Synthesis And Properties Of Low Generation Polyethylene Glycol Dendritic Polymer/clay Composite Hydrogel

As a unique soft material, hydrogel has always been concerned by many domestic andforeign research workers because of its unique properties and potential applications in manyfields. In recent years, development and preparation of hydrogels with excellent mechanicalproperties become its direction of research in order to maximize its potential applications.And organic/inorganic nanocomposite hydrogels has gained the wide attention of scholarsboth at home and abroad attributing to its adwantages, such as cheaper raw materials, simplepreparation method and excellent performance, etc. Polyethylene glycol (PEG) is a commonwater-soluble polyether polymer, low toxicity, good biocompatibility. Its reactive hydroxylend groups can be easily modified into macromonomer with functional units, which are easilyused to prepare hydrogel with novel structure and excellent performance. In this paper,combining the excellent features of PEG and dendritic polymers, we use linear PEG, cationicmonomer (MAPTAC) and inorganic clay as raw materials, design and prepare a novel organic(polymer)/inorganic (clay) composite hydrogel. The research content and results include thefollowing aspects:(1) Synthesis and characterization of low generation polyethylene glycol dendriticpolymerThe terminal hydroxyl groups of PEG was modified by methylsulfonic acid esterificationreaction and amination reaction to abtain a two-terminal amino polyethylene glycol, then itwas used to have Michael addition reaction with cationic macromonomer methacryloyltrimethylammonium chloride (MAPTAC) in the system of Zn/NH4Cl saturated aqueoussolution, and finally we got a low generation polyethylene glycol dendritic polymer. Besides,the structure of the synthetic polymers were characterized by means of Ninhydrin colorreaction, Fourier transform infrared spectroscopy (FTIR), H nuclear magneticresonance(1H-NMR), and Gel permeation chromatography (GPC). The results showed thatthe structure of all products were consistent with the designed ones, the target products weresynthesized.(2) Preparation and characterization of dendrimer/clay composite hydrogelConsidered the synthesized dendritic polymer as a gelator and had it interact withorganic clay. The electrostatic interaction between the positive charges on the polymer chainsand the negative charges on the clay sheets (homogeneously separated by sodium polyacrylic(ASAP)) crosslinked them to an organic/inorganic composite hydrogel. By changing the amount of each component of the gel, several hydrogels in different ratios were prepared.FTIR, X-ray diffraction (XRD), scanning electron microscopy (SEM) were carried out tocharacterize the hydrogel’s structure. Its morphology was analyzed and it is proved to be aphysically crosslinked hydrogel.(3) Properties of the dendritic polymer/clay composite hydrogelSwelling behavior and mechanical properties of the hydrogel were studied, and theeffects of clay content on its performance were investigated. Experimental results showed that:the hydrogel has a good mechanical property and swelling property, the content of the clayhas a great influence on both. As the clay content increases, the degree of swelling and theswelling rate decreases. However, for the mechanical property, the increasing in the claycontent improved the mechanical strength. When the clay content is5%, a dendrimerconcentration of1.40%and ASAP of0.15%, the crosslinked hydrogel had the maximummechanical strength, G’can reach up to9KPa in this case, which is higher than many physicalhydrogels. In addition, though the G’ of the hydrogel without ASAP had the same trend, itsvalue is much lower.