Abstract:

Poly (organophosphazenes) possesses a backbone of alternating nitrogen and phosphorus atoms with two organic side groups attached to the phosphorus atoms. A unique property of poly (organophosphazenes) is that polymers with tailored physical and chemical properties can be prepared by using appropriate nuclephiles. This feature is useful in developing polymers that are good candidates for biomedical materials. In this study, a mixed substituted poly(organophosphazene) bearing propyl 4-oxybenzoate and glycine ethyl ester side groups was synthesized via macromolecular substitution reactions of poly (dichlorophosphazene) with sodium salt of propyl 4-hydroxybenzoate and glycine ethyl ester. The stepwise substitution reactions were monitored by \{\}\+\{31\}P NMR spectroscopy. ³¹P NMR spectra were acquired repeatedly in a 4-hour interval during the synthetic reaction. The results showed that more than 20 hours and 24 hours were required, respectively, to complete the first step reaction and the second step reaction. Two types of skeleton phosphorus atoms existed in the final polymer product, one with the same two side groups (two -OC₆H₄COOCH₂CH₂CH₃ or two -NHCH₂COOEt) attached, and the other type of phosphorus atoms had two different side groups (one {-OC₆H₄COOCH₂CH₂CH₃} and one -NHCH₂COOEt). The relative content of the propyl 4-oxybenzoate substitute and the glycine ethyl ester substitute was 0.49∶0.51. The results obtained were of interest for understanding the mechanism of the macromolecular substitution reactions, for optimizing the reactive condition for synthesizing the mixed substituted poly(organophosphazene) and for increasing the yield of the polymer product.

Key words: NMR, synthesis of mixed substituted poly(organophosphazene), ³¹P NMR, propyl 4-oxybenzoate, glycine ethyl ester