfer agents were purified by different methods, and their structures were characterized by 1H NMR and FT-IR spectra. Polystyrene(HOOC-PS-COOH) and poly(4-vinylpyridine)(P4VP) polymers were synthesized by using BDATC as CTA. The molecular weight of HOOC-PS-COOH and P4VP can be controlled by the feed ratio. The structure, molecular weight and functional groups were characterized by 1H NMR, GPC and FT-IR.2. The synthesis of ionic hydrogels. Firstly, the polymer HOOC-PS-COOH (Mn,GPC=1500 g/mol) with the TTC group and two terminal carboxyl group was acylated with oxalyl chloride and esterified with bromoethanol to convert the terminal carboxyl group to bromine,then the bromo terminated PS (Br-PS-Br) was obtained. After it, Br atom could be quaternized with N atom of pyridine in P4VP (Mn, GPC=25300 g/mol) polymer, and finally in the form of quaternary ammonium salt in the cross-linked structure. The 1H NMR and FT-IR spectra were used to determine the structure. Finally, the ionic hydrogel was formed by the crosslinking reaction under UV light.3. Study on self-healing property of ionic hydrogel. The healing effect of hydrogels with different shapes were analyzed and the mechanism of healing was verified. It was verified that the hydrogel was healed under aqueous conditions by comparing the hydrogel and xerogel. It was found that hydrogel healing must be achieved in contact with each other. By comparing the healing effect of the hydrogel in the dark environment and the UV light environment, it is verified that the UV light is an indispensable condition in the healing process. In the hydrogel, the contacting condition and UV light are the necessary. The sheared hydrogel can be healed in one hour with a quckily speed. In addition, the process of breaking and healing can be repeated more than 3 times.