UV-Visible Spectroscopy To Determine Free-Volume Distributions During Multifunctional Monomer Polymerizations

摘要

Efforts have focused on developing a spectroscopic technique to characterize the microstructural heterogeneity and free volume distribution during the polymerization of multifunctional monomers. The technique uses UV-Vis spectroscopy to monitor the trans to cis conformational changes in photochromic probes. Since the absorbance spectra of the two conformations are significantly different, UV-Vis spectroscopy can be used to monitor the isomerization rate of the probe by measuring the absorbance at certain wavelengths. The photoinduced forward isomerization of the photochromic probe is a sensitive measure of the local microstructure and free volume, Therefore, this experimental technique which combines UV-Vis spectroscopy and photochromic probes provides a method to monitor the free volume distributions in situ during the polymerization. The analysis has been discussed in detail, and results are presented for a series of multiethylene glycol dimethacrylate polymerizations. The photochromic probes studied were azobenzene, m-azotoluene, stilbene, and 4,4'-diphenylstilbene.