Chemical and photochemical dual polymerization in a mixed langmuir monolayer of diacetylene derivatives and octadecyltrimethoxysilane

A chemical-and-photochemical-induced dual polymerization at the air- water interface was performed for the first time, by using a ternary mixture of a octadecyltrimethoxysilane (C₁₈TMS), 10,12-pentacosadiynoic acid (PDA), and N-(11-O-α-D)-mannopyranosyl-3,6,9-trioxa) undecyl 10,12-pentacosa- diynamide (PDTM). Different dual polymerization behaviors of the mixed monolayers of PDA/PDTM/C₁₈TMS (7:1:8 molar ratio) at different subphase pH were monitored by surface pressure-area isotherms and UV-vis spectra. At pH 1, the C₁₈TMS formed a long linear polymer network by strong intermolecular condensation. The PDA/PDTM was isolated to small domains by this network and can only be polymerized weakly upon UV irradiation. At pH 2.6, the weak condensation of C₁₈TMS formed short linear polymers, which caused phase separation between C₁₈TMS and PDA/PDTM. The strong photochemical polymerization of the PDA/PDTM rich domain was similar to the PDA/PDTM binary mixed monolayer. At pH 4.0, the partially hydrolyzed C₁₈TMS was miscible with PDA/ PDTM and slowed the polymerization process of PDA/PDTM upon UV irradiation. These results show geometry and kinetic controls of the PDA/PDTM polymer in 2D by using the C₁₈TMS polymer network.