Control of polymerization processes of 10,12‐pentacosadiynoic acid LB films

Abstract

AbstractStudies have been carried out on KrF excimer laser light (EX), X‐ray or electron beam (EB) induced polymerization of 10,12‐pentacosadiynoic acid (PDA) Langmuir‐Blodgett (LB) films in relation to molecular density or molecular arrangement of the films using X‐ray diffraction analysis, infrared (IR) spectroscopy and Raman spectroscopy. The molecular arrangement or density of the PDA LB films was controlled by subphase conditions when the films were built up, such as pH, temperature of a subphase or salt concentration in the subphase. Polymerization sensitivity of the PDA LB film was affected by the arrangement or molecular density. On low density (A type) films the polymerization occurred by irradiation with EX, X‐ray or EB, but on high density (B type) films the polymerization occurred only when the irradiation was carried out by high energy beams such as X‐ray or EB. Decomposition of polymerized films was observed further by excessive irradiation of EX or X‐ray, but not on the B type films. It was revealed by X‐ray diffraction analysis that in the A type film, the PDA molecules bent to a larger extent than those in the B type film and the polymerization proceeded topochemically, that is, the thickness decreased little after EB irradiation in a helium atmosphere. On the other hand, in the B type film, the thickness decreased by about 10% as a result of EB irradiation. By IR reflection‐absorption (RA) and Raman measurements, it was confirmed that conjugated diacetylenic bonds disappeared and conjugated double and new conjugated triple bonds appeared after high energy beam irradiations. These results support the supposition that 1,4‐polymerization, i.e. polydiacetylene type polymerization, occurs easily in the A type film and 1,2‐ or 3,4‐polymerization, i.e. polyacetylene type polymerization, occurs in the B type film, and that the polymerized A type film was decomposed at the polydiacetylenic bond when the irradiation continued further. It was also shown that the polyacetylene type polymer was obtained only when the B type film was irradiated with the high energy beam.