Synthesis of Swellable Functionalized Polymer Microspheres and Study of their Selective Optical Sensing Properties

An optical chemical sensor based on polymer swelling and shrinking has been studied by way of optical transmission. Tris(2-aminoethyl)amine-polymer is synthesized. The sensing Polymer has been formed from poly(vinylbenzylchloride), Tris(2-aminoethyl)amine by a nucleophilic substitution reaction then, acidified with Chloroacitic acid. The sensing element has been produced by dispersing the acidified Tris(2-aminoethyl)amine-polymer beads and entrapping them as microspheres in a hydrogel membrane formed by cross linking of poly (vinylalcohol) with glutaraldehyde . The response is based on the interaction between the metal cations and the deprotonated acidified Tris(2-aminoethyl)amine functional group, whereby the swellable polymer undergoes shrinking as a result of neutralization of the negative charges of this functional group. This complex formation of a metal cation with acidified Tris(2-aminoethyl)amine functionality causes significant changes in the optical properties of the sensing element. Shrinking of the polymer microspheres resulted in a decrease in the optical transmission through the sensing membrane. This is due to the increasing difference in the refractive indices between the microspheres and the dispersing hydrogel membrane. This sensor showed good response particularly to copper ions. Also, there was insignificant response to pH 5 up to pH 8.In addition, there was no detectable response towards alkali, alkaline earth metals and other metal ions such as Ni2+, Co2+, Hg2+, and Al3+.