Molecular arrangement and photopatterning of copolymer containing ketal-protected group in ultrathin nanosheets

A novel series of ketal-protected copolymer, poly(N-dodecylmethacrylamide-co-1,4-dioxaspiro [4.4] nonane-2-methyl methacrylate) (p(DDMA–DNMMA)), was synthesized and their monolayer and multilayer nanosheets were deposited by Langmuir–Blodgett (LB) technique. The surface behavior of the copolymer monolayer at the air/water interface was investigated by measuring the surface pressure (π) and the static elasticity (Es) as a function of mean repeat area (A) isotherm. The results showed that p(DDMA–DNMMA) could form the stable, well-defined molecular orientation Langmuir monolayer on the water surface, which was further proved by the measurements of atomic force microscopy (AFM). The polymer main chain lies flat on a water surface and the side chains attached to the main chain stretch out of the angle of about 62°. The static elasticity (Es)-surface pressure (π) isotherm was used to achieve optimum conditions for LB films deposition, because it could give more detailed information on molecular interaction and motion than π–A isotherm. UV–visible absorption spectra indicated that a well-ordered layer-by-layer structure was successfully controlled in the LB films. Upon deep UV light irradiation, photochemical reaction could also occur in the ultrathin nanosheets and the positive-tone photopatterning was obtained followed by development with alkali aqueous solution. The p(DDMA–DNMMA) LB films also show higher resistance ability in the process of etching gold film. The morphology of the patterns on the mica substrate was investigated by AFM.