Polymerization of 10,12-pentacosadiynoic acid monolayer at varying surfacepressure and temperature

Isotherms of a PDA monolayer were measured on a subphase of 4 x 10(-4) M Cd Cl2 at different temperatures. UV polymerization of the PDA monolayer was c arried out at different temperatures and surface pressures, and expansions or contractions were observed to depend on the applied surface pressure. Th e polymerization rate constant was found to decrease with increased applied surface pressure, but it increased with temperature. From the temperature dependence of the polymerization of the PDA monolayer, the apparent activat ion energy of the 1,4-addition polymerization was estimated to be 63.6-89.7 kJ/mol depending on the surface pressure at which UV polymerization was ca rried out. The apparent activation energy had a minimum of 63.6 kJ/mol at t he surface pressure of 20 mN/m, and there would be an obvious increase of t he activation energy when the surface pressure deviated from this value. Th e surface pressure dependence of the apparent activation energy was interpr eted in terms of molecular packing in the monolayer.