Preparation of a novel infrared photoinitiator and kinetic monitoring of photopolymerization by real time FT-IR spectroscopy

Abstract

In this paper, a novel cationic cyanine dye-borate complex, 1,3,3,1′,3′,3′-hexamethyl-11-chloro- 10,12-propylenetricarbocyanine triphenylbutylborate was prepared and used as the photoinitiator in infrared laser-induced photopolymerization of acrylates. It had a maximum electron absorption at 786 nm, which matched well with the output wavelength of the adopted infrared laser diode, with a maximum molar extinction coefficient of 1.4 × 105 L mol -1 cm -1 in chloroform solution. Under the irradiation of infrared laser the polymeric samples based on phthalicdiglycol diacrylate (PDDA), binder, photoinitiator and solvent polymerized and the polymerizing process was monitored through Real Time FT-IR spectroscopy (RTFT-IR). The double bond conversion was determined from the reduction of the absorption of acrylate monomer at 1635 cm -1 and 1620 cm-1 (CH2=CH strentching) in FT-IR spectra during laser irradiation. As the concentration of photoinitiator rose, the polymerization rate (Rp) increased rapidly but then decreased when the concentration reached a critical value. Rp and the ultimate double bond conversion of sample increased when the infrared laser power was enhanced, whereas they fell greatly as the thickness of the polymeric sample layer increased.