Synthesis And Swelling Behaviors Of Physical Crosslinking Type Polyurethane Hydrogels

Hydrogel was a kind of polymer that could absorb a large number of moisture and swelling, but would not be dissolved. It could meet application requirements for different properties, such as mechanical properties and swelling behaviors through designing its molecular chain structure. Polyurethane was a kind of typical block polymer, it could show good wear resistance, low temperature flexibility performance and so on, through the molecular structure designed. Polyurethane urea hydrogel could be combined with advantages of polyurethane and hydrogels, and now it had a wide range of applications. In this paper, physical crosslinking type polyurethane urea hydrogels and polyurethane urea-poly (vinyl alcohol) physical blending hydrogels were synthesized, and the mechanical properties, swelling behaviors as well as environmental response performances of those hydrogels were studied. This article was mainly divided into the following three parts:(1)Influence of urea content on the mechanical properties and swelling behaviors of polyurethane urea hydrogels.Firstly, a series of polyurethane prepolymers were synthesized with polyethylene glycol (PEG) and polyether glycol (PPG) as soft segments, isophorone diisocyanate (IPDI) as hard segment, dimethylol propionic acid (DMPA), diethylene glycol (DEG) as hydrophilic chain extender and small molecule chain extender. And then water was used as indirect chain extender, reacted with the residual NCO group, finally, a series of polyurethane urea hydrogels were synthesized with different content of urea. Properties of polyurethane urea hydrogels with different content of urea were studied through tests of Fourier transform infrared spectrum (FTIR), Scanning electron microscopy (SEM), Swelling behaviors and thermogravimetry(TG) and so on. This kind of hydrogels had no obvious porous structure, with the increase of urea content, the compression strength and mechanical properties of polyurethane urea hydrogels films were increased gradually, the water absorption of equilibrium swelling was gradually reduced. They had certainly environmental responsive, and with the increase of temperature, the equilibrium swelling rate reduced. In the acidic condition, the swelling degree changed slightly, but in the alkaline conditions (especially pH>10), the equilibrium swelling rate increased obviously. With the increase of ionic strength of solution concentration, the equilibrium swelling rate of the hydrogels decreased. With the increase of urea content, the heat resistant performance of the hydrogel films was not changed obviously, just reduced slightly.(2) Influence of porogen content on the mechanical properties and swelling behaviors of polyurethane urea hydrogels.In this chapter, we had selected a formula with the best mechanical properties. A series of polyurethane urea hydrogels were synthesized with polyethylene glycol (PEG) and polyether glycol (PPG) as soft segments, isophorone diisocyanate (IPDI) as hard segment, dimethylol propionic acid (DMPA), diethylene glycol (DEG) as hydrophilic chain extender and small molecule chain extender, water as indirect chain extender, and finally, we used polyethylene glycol (Mn=1000) as porogen. Properties of polyurethane urea hydrogels with different porogen content were studied through tests of Fourier transform infrared spectrum (FTIR), Scanning electron microscopy (SEM), Swelling behaviors and so on. The porogen of polyethylene glycol (Mn=1000) had a good performance to the hole, when the content of porogen was 12%, the polyurethane urea hydrogels had a well porous structure, and the water absorption swelling ratio could be improved nearly one times. With the increase of the porogens(PEG1000) content, the compression strength and mechanical properties of polyurethane urea hydrogel films reduced gradually; however, when the content of porogens was 12%, the films could still maintained well mechanical properties, the tensile strength and elongation at break could reached to 8.17 MPa and 2145%, respectively. This series of polyurethane urea hydrogels had certainly pH and ionic concentration sensitively, and when they were alternately placed in different pH buffer solutions, they could present cyclically change.(3) Synthesis and characterization of polyurethane-poly (vinyl alcohol) physical blending hydrogelsIn the previous chapter, with the join of porogen, the swelling behaviors of hydrogels could be improved, but the degree of equilibrium swelling rate was not improved obviously. In order to improve the swelling behaviors of hydrogels further, in this chapter, we used polyvinyl alcohol (PVA) materials which had a better hydrophilic, by physical blending method, a series of polyurethane-poly (vinyl alcohol) physical blending hydrogels were synthesized. Properties of polyurethane-poly(vinyl alcohol) physical blending hydrogels with different poly(vinyl alcohol) (PVA) content were studied through tests of Fourier transform infrared spectrum (FTIR), Scanning electron microscopy (SEM), compression strength, Swelling behaviors, water retention and so on. This series of hydrogels had a good water absorption performance with uniform porous structure, when the content of polyvinyl alcohol (PVA) was 30%, the equilibrium swelling rate could reach to 3.2, and the compression strength increased with the increase of PVA content. With the increase of solution pH, the equilibrium swelling ratio (ESR) of hydrogels increased gradually, but decreased with the increase of solution ionic concentration. It showed that those hydrogels had obvious responsiveness to the pH and ionic concentration. The structure of hydrogel samples was very stable, and they all had well swelling behaviors. The drying process of hydrogels could conform to the drying kinetics curve, and they had a very well performance of water retention.