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.