Functionalization And Properties Of Polyphosphazenes Based On Thiol-Ene Click Reaction

Polyphosphazenes are organic-inorganic hybrid polymers with tunable physical and chemical properties, which can be achieved by macromolecular substitution reactions. However, this reaction has some limitations because of the lack of selectivity exhibited by the P-Cl bond and the steric effect from bulky substituent groups. In this thesis, polyphosphazenes were functionalized via thiol-ene click reaction due to its modularity, high efficiency, mild reaction condition, and simple operation. The specific studies are concentrated on the following aspects:Poly[bis(allylamino)phosphazene] (PBAAP) synthesized by nucleophilic substitution of poly(dichlorophosphazene) with allylamine was reacted with thiol reagents under UV irradiation. The influence of molecular size and chemical characteristic of thiol reagents on the reaction process were investigated. It is found that the conversion rate of the allyl groups decreases with the increase of the molecular size of thiol reagents; and the intramolecular cyclization was not observed during thiol-ene reaction. Besides, bifunctional polyphosphazene was synthesized via a two-step "click" reaction. Characterization by DSC, TEM, contact angle measurements and platelet adhesion test show that the properties of polyphosphazenes can be facilely tuned by changing the thiol reagents.From the viewpoint of environmental friendly chemical processes, the thiol-ene click reaction between PBAAP and thiol reagents were conducted in aqueous medium. The interactions between PBAAP and aicd molecules were investigated by quartz crystal microbalance. Based on these results, some tentative conclusions were drawn on the mechanism of the dissolution of PBAAP in water. Comparisons with organic reactions indicate that aqueous reactions are competitive in the aspects of regioselectivity and inhibition of macromolecular crosslinking.Ionic allyl polyphosphazenes synthesized by nucleophilic substitution of N,N-dimethylethylenediamine with poly(dichlorophosphazene) and subsequent quaternization with allyl bromide were reacted with dithiol polyethyleneglycol to produce hydrogels for lipase immobilization. Fluorescence microscopic characterization confirms that proteins distribute evenly inside the hydrogels. Immobilization of lipase was carefully studied, including the amount of immobilized lipase, the activity and the stability. It is found that larger mesh size of hydrogels result in larger amount of immobilized enzyme and higher activity. Moreover, the binding between enzyme and hydrogel is reversible by adjusting the ionic strength of the solution.