Concise synthesis of a light/temperature/pH/CO2-quadruple responsive azobenzene functionalized homopolymer for reversible photopatterning†

A novel light/temperature/pH/CO₂-quadruple responsive azobenzene functionalized homopolymer of poly[(E)-3,14-dimethyl-13-oxo-6,9,12-trioxa-3-azapentadec-14-en-1-yl 4-(phenyldiazenyl)benzoate] [P(Azo-N-EO₂MA)] was prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization. The light-responsiveness of P(Azo-N-EO₂MA) was demonstrated by examining the UV/vis absorption spectra under alternating UV/blue light irradiation or UV irradiation/heating conditions. P(Azo-N-EO₂MA) has an upper critical solution temperature (UCST) in the co-solvent of n-butanol/water and a critical pH in aqueous solution. The effects of different molecular structures, molecular weights and concentrations on the UCST and critical pH were investigated. The response of P(Azo-N-EO₂MA) to CO₂ was demonstrated via the cyclic bubbling of CO₂/N₂ through a solution of P(Azo-N-EO₂MA). Then, the interaction between the different response was explored. The critical micelle concentration (cmc) of P(Azo-N-EO₂MA) was tested. Micelles of P(Azo-N-EO₂MA) were prepared by self-assembly, and the morphology or size of the micelles can be changed by applying acid or irradiating with UV light. Finally, P(Azo-N-EO₂MA) was applied to the preparation of rewritable paper, and it is proved that the rewritable paper has good cyclability, stability and high resolution during the process of “writing–erasing–writing” of different patterns. P(Azo-N-EO₂MA) expands the types of multistimuli-responsive homopolymers available to researchers and has good prospects for applications in self-assembly, drug delivery and optical storage.