Preparation And Photo-response Study Of Self-assembly Polymer Networks Based On α-CD

Self-assembly polymer networks based on a-CD have attracted much attention. In this paper, a kind of photoresponsive polymer network based on the photo-regulated interaction of azobenzene and a-CD was prepared, which has potential application in photonic, photo storage, photo switch and so on.Two kinds of polymers,α-CD modified poly(acrylic acid)s (α-CD-PAA) and azobenzene modified poly(acrylic acid)s (azo-PAA) were synthesized first. The photoresponsive polymer network was prepared by mixingα-CD-PAA and azo-PAA in water and then studied by rheology. Viscosity of the system changed repetitively and reversibly under UV irradiation and in dark, indicating the successful preparation of photoresponsive polymer network. Photoresponse mechanism was studied by UV-Vis absorption spectra and 1H NMR.For synthesis ofα-CD-PAA, mono-sulfonatedα-CD(a-CD-6-OTs) was synthesized first. Then mono-aminatedα-CD (α-CD-6-EDA) was obtained withα-CD-6-OTs and ethylenediamine. At lastα-CD-PAA was prepared by graftingα-CD-6-EDA onto PAA chain. Azo-PAA was prepared by reaction of p-amino-azobenzene with PAA.Photoresponsive polymer network was prepared with a-CD-PAA and azo-PAA. Rheological studies show that viscosity ofα-CD-PAA/azo-PAA aqueous solution could respond to UV light and darkness repetitively and reversibly. It decreased under UV irradiation and went back in dark. Effects of polymer concentration and mono-α-CD on viscosity ofα-CD-PAA/azo-PAA system were studied. The results are that the viscosity increased with polymer concentration and decreased with amount of mono-α-CD.Interaction ofα-CD and azo was studied by UV-Vis absorption spectra, which show the photoresponsive mechanism of polymer network. Binding ofα-CD with azo is much stronger thanβ-CD andγ-CD.α-CD and azo-PAA forms 1 to 1 complex and the binding constant was calculated to be 4.7X10 M-1. Azo-PAA can isomerize from trans to cis and cis to trans successfully.10% azo moeties on azo-PAA are in cis form before UV irradiation and 78% after UV irradiation. The trans-cis isomerization was accelerated by addingα-CD and the rate constants in the presence and absence of a-CD were calculated to be 0.084 and 0.14s-1.