The Effect of Visible-light on the UV-Polymerization of 10,12-Pentacosadiynoic Acid Monolayers

This paper measured the π-Aisotherms of the monomer and polymerized 10,12-pentacosadiynoic acid(PDA).If defining A0 as the surface pressure onset(the area at which an appreciable rise in surface pressure was observed),the A0 are 0.35 and 0.48nm2/mol,the collapse pressure are 51 and 38mN/m and the molecule area at collapse point are 0.2 and 0.28nm2/mol for PDA monomer and polymer respectively.The chain segment of PDA polymer occupied more area than the corresponding monomer.So expansion could be expected in the polymerization reaction.The PDA molecule area changes during polymerization at the surface pressure of 10mN/m was recorded.It was obvious an expansion process.The UV-visible absorption and emission spectroscopy of the polymerized products were measured.The 500 and 550nm absorption peak indicated that the polymerization was really occurred in the monolayer state.The acceleration effect of visible-light on the monolayer UV-polymerization was investigated by periodically switch on and off the visible-light under constant UV-irradiation.The barrier speed at the visible-irradiation periods was larger than that at the no-visible-irradiation periods.This indicated that the visible-light can truly accelerate the UV-polymerization of PDA monolayer.Because the visible-light itself can not initiate the polymerization without UV-irradiation,it can be concluded that the visible-light can only accelerated the chain propagation process,thus can produce larger molecule weight polymer.The acceleration effect was explained with the polymerization mechanism and the electronic state of the polymerization intermediates.